Copy go-bip39 into internal/bip39 (closes #42)

go-bip39's repository no longer exists, so keyfunc now carries the
part of v1.1.0 it uses, with the upstream LICENSE beside it, and
imports it from internal/bip39. Upstream's tests and test vectors for
the kept code come along unchanged; where they called a removed
function, crypto/rand stands in for NewEntropy and EntropyFromMnemonic
for MnemonicToByteArray.

Changes beyond the trimming are what the linter asked for: the
package-level variables moved into the functions that use them, three
error strings were lower-cased, and the unknown-word error now wraps
ErrInvalidMnemonic.

go.mod no longer requires go-bip39. go mod tidy keeps its two go.sum
lines, because a test in sneak/secret's bip85 package imports it, and
drops six lines that only go-bip39's own requirements needed.

Model: opus-5-5

.dockerignore

@@ -1,3 +1,75 @@
-.git
+# .dockerignore does NOT use .gitignore semantics. Docker matches with
-.gitea
+# moby/patternmatcher: filepath.Match plus `**`, so `*` does not cross
+# `/` and an unprefixed pattern is anchored at the context root. Every
+# depth-independent pattern therefore needs `**/`, or `config/.env` and
+# `certs/server.key` still ship while this file reads as solved. Only
+# genuinely root-anchored entries go unprefixed. Never transplant these
+# into .gitignore, where `**/` is wrong.
+#
+# Matching is case-sensitive, so secrets use character ranges rather
+# than an ALL-CAPS twin, which would still miss `Server.Key`.
+#
+# Extend with this repo's own host-built artifacts, written anchored:
+# `/myapp`, never `**/myapp`, which also matches `cmd/myapp/` and
+# deletes the package directory from the context.
+
+# .git is sent without its config. Without a VERSION build argument the
+# stage that compiles runs `git describe --tags --always` on .git, which
+# does not need .git/config; that file can hold a credential, such as a
+# password in a remote URL or the token the CI checkout step stores there.
+# Each submodule keeps a config with the same exposure in its git directory
+# under .git/modules/, nested again for a submodule's own submodules, or in
+# its own .git directory when it keeps one.
+# KNOWN GAP: a submodule whose name has a `config` segment (`config`,
+# `deploy/config`, `config/lib`) loses its whole git directory, because
+# `**/.git/modules/**/config` also matches that segment's directory
+# under .git/modules/. Go's version stamping then fails the build;
+# nothing leaks. Name such a submodule without that segment:
+# `git submodule add --name`.
+**/.git/config
+**/.git/modules/**/config
+
+# Agent scratch: one full checkout of the repo per in-flight agent.
+# Anchored because it occurs once where agents run at the repo root.
+# KNOWN GAP: a repo running agents in subdirectories still ships
+# `services/api/.claude/` and must add its own anchored entry.
+.claude
+
+# Environment files. `*.env` covers bare `.env` and the `prod.env`
+# convention. Re-include a committed template with a negation if the
+# build needs one: `!docs/example.env`.
+**/*.[eE][nN][vV]
+**/.[eE][nN][vV].*
+**/.[eE][nN][vV][rR][cC]
+
+# Private keys and the bundles carrying them. Public certificates
+# (*.crt, *.cer) are deliberately absent: they are legitimate inputs.
+**/*.[pP][eE][mM]
+**/*.[kK][eE][yY]
+**/*.[pP]12
+**/*.[pP][fF][xX]
+**/[iI][dD]_[rR][sS][aA]
+**/[iI][dD]_[dD][sS][aA]
+**/[iI][dD]_[eE][cC][dD][sS][aA]
+**/[iI][dD]_[eE][cC][dD][sS][aA]_[sS][kK]
+**/[iI][dD]_[eE][dD]25519
+**/[iI][dD]_[eE][dD]25519_[sS][kK]
+
+# Dependencies: restored inside the image, never copied in.
+**/node_modules
+
+# OS metadata.
+**/.DS_Store
+**/Thumbs.db
+
+# Editor state: never a build input, and it churns COPY.
+**/*.swp
+**/*.swo
+**/*~
+**/*.bak
+**/.idea
+**/.vscode
+**/*.sublime-*
+
+# The binary `make build` writes.
 /keyfunc

.gitea/workflows/check.yml

@@ -6,4 +6,7 @@ jobs:
         steps:
             # actions/checkout v4.2.2, 2026-02-22
             - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+              with:
+                  # All history and tags, which `git describe --tags` needs.
+                  fetch-depth: 0
             - run: script/cibuild

.gitignore

@@ -1,6 +1,3 @@
-# The built binary
-/keyfunc
-
 # OS
 .DS_Store
 Thumbs.db
@@ -14,8 +11,40 @@ Thumbs.db
 .vscode/
 *.sublime-*
 
-# Environment / secrets
+# Agent scratch (worktrees of this repo, created and destroyed by
-.env
+# in-flight tooling). Unanchored: .gitignore patterns already match at
-.env.*
+# every depth, so no prefix is wanted here. This is not a .dockerignore
-*.pem
+# entry and must not be given a `**/` prefix on the way into one.
-*.key
+.claude/
+
+# Node
+node_modules/
+
+# Secrets. Unanchored like every entry above, so each matches at every
+# depth. Matching is case-sensitive on Linux, so names use character
+# ranges rather than a lowercase form that misses `Server.Key`.
+
+# Environment files. `*.env` covers bare `.env` and the `prod.env`
+# convention. Only the templates `example.env` and `sample.env` are
+# re-included below. A repository that commits any other template adds
+# its own negation after these lines, for example `!.env.example`.
+*.[eE][nN][vV]
+.[eE][nN][vV].*
+.[eE][nN][vV][rR][cC]
+!example.env
+!sample.env
+
+# Private keys and the bundles carrying them.
+*.[pP][eE][mM]
+*.[kK][eE][yY]
+*.[pP]12
+*.[pP][fF][xX]
+[iI][dD]_[rR][sS][aA]
+[iI][dD]_[dD][sS][aA]
+[iI][dD]_[eE][cC][dD][sS][aA]
+[iI][dD]_[eE][cC][dD][sS][aA]_[sS][kK]
+[iI][dD]_[eE][dD]25519
+[iI][dD]_[eE][dD]25519_[sS][kK]
+
+# The binary `make build` writes.
+/keyfunc

.golangci.yml

@@ -10,14 +10,21 @@ run:
 
 linters:
   default: all
+  enable:
+    # Successor to the deprecated gomodguard. Named explicitly, rather than
+    # left to `default: all`, because it carries the module policy below.
+    - gomodguard_v2
   disable:
     # Genuinely incompatible with project patterns
     - exhaustruct      # Requires all struct fields
-    - depguard         # Dependency allow/block lists
+    - exhaustruct_v5   # Requires all struct fields (successor to exhaustruct)
     - godot            # Requires comments to end with periods
-    - wsl              # Deprecated, replaced by wsl_v5
     - wrapcheck        # Too verbose for internal packages
     - varnamelen       # Short names like db, id are idiomatic Go
+    # Deprecated: the warning is attached to the old name, so it is
+    # silenced by disabling that name, not by enabling the successor.
+    - wsl              # Deprecated, replaced by wsl_v5
+    - gomodguard       # Deprecated, replaced by gomodguard_v2
   settings:
     lll:
       line-length: 88
@@ -28,6 +35,64 @@ linters:
       max-complexity: 15
     dupl:
       threshold: 100
+    depguard:
+      # Test-support code must not be compiled into the shipped binary. A
+      # test-support package exists to hand a test privileges the program
+      # itself must never have, so a file that is not a test must not import
+      # one. Test files, and the files inside a package whose directory name
+      # ends in `test`, are where that code belongs, and are exempt.
+      #
+      # The deny list below is the one part of this file a repository is
+      # expected to extend, and the only part it may. depguard matches an
+      # import path against a list of prefixes, so it cannot be told "any path
+      # whose last segment ends in test"; a repository's own test-support
+      # packages have to be named here one at a time, by full import path,
+      # under a module path that differs from repository to repository. Add
+      # them; change nothing else.
+      rules:
+        test-support:
+          list-mode: lax
+          files:
+            - "$all"
+            - "!$test"
+            - "!**/*test/**"
+          deny:
+            - pkg: net/http/httptest
+              desc: >-
+                Test-support code belongs in test files and in packages whose
+                directory name ends in test, not in the shipped binary.
+    # Only decisions already recorded in the Go package defaults are
+    # listed here. Every entry matches the module path exactly.
+    gomodguard_v2:
+      blocked:
+        - module: github.com/rs/zerolog
+          recommendations:
+            - log/slog
+          reason: "Structured logging is stdlib log/slog."
+        # One entry per pre-fork module path, because the later releases
+        # are separate paths. A prefix match would be shorter but would
+        # also reach github.com/go-redis/redismock, the test double for
+        # the successor these entries recommend.
+        - module: github.com/go-redis/redis
+          recommendations:
+            - github.com/redis/go-redis/v9
+          reason: "Pre-fork module; use the maintained go-redis v9."
+        - module: github.com/go-redis/redis/v7
+          recommendations:
+            - github.com/redis/go-redis/v9
+          reason: "Pre-fork module; use the maintained go-redis v9."
+        - module: github.com/go-redis/redis/v8
+          recommendations:
+            - github.com/redis/go-redis/v9
+          reason: "Pre-fork module; use the maintained go-redis v9."
+        - module: github.com/sergi/go-diff
+          recommendations:
+            - github.com/aymanbagabas/go-udiff
+          reason: "No unified diff output; use go-udiff."
+        - module: github.com/hexops/gotextdiff
+          recommendations:
+            - github.com/aymanbagabas/go-udiff
+          reason: "Unmaintained fork; use go-udiff."
 
 issues:
   max-issues-per-linter: 0

.prettierrc

@@ -0,0 +1,4 @@
+{
+    "tabWidth": 4,
+    "proseWrap": "always"
+}

Dockerfile

@@ -1,11 +1,11 @@
-# The formatting check, the tests and the build. Linting is not here:
+# The lint phase, the test phase and a development environment.
-# it runs in its own pinned image, see Dockerfile.lint and script/lint,
+# script/lint and script/test each build one phase alone; a plain
-# which script/cibuild runs before this file.
+# `docker build .` builds both, because the last stage copies a file from
+# each. Formatting is checked on the host by script/fmt-check, not here.
 
-# golang:1.26-alpine, 2026-09-07
+# Lint phase
-FROM golang@sha256:ce864e7223ac17b1775e6fd0b4c0db580c2eb50e7953a427916379e4b92a1628 AS builder
+# golangci/golangci-lint:v2.14.0, 2026-10-04
-
+FROM golangci/golangci-lint@sha256:ad862ba6b3798cbe0fd9fd7408d498fd74fbd2623a92406b2fd3898faf0bf98f AS lint
-RUN apk add --no-cache make git
 
 WORKDIR /src
 
@@ -14,13 +14,59 @@ RUN go mod download
 
 COPY . .
 
-RUN make fmt-check
+RUN golangci-lint run --config .golangci.yml ./...
-RUN make test
-RUN make build
 
-# alpine:3.23, 2026-09-07
+# Test phase. -race needs cgo and so a C compiler, which the Debian Go
-FROM alpine@sha256:fd791d74b68913cbb027c6546007b3f0d3bc45125f797758156952bc2d6daf40
+# image ships.
+# golang:1.26.8-trixie, 2026-10-04. It carries Go 1.26.8, the version
+# script/bootstrap installs on the host; change both together, and the
+# same image in the last stage.
+FROM golang@sha256:eae2aaa6add2936cbf350dd0d2628b363461542f0c4b3c0b558957e0f2997379 AS test
 
-COPY --from=builder /src/keyfunc /usr/local/bin/keyfunc
+WORKDIR /src
 
-ENTRYPOINT ["keyfunc"]
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+
+RUN go test -timeout 90s -race -cover ./... || \
+    { echo "--- Rerunning with -v for details ---"; \
+      go test -timeout 90s -race -v ./...; exit 1; }
+
+# Development environment, and the last stage: a plain `docker build .`
+# builds this one. It holds the source tree in /src, what
+# script/bootstrap installs, and keyfunc built from that tree on the
+# PATH. Nothing is wanted from either phase above; the copies are what
+# make BuildKit build them first, so this stage cannot run unless lint
+# and test passed.
+# golang:1.26.8-trixie, 2026-10-04
+FROM golang@sha256:eae2aaa6add2936cbf350dd0d2628b363461542f0c4b3c0b558957e0f2997379
+
+COPY --from=lint /src/go.sum /dev/null
+COPY --from=test /src/go.sum /dev/null
+
+# A tar-stream context keeps the sender's file owners, which git refuses.
+RUN git config --system --add safe.directory /src
+
+WORKDIR /src
+
+# script/bootstrap needs only script/ and the dependency manifests.
+COPY script/ script/
+COPY go.mod go.sum package.json yarn.lock ./
+RUN script/bootstrap
+
+COPY . .
+
+# The version stamped into the binary: the VERSION build argument when one
+# is given, otherwise `git describe --tags --always` of the .git in the
+# build context. A context that carries .git and still yields no version
+# fails the build; with neither, as from a source tarball, it is "dev".
+ARG VERSION
+RUN version="${VERSION:-$(git describe --tags --always || echo dev)}"; \
+    if [ -e .git ] && { [ -z "$version" ] || [ "$version" = dev ] || \
+        [ "$version" = unknown ]; }; then \
+        echo "no version could be derived although the build context carries .git" >&2; \
+        exit 1; \
+    fi; \
+    make build VERSION="$version" && mv keyfunc /usr/local/bin/keyfunc

Dockerfile.lint

@@ -1,15 +0,0 @@
-# The linter, pinned by hash, with this repository linted inside it.
-# Building this file is how linting happens; see script/lint. Nothing
-# lints on the host, so the answer is the same everywhere.
-
-# golangci/golangci-lint:v2.12.2, 2026-09-07
-FROM golangci/golangci-lint:v2.12.2@sha256:5cceeef04e53efe1470638d4b4b4f5ceefd574955ab3941b2d9a68a8c9ad5240
-
-WORKDIR /src
-
-COPY go.mod go.sum ./
-RUN go mod download
-
-COPY . .
-
-RUN golangci-lint run --timeout 5m

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 sneak
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

Makefile

@@ -3,7 +3,10 @@
 # which needs the version stamped into the binary.
 
 VERSION := $(shell git describe --tags --always --dirty 2>/dev/null || echo dev)
-LDFLAGS := -s -w -X 'git.eeqj.de/sneak/keyfunc/internal/cli.Version=$(VERSION)'
+LDFLAGS := -s -w -X 'sneak.berlin/go/keyfunc/internal/cli.Version=$(VERSION)'
+
+# Where script/bootstrap installs Go; it cannot put it on our PATH.
+export PATH := $(HOME)/.local/go/bin:$(PATH)
 
 .PHONY: default bootstrap setup build test lint fmt fmt-check check \
 	docker cibuild hooks clean

README.md

@@ -1,16 +1,82 @@
 # keyfunc
 
-`keyfunc` turns a BIP-39 mnemonic into key pairs that can be recreated from
+`keyfunc` is an MIT-licensed Go command-line tool by
-that mnemonic at any time. The same mnemonic, key type and index always give the
+[@sneak](https://sneak.berlin) that turns a BIP-39 mnemonic into SSH keys, age
-same key.
+identities and child mnemonics, each of which can be recreated from that
+mnemonic at any time. The same mnemonic, key type and index always give the same
+key.
 
 It uses the BIP-85 entropy deriver from `git.eeqj.de/sneak/secret/pkg/bip85` and
 takes the same steps as that repository's `agehd` package.
 
-Commands are grouped by what is derived: `keyfunc ssh ...` for ed25519 SSH
+Commands are grouped by what is derived: `keyfunc ssh ...` for ed25519 SSH keys,
-keys, `keyfunc age ...` for age identities and for encrypting and decrypting
+`keyfunc age ...` for age identities and for encrypting and decrypting with
-with them, and `keyfunc mnemonic ...` for child mnemonics derived from the
+them, and `keyfunc mnemonic ...` for child mnemonics derived from the main one.
-main one.
+
+## Getting Started
+
+Install with Go:
+
+```
+go install sneak.berlin/go/keyfunc/cmd/keyfunc@latest
+```
+
+Or build from a clone and run the binary:
+
+```
+git clone git@git.eeqj.de:sneak/keyfunc.git
+cd keyfunc
+make build
+./keyfunc --version
+```
+
+`make build` produces `./keyfunc`. Every deriving command needs a mnemonic; see
+[Giving it the mnemonic](#giving-it-the-mnemonic) for where it is read from,
+then for example:
+
+```
+./keyfunc ssh pub -n 0 --mnemonic-command 'secret get foo'
+```
+
+## Rationale
+
+A key you can derive again never has to be backed up. One mnemonic, kept safe
+once, stands behind every key this tool produces: lose a laptop and the SSH key,
+the age identity and any child mnemonic on it come back from the mnemonic alone,
+at the same index, byte for byte. Nothing else has to be written down, copied
+between machines, or stored in a secret manager, because it can always be
+derived again.
+
+## Design
+
+The entry point is a thin `cmd/keyfunc/main.go` (what `make build` builds) that
+calls into `internal/`. The packages there are:
+
+- `internal/derive` turns a mnemonic into the 32 bytes a key is made from: it
+  walks BIP-39 seed, BIP-32 master key and BIP-85 entropy, and holds the shared
+  constants (the byte count and the largest key index).
+- `internal/mnemonic` finds the mnemonic to work from — a command, an
+  environment variable, or a terminal prompt — and refuses one that fails the
+  BIP-39 checksum.
+- `internal/sshkey` turns the derived bytes into an ed25519 SSH key
+  (`sshkey.go`) and serves that key from an in-process SSH agent on a private
+  unix socket, keeping it out of any file (`agent.go`).
+- `internal/agekey` turns the derived bytes into an age identity and encrypts
+  and decrypts with it.
+- `internal/childmnemonic` derives a child mnemonic from the main one using
+  BIP-85's own mnemonic application.
+- `internal/cli` builds the cobra command tree and runs it. Under it,
+  `cli/options` holds the flags every command shares, `cli/signals` catches
+  SIGINT, SIGTERM and SIGHUP for the commands that clean up before they end, and
+  `cli/ssh`, `cli/age` and `cli/mnemonic` are the command groups.
+- `internal/bip39` is a copy of `github.com/tyler-smith/go-bip39` v1.1.0,
+  trimmed to what keyfunc uses.
+
+### Adding a key type
+
+Adding a key type is one package under `internal/` that turns the 32 derived
+bytes into that type's key, plus one cobra subcommand under `internal/cli/` that
+groups its commands.
 
 ## Derivation
 
@@ -42,26 +108,32 @@ The mnemonic itself is never a command-line argument. It is looked for in this
 order; the first one found wins:
 
 1. `--mnemonic-command <command>`: a shell command, run with `sh -c`, whose
-   standard output is the mnemonic. Example: `--mnemonic-command 'secret get
+   standard output is the mnemonic. Example:
-   foo'`. Whitespace around the output is dropped. If the command exits with a
+   `--mnemonic-command 'secret get foo'`. If the command exits with a non-zero
-   non-zero status, the tool prints its standard error and exits with status 1.
+   status, the tool prints its standard error and exits with status 1.
-2. Environment variable `KEYFUNC_MNEMONIC_COMMAND`: the same, as a shell
+2. Environment variable `KEYFUNC_MNEMONIC_COMMAND`: the same, as a shell command
-   command held in the environment.
+   held in the environment.
 3. Environment variable `KEYFUNC_MNEMONIC`: the mnemonic itself.
 4. A prompt on the terminal with echo turned off.
 
 If none of these is available and standard input is not a terminal, the tool
 refuses and exits with status 1. A mnemonic that fails the BIP-39 checksum is
-refused with a message saying so.
+refused with a message saying so. Keys are derived from the mnemonic's words
+joined by single spaces, whatever whitespace is around or between them, so one
+word per line, tabs or extra spaces give the same keys.
+
+`KEYFUNC_MNEMONIC` and `KEYFUNC_MNEMONIC_COMMAND` are removed from the
+environment before the system `ssh` (`keyfunc ssh to`) and `sftp`
+(`keyfunc ssh install`) are started, so the mnemonic is never handed on to them.
 
 Every command takes `--index` / `-n` and `--mnemonic-command`, and has `--help`.
-`keyfunc --version` prints the version set at build time.
+`keyfunc --version` prints the version. `make build` stamps it; a binary
+installed with `go install` reports the module version instead.
 
 ## SSH keys: `keyfunc ssh`
 
-Only ed25519 keys are produced. The application number is `838372`, so the
+Only ed25519 keys are produced. The application number is `838372`, so the path
-path is `m/83696968'/838372'/<n>'`. The 32 bytes from step 4 are the ed25519
+is `m/83696968'/838372'/<n>'`. The 32 bytes from step 4 are the ed25519 seed.
-seed.
 
 Test vector, mnemonic
 `abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about`:
@@ -91,25 +163,32 @@ same as for `pub`.
 ### `keyfunc ssh install <[user@]host> [-- sftp options...]`
 
 Adds the `pub` line to `~/.ssh/authorized_keys` on the host. No command is run
-on the host: the file is fetched, changed here, and written back with the
+on the host: the file is fetched, changed here, and written back with the system
-system `sftp` client in batch mode.
+`sftp` client in batch mode.
 
-The first connection fetches `~/.ssh/authorized_keys`. The file reads as empty
+The first connection lists `~/.ssh`, then `~/.ssh/.`, and then fetches
-only when `sftp` reported that file as not being there — the one line naming
+`~/.ssh/authorized_keys`. The file reads as empty in two cases only: `sftp`
-that path. The same wording anywhere else in the session does not count: `ssh`
+reported `~/.ssh` itself as not being there, or both listings came up and the
-writes `No such file or directory` about an `-i` it cannot find, on a session
+file was not found. Any other outcome of that connection fails the run — a
-that then authenticates through the agent. When `sftp` failed for any other
+`~/.ssh` that is there but cannot be read or entered, an `authorized_keys` that
-reason — the file is there and cannot be read, the connection did not come up —
+is there but cannot be read, or a connection that did not come up — and the tool
-the tool prints what `sftp` said and exits with status 1 without writing
+prints what `sftp` said and exits with status 1 without writing anything, rather
-anything, rather than put a file back holding the new key alone. What `sftp`
+than put a file back holding the new key alone. The listings are what tell a
-cannot tell apart is a missing file and one in a directory it cannot enter, so a
+missing directory from one shut to the user, which `sftp` reports on a fetch the
-`~/.ssh` whose mode shuts the user out reads as a host with no file; the second
+same way: one that cannot be read fails the first listing, and one that can be
-connection sets that mode to `0700` and writes, as on a host that has none. If
+read but not entered fails the second, after which the tool says that `~/.ssh`
-an identical line is already in the file, the tool prints
+cannot be entered. The wording of a missing file elsewhere does not count
-`already present` and connects no further. Otherwise the line is added (after a
+either, since `ssh` writes `No such file or directory` about an `-i` it cannot
-newline, if the file did not end with one) and a second connection:
+find on a session that then authenticates through the agent. An
+`authorized_keys` that the first listing shows to be a symlink is refused and
+left as it is, since the rename below would replace the link itself and the file
+it points at would never get the key. If an identical line is already in the
+file, the tool prints `already present` and connects no further. Otherwise the
+line is added (after a newline, if the file did not end with one) and a second
+connection:
 
-- creates `~/.ssh` and sets it to mode `0700`;
+- makes `~/.ssh` and sets it to mode `0700`, but only when the first connection
+  found none; a `~/.ssh` that was already there keeps the mode it had;
 - uploads the new file as `~/.ssh/authorized_keys.keyfunc-<random>` and sets it
   to mode `0600`;
 - renames that file over `~/.ssh/authorized_keys`.
@@ -117,20 +196,22 @@ newline, if the file did not end with one) and a second connection:
 The tool then prints `added`. So a run that adds a line connects twice. The
 rename is the step that either happens or does not: the file on the host is
 never half-written. `sftp` does it in one step against servers that offer
-OpenSSH's POSIX rename extension, as OpenSSH's own server does; a server
+OpenSSH's POSIX rename extension, as OpenSSH's own server does; a server without
-without it may refuse to rename onto a file that is already there.
+it may refuse to rename onto a file that is already there.
 
 If a step fails, the tool prints what `sftp` said, removes nothing, and exits
-with status 1. It names the uploaded file only when the step that failed was
+with status 1. It names the uploaded file only when the step that failed was the
-the upload or one after it, which is where a file of that name can be on the
+upload or one after it, which is where a file of that name can be on the host; a
-host; a failure before the upload names none. Everything `sftp`
+failure before the upload names none. Everything `sftp` writes goes to standard
-writes goes to standard error, so the tool's own standard output is only
+error, so the tool's own standard output is only `added` or `already present`.
-`added` or `already present`.
 
 Anything after `--` is passed to `sftp` unchanged, which is where the port goes
 (`-P 2222`, not `-p`). How the connection authenticates is up to the user's
 normal `ssh` setup, except that batch mode does not prompt: a key or an agent
-has to do it, not a typed password.
+has to do it, not a typed password. Nor does it ask whether to trust a host key
+it has not seen, so the host has to be in `known_hosts` already, or the run
+fails with `Host key verification failed`. Connect to the host once with `ssh`
+first, or pass `-o StrictHostKeyChecking=accept-new` after `--`.
 
 ### `keyfunc ssh to <host> [ssh arguments...]`
 
@@ -138,15 +219,26 @@ Derives the key, serves it from an SSH agent that runs inside the tool on a unix
 socket in a new private `0700` temporary directory, then runs the system `ssh`
 with `-o IdentityAgent=<that socket>` followed by the host and all remaining
 arguments unchanged. The tool exits with `ssh`'s exit status and removes the
-socket and directory on the way out. The private key is never written to disk.
+socket and directory on the way out. The private key is never written to disk. A
+SIGINT, SIGTERM or SIGHUP ends `ssh` and still removes the socket and directory,
+and the tool then exits with status 1 unless `ssh` reported one of its own.
 
 ## age identities: `keyfunc age`
 
 The application number is `657169`, path `m/83696968'/657169'/<n>'`. The 32
-bytes from step 4 are clamped as X25519 requires and become an age identity,
+bytes from step 4 are clamped as X25519 requires and become an age identity, the
-the same steps `sneak/secret` takes in its `agehd` package. `secret` derives at
+same steps `sneak/secret` takes in its `agehd` package. `secret` derives at a
-a vendor-specific path today; for its keys to equal this tool's it moves to
+vendor-specific path today; for its keys to equal this tool's it moves to this
-this path, which is a change in `secret`, not here.
+path, which is a change in `secret`, not here.
+
+Test vectors, mnemonic
+`abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about`:
+
+```
+recipient index 0: age1xwdy9y6ckyfsgjc8k02e9uhsf3fmjy0ufysewlj68kmx5n67e3nsg2mftq
+recipient index 1: age1pmm92sxaf5mazjwvjph7dx2zq9r5p8l3rarfgqm7hmakqhvgyy4q5p3w7j
+identity index 0: AGE-SECRET-KEY-19QKK2P38598XLXMQFFU3P7J9PLDD7527T70JDHGDJ7AMNF3XT44S00JFU5
+```
 
 ### `keyfunc age pub`
 
@@ -163,50 +255,132 @@ identity's own recipient, plus any given with `--to`, so the same mnemonic can
 always decrypt what it encrypted. Output goes to `-o` or standard output;
 `--armor` writes the text form. Nothing is written except the output.
 
+A `-o` path that is the same file as the tool's own standard output or standard
+error, under any name such as `/dev/stdout` or `/dev/fd/2`, is written to that
+stream, as leaving out `-o` writes to standard output; the file the stream is
+redirected to is written as the redirect says and never replaced, so with `>>`
+the output follows what the file already held. Otherwise, a regular file already
+at the `-o` path is replaced, and the new file has mode `0600`. A symlink there
+is followed, and what it points at is treated the same way, so the link keeps
+pointing where it did; a symlink that points at nothing is refused. A named pipe
+or a device, such as `/dev/null`, is written to directly.
+
 ### `keyfunc age decrypt [-n N] [-o <file>] [<file>]`
 
 Decrypts the file (or standard input) with the derived identity. Output goes to
-`-o` or standard output. If the identity is not one of the recipients, the tool
+`-o`, which is treated as for `encrypt`, or standard output. If the identity is
-says so and exits with status 1.
+not one of the recipients, the tool says so and exits with status 1.
 
 ## Derived mnemonics: `keyfunc mnemonic`
 
 ### `keyfunc mnemonic [-n N] [--words 12|18|24]`
 
 Prints a child mnemonic derived from the main one, using BIP-85's own mnemonic
-application (number `39`, English, path
+application (number `39`, English, path `m/83696968'/39'/0'/<words>'/<n>'`,
-`m/83696968'/39'/0'/<words>'/<n>'`, entropy taken as the specification says,
+entropy taken as the specification says, not through step 4). Default 12 words.
-not through step 4). Default 12 words. A child mnemonic is a full mnemonic in
+A child mnemonic is a full mnemonic in its own right: it can seed another
-its own right: it can seed another `keyfunc`, another wallet, or `secret`, and
+`keyfunc`, another wallet, or `secret`, and it never has to be written down,
-it never has to be written down, since it can be derived again.
+since it can be derived again.
 
-## Adding a key type
+Test vector, mnemonic
+`abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about`:
 
-Adding a key type is one package under `internal/` that turns the 32 derived
+```
-bytes into that type's key, plus one cobra subcommand under `internal/cli/` that
+index 0: prosper short ramp prepare exchange stove life snack client enough purpose fold
-groups its commands.
+```
+
+The child-mnemonic step is also checked against BIP-85's own published vectors.
+Those start from the specification's master key
+`xprv9s21ZrQH143K2LBWUUQRFXhucrQqBpKdRRxNVq2zBqsx8HVqFk2uYo8kmbaLLHRdqtQpUm98uKfu3vca1LqdGhUtyoFnCNkfmXRyPXLjbKb`
+rather than from a mnemonic, so they cannot be given to `keyfunc`; at key index
+0 the 12-word English child mnemonic of that key is:
+
+```
+girl mad pet galaxy egg matter matrix prison refuse sense ordinary nose
+```
 
 ## Errors
 
-Errors go to standard error and the exit status is 1, except for `ssh to`,
+Errors go to standard error and the exit status is 1, except for `ssh to`, which
-which passes through `ssh`'s own exit status.
+passes through `ssh`'s own exit status.
 
-## Building and running
+SIGINT, SIGTERM and SIGHUP end any command at once, at the mnemonic prompt too,
+with the status a shell gives a program killed by that signal (130 for SIGINT).
+While `age encrypt -o` or `age decrypt -o` is writing a new file or replacing a
+regular one, the signal makes it remove the unfinished file, leave a file
+already at the named path as it was, and exit with status 1. That holds for a
+signal that has reached `keyfunc` when its input ends; a later one leaves the
+whole file in place. Ctrl-C on a pipeline ends the input at the same moment, and
+on Linux `keyfunc` sees the signal first, though no system promises that. A
+named pipe or a device at the `-o` path, or a path that is the same file as
+standard output or standard error, is written to directly, and the signal ends
+the tool there as it ends any other command. While `ssh to` or `ssh install` has
+`ssh` or `sftp` running, the signal ends that program instead, the tool removes
+its agent socket or working files, and it exits with status 1, or for `ssh to`
+with `ssh`'s own status if `ssh` reported one.
 
-```
+## Entrypoints
-make build    # produces ./keyfunc
-make check    # fmt-check, lint (golangci-lint) and tests
-```
 
-Examples:
+The repo adheres to the
+[Scripts to Rule Them All](https://github.com/github/scripts-to-rule-them-all)
+standard: most Makefile targets are thin shims over an executable in `script/`
+(`build` and `clean` are the exceptions).
 
-```
+- `script/bootstrap` installs, idempotently, everything needed to build and
-keyfunc ssh pub -n 3 --mnemonic-command 'secret get foo'
+  develop apart from Docker, which it only warns about when it is missing, and
-keyfunc ssh priv -n 3 > ~/.ssh/id_bip85_3
+  the linter, which only runs inside Docker. In this order:
-keyfunc ssh install -n 3 user@example.com
+    - git and make from nix, apt, brew or apk, and from there too curl and bash
-keyfunc ssh to -n 3 user@example.com uptime
+      when a later step needs them;
-keyfunc age pub -n 0
+    - Go at the version the `Dockerfile`'s Go image carries, from the official
-keyfunc age encrypt -n 0 --armor -o notes.age notes.txt
+      release archive at go.dev (checked against a sha256 in the script) into
-keyfunc age decrypt -n 0 notes.age
+      `~/.local/go`, unless the `go` first on the `PATH` already is that
-keyfunc mnemonic -n 1 --words 24
+      version; then the Go modules. `script/bootstrap` itself, `script/fmt`,
-```
+      `script/fmt-check`, `script/precommit` and the `Makefile` put
+      `~/.local/go/bin` first on their `PATH`, so they use that Go;
+    - node: an installed one is used as it is, otherwise a pinned one is
+      installed through nvm, which, when it is missing, comes from its release
+      archive, checked against a sha256;
+    - yarn: an installed one is used as it is, otherwise the pinned version
+      through corepack, or through npm where there is no corepack;
+    - the pinned prettier, through yarn.
+- `script/setup` prepares a fresh clone: it runs `bootstrap`, then installs the
+  git pre-commit hook.
+- `script/projectname` prints the project name; other scripts call it so they
+  stay identical across repos.
+- `script/test` builds the `test` phase of the `Dockerfile` alone, uncached: the
+  test suite runs with the race detector inside the build, rerunning verbosely
+  if a test fails.
+- `script/lint` builds the `lint` phase of the `Dockerfile` alone, uncached: the
+  linter, pinned by hash, runs inside the build, so a complaint fails it and
+  leaves no container behind.
+- `script/fmt` formats in place: the Go source with `go fmt`, then every
+  Markdown file with prettier (four-space indents, prose wrapped at 80 columns).
+- `script/fmt-check` checks the same files the same way without writing, failing
+  if anything is unformatted. Both need the node, yarn and prettier that
+  `bootstrap` installs.
+- `script/check` runs `test`, `lint` and `fmt-check` and changes no files.
+- `script/docker` builds the Docker image, uncached, tagged with the project
+  name and stamped with the version `git describe` gives on the host. The image
+  cannot be built unless the `lint` and `test` phases pass, so a plain
+  `docker build .` runs them too. The image is a development environment, not a
+  runtime image: the Debian Go image with what `script/bootstrap` installs, the
+  source tree in `/src`, and `keyfunc` built from it on the `PATH`.
+  `docker run --rm -it keyfunc` opens a shell in it.
+- `script/cibuild` is the CI build the Gitea workflow calls: it runs
+  `bootstrap`, then `check`, then builds the image as `script/docker` does.
+- `script/precommit` is what the git pre-commit hook runs: `go mod tidy` and
+  `go fmt`, failing if `go.mod` or `go.sum` changed, then `check`.
+- `script/install-precommit` installs the git pre-commit hook that runs
+  `script/precommit`.
+
+## TODO
+
+No issues are open.
+
+## License
+
+MIT. The full text is in [`LICENSE`](LICENSE).
+
+## Author
+
+[@sneak](https://sneak.berlin).

REPO_POLICIES.md

@@ -1,6 +1,6 @@
 ---
 title: Repository Policies
-last_modified: 2026-08-19
+last_modified: 2026-10-04
 ---
 
 This document covers repository structure, tooling, and workflow standards. Code
@@ -60,17 +60,28 @@ style conventions are in separate documents:
   prerequisite since nvm requires bash. yarn is then pinned via
   `corepack prepare yarn@<version> --activate`. Never install "latest" or "lts";
   always exact versions. `script/cibuild` runs the CI build: it changes to the
-  repo root and runs `docker build .`; the Gitea workflow calls it. Four further
+  repo root, runs `script/bootstrap`, runs `script/check`, and builds the image
-  scripts are our own extensions to the standard: `script/check` runs
+  with the version; the Gitea workflow calls it. **`script/cibuild` runs
-  `script/test`, `script/lint`, and `script/fmt-check`; `script/precommit` is
+  `script/bootstrap` first**, because the workflow checks out the repo and runs
-  what the git pre-commit hook runs, and it calls `script/check`;
+  nothing else, while `script/fmt-check` runs the formatter on the host: on a
-  `script/install-precommit` installs the git pre-commit hook (the `make hooks`
+  pristine checkout with nothing installed the run dies there, after the
-  target shims to it); and `script/projectname` (literally that filename) simply
+  containerised gates have passed. **The bootstrap alone is not enough**:
-  outputs the project's name. Scripts that need the name call
+  `script/bootstrap` installs node and yarn under nvm and leaves neither on the
-  `script/projectname` — e.g. `script/docker` assembles its image tag from it —
+  `PATH` of the shell that called it, so a bare `yarn` still exits 127. The host
-  so those scripts stay byte-identical across all repos. Repo-type-specific
+  entrypoints that need yarn — `script/fmt` and `script/fmt-check` — therefore
-  pre-commit extras (e.g. `go mod tidy` verification in Go repos) belong in
+  source nvm for the pinned node version before invoking it, exactly as
-  `script/precommit`, not in the hook itself. Model scripts are at
+  `script/bootstrap`'s own install step does. A runner carrying nothing but
+  docker and git then gets through `script/check`. Four further scripts are our
+  own extensions to the standard: `script/check` runs `script/test`,
+  `script/lint` and `script/fmt-check`; `script/precommit` is what the git
+  pre-commit hook runs, and it calls `script/check`; `script/install-precommit`
+  installs the git pre-commit hook (the `make hooks` target shims to it); and
+  `script/projectname` (literally that filename) simply outputs the project's
+  name. Scripts that need the name call `script/projectname` — e.g.
+  `script/docker` assembles its image tag from it — so those scripts stay
+  byte-identical across all repos. Repo-type-specific pre-commit extras (e.g.
+  `go mod tidy` verification in Go repos) belong in `script/precommit`, not in
+  the hook itself. Model scripts are at
   `https://git.eeqj.de/sneak/prompts/raw/branch/main/script/<name>`. The README
   must document the provided scripts in an **Entrypoints** section (see the
   README requirements below).
@@ -89,87 +100,198 @@ style conventions are in separate documents:
   contributor should be able to understand the entire development workflow by
   reading the Makefile.
 
-- Every repo should have a `Dockerfile`. All Dockerfiles must run `make check`
+- Every repo should have a `Dockerfile`, and it carries the repo's gates: a
-  as a build step so the build fails if the branch is not green. For non-server
+  `lint` phase and a `test` phase, with the final stage depending on both so the
-  repos, the Dockerfile should bring up a development environment and run
+  image cannot be built unless they pass. For non-server repos the final stage
-  `make check`. For server repos, `make check` should run as an early build
+  brings up a development environment; for server repos it is the runtime image.
-  stage before the final image is assembled. Dockerfiles install development
+  The gate phases and the build stage start from their pinned base images and
-  prerequisites by running `script/bootstrap` rather than duplicating installs
+  install what those images lack either inline, as the canonical Go `Dockerfile`
-  inline; COPY `script/` and the dependency manifests (`package.json` +
+  below does for `git`, or by running `script/bootstrap`, as the `prompts`
-  `yarn.lock`, `go.mod` + `go.sum`, etc.) before running it so the bootstrap
+  repo's own `Dockerfile` does for its yarn packages. The development
-  layer stays cached until dependencies change.
+  environment stage installs development prerequisites by running
+  `script/bootstrap` rather than duplicating its installs inline. A stage that
+  runs `script/bootstrap` COPYs `script/` and the dependency manifests
+  (`package.json` + `yarn.lock`, `go.mod` + `go.sum`, etc.) before running it.
 
-- **Dockerfiles must use a separate lint stage for fail-fast feedback.** Go
+- **Linting and testing run in Docker, as phases of the `Dockerfile`.** There is
-  repos use a multistage build where linting runs in an independent stage based
+  no separate lint file. `script/lint` and `script/test` each build one phase
-  on the `golangci/golangci-lint` image (pinned by hash). This stage runs
+  and nothing else:
-  `make fmt-check` and `make lint` before the full build begins. The build stage
-  then declares an explicit dependency on the lint stage via
-  `COPY --from=lint /src/go.sum /dev/null`, which forces BuildKit to complete
-  linting before proceeding to compilation and tests. This ensures lint failures
-  surface in seconds rather than minutes, without blocking on dependency
-  download or compilation in the build stage.
 
-    The standard pattern for a Go repo Dockerfile is:
+    ```sh
+    docker build --no-cache --target lint -t "$(script/projectname)-lint" .
+    docker build --no-cache --target test -t "$(script/projectname)-test" .
+    ```
+
+    **A stage that is not the last one in the file is built only when the final
+    stage's chain depends on it, or when `--target` names it.** That is why the
+    two gates are always invoked by name here, and why the final stage carries a
+    `COPY --from=` of a harmless file from each of them: without that edge a
+    plain `docker build .` builds the last stage alone and exits 0 having linted
+    and tested nothing.
+
+    **Every `docker build` in `script/` is tagged**, here and in
+    `script/cibuild` and `script/docker`. An untagged build leaves a dangling
+    image behind on every invocation, on every developer host and every CI
+    runner; a tagged one replaces the previous image.
+
+    Inside a phase the tool is invoked directly — `golangci-lint`, `go test`,
+    `eslint`, `prettier` — never through `make lint` or `script/test`, which are
+    themselves a `docker build` and would recurse into a daemon that does not
+    exist in a build step. Formatting is the exception and stays on the host:
+    `script/fmt` writes the working tree, and `script/fmt-check` is its
+    read-only twin.
+
+    **No lint verdict may come from a host invocation of the linter.** On a
+    shared host golangci-lint reads a result cache keyed on file content rather
+    than location, so a second checkout of the same content is served the first
+    one's findings, and a host-global lock in `$TMPDIR` makes concurrent runs
+    exit non-zero with `parallel golangci-lint is running` — a status a caller
+    cannot tell from real findings. Both have produced wrong verdicts in this
+    org, in both directions. A container has its own cache, its own `TMPDIR` and
+    a digest-pinned binary, so neither is reachable.
+
+- **Any build that runs checks is built with `--no-cache`.** Docker invalidates
+  a `COPY` layer only when the copied content changes, so on an unchanged tree
+  the check `RUN` is served from cache, nothing executes, and the build still
+  exits 0. Every `docker build` in `script/` therefore passes `--no-cache`:
+  `script/lint`, `script/test`, `script/cibuild` and `script/docker` are the
+  four, and there is no fifth — `script/check` runs the two gate phases and
+  `script/fmt-check`, and builds no image of its own. A bare `docker build .` is
+  not evidence that anything ran: a sub-second build reporting success is a
+  cache hit, not a result. Never invalidate by pruning — `docker builder prune`
+  and friends destroy a build cache shared with every other build on the host.
+  When a check is added or changed, prove it works by planting a defect it must
+  catch and watching the run fail on it, then revert the defect. A green run
+  alone shows neither that the check ran nor that it covers what it should.
+
+- **The gate phases are separate stages, and the build stage depends on both.**
+  The lint phase is based on the `golangci/golangci-lint` image (pinned by
+  hash), so lint failures surface in seconds rather than after a full compile,
+  and the test phase is based on the Debian Go image. The canonical Go repo
+  `Dockerfile`:
 
     ```dockerfile
-    # Lint stage — fast feedback on formatting and lint issues
+    # Lint phase
     # golangci/golangci-lint:v2.x.x, YYYY-MM-DD
     FROM golangci/golangci-lint@sha256:... AS lint
     WORKDIR /src
     COPY go.mod go.sum ./
     RUN go mod download
     COPY . .
-    RUN make fmt-check
+    RUN golangci-lint run --config .golangci.yml ./...
-    RUN make lint
 
-    # Build stage
+    # Test phase. -race needs cgo and so a C compiler, which the Debian Go
-    # golang:1.x-alpine, YYYY-MM-DD
+    # image ships and the alpine one does not.
-    FROM golang@sha256:... AS builder
+    # golang:1.x, YYYY-MM-DD
+    FROM golang@sha256:... AS test
     WORKDIR /src
-
-    # Force BuildKit to run the lint stage before proceeding
-    COPY --from=lint /src/go.sum /dev/null
-
     COPY go.mod go.sum ./
     RUN go mod download
     COPY . .
-    RUN make test
+    RUN go test -timeout 90s -race -cover ./... || \
+        { echo "--- Rerunning with -v for details ---"; \
+          go test -timeout 90s -race -v ./...; exit 1; }
 
-    ARG VERSION=dev
+    # Build stage. Nothing is wanted from either phase above; the copies
-    RUN CGO_ENABLED=0 go build -trimpath \
+    # are what make BuildKit build them first, so this stage cannot run
-        -ldflags="-s -w -X main.Version=${VERSION}" \
+    # unless lint and test passed.
-        -o /app ./cmd/app/
+    # golang:1.x-alpine, YYYY-MM-DD
+    FROM golang@sha256:... AS builder
+    COPY --from=lint /src/go.sum /dev/null
+    COPY --from=test /src/go.sum /dev/null
+    RUN apk add --no-cache git
+    # A tar-stream context keeps the sender's file owners, which git refuses.
+    RUN git config --system --add safe.directory /src
+    WORKDIR /src
+    COPY go.mod go.sum ./
+    RUN go mod download
+    COPY . .
 
-    # Runtime stage
+    # The VERSION build arg when one is given, otherwise
+    # `git describe --tags --always` on the .git in the build context. With
+    # .git present, a version that is still empty, dev or unknown fails the
+    # build: git is missing or could not read the checkout.
+    ARG VERSION
+    RUN VERSION="${VERSION:-$(git describe --tags --always)}"; \
+        if [ -e .git ]; then \
+            case "$VERSION" in ""|dev|unknown) \
+                echo "version is '$VERSION' although .git is present" >&2; \
+                exit 1 ;; \
+            esac; \
+        fi; \
+        CGO_ENABLED=0 go build -trimpath \
+            -ldflags="-s -w -X main.Version=${VERSION}" \
+            -o /app ./cmd/app/
+
+    # Runtime stage, and the last one
     FROM alpine@sha256:...
     COPY --from=builder /app /usr/local/bin/app
     ENTRYPOINT ["app"]
     ```
 
     Key points:
-    - The lint stage uses the `golangci/golangci-lint` image directly (it
+    - The lint phase uses the `golangci/golangci-lint` image directly (it has
-      includes both Go and the linter), so there is no need to install the
+      both Go and the linter), so nothing needs installing.
-      linter separately.
+    - `COPY --from=<phase> /src/go.sum /dev/null` is a no-op copy whose only
-    - `COPY --from=lint /src/go.sum /dev/null` is a no-op file copy that creates
+      purpose is the ordering edge. BuildKit runs stages in parallel by default,
-      a stage dependency. BuildKit runs stages in parallel by default; without
+      and a stage nothing depends on is not built at all, so without these two
-      this line, the build stage would not wait for lint to finish and a lint
+      lines a red gate would not fail the build.
-      failure might not fail the overall build.
+    - Keep the runtime stage last, and if you add a stage after it, give it the
+      same two copies. A plain `docker build .` builds the last stage's chain
+      and nothing else.
     - If the project uses `//go:embed` directives that reference build artifacts
-      (e.g. a web frontend compiled in a separate stage), the lint stage must
+      (e.g. a web frontend compiled in a separate stage), the lint phase must
       create placeholder files so the embed directives resolve. Example:
       `RUN mkdir -p web/dist && touch web/dist/index.html web/dist/style.css`.
-      The lint stage should not depend on the actual build output — it exists to
+    - If the project requires CGO or system libraries for linting, install them
-      fail fast.
+      in the lint phase. The `golangci/golangci-lint` image is Debian-based and
-    - If the project requires CGO or system libraries for linting (e.g.
+      has no `apk`, so install with `apt-get` under the Debian package name
-      `vips-dev`), install them in the lint stage with `apk add`.
+      (`libvips-dev`, where alpine says `vips-dev`), and delete the package
-    - The build stage runs `make test` after compilation setup. Tests run in the
+      lists in the same `RUN`, so the layer does not keep them:
-      build stage, not the lint stage, because they may require compiled
+
-      artifacts or heavier dependencies.
+        ```dockerfile
+        RUN apt-get update \
+            && apt-get install -y --no-install-recommends libvips-dev \
+            && rm -rf /var/lib/apt/lists/*
+        ```
+
+    - `.dockerignore` lets `.git` into the build context. It keeps out every git
+      `config` at any depth (`**/.git/config`, `**/.git/modules/**/config`): the
+      repository's own, each submodule's under `.git/modules/`, and that of a
+      submodule keeping its own `.git` directory. `git describe` does not need
+      them, and each can hold a credential: a password in a remote URL, or the
+      token the CI checkout step stores there. A submodule whose name has a
+      `config` segment (`config`, `deploy/config`, `config/lib`) loses its whole
+      git directory to `**/.git/modules/**/config`, and Go's version stamping
+      then fails the build: give it a name without that segment
+      (`git submodule add --name`). The stage that compiles has `git` (the
+      Debian Go image has it; an alpine one needs `apk add --no-cache git`) and
+      takes the version from the `VERSION` build argument when one is given,
+      otherwise from `git describe --tags --always`. That gives the tag on a
+      tagged commit; on a later commit, the tag, the number of commits since it
+      and the short commit (`v1.2.3-4-gabc1234`); and the short commit when no
+      tag is reachable. The stage that compiles also marks its working directory
+      safe for git (`git config --system --add safe.directory /src`): a context
+      sent as a tar stream keeps the sender's file owners, and git refuses a
+      checkout owned by another user, so the version would come out empty.
+      `ARG VERSION` has no default, and the build fails if the context carries
+      `.git` and the version still comes out empty, `dev` or `unknown`. A plain
+      `docker build .` with no build arguments must succeed; a Dockerfile that
+      refuses an empty build argument drops that refusal and keeps the argument.
 
 - Every repo should have a Gitea Actions workflow (`.gitea/workflows/`) that
-  runs `script/cibuild` (which runs `docker build .`) on push. Since the
+  runs `script/cibuild` on push, and checks out the repo as its only other step.
-  Dockerfile already runs `make check`, a successful build implies all checks
+  That script bootstraps, runs the gate phases, and then builds the image, so a
-  pass.
+  successful run means every check passed; a bare `docker build .` does not
+  carry the same guarantee, because its gate phases may come from the cache. The
+  image build is uncached and so runs the gate phases a second time. That is the
+  price of the rule above, and it is worth paying: the image that ships is built
+  from a run of its own gates rather than from a cache entry. A separate
+  workflow limited to `main` by a `branches` list under `on: push` cannot be
+  checked by review: to try a change to it, add the feature branch to that list
+  and push, then remove the branch from the list again before merging. Keep any
+  job in it that publishes behind `if: github.ref_name == 'main'`, so the run
+  from the feature branch publishes nothing.
 
 - Use platform-standard formatters: `black` for Python, `prettier` for
   JS/CSS/Markdown/HTML, `go fmt` for Go. Always use default configuration with
@@ -193,15 +315,17 @@ style conventions are in separate documents:
   suite that exceeds it fails. Under 20 seconds is the target. A suite between
   20 and 60 seconds is still green, but the overage must be filed as an
   improvement bug against that repo. Add a 90-second timeout to the test
-  invocation in the Makefile (`go test -timeout 90s`). The backstop deliberately
+  invocation (`go test -timeout 90s`). The backstop deliberately sits above the
-  sits above the hard cap so that it catches a genuinely hung test rather than a
+  hard cap so that it catches a genuinely hung test rather than a merely slow
-  merely slow one.
+  one.
 
-- **`make test` should use the conditional verbose rerun pattern.** Run tests
+- **The test command should use the conditional verbose rerun pattern.** Run
-  without `-v` (verbose) first. If tests fail, automatically rerun with `-v` to
+  tests without `-v` (verbose) first. If tests fail, automatically rerun with
-  show full output. This keeps CI logs and `docker build` output clean on
+  `-v` to show full output. This keeps CI logs and `docker build` output clean
-  success (just package/suite summaries) while providing full diagnostic detail
+  on success (just package/suite summaries) while providing full diagnostic
-  on failure (every test case, every assertion). The general shell pattern:
+  detail on failure (every test case, every assertion). The command lives in the
+  `test` phase of the `Dockerfile`, since `script/test` builds that phase; the
+  Makefile form below is the same pattern for any repo-local invocation:
 
     ```makefile
     test:
@@ -214,11 +338,26 @@ style conventions are in separate documents:
 
     ```makefile
     test:
-    	@go test -timeout 90s -race -cover ./... || \
+    	@go test -count=1 -timeout 90s -race -cover ./... || \
     		{ echo "--- Rerunning with -v for details ---"; \
-    		  go test -timeout 90s -race -v ./...; exit 1; }
+    		  go test -count=1 -timeout 90s -race -v ./...; exit 1; }
     ```
 
+    `-count=1` is required on both invocations: it defeats Go's test _result_
+    cache, so neither run can report a stored pass in place of running the
+    tests. It leaves the build cache alone, so it costs the runtime of the suite
+    and no recompilation.
+
+    That cache is Go's own, separate from Docker's layer cache. Go stores a
+    passing result in its cache directory (`GOCACHE`), and when the same tests
+    run again on unchanged code it prints that result, marked `(cached)`,
+    without running them. That matters on a developer's machine, where this
+    target runs and the directory lasts from one run to the next. The `test`
+    phase of the `Dockerfile` needs no `-count=1`: its base image holds no
+    result for this repo's tests and nothing before its `go test` step runs a
+    test, so there is nothing to replay. `--no-cache` (above) is what makes that
+    step run on an unchanged tree.
+
     Python example:
 
     ```makefile
@@ -244,10 +383,84 @@ style conventions are in separate documents:
   must be in `.gitignore`. No exceptions.
 
 - `.gitignore` should be comprehensive from the start: OS files (`.DS_Store`),
-  editor files (`.swp`, `*~`), language build artifacts, and `node_modules/`.
+  editor files (`.swp`, `*~`), in-repo agent scratch directories (`.claude/`),
-  Fetch the standard `.gitignore` from
+  language build artifacts, and `node_modules/`. Fetch the standard `.gitignore`
-  `https://git.eeqj.de/sneak/prompts/raw/branch/main/.gitignore` when setting up
+  from `https://git.eeqj.de/sneak/prompts/raw/branch/main/.gitignore` when
-  a new repo.
+  setting up a new repo. These patterns are written to `.gitignore`'s own
+  semantics, in which an unanchored pattern already matches at every depth; they
+  are not a `.dockerignore` and must not be transplanted into one unmodified.
+
+- **`.dockerignore` does not use `.gitignore` semantics, and copying patterns
+  across unmodified leaves secrets in the build context.** Docker matches with
+  `moby/patternmatcher`: `filepath.Match` semantics plus a `**` extension, so
+  `*` does not cross `/` and a pattern without a leading `**/` is anchored at
+  the build-context root. A `.dockerignore` listing `.env`, `*.pem` and `*.key`
+  therefore excludes only the copies at the repository root, while `config/.env`
+  and `certs/server.key` still reach the context and can land in an image layer
+  — which is more dangerous than a short file with no secret patterns at all,
+  because it reads as solved and stops anyone looking. Give every
+  depth-independent pattern the `**/` prefix and leave only genuinely
+  root-anchored entries unprefixed: `.claude`, and the repo's own host-built
+  binary, written `/myapp` and never `**/myapp`, which would also match
+  `cmd/myapp/` and delete the package directory from the context. Matching is
+  case-sensitive, and an ALL-CAPS twin per pattern still misses `Server.Key`, so
+  secret names use character ranges — `**/*.[kK][eE][yY]`, `**/*.[pP][eE][mM]`,
+  and likewise for `.envrc` and the extensionless SSH keys. Where such a pattern
+  also catches something the build needs, re-include it with a negation
+  (`!docs/example.env`); deleting the pattern reopens the exposure for every
+  other file it covers. Fetch the standard `.dockerignore` from
+  `https://git.eeqj.de/sneak/prompts/raw/branch/main/.dockerignore` and extend
+  it with the repo's own artifacts.
+
+- **In-repo agent scratch belongs in both files, written to each file's own
+  semantics.** `.claude/` holds one worktree per in-flight agent — an entire
+  additional checkout of the repo — so under `COPY . .` the build context
+  inflates by a multiple of the repo and another session's unreviewed work can
+  be copied into an image layer. In `.gitignore` the entry is `.claude/`,
+  unanchored. In `.dockerignore` it is `.claude`, anchored and with **no** `**/`
+  prefix, because the prefixed form would also delete any nested directory of
+  that name from the build. Anchoring carries a known gap that the canonical
+  `.dockerignore` states in its own comment, since consuming repos receive the
+  file and not the tracker: the directory is created in the agent's working
+  directory, so a repo running agents in subdirectories still ships
+  `services/api/.claude/` and must add its own anchored entry there.
+
+- **A plain `docker build .` of a clone stamps the version that
+  `git describe --tags --always` gives**, derived from the `.git` in the build
+  context as the canonical `Dockerfile` above shows. Without its failure check,
+  a missing `git` or an unreadable checkout would leave `-X main.Version=` empty
+  and the build would still exit 0. `script/docker` and `script/cibuild` pass
+  the version they compute on the host; it takes precedence. They do this
+  byte-identically across repos:
+
+    ```sh
+    # Own line: a failing command substitution inside an argument does not
+    # trip `set -e`, so the inline form degrades to an empty constant.
+    version="$(git describe --tags --always --dirty 2>/dev/null || true)"
+    [ -n "$version" ] || version="unknown"
+    docker build --no-cache \
+        --build-arg VERSION="$version" \
+        -t "$(script/projectname)" .
+    ```
+
+    `--always` makes an untagged repo yield an abbreviated commit hash rather
+    than failing, and the `[ -n "$version" ]` line is the single place the
+    fallback is applied — a live check that fires on a build from an export with
+    no `.git` and on a repository with no commits yet. Do not fold it into the
+    substitution as `|| echo unknown`, which makes the guard unreachable. The
+    Dockerfile's side is `ARG VERSION` in the stage that compiles, declared
+    there because `ARG` is stage-scoped; passing `VERSION` to a repo whose
+    Dockerfile declares no such `ARG` is ignored and costs nothing, which is why
+    the scripts stay byte-identical. One consequence for CI: the standard
+    checkout action clones shallow and fetches no tags, so a repo that embeds a
+    tag-derived version must set `fetch-depth: 0` on its checkout step.
+
+- **Verify `.dockerignore` by enumerating the image, not by reading the
+  patterns.** Plant files at the root _and_ at least two directories deep, build
+  a probe image that does `COPY . .`, and list what actually landed
+  (`docker run --rm --entrypoint find IMAGE /app`). The `transferring context`
+  size is not a substitute: a nested secret is a few bytes, and BuildKit
+  transfers only the delta from the previous build.
 
 - **No build artifacts in version control.** Code-derived data (compiled
   bundles, minified output, generated assets) must never be committed to the
@@ -269,9 +482,50 @@ style conventions are in separate documents:
   byte-identical, so that no repo can quietly loosen its own linting. Linter
   configuration changes are made to the canonical copy in the `prompts` repo and
   reach consuming repos by re-vendoring; an agent may open a PR against
-  canonical, which only the user merges. The canonical golangci-lint version is
+  canonical, which only the user merges. One list is exempt from byte-identity,
-  v2.12.2 (released 2026-05-06), installed commit-pinned via
+  because it cannot be written once for every repo: the `deny` list of the
-  `go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@c0d3ddc9cf3faa61a4e378e879ece580256d76e5`.
+  `test-support` depguard rule, where a repo names its own test-support packages
+  by full import path. A repo adds entries there and changes nothing else, and a
+  re-vendor carries its entries forward. The canonical golangci-lint version is
+  v2.14.0 (released 2026-09-24), pinned as the digest of the lint phase's base
+  image
+  (`golangci/golangci-lint@sha256:ad862ba6b3798cbe0fd9fd7408d498fd74fbd2623a92406b2fd3898faf0bf98f`,
+  which reports `2.14.0 built with go1.27.0 from 114493f9`). A module's `go`
+  directive must not name a newer Go minor version than the one golangci-lint
+  was built with, or golangci-lint refuses to lint it: this release lints
+  `go 1.27.1` but not `go 1.28`. That digest is the only pin, since no repo
+  installs golangci-lint on the host. A repo sets the lint phase digest to the
+  one named here and re-vendors `.golangci.yml` in the same commit, whichever of
+  the two prompted the change: the canonical copy can name linters that an older
+  golangci-lint rejects, and a newer golangci-lint can add linters that
+  `default: all` switches on until the canonical copy disables them.
+
+- **`script/bootstrap` installs a pinned tool by comparing versions, never by
+  testing presence.** An `if ! command -v <tool>; then install; fi` guard tests
+  `PATH` only, so on an already-provisioned machine the pin is inert and a
+  version bump is a silent no-op — while the Dockerfile, installing into a clean
+  image, gets the pinned version, so a local `make check` and `make docker` can
+  disagree about what the tool even is. The canonical form:
+    - compares the installed version against the pin over the **whole** version
+      token; a parser that stops at the first `-` reports `2.12.2` for a host
+      running `2.12.2-rc1` and skips the install;
+    - treats absent, non-zero, empty or unrecognised `--version` output as a
+      mismatch, so the failure direction is a redundant install and never a
+      skipped one;
+    - after installing, re-resolves the binary the way callers do — `hash -r`,
+      then through `PATH`, not through the directory the installer wrote to —
+      and fails naming the resolved path, since an install that a shadowing
+      binary hides succeeds while changing nothing any caller sees;
+    - is actually called, and prints the version on both success paths: a
+      function defined and never invoked has the same exit status and the same
+      empty output as one that worked.
+
+    Keep it POSIX sh: no arrays, no `[[`, no `grep -P`.
+
+    A Go tool a repo needs on the host is installed with `go install` pinned to
+    a commit hash (`go install <package>@<commit hash>`). It is never tracked as
+    a `go.mod` tool dependency or through a `tools.go` file, either of which
+    pulls the tool's own dependencies into the repo's `go.mod` and `go.sum`.
 
 - When pinning images or packages by hash, add a comment above the reference
   with the version and date (YYYY-MM-DD).
@@ -385,10 +639,10 @@ style conventions are in separate documents:
   settings.
 
 - Avoid putting files in the repo root unless necessary. Root should contain
-  only project-level config files (`README.md`, `Makefile`, `Dockerfile`,
+  only project-level config files (`README.md`, `AGENTS.md`, `Makefile`,
-  `LICENSE`, `.gitignore`, `.editorconfig`, `REPO_POLICIES.md`, and
+  `Dockerfile`, `LICENSE`, `.gitignore`, `.editorconfig`, `REPO_POLICIES.md`,
-  language-specific config). Everything else goes in a subdirectory. Canonical
+  and language-specific config). Everything else goes in a subdirectory.
-  subdirectory names:
+  Canonical subdirectory names:
     - `bin/` — executable scripts and tools
     - `cmd/` — Go command entrypoints; thin only: one `main.go` per binary whose
       body is a single call into `internal/` or `pkg/`, no project logic in
@@ -419,3 +673,7 @@ style conventions are in separate documents:
     - Go: `go.mod`, `go.sum`, `.golangci.yml`
     - JS: `package.json`, `yarn.lock`, `.prettierrc`, `.prettierignore`
     - Python: `pyproject.toml`
+
+- Guidance for coding agents lives in one `AGENTS.md` at the repository root. It
+  is never committed under a file or directory named after one agent tool, such
+  as `CLAUDE.md` or `.claude/`, and never split into separate memory files.

cmd/keyfunc/main.go

@@ -4,7 +4,7 @@ package main
 import (
 	"os"
 
-	"git.eeqj.de/sneak/keyfunc/internal/cli"
+	"sneak.berlin/go/keyfunc/internal/cli"
 )
 
 func main() {

go.mod

@@ -1,27 +1,26 @@
-module git.eeqj.de/sneak/keyfunc
+module sneak.berlin/go/keyfunc
 
-go 1.26
+go 1.26.0
 
 require (
-	filippo.io/age v1.2.1
+	filippo.io/age v1.3.2
 	git.eeqj.de/sneak/secret v0.0.0-20260810132333-41cea400a7fd
-	github.com/btcsuite/btcd v0.24.2
+	github.com/btcsuite/btcd v0.25.0
-	github.com/btcsuite/btcd/btcutil v1.1.6
+	github.com/btcsuite/btcd/btcutil v1.2.0
-	github.com/spf13/cobra v1.9.1
+	github.com/spf13/cobra v1.10.2
-	github.com/stretchr/testify v1.8.4
+	github.com/stretchr/testify v1.12.1
-	github.com/tyler-smith/go-bip39 v1.1.0
+	golang.org/x/crypto v0.57.0
-	golang.org/x/crypto v0.38.0
+	golang.org/x/term v0.46.0
-	golang.org/x/term v0.32.0
 )
 
 require (
-	github.com/btcsuite/btcd/btcec/v2 v2.1.3 // indirect
+	filippo.io/hpke v0.4.0 // indirect
-	github.com/btcsuite/btcd/chaincfg/chainhash v1.1.0 // indirect
+	github.com/btcsuite/btcd/btcec/v2 v2.5.0 // indirect
-	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/btcsuite/btcd/chaincfg/chainhash v1.2.0 // indirect
-	github.com/decred/dcrd/dcrec/secp256k1/v4 v4.0.1 // indirect
+	github.com/decred/dcrd/dcrec/secp256k1/v4 v4.4.0 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
-	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/kcalvinalvin/anet v0.0.0-20251112173137-d8ddc1f6dbee // indirect
-	github.com/spf13/pflag v1.0.6 // indirect
+	github.com/spf13/pflag v1.0.9 // indirect
-	golang.org/x/sys v0.33.0 // indirect
+	go.yaml.in/yaml/v3 v3.0.5 // indirect
-	gopkg.in/yaml.v3 v3.0.1 // indirect
+	golang.org/x/sys v0.48.0 // indirect
 )

go.sum

@@ -1,136 +1,44 @@
-c2sp.org/CCTV/age v0.0.0-20240306222714-3ec4d716e805 h1:u2qwJeEvnypw+OCPUHmoZE3IqwfuN5kgDfo5MLzpNM0=
+c2sp.org/CCTV/age v0.0.0-20260829155415-4448f2097b2d h1:Blprhc2SbChNZtWcU+BLTM4YdoqYAS9V7cJgOwJKyAs=
-c2sp.org/CCTV/age v0.0.0-20240306222714-3ec4d716e805/go.mod h1:FomMrUJ2Lxt5jCLmZkG3FHa72zUprnhd3v/Z18Snm4w=
+c2sp.org/CCTV/age v0.0.0-20260829155415-4448f2097b2d/go.mod h1:SrHC2C7r5GkDk8R+NFVzYy/sdj0Ypg9htaPXQq5Cqeo=
-filippo.io/age v1.2.1 h1:X0TZjehAZylOIj4DubWYU1vWQxv9bJpo+Uu2/LGhi1o=
+filippo.io/age v1.3.2 h1:r6RSZLFSMm6rzKepZ7ZAYkKCu14f3/Me8c7uKYh7C8c=
-filippo.io/age v1.2.1/go.mod h1:JL9ew2lTN+Pyft4RiNGguFfOpewKwSHm5ayKD/A4004=
+filippo.io/age v1.3.2/go.mod h1:TH/Yr2sSRhCKbaH4XPxpUV0Us8Gv6txYUpiZQWz8Evk=
+filippo.io/hpke v0.4.0 h1:p575VVQ6ted4pL+it6M00V/f2qTZITO0zgmdKCkd5+A=
+filippo.io/hpke v0.4.0/go.mod h1:EmAN849/P3qdeK+PCMkDpDm83vRHM5cDipBJ8xbQLVY=
 git.eeqj.de/sneak/secret v0.0.0-20260810132333-41cea400a7fd h1:6YFV6horz2wDFPWWhour8qx8gLGyO0qoplwEeOuQ2J4=
 git.eeqj.de/sneak/secret v0.0.0-20260810132333-41cea400a7fd/go.mod h1:gKCcMZvlBOqusn/BxR8IyFmSJQr6R4vvjJ926iNpOSI=
-github.com/aead/siphash v1.0.1/go.mod h1:Nywa3cDsYNNK3gaciGTWPwHt0wlpNV15vwmswBAUSII=
+github.com/btcsuite/btcd v0.25.0 h1:JPbjwvHGpSywBRuorFFqTjaVP4y6Qw69XJ1nQ6MyWJM=
-github.com/btcsuite/btcd v0.20.1-beta/go.mod h1:wVuoA8VJLEcwgqHBwHmzLRazpKxTv13Px/pDuV7OomQ=
+github.com/btcsuite/btcd v0.25.0/go.mod h1:qbPE+pEiR9643E1s1xu57awsRhlCIm1ZIi6FfeRA4KE=
-github.com/btcsuite/btcd v0.22.0-beta.0.20220111032746-97732e52810c/go.mod h1:tjmYdS6MLJ5/s0Fj4DbLgSbDHbEqLJrtnHecBFkdz5M=
+github.com/btcsuite/btcd/btcec/v2 v2.5.0 h1:KioMXOWa76b86sTZZOmbzv/ldaQCmB8KFAyn5PbB8E8=
-github.com/btcsuite/btcd v0.23.5-0.20231215221805-96c9fd8078fd/go.mod h1:nm3Bko6zh6bWP60UxwoT5LzdGJsQJaPo6HjduXq9p6A=
+github.com/btcsuite/btcd/btcec/v2 v2.5.0/go.mod h1:+K/MYXcLBtHEQjRbjHuJChuybk4LCgjdjgRwil+e+Kk=
-github.com/btcsuite/btcd v0.24.2 h1:aLmxPguqxza+4ag8R1I2nnJjSu2iFn/kqtHTIImswcY=
+github.com/btcsuite/btcd/btcutil v1.2.0 h1:p3+S2g3Q+7G5NOh4Ji+2UrBOrg5Z0Q4ykzShWG1Dhgs=
-github.com/btcsuite/btcd v0.24.2/go.mod h1:5C8ChTkl5ejr3WHj8tkQSCmydiMEPB0ZhQhehpq7Dgg=
+github.com/btcsuite/btcd/btcutil v1.2.0/go.mod h1:/Taflm113pYjUpbWKKQEfa6XOtI/+WS8awxeMZpY75k=
-github.com/btcsuite/btcd/btcec/v2 v2.1.0/go.mod h1:2VzYrv4Gm4apmbVVsSq5bqf1Ec8v56E48Vt0Y/umPgA=
+github.com/btcsuite/btcd/chaincfg/chainhash v1.2.0 h1:yMIg99+4aBvqfl/HzJRKfxTX9rGfikoI9uvFzterhc8=
-github.com/btcsuite/btcd/btcec/v2 v2.1.3 h1:xM/n3yIhHAhHy04z4i43C8p4ehixJZMsnrVJkgl+MTE=
+github.com/btcsuite/btcd/chaincfg/chainhash v1.2.0/go.mod h1:Y72Ren9gfhlEvnwnT78BGcSNO2UMphTKLn9AorF+5rg=
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-google.golang.org/protobuf v1.21.0/go.mod h1:47Nbq4nVaFHyn7ilMalzfO3qCViNmqZ2kzikPIcrTAo=
-google.golang.org/protobuf v1.23.0/go.mod h1:EGpADcykh3NcUnDUJcl1+ZksZNG86OlYog2l/sGQquU=
-gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
-gopkg.in/fsnotify.v1 v1.4.7/go.mod h1:Tz8NjZHkW78fSQdbUxIjBTcgA1z1m8ZHf0WmKUhAMys=
-gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7/go.mod h1:dt/ZhP58zS4L8KSrWDmTeBkI65Dw0HsyUHuEVlX15mw=
-gopkg.in/yaml.v2 v2.2.1/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
-gopkg.in/yaml.v2 v2.2.4/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
-gopkg.in/yaml.v2 v2.3.0/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
-gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
-gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
-gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

internal/agekey/agekey_test.go

@@ -5,9 +5,9 @@ import (
 	"strings"
 	"testing"
 
-	"git.eeqj.de/sneak/keyfunc/internal/agekey"
-	"git.eeqj.de/sneak/keyfunc/internal/derive"
 	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/keyfunc/internal/agekey"
+	"sneak.berlin/go/keyfunc/internal/derive"
 )
 
 // The recipients the example mnemonic produces at the first two

internal/bip39/LICENSE

@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2014-2018 Tyler Smith and contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

internal/bip39/bip39.go

@@ -0,0 +1,268 @@
+// Package bip39 is the Golang implementation of the BIP39 spec.
+//
+// The official BIP39 spec can be found at
+// https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki
+//
+// It is a copy of github.com/tyler-smith/go-bip39 v1.1.0, trimmed to what
+// keyfunc uses.
+//
+//nolint:mnd // the numbers are BIP-39's own, written as upstream writes them
+package bip39
+
+import (
+	"crypto/sha256"
+	"crypto/sha512"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"math/big"
+	"strings"
+
+	"golang.org/x/crypto/pbkdf2"
+)
+
+var (
+	// ErrInvalidMnemonic is returned when trying to use a malformed mnemonic.
+	ErrInvalidMnemonic = errors.New("invalid mnenomic")
+
+	// ErrEntropyLengthInvalid is returned when trying to use an entropy set with
+	// an invalid size.
+	ErrEntropyLengthInvalid = errors.New(
+		"entropy length must be [128, 256] and a multiple of 32",
+	)
+
+	// ErrChecksumIncorrect is returned when entropy has the incorrect checksum.
+	ErrChecksumIncorrect = errors.New("checksum incorrect")
+)
+
+// EntropyFromMnemonic takes a mnemonic generated by this library,
+// and returns the input entropy used to generate the given mnemonic.
+// An error is returned if the given mnemonic is invalid.
+func EntropyFromMnemonic(mnemonic string) ([]byte, error) {
+	mnemonicSlice, isValid := splitMnemonicWords(mnemonic)
+	if !isValid {
+		return nil, ErrInvalidMnemonic
+	}
+
+	// Some bitwise operands for working with big.Ints
+	shift11BitsMask := big.NewInt(2048)
+	bigOne := big.NewInt(1)
+
+	// used to isolate the checksum bits from the entropy+checksum byte array
+	wordLengthChecksumMasksMapping := map[int]*big.Int{
+		12: big.NewInt(15),
+		15: big.NewInt(31),
+		18: big.NewInt(63),
+		21: big.NewInt(127),
+		24: big.NewInt(255),
+	}
+	// used to use only the desired x of 8 available checksum bits.
+	// 256 bit (word length 24) requires all 8 bits of the checksum,
+	// and thus no shifting is needed for it (we would get a divByZero crash if we did)
+	wordLengthChecksumShiftMapping := map[int]*big.Int{
+		12: big.NewInt(16),
+		15: big.NewInt(8),
+		18: big.NewInt(4),
+		21: big.NewInt(2),
+	}
+
+	// wordMap is a reverse lookup map for the word list
+	wordMap := map[string]int{}
+	for i, v := range English() {
+		wordMap[v] = i
+	}
+
+	// Decode the words into a big.Int.
+	b := big.NewInt(0)
+
+	for _, v := range mnemonicSlice {
+		index, found := wordMap[v]
+		if !found {
+			return nil, fmt.Errorf(
+				"%w: word `%v` not found in reverse map", ErrInvalidMnemonic, v,
+			)
+		}
+
+		var wordBytes [2]byte
+
+		//nolint:gosec // the index of a word in the list is below 2048
+		binary.BigEndian.PutUint16(wordBytes[:], uint16(index))
+
+		b = b.Mul(b, shift11BitsMask)
+		b = b.Or(b, big.NewInt(0).SetBytes(wordBytes[:]))
+	}
+
+	// Build and add the checksum to the big.Int.
+	checksum := big.NewInt(0)
+	checksumMask := wordLengthChecksumMasksMapping[len(mnemonicSlice)]
+	checksum = checksum.And(b, checksumMask)
+
+	b.Div(b, big.NewInt(0).Add(checksumMask, bigOne))
+
+	// The entropy is the underlying bytes of the big.Int. Any upper bytes of
+	// all 0's are not returned so we pad the beginning of the slice with empty
+	// bytes if necessary.
+	entropy := b.Bytes()
+	entropy = padByteSlice(entropy, len(mnemonicSlice)/3*4)
+
+	// Generate the checksum and compare with the one we got from the mneomnic.
+	entropyChecksumBytes := computeChecksum(entropy)
+	entropyChecksum := big.NewInt(int64(entropyChecksumBytes[0]))
+
+	if l := len(mnemonicSlice); l != 24 {
+		checksumShift := wordLengthChecksumShiftMapping[l]
+		entropyChecksum.Div(entropyChecksum, checksumShift)
+	}
+
+	if checksum.Cmp(entropyChecksum) != 0 {
+		return nil, ErrChecksumIncorrect
+	}
+
+	return entropy, nil
+}
+
+// NewMnemonic will return a string consisting of the mnemonic words for
+// the given entropy.
+// If the provide entropy is invalid, an error will be returned.
+func NewMnemonic(entropy []byte) (string, error) {
+	// Compute some lengths for convenience.
+	entropyBitLength := len(entropy) * 8
+	checksumBitLength := entropyBitLength / 32
+	sentenceLength := (entropyBitLength + checksumBitLength) / 11
+
+	// Validate that the requested size is supported.
+	err := validateEntropyBitSize(entropyBitLength)
+	if err != nil {
+		return "", err
+	}
+
+	// Some bitwise operands for working with big.Ints
+	last11BitsMask := big.NewInt(2047)
+	shift11BitsMask := big.NewInt(2048)
+
+	// wordList is the set of words to use
+	wordList := English()
+
+	// Add checksum to entropy.
+	entropy = addChecksum(entropy)
+
+	// Break entropy up into sentenceLength chunks of 11 bits.
+	// For each word AND mask the rightmost 11 bits and find the word at that index.
+	// Then bitshift entropy 11 bits right and repeat.
+	// Add to the last empty slot so we can work with LSBs instead of MSB.
+
+	// Entropy as an int so we can bitmask without worrying about bytes slices.
+	entropyInt := new(big.Int).SetBytes(entropy)
+
+	// Slice to hold words in.
+	words := make([]string, sentenceLength)
+
+	// Throw away big.Int for AND masking.
+	word := big.NewInt(0)
+
+	for i := sentenceLength - 1; i >= 0; i-- {
+		// Get 11 right most bits and bitshift 11 to the right for next time.
+		word.And(entropyInt, last11BitsMask)
+		entropyInt.Div(entropyInt, shift11BitsMask)
+
+		// Get the bytes representing the 11 bits as a 2 byte slice.
+		wordBytes := padByteSlice(word.Bytes(), 2)
+
+		// Convert bytes to an index and add that word to the list.
+		words[i] = wordList[binary.BigEndian.Uint16(wordBytes)]
+	}
+
+	return strings.Join(words, " "), nil
+}
+
+// NewSeed creates a hashed seed output given a provided string and password.
+// No checking is performed to validate that the string provided is a valid mnemonic.
+func NewSeed(mnemonic string, password string) []byte {
+	return pbkdf2.Key([]byte(mnemonic), []byte("mnemonic"+password), 2048, 64, sha512.New)
+}
+
+// IsMnemonicValid attempts to verify that the provided mnemonic is valid.
+// Validity is determined by both the number of words being appropriate,
+// and that all the words in the mnemonic are present in the word list.
+func IsMnemonicValid(mnemonic string) bool {
+	_, err := EntropyFromMnemonic(mnemonic)
+
+	return err == nil
+}
+
+// Appends to data the first (len(data) / 32)bits of the result of sha256(data)
+// Currently only supports data up to 32 bytes
+func addChecksum(data []byte) []byte {
+	// Some bitwise operands for working with big.Ints
+	bigOne := big.NewInt(1)
+	bigTwo := big.NewInt(2)
+
+	// Get first byte of sha256
+	hash := computeChecksum(data)
+	firstChecksumByte := hash[0]
+
+	// len() is in bytes so we divide by 4
+	checksumBitLength := uint(len(data) / 4)
+
+	// For each bit of check sum we want we shift the data one the left
+	// and then set the (new) right most bit equal to checksum bit at that index
+	// staring from the left
+	dataBigInt := new(big.Int).SetBytes(data)
+	for i := range checksumBitLength {
+		// Bitshift 1 left
+		dataBigInt.Mul(dataBigInt, bigTwo)
+
+		// Set rightmost bit if leftmost checksum bit is set
+		if firstChecksumByte&(1<<(7-i)) > 0 {
+			dataBigInt.Or(dataBigInt, bigOne)
+		}
+	}
+
+	return dataBigInt.Bytes()
+}
+
+func computeChecksum(data []byte) []byte {
+	hasher := sha256.New()
+	hasher.Write(data)
+
+	return hasher.Sum(nil)
+}
+
+// validateEntropyBitSize ensures that entropy is the correct size for being a
+// mnemonic.
+func validateEntropyBitSize(bitSize int) error {
+	if (bitSize%32) != 0 || bitSize < 128 || bitSize > 256 {
+		return ErrEntropyLengthInvalid
+	}
+
+	return nil
+}
+
+// padByteSlice returns a byte slice of the given size with contents of the
+// given slice left padded and any empty spaces filled with 0's.
+func padByteSlice(slice []byte, length int) []byte {
+	offset := length - len(slice)
+	if offset <= 0 {
+		return slice
+	}
+
+	newSlice := make([]byte, length)
+	copy(newSlice[offset:], slice)
+
+	return newSlice
+}
+
+func splitMnemonicWords(mnemonic string) ([]string, bool) {
+	// Create a list of all the words in the mnemonic sentence
+	words := strings.Fields(mnemonic)
+
+	// Get num of words
+	numOfWords := len(words)
+
+	// The number of words should be 12, 15, 18, 21 or 24
+	if numOfWords%3 != 0 || numOfWords < 12 || numOfWords > 24 {
+		return nil, false
+	}
+
+	return words, true
+}

internal/bip39/bip39_internal_test.go

@@ -0,0 +1,442 @@
+package bip39
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"testing"
+)
+
+type vector struct {
+	entropy  string
+	mnemonic string
+	seed     string
+}
+
+func TestNewMnemonic(t *testing.T) {
+	t.Parallel()
+
+	for _, vector := range testVectors() {
+		entropy, err := hex.DecodeString(vector.entropy)
+		assertNil(t, err)
+
+		mnemonic, err := NewMnemonic(entropy)
+		assertNil(t, err)
+		assertEqualString(t, vector.mnemonic, mnemonic)
+
+		seed := NewSeed(mnemonic, "TREZOR")
+		assertEqualString(t, vector.seed, hex.EncodeToString(seed))
+	}
+}
+
+func TestNewMnemonicInvalidEntropy(t *testing.T) {
+	t.Parallel()
+
+	_, err := NewMnemonic([]byte{})
+	assertNotNil(t, err)
+}
+
+func TestIsMnemonicValid(t *testing.T) {
+	t.Parallel()
+
+	for _, vector := range badMnemonicSentences() {
+		assertFalse(t, IsMnemonicValid(vector.mnemonic))
+	}
+
+	for _, vector := range testVectors() {
+		assertTrue(t, IsMnemonicValid(vector.mnemonic))
+	}
+}
+
+func TestPadByteSlice(t *testing.T) {
+	t.Parallel()
+
+	assertEqualByteSlices(t, []byte{0}, padByteSlice([]byte{}, 1))
+	assertEqualByteSlices(t, []byte{0, 1}, padByteSlice([]byte{1}, 2))
+	assertEqualByteSlices(t, []byte{1, 1}, padByteSlice([]byte{1, 1}, 2))
+	assertEqualByteSlices(t, []byte{1, 1, 1}, padByteSlice([]byte{1, 1, 1}, 2))
+}
+
+//nolint:funlen // the test vectors, kept as upstream wrote them
+func TestMnemonicToByteArrayForZeroLeadingSeeds(t *testing.T) {
+	t.Parallel()
+
+	ms := []string{
+		"00000000000000000000000000000000",
+		"00a84c51041d49acca66e6160c1fa999",
+		"00ca45df1673c76537a2020bfed1dafd",
+		"0019d5871c7b81fd83d474ef1c1e1dae",
+		"00dcb021afb35ffcdd1d032d2056fc86",
+		"0062be7bd09a27288b6cf0eb565ec739",
+		"00dc705b5efa0adf25b9734226ba60d4",
+		"0017747418d54c6003fa64fade83374b",
+		"000d44d3ee7c3dfa45e608c65384431b",
+		"008241c1ef976b0323061affe5bf24b9",
+		"00a6aec77e4d16bea80b50a34991aaba",
+		"0011527b8c6ddecb9d0c20beccdeb58d",
+		"001c938c503c8f5a2bba2248ff621546",
+		"0002f90aaf7a8327698f0031b6317c36",
+		"00bff43071ed7e07f77b14f615993bac",
+		"00da143e00ef17fc63b6fb22dcc2c326",
+		"00ffc6764fb32a354cab1a3ddefb015d",
+		"0062ef47e0985e8953f24760b7598cdd",
+		"003bf9765064f71d304908d906c065f5",
+		"00993851503471439d154b3613947474",
+		"007ad0ffe9eae753a483a76af06dfa67",
+		"00091824db9ec19e663bee51d64c83cc",
+		"00f48ac621f7e3cb39b2012ac3121543",
+		"0072917415cdca24dfa66c4a92c885b4",
+		"0027ced2b279ea8a91d29364487cdbf4",
+		"00b9c0d37fb10ba272e55842ad812583",
+		"004b3d0d2b9285946c687a5350479c8c",
+		"00c7c12a37d3a7f8c1532b17c89b724c",
+		"00f400c5545f06ae17ad00f3041e4e26",
+		"001e290be10df4d209f247ac5878662b",
+		"00bf0f74568e582a7dd1ee64f792ec8b",
+		"00d2e43ecde6b72b847db1539ed89e23",
+		"00cecba6678505bb7bfec8ed307251f6",
+		"000aeed1a9edcbb4bc88f610d3ce84eb",
+		"00d06206aadfc25c2b21805d283f15ae",
+		"00a31789a2ab2d54f8fadd5331010287",
+		"003493c5f520e8d5c0483e895a121dc9",
+		"004706112800b76001ece2e268bc830e",
+		"00ab31e28bb5305be56e38337dbfa486",
+		"006872fe85df6b0fa945248e6f9379d1",
+		"00717e5e375da6934e3cfdf57edaf3bd",
+		"007f1b46e7b9c4c76e77c434b9bccd6b",
+		"00dc93735aa35def3b9a2ff676560205",
+		"002cd5dcd881a49c7b87714c6a570a76",
+		"0013b5af9e13fac87e0c505686cfb6bf",
+		"007ab1ec9526b0bc04b64ae65fd42631",
+		"00abb4e11d8385c1cca905a6a65e9144",
+		"00574fc62a0501ad8afada2e246708c3",
+		"005207e0a815bb2da6b4c35ec1f2bf52",
+		"00f3460f136fb9700080099cbd62bc18",
+		"007a591f204c03ca7b93981237112526",
+		"00cfe0befd428f8e5f83a5bfc801472e",
+		"00987551ac7a879bf0c09b8bc474d9af",
+		"00cadd3ce3d78e49fbc933a85682df3f",
+		"00bfbf2e346c855ccc360d03281455a1",
+		"004cdf55d429d028f715544ce22d4f31",
+		"0075c84a7d15e0ac85e1e41025eed23b",
+		"00807dddd61f71725d336cab844d2cb5",
+		"00422f21b77fe20e367467ed98c18410",
+		"00b44d0ac622907119c626c850a462fd",
+		"00363f5e7f22fc49f3cd662a28956563",
+		"000fe5837e68397bbf58db9f221bdc4e",
+		"0056af33835c888ef0c22599686445d3",
+		"00790a8647fd3dfb38b7e2b6f578f2c6",
+		"00da8d9009675cb7beec930e263014fb",
+		"00d4b384540a5bb54aa760edaa4fb2fe",
+		"00be9b1479ed680fdd5d91a41eb926d0",
+		"009182347502af97077c40a6e74b4b5c",
+		"00f5c90ee1c67fa77fd821f8e9fab4f1",
+		"005568f9a2dd6b0c0cc2f5ba3d9cac38",
+		"008b481f8678577d9cf6aa3f6cd6056b",
+		"00c4323ece5e4fe3b6cd4c5c932931af",
+		"009791f7550c3798c5a214cb2d0ea773",
+		"008a7baab22481f0ad8167dd9f90d55c",
+		"00f0e601519aafdc8ff94975e64c946d",
+		"0083b61e0daa9219df59d697c270cd31",
+	}
+
+	for _, m := range ms {
+		seed, _ := hex.DecodeString(m)
+
+		mnemonic, err := NewMnemonic(seed)
+		if err != nil {
+			t.Errorf("%v", err)
+		}
+
+		_, err = EntropyFromMnemonic(mnemonic)
+		if err != nil {
+			t.Errorf("Failed for %x - %v", seed, mnemonic)
+		}
+	}
+}
+
+func TestEntropyFromMnemonic128(t *testing.T) {
+	t.Parallel()
+
+	testEntropyFromMnemonic(t, 128)
+}
+
+func TestEntropyFromMnemonic160(t *testing.T) {
+	t.Parallel()
+
+	testEntropyFromMnemonic(t, 160)
+}
+
+func TestEntropyFromMnemonic192(t *testing.T) {
+	t.Parallel()
+
+	testEntropyFromMnemonic(t, 192)
+}
+
+func TestEntropyFromMnemonic224(t *testing.T) {
+	t.Parallel()
+
+	testEntropyFromMnemonic(t, 224)
+}
+
+func TestEntropyFromMnemonic256(t *testing.T) {
+	t.Parallel()
+
+	testEntropyFromMnemonic(t, 256)
+}
+
+//nolint:dupword,lll // the test vector, kept as upstream wrote it
+func TestEntropyFromMnemonicInvalidChecksum(t *testing.T) {
+	t.Parallel()
+
+	_, err := EntropyFromMnemonic("abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon yellow")
+	assertEqual(t, ErrChecksumIncorrect, err)
+}
+
+//nolint:dupword // the test vectors, kept as upstream wrote them
+func TestEntropyFromMnemonicInvalidMnemonicSize(t *testing.T) {
+	t.Parallel()
+
+	for _, mnemonic := range []string{
+		"a a a a a a a a a a a a a a a a a a a a a a a a a", // Too many words
+		"a",                           // Too few
+		"a a a a a a a a a a a a a a", // Not multiple of 3
+	} {
+		_, err := EntropyFromMnemonic(mnemonic)
+		assertEqual(t, ErrInvalidMnemonic, err)
+	}
+}
+
+func testEntropyFromMnemonic(t *testing.T, bitSize int) {
+	t.Helper()
+
+	for range 512 {
+		expectedEntropy := make([]byte, bitSize/8)
+		_, err := rand.Read(expectedEntropy)
+		assertNil(t, err)
+		assertTrue(t, len(expectedEntropy) != 0)
+
+		mnemonic, err := NewMnemonic(expectedEntropy)
+		assertNil(t, err)
+		assertTrue(t, len(mnemonic) != 0)
+
+		actualEntropy, err := EntropyFromMnemonic(mnemonic)
+		assertNil(t, err)
+		assertEqualByteSlices(t, expectedEntropy, actualEntropy)
+	}
+}
+
+//nolint:dupword,funlen,lll // the BIP-39 test vectors, kept as upstream wrote them
+func testVectors() []vector {
+	return []vector{
+		{
+			entropy:  "00000000000000000000000000000000",
+			mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about",
+			seed:     "c55257c360c07c72029aebc1b53c05ed0362ada38ead3e3e9efa3708e53495531f09a6987599d18264c1e1c92f2cf141630c7a3c4ab7c81b2f001698e7463b04",
+		},
+		{
+			entropy:  "7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f",
+			mnemonic: "legal winner thank year wave sausage worth useful legal winner thank yellow",
+			seed:     "2e8905819b8723fe2c1d161860e5ee1830318dbf49a83bd451cfb8440c28bd6fa457fe1296106559a3c80937a1c1069be3a3a5bd381ee6260e8d9739fce1f607",
+		},
+		{
+			entropy:  "80808080808080808080808080808080",
+			mnemonic: "letter advice cage absurd amount doctor acoustic avoid letter advice cage above",
+			seed:     "d71de856f81a8acc65e6fc851a38d4d7ec216fd0796d0a6827a3ad6ed5511a30fa280f12eb2e47ed2ac03b5c462a0358d18d69fe4f985ec81778c1b370b652a8",
+		},
+		{
+			entropy:  "ffffffffffffffffffffffffffffffff",
+			mnemonic: "zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo wrong",
+			seed:     "ac27495480225222079d7be181583751e86f571027b0497b5b5d11218e0a8a13332572917f0f8e5a589620c6f15b11c61dee327651a14c34e18231052e48c069",
+		},
+		{
+			entropy:  "000000000000000000000000000000000000000000000000",
+			mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon agent",
+			seed:     "035895f2f481b1b0f01fcf8c289c794660b289981a78f8106447707fdd9666ca06da5a9a565181599b79f53b844d8a71dd9f439c52a3d7b3e8a79c906ac845fa",
+		},
+		{
+			entropy:  "7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f",
+			mnemonic: "legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal will",
+			seed:     "f2b94508732bcbacbcc020faefecfc89feafa6649a5491b8c952cede496c214a0c7b3c392d168748f2d4a612bada0753b52a1c7ac53c1e93abd5c6320b9e95dd",
+		},
+		{
+			entropy:  "808080808080808080808080808080808080808080808080",
+			mnemonic: "letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter always",
+			seed:     "107d7c02a5aa6f38c58083ff74f04c607c2d2c0ecc55501dadd72d025b751bc27fe913ffb796f841c49b1d33b610cf0e91d3aa239027f5e99fe4ce9e5088cd65",
+		},
+		{
+			entropy:  "ffffffffffffffffffffffffffffffffffffffffffffffff",
+			mnemonic: "zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo when",
+			seed:     "0cd6e5d827bb62eb8fc1e262254223817fd068a74b5b449cc2f667c3f1f985a76379b43348d952e2265b4cd129090758b3e3c2c49103b5051aac2eaeb890a528",
+		},
+		{
+			entropy:  "0000000000000000000000000000000000000000000000000000000000000000",
+			mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon art",
+			seed:     "bda85446c68413707090a52022edd26a1c9462295029f2e60cd7c4f2bbd3097170af7a4d73245cafa9c3cca8d561a7c3de6f5d4a10be8ed2a5e608d68f92fcc8",
+		},
+		{
+			entropy:  "7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f",
+			mnemonic: "legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth title",
+			seed:     "bc09fca1804f7e69da93c2f2028eb238c227f2e9dda30cd63699232578480a4021b146ad717fbb7e451ce9eb835f43620bf5c514db0f8add49f5d121449d3e87",
+		},
+		{
+			entropy:  "8080808080808080808080808080808080808080808080808080808080808080",
+			mnemonic: "letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic bless",
+			seed:     "c0c519bd0e91a2ed54357d9d1ebef6f5af218a153624cf4f2da911a0ed8f7a09e2ef61af0aca007096df430022f7a2b6fb91661a9589097069720d015e4e982f",
+		},
+		{
+			entropy:  "ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff",
+			mnemonic: "zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo vote",
+			seed:     "dd48c104698c30cfe2b6142103248622fb7bb0ff692eebb00089b32d22484e1613912f0a5b694407be899ffd31ed3992c456cdf60f5d4564b8ba3f05a69890ad",
+		},
+		{
+			entropy:  "77c2b00716cec7213839159e404db50d",
+			mnemonic: "jelly better achieve collect unaware mountain thought cargo oxygen act hood bridge",
+			seed:     "b5b6d0127db1a9d2226af0c3346031d77af31e918dba64287a1b44b8ebf63cdd52676f672a290aae502472cf2d602c051f3e6f18055e84e4c43897fc4e51a6ff",
+		},
+		{
+			entropy:  "b63a9c59a6e641f288ebc103017f1da9f8290b3da6bdef7b",
+			mnemonic: "renew stay biology evidence goat welcome casual join adapt armor shuffle fault little machine walk stumble urge swap",
+			seed:     "9248d83e06f4cd98debf5b6f010542760df925ce46cf38a1bdb4e4de7d21f5c39366941c69e1bdbf2966e0f6e6dbece898a0e2f0a4c2b3e640953dfe8b7bbdc5",
+		},
+		{
+			entropy:  "3e141609b97933b66a060dcddc71fad1d91677db872031e85f4c015c5e7e8982",
+			mnemonic: "dignity pass list indicate nasty swamp pool script soccer toe leaf photo multiply desk host tomato cradle drill spread actor shine dismiss champion exotic",
+			seed:     "ff7f3184df8696d8bef94b6c03114dbee0ef89ff938712301d27ed8336ca89ef9635da20af07d4175f2bf5f3de130f39c9d9e8dd0472489c19b1a020a940da67",
+		},
+		{
+			entropy:  "0460ef47585604c5660618db2e6a7e7f",
+			mnemonic: "afford alter spike radar gate glance object seek swamp infant panel yellow",
+			seed:     "65f93a9f36b6c85cbe634ffc1f99f2b82cbb10b31edc7f087b4f6cb9e976e9faf76ff41f8f27c99afdf38f7a303ba1136ee48a4c1e7fcd3dba7aa876113a36e4",
+		},
+		{
+			entropy:  "72f60ebac5dd8add8d2a25a797102c3ce21bc029c200076f",
+			mnemonic: "indicate race push merry suffer human cruise dwarf pole review arch keep canvas theme poem divorce alter left",
+			seed:     "3bbf9daa0dfad8229786ace5ddb4e00fa98a044ae4c4975ffd5e094dba9e0bb289349dbe2091761f30f382d4e35c4a670ee8ab50758d2c55881be69e327117ba",
+		},
+		{
+			entropy:  "2c85efc7f24ee4573d2b81a6ec66cee209b2dcbd09d8eddc51e0215b0b68e416",
+			mnemonic: "clutch control vehicle tonight unusual clog visa ice plunge glimpse recipe series open hour vintage deposit universe tip job dress radar refuse motion taste",
+			seed:     "fe908f96f46668b2d5b37d82f558c77ed0d69dd0e7e043a5b0511c48c2f1064694a956f86360c93dd04052a8899497ce9e985ebe0c8c52b955e6ae86d4ff4449",
+		},
+		{
+			entropy:  "eaebabb2383351fd31d703840b32e9e2",
+			mnemonic: "turtle front uncle idea crush write shrug there lottery flower risk shell",
+			seed:     "bdfb76a0759f301b0b899a1e3985227e53b3f51e67e3f2a65363caedf3e32fde42a66c404f18d7b05818c95ef3ca1e5146646856c461c073169467511680876c",
+		},
+		{
+			entropy:  "7ac45cfe7722ee6c7ba84fbc2d5bd61b45cb2fe5eb65aa78",
+			mnemonic: "kiss carry display unusual confirm curtain upgrade antique rotate hello void custom frequent obey nut hole price segment",
+			seed:     "ed56ff6c833c07982eb7119a8f48fd363c4a9b1601cd2de736b01045c5eb8ab4f57b079403485d1c4924f0790dc10a971763337cb9f9c62226f64fff26397c79",
+		},
+		{
+			entropy:  "4fa1a8bc3e6d80ee1316050e862c1812031493212b7ec3f3bb1b08f168cabeef",
+			mnemonic: "exile ask congress lamp submit jacket era scheme attend cousin alcohol catch course end lucky hurt sentence oven short ball bird grab wing top",
+			seed:     "095ee6f817b4c2cb30a5a797360a81a40ab0f9a4e25ecd672a3f58a0b5ba0687c096a6b14d2c0deb3bdefce4f61d01ae07417d502429352e27695163f7447a8c",
+		},
+		{
+			entropy:  "18ab19a9f54a9274f03e5209a2ac8a91",
+			mnemonic: "board flee heavy tunnel powder denial science ski answer betray cargo cat",
+			seed:     "6eff1bb21562918509c73cb990260db07c0ce34ff0e3cc4a8cb3276129fbcb300bddfe005831350efd633909f476c45c88253276d9fd0df6ef48609e8bb7dca8",
+		},
+		{
+			entropy:  "18a2e1d81b8ecfb2a333adcb0c17a5b9eb76cc5d05db91a4",
+			mnemonic: "board blade invite damage undo sun mimic interest slam gaze truly inherit resist great inject rocket museum chief",
+			seed:     "f84521c777a13b61564234bf8f8b62b3afce27fc4062b51bb5e62bdfecb23864ee6ecf07c1d5a97c0834307c5c852d8ceb88e7c97923c0a3b496bedd4e5f88a9",
+		},
+		{
+			entropy:  "15da872c95a13dd738fbf50e427583ad61f18fd99f628c417a61cf8343c90419",
+			mnemonic: "beyond stage sleep clip because twist token leaf atom beauty genius food business side grid unable middle armed observe pair crouch tonight away coconut",
+			seed:     "b15509eaa2d09d3efd3e006ef42151b30367dc6e3aa5e44caba3fe4d3e352e65101fbdb86a96776b91946ff06f8eac594dc6ee1d3e82a42dfe1b40fef6bcc3fd",
+		},
+	}
+}
+
+//nolint:dupword,lll // the test vectors, kept as upstream wrote them
+func badMnemonicSentences() []vector {
+	return []vector{
+		{mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon"},
+		{mnemonic: "legal winner thank year wave sausage worth useful legal winner thank yellow yellow"},
+		{mnemonic: "letter advice cage absurd amount doctor acoustic avoid letter advice caged above"},
+		{mnemonic: "zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo, wrong"},
+		{mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon"},
+		{mnemonic: "legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal will will will"},
+		{mnemonic: "letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter always."},
+		{mnemonic: "zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo why"},
+		{mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon art art"},
+		{mnemonic: "legal winner thank year wave sausage worth useful legal winner thanks year wave worth useful legal winner thank year wave sausage worth title"},
+		{mnemonic: "letter advice cage absurd amount doctor acoustic avoid letters advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic bless"},
+		{mnemonic: "zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo voted"},
+		{mnemonic: "jello better achieve collect unaware mountain thought cargo oxygen act hood bridge"},
+		{mnemonic: "renew, stay, biology, evidence, goat, welcome, casual, join, adapt, armor, shuffle, fault, little, machine, walk, stumble, urge, swap"},
+		{mnemonic: "dignity pass list indicate nasty"},
+
+		// From issue 32
+		{mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon letter"},
+	}
+}
+
+func assertNil(t *testing.T, object any) {
+	t.Helper()
+
+	if object != nil {
+		t.Errorf("Expected nil, got %v", object)
+	}
+}
+
+func assertNotNil(t *testing.T, object any) {
+	t.Helper()
+
+	if object == nil {
+		t.Error("Expected not nil")
+	}
+}
+
+func assertTrue(t *testing.T, a bool) {
+	t.Helper()
+
+	if !a {
+		t.Error("Expected true, got false")
+	}
+}
+
+func assertFalse(t *testing.T, a bool) {
+	t.Helper()
+
+	if a {
+		t.Error("Expected false, got true")
+	}
+}
+
+func assertEqual(t *testing.T, a, b any) {
+	t.Helper()
+
+	if a != b {
+		t.Errorf("Objects not equal, expected `%s` and got `%s`", a, b)
+	}
+}
+
+func assertEqualString(t *testing.T, a, b string) {
+	t.Helper()
+
+	if a != b {
+		t.Errorf("Strings not equal, expected `%s` and got `%s`", a, b)
+	}
+}
+
+func assertEqualByteSlices(t *testing.T, a, b []byte) {
+	t.Helper()
+
+	if len(a) != len(b) {
+		t.Errorf("Byte slices not equal, expected %v and got %v", a, b)
+
+		return
+	}
+
+	for i := range a {
+		if a[i] != b[i] {
+			t.Errorf("Byte slices not equal, expected %v and got %v", a, b)
+
+			return
+		}
+	}
+}

internal/bip39/english_internal_test.go

@@ -0,0 +1,19 @@
+package bip39
+
+import (
+	"hash/crc32"
+	"testing"
+)
+
+func TestEnglishChecksum(t *testing.T) {
+	t.Parallel()
+
+	// Ensure word list is correct
+	// $ wget https://raw.githubusercontent.com/bitcoin/bips/master/bip-0039/english.txt
+	// $ crc32 english.txt
+	// c1dbd296
+	checksum := crc32.ChecksumIEEE([]byte(english))
+	if checksum != 0xc1dbd296 {
+		t.Error("english checksum invalid")
+	}
+}

internal/bip39/example_test.go

@@ -0,0 +1,30 @@
+package bip39_test
+
+import (
+	"encoding/hex"
+	"fmt"
+
+	"sneak.berlin/go/keyfunc/internal/bip39"
+)
+
+//nolint:lll // the test vector and its output, kept as upstream wrote them
+func ExampleNewMnemonic() {
+	// the entropy can be any byte slice, generated how pleased,
+	// as long its bit size is a multiple of 32 and is within
+	// the inclusive range of {128,256}
+	entropy, _ := hex.DecodeString("066dca1a2bb7e8a1db2832148ce9933eea0f3ac9548d793112d9a95c9407efad")
+
+	// generate a mnemomic
+	mnemomic, _ := bip39.NewMnemonic(entropy)
+	fmt.Println(mnemomic)
+	// output:
+	// all hour make first leader extend hole alien behind guard gospel lava path output census museum junior mass reopen famous sing advance salt reform
+}
+
+//nolint:lll // the test vector and its output, kept as upstream wrote them
+func ExampleNewSeed() {
+	seed := bip39.NewSeed("all hour make first leader extend hole alien behind guard gospel lava path output census museum junior mass reopen famous sing advance salt reform", "TREZOR")
+	fmt.Println(hex.EncodeToString(seed))
+	// output:
+	// 26e975ec644423f4a4c4f4215ef09b4bd7ef924e85d1d17c4cf3f136c2863cf6df0a475045652c57eb5fb41513ca2a2d67722b77e954b4b3fc11f7590449191d
+}

internal/childmnemonic/childmnemonic.go

@@ -5,10 +5,10 @@ import (
 	"errors"
 	"fmt"
 
-	"git.eeqj.de/sneak/keyfunc/internal/derive"
 	"git.eeqj.de/sneak/secret/pkg/bip85"
 	"github.com/btcsuite/btcd/btcutil/hdkeychain"
-	bip39 "github.com/tyler-smith/go-bip39"
+	"sneak.berlin/go/keyfunc/internal/bip39"
+	"sneak.berlin/go/keyfunc/internal/derive"
 )
 
 // english is the number BIP-85 gives the English word list.

internal/childmnemonic/childmnemonic_test.go

@@ -4,11 +4,11 @@ import (
 	"strings"
 	"testing"
 
-	"git.eeqj.de/sneak/keyfunc/internal/childmnemonic"
-	"git.eeqj.de/sneak/keyfunc/internal/derive"
 	"github.com/btcsuite/btcd/btcutil/hdkeychain"
 	"github.com/stretchr/testify/require"
-	bip39 "github.com/tyler-smith/go-bip39"
+	"sneak.berlin/go/keyfunc/internal/bip39"
+	"sneak.berlin/go/keyfunc/internal/childmnemonic"
+	"sneak.berlin/go/keyfunc/internal/derive"
 )
 
 // The lengths the tool offers, and one it does not.

internal/cli/age/age.go

@@ -3,15 +3,26 @@
 package age
 
 import (
+	"context"
+	"errors"
 	"fmt"
 	"io"
+	"io/fs"
 	"os"
+	"os/signal"
 	"path/filepath"
 
-	"git.eeqj.de/sneak/keyfunc/internal/agekey"
-	"git.eeqj.de/sneak/keyfunc/internal/cli/options"
-	"git.eeqj.de/sneak/keyfunc/internal/derive"
 	"github.com/spf13/cobra"
+	"sneak.berlin/go/keyfunc/internal/agekey"
+	"sneak.berlin/go/keyfunc/internal/cli/options"
+	"sneak.berlin/go/keyfunc/internal/cli/signals"
+	"sneak.berlin/go/keyfunc/internal/derive"
+)
+
+// ErrInterrupted is returned when SIGINT, SIGTERM or SIGHUP has been
+// received by the time the work writing the file --output names ends.
+var ErrInterrupted = errors.New(
+	"interrupted by a signal; the output file was left as it was",
 )
 
 // Command returns the age command and everything under it.
@@ -128,8 +139,12 @@ func runDecrypt(cmd *cobra.Command, args []string) error {
 	return through(cmd, args, key.Decrypt)
 }
 
-// through opens the input and the output the arguments ask for, hands
+// through opens the input the arguments ask for and hands it to the
-// them to the work, and finishes the output afterwards either way.
+// work, with the file --output names to write to, or the command's own
+// output when it names none or names the same file as that output, and
+// the command's own error output when it names the same file as that.
+// Those two are the streams the tool already has, so whatever they are
+// redirected to is written as the redirect says, never replaced.
 func through(
 	cmd *cobra.Command, args []string,
 	work func(io.Writer, io.Reader) error,
@@ -141,14 +156,41 @@ func through(
 
 	defer closeSrc()
 
-	dst, done, err := output(cmd)
+	name, err := cmd.Flags().GetString("output")
 	if err != nil {
-		return err
+		return fmt.Errorf("reading the output file: %w", err)
 	}
 
-	err = work(dst, src)
+	switch {
+	case name == "", same(name, cmd.OutOrStdout()):
+		return work(cmd.OutOrStdout(), src)
+	case same(name, cmd.ErrOrStderr()):
+		return work(cmd.ErrOrStderr(), src)
+	default:
+		return output(name, src, work)
+	}
+}
 
-	return done(err)
+// same reports whether the named path, followed to the end, is the
+// file the stream writes to, whatever name it is reached by, such as
+// /dev/stdout or /dev/fd/1 for standard output.
+func same(name string, stream io.Writer) bool {
+	file, ok := stream.(*os.File)
+	if !ok {
+		return false
+	}
+
+	streamInfo, err := file.Stat()
+	if err != nil {
+		return false
+	}
+
+	info, err := os.Stat(name)
+	if err != nil {
+		return false
+	}
+
+	return os.SameFile(info, streamInfo)
 }
 
 // input returns what to read from: the named file, or the command's
@@ -167,35 +209,127 @@ func input(cmd *cobra.Command, args []string) (io.Reader, func(), error) {
 	return file, func() { _ = file.Close() }, nil
 }
 
-// output returns what to write to: a new file beside the one --output
+// output has the work write to the named path, going by what is there
-// names, or the command's own output when it names none. The second
+// without following a final symlink:
-// result finishes the write, and is given whatever the work returned:
+//
-// the new file takes the named file's place only when the work
+//   - nothing, or a regular file: replace writes a new file beside it
-// succeeded, so a file that is already there survives a run that
+//     and renames that over it;
-// failed.
+//   - a symlink: the same for what it points at, so that the link keeps
-func output(cmd *cobra.Command) (io.Writer, func(error) error, error) {
+//     pointing where it did; one that points at nothing is refused;
-	name, err := cmd.Flags().GetString("output")
+//   - anything else, such as a named pipe or a device like /dev/null:
+//     direct writes to it, since a rename would put a regular file in
+//     its place.
+func output(
+	name string, src io.Reader, work func(io.Writer, io.Reader) error,
+) error {
+	info, err := os.Lstat(name)
+
+	switch {
+	case errors.Is(err, fs.ErrNotExist):
+		return replace(name, src, work)
+	case err != nil:
+		return fmt.Errorf("looking at %s: %w", name, err)
+	case info.Mode().IsRegular():
+		return replace(name, src, work)
+	case info.Mode().Type() == fs.ModeSymlink:
+		// os.Stat follows the link as opening it would. /dev/fd/3
+		// needs that: it reaches a pipe or a terminal through a link
+		// that names no path.
+		info, err = os.Stat(name)
+		if err != nil {
+			return fmt.Errorf("following %s: %w", name, err)
+		}
+
+		if !info.Mode().IsRegular() {
+			return direct(name, src, work)
+		}
+
+		target, err := filepath.EvalSymlinks(name)
+		if err != nil {
+			return fmt.Errorf("following %s: %w", name, err)
+		}
+
+		return replace(target, src, work)
+	default:
+		return direct(name, src, work)
+	}
+}
+
+// direct has the work write straight to the named path, which is there
+// and is not a regular file. No signal is caught, so one ends the tool
+// as it ends any other command.
+func direct(
+	name string, src io.Reader, work func(io.Writer, io.Reader) error,
+) error {
+	file, err := os.OpenFile(name, os.O_WRONLY, 0) //nolint:gosec // the -o path
 	if err != nil {
-		return nil, nil, fmt.Errorf("reading the output file: %w", err)
+		return fmt.Errorf("opening %s: %w", name, err)
 	}
 
-	if name == "" {
+	failed := work(file, src)
-		return cmd.OutOrStdout(), func(failed error) error {
+	closeErr := file.Close()
-			return failed
+
-		}, nil
+	if failed != nil {
+		return failed
 	}
 
+	if closeErr != nil {
+		return fmt.Errorf("finishing %s: %w", name, closeErr)
+	}
+
+	return nil
+}
+
+// replace has the work write a new file beside the named one, and puts
+// the new file in the named file's place only when the work succeeded,
+// so a file that is already there survives a run that failed.
+//
+// Meanwhile SIGINT, SIGTERM and SIGHUP are caught, as signals.Context
+// does. One the tool has received by the time the work ends wins: the
+// new file is removed and ErrInterrupted returned, at once if the work
+// is still running, without waiting for it, since it may be blocked
+// reading its input.
+func replace(
+	name string, src io.Reader, work func(io.Writer, io.Reader) error,
+) error {
+	// received is registered before the context, so it gets every
+	// signal the context gets.
+	received := make(chan os.Signal, 1)
+	signals.Notify(received)
+
+	defer signal.Stop(received)
+
+	// The context goes on catching the signals until the file is in
+	// place or removed, so that a later one cannot end the tool with
+	// the new file left beside the named one.
+	interrupted, stop := signals.Context(context.Background())
+	defer stop()
+
 	// The file is made in the same directory so that putting it in
 	// place is a rename and never a copy, and it is readable only by
 	// its owner, which is the mode it keeps once renamed.
 	file, err := os.CreateTemp(filepath.Dir(name), filepath.Base(name)+".")
 	if err != nil {
-		return nil, nil, fmt.Errorf("creating a file beside %s: %w", name, err)
+		return fmt.Errorf("creating a file beside %s: %w", name, err)
 	}
 
-	return file, func(failed error) error {
+	worked := make(chan error, 1)
-		return finish(file, name, failed)
+
-	}, nil
+	go func() { worked <- work(file, src) }()
+
+	select {
+	case failed := <-worked:
+		// Stop returns only once every signal the tool has received
+		// has been handed over, so an empty received means none came.
+		signal.Stop(received)
+
+		if len(received) == 0 {
+			return finish(file, name, failed)
+		}
+	case <-interrupted.Done():
+	}
+
+	return finish(file, name, ErrInterrupted)
 }
 
 // finish closes the new file and puts it in the named file's place, or

internal/cli/age_test.go

@@ -1,14 +1,23 @@
 package cli_test
 
 import (
+	"errors"
+	"io"
+	"io/fs"
 	"os"
+	"os/exec"
+	"os/signal"
 	"path/filepath"
 	"strings"
+	"syscall"
 	"testing"
+	"time"
 
-	"git.eeqj.de/sneak/keyfunc/internal/agekey"
-	"git.eeqj.de/sneak/keyfunc/internal/mnemonic"
 	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/keyfunc/internal/agekey"
+	"sneak.berlin/go/keyfunc/internal/cli"
+	"sneak.berlin/go/keyfunc/internal/cli/age"
+	"sneak.berlin/go/keyfunc/internal/mnemonic"
 )
 
 func TestTheAgeCommandsPrintTheKey(t *testing.T) {
@@ -90,6 +99,360 @@ func TestARefusedDecryptionLeavesTheOutputFileAlone(t *testing.T) {
 	require.Equal(t, "what was already there\n", string(kept))
 }
 
+func TestASymlinkAtTheOutputPathStaysAndItsTargetGetsTheOutput(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	plain := written(t, "notes.txt", "the secret\n")
+	target := written(t, "notes.age", "what was already there\n")
+	link := filepath.Join(t.TempDir(), "notes.age")
+	require.NoError(t, os.Symlink(target, link))
+
+	run(t, "age", "encrypt", "-o", link, plain)
+
+	pointsAt, err := os.Readlink(link)
+	require.NoError(t, err)
+	require.Equal(t, target, pointsAt)
+	require.Equal(t, "the secret\n", run(t, "age", "decrypt", target))
+}
+
+func TestANamedPipeAtTheOutputPathIsWrittenToAndStaysAPipe(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	plain := written(t, "notes.txt", "the secret\n")
+	pipe := filepath.Join(t.TempDir(), "notes.age")
+	require.NoError(t, syscall.Mkfifo(pipe, fileMode))
+
+	// Opening the pipe to read waits until the tool opens it to write.
+	var sealed []byte
+
+	finished := make(chan error, 1)
+
+	go func() {
+		var err error
+
+		sealed, err = os.ReadFile(pipe) //nolint:gosec // the test's own path
+		finished <- err
+	}()
+
+	run(t, "age", "encrypt", "-o", pipe, plain)
+
+	select {
+	case err := <-finished:
+		require.NoError(t, err)
+	case <-time.After(5 * time.Second):
+		t.Fatal("nothing was written to the pipe")
+	}
+
+	info, err := os.Lstat(pipe)
+	require.NoError(t, err)
+	require.Equal(t, fs.ModeNamedPipe, info.Mode().Type())
+
+	sealedFile := written(t, "notes.age", string(sealed))
+	require.Equal(t, "the secret\n", run(t, "age", "decrypt", sealedFile))
+}
+
+func TestANameForStandardOutputAddsToTheFileItIsAppendedTo(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	sealed := filepath.Join(t.TempDir(), "notes.age")
+	run(t, "age", "encrypt", "-o", sealed, written(t, "notes.txt", "the secret\n"))
+
+	for _, name := range []string{"/dev/stdout", "/dev/fd/1"} {
+		appendedThrough(t, name, sealed)
+	}
+}
+
+// appendedThrough decrypts sealed with -o name while the tool's standard
+// output is appended to a file that already has contents, as the shell's
+// ">> notes.out" does, and checks that the file is the same one, with
+// the same mode, and holds its earlier contents and then the output.
+func appendedThrough(t *testing.T, name, sealed string) {
+	t.Helper()
+
+	// A mode of its own, so that a replaced file would show.
+	const ownMode = 0o644
+
+	existing := written(t, "notes.out", "what was already there\n")
+	require.NoError(t, os.Chmod(existing, ownMode))
+
+	before, err := os.Stat(existing)
+	require.NoError(t, err)
+
+	//nolint:gosec // the test made this path itself
+	appended, err := os.OpenFile(existing, os.O_WRONLY|os.O_APPEND, 0)
+	require.NoError(t, err)
+
+	defer func() { _ = appended.Close() }()
+
+	//nolint:gosec // this test's own binary as the tool
+	command := exec.CommandContext(
+		t.Context(), os.Args[0], "age", "decrypt", "-o", name, sealed,
+	)
+
+	command.Env = append(os.Environ(), runAsTool+"=1")
+	command.Stdout = appended
+
+	require.NoError(t, command.Run(), name)
+	require.Equal(t,
+		"what was already there\nthe secret\n", read(t, existing), name,
+	)
+
+	after, err := os.Stat(existing)
+	require.NoError(t, err)
+	require.True(t, os.SameFile(before, after), name)
+	require.Equal(t, os.FileMode(ownMode), after.Mode().Perm(), name)
+}
+
+func TestASignalStopsAnEncryptionAndLeavesNoFile(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	for _, ending := range []os.Signal{
+		syscall.SIGTERM, syscall.SIGINT, syscall.SIGHUP,
+	} {
+		interrupted(t, ending, "encrypt", "the start of the secret\n")
+	}
+}
+
+func TestASignalStopsADecryptionAndLeavesNoFile(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	// All of an encryption but its last byte, so the tool reads the
+	// header and then waits for the rest.
+	sealed := run(t, "age", "encrypt", written(t, "notes.txt", "the secret\n"))
+	cut := sealed[:len(sealed)-1]
+
+	for _, ending := range []os.Signal{
+		syscall.SIGTERM, syscall.SIGINT, syscall.SIGHUP,
+	} {
+		interrupted(t, ending, "decrypt", cut)
+	}
+}
+
+func TestASignalReceivedAsTheInputEndsLeavesTheFileAsItWas(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	sealed := run(t, "age", "encrypt", written(t, "notes.txt", "the secret\n"))
+
+	for _, ending := range []syscall.Signal{
+		syscall.SIGTERM, syscall.SIGINT, syscall.SIGHUP,
+	} {
+		receivedAtTheEnd(t, ending, "encrypt", "the secret\n")
+		receivedAtTheEnd(t, ending, "decrypt", sealed)
+	}
+}
+
+func TestASignalAsTheInputEndsLeavesNoUnfinishedFile(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	sealed := run(t, "age", "encrypt", written(t, "notes.txt", "the secret\n"))
+
+	// Ctrl-C on "producer | keyfunc age encrypt -o file" ends the
+	// producer too, so the input ends just as the signal comes, with
+	// enough of it in hand for a whole encryption or decryption. Which
+	// of the two the tool has first varies, so it is tried often, and
+	// a whole file in place is accepted as well as none.
+	for range 25 {
+		named := signalledAsTheInputEnds(t, "encrypt", "the start of the secret\n")
+		if named != "" {
+			require.Equal(t,
+				"the start of the secret\n", run(t, "age", "decrypt", named),
+			)
+		}
+
+		named = signalledAsTheInputEnds(t, "decrypt", sealed)
+		if named != "" {
+			require.Equal(t, "the secret\n", read(t, named))
+		}
+	}
+}
+
+func TestAnEncryptionStartedUnderNohupSurvivesAHangup(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	directory := t.TempDir()
+	named := filepath.Join(directory, "notes")
+
+	// nohup starts the tool with SIGHUP ignored. A tool that caught it
+	// anyway would turn it back on and be ended by it.
+	command, producer := writing(
+		t, directory, "the secret\n",
+		"nohup", os.Args[0], "age", "encrypt", "-o", named,
+	)
+
+	require.NoError(t, command.Process.Signal(syscall.SIGHUP))
+	require.NoError(t, producer.Close())
+	waitForTool(t, "SIGHUP under nohup", command)
+
+	require.Equal(t, 0, command.ProcessState.ExitCode())
+
+	left, err := os.ReadDir(directory)
+	require.NoError(t, err)
+	require.Len(t, left, 1)
+	require.Equal(t, "the secret\n", run(t, "age", "decrypt", named))
+}
+
+// interrupted runs "age encrypt -o" or "age decrypt -o", as the
+// operation says, writing into a directory of its own, and once it has
+// begun writing sends it the signal and leaves the input open. The tool
+// has to end with status 1 and leave the directory empty. A tool that
+// went on reading would not end until the input did; one that did not
+// remove the file it was writing would leave it there, with what it had
+// written so far.
+func interrupted(t *testing.T, ending os.Signal, operation, input string) {
+	t.Helper()
+
+	name := operation + " " + ending.String()
+	directory := t.TempDir()
+
+	command, _ := writing(
+		t, directory, input,
+		os.Args[0], "age", operation, "-o", filepath.Join(directory, "notes"),
+	)
+
+	require.NoError(t, command.Process.Signal(ending))
+	waitForTool(t, name, command)
+
+	require.Equal(t, 1, command.ProcessState.ExitCode(), name)
+
+	left, err := os.ReadDir(directory)
+	require.NoError(t, err)
+	require.Empty(t, left, name)
+}
+
+// signalledAsTheInputEnds runs "age encrypt -o" or "age decrypt -o", as
+// the operation says, writing into a directory of its own, and once it
+// has begun writing sends it SIGINT and at once ends its input. Either
+// the tool ends with status 1 and leaves the directory empty, and ""
+// is returned, or it ends otherwise and leaves only the named file,
+// whose path is returned for the caller to check that it is whole.
+func signalledAsTheInputEnds(t *testing.T, operation, input string) string {
+	t.Helper()
+
+	directory := t.TempDir()
+	named := filepath.Join(directory, "notes")
+
+	command, producer := writing(
+		t, directory, input, os.Args[0], "age", operation, "-o", named,
+	)
+
+	require.NoError(t, command.Process.Signal(syscall.SIGINT))
+	require.NoError(t, producer.Close())
+	waitForTool(t, operation, command)
+
+	left, err := os.ReadDir(directory)
+	require.NoError(t, err)
+
+	if command.ProcessState.ExitCode() == failedStatus {
+		require.Empty(t, left, operation)
+
+		return ""
+	}
+
+	require.Len(t, left, 1, operation)
+
+	return named
+}
+
+// receivedAtTheEnd runs "age encrypt -o" or "age decrypt -o", as the
+// operation says, in this process, over a file that is already there,
+// with an input that at its end sends this process the signal and waits
+// until it has been received. The tool has to return ErrInterrupted and
+// leave that file as it was, with nothing beside it. A tool that went
+// by the end of the input alone would put its new file in place.
+func receivedAtTheEnd(
+	t *testing.T, ending syscall.Signal, operation, input string,
+) {
+	t.Helper()
+
+	name := operation + " " + ending.String()
+	existing := written(t, "notes", "what was already there\n")
+
+	// The test catches the signal as well, so that it does not end the
+	// test binary and so that the input can wait for it.
+	received := make(chan os.Signal, 1)
+	signal.Notify(received, ending)
+
+	defer signal.Stop(received)
+
+	root := cli.Root()
+	root.SetIn(&endingInASignal{
+		rest: strings.NewReader(input), ending: ending, received: received,
+	})
+	root.SetOut(io.Discard)
+	root.SetErr(io.Discard)
+	root.SetArgs([]string{"age", operation, "-o", existing})
+
+	err := root.ExecuteContext(t.Context())
+	require.ErrorIs(t, err, age.ErrInterrupted, name)
+
+	require.Equal(t, "what was already there\n", read(t, existing), name)
+
+	left, err := os.ReadDir(filepath.Dir(existing))
+	require.NoError(t, err)
+	require.Len(t, left, 1, name)
+}
+
+// endingInASignal is an input that, when it runs out, sends this
+// process its signal and waits for it on received before it reports its
+// end. It sends the signal only once: once nothing catches it, another
+// would end the test binary.
+type endingInASignal struct {
+	rest     io.Reader
+	ending   syscall.Signal
+	received chan os.Signal
+	sent     bool
+}
+
+func (input *endingInASignal) Read(buffer []byte) (int, error) {
+	n, err := input.rest.Read(buffer)
+	if !errors.Is(err, io.EOF) || input.sent {
+		return n, err
+	}
+
+	input.sent = true
+
+	err = syscall.Kill(os.Getpid(), input.ending)
+	if err != nil {
+		return n, err
+	}
+
+	<-input.received
+
+	return n, io.EOF
+}
+
+// writing starts argv, the tool told to write into directory, as a
+// subprocess reading the input from a pipe, and returns once the tool
+// has begun writing the file beside the one it was named. The pipe is
+// left open for the caller to end.
+func writing(
+	t *testing.T, directory, input string, argv ...string,
+) (*exec.Cmd, io.WriteCloser) {
+	t.Helper()
+
+	//nolint:gosec // this test's own binary as the tool, or nohup running it
+	command := exec.CommandContext(t.Context(), argv[0], argv[1:]...)
+
+	command.Env = append(os.Environ(), runAsTool+"=1")
+
+	producer, err := command.StdinPipe()
+	require.NoError(t, err)
+	require.NoError(t, command.Start())
+
+	_, err = io.WriteString(producer, input)
+	require.NoError(t, err)
+
+	// The file beside the named one is made once the mnemonic has been
+	// read, before any input is.
+	require.Eventually(t, func() bool {
+		entries, err := os.ReadDir(directory)
+
+		return err == nil && len(entries) > 0
+	}, 5*time.Second, 5*time.Millisecond)
+
+	return command, producer
+}
+
 // written puts the contents in a file of that name in a directory of
 // this test's own and returns the path to it.
 func written(t *testing.T, name, contents string) string {

internal/cli/cli.go

@@ -5,28 +5,53 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"runtime"
+	"runtime/debug"
 
-	"git.eeqj.de/sneak/keyfunc/internal/cli/age"
-	"git.eeqj.de/sneak/keyfunc/internal/cli/mnemonic"
-	"git.eeqj.de/sneak/keyfunc/internal/cli/options"
-	"git.eeqj.de/sneak/keyfunc/internal/cli/ssh"
 	"github.com/spf13/cobra"
+	"sneak.berlin/go/keyfunc/internal/cli/age"
+	"sneak.berlin/go/keyfunc/internal/cli/mnemonic"
+	"sneak.berlin/go/keyfunc/internal/cli/options"
+	"sneak.berlin/go/keyfunc/internal/cli/ssh"
 )
 
-// Version is what --version prints. The build sets it.
+// devVersion is what Version holds until a build stamps a real one.
+const devVersion = "dev"
+
+// Version is what --version prints. make build stamps it with -ldflags.
 //
 //nolint:gochecknoglobals // set at build time with -ldflags
-var Version = "dev"
+var Version = devVersion
+
+// resolveVersion chooses what --version reports. A value stamped at
+// build time wins. Otherwise, for a binary from go install, the module
+// version recorded in the build info is used, unless that is empty or
+// the "(devel)" of a local build. When neither names a version, the
+// "dev" fallback stays.
+func resolveVersion(stamped string, info *debug.BuildInfo) string {
+	if stamped != devVersion {
+		return stamped
+	}
+
+	if info != nil && info.Main.Version != "" &&
+		info.Main.Version != "(devel)" {
+		return info.Main.Version
+	}
+
+	return devVersion
+}
 
 // Root returns the whole command tree.
 func Root() *cobra.Command {
+	info, _ := debug.ReadBuildInfo()
+
 	root := &cobra.Command{
 		Use:   "keyfunc",
 		Short: "derive key pairs from a BIP-39 mnemonic",
 		Long: "keyfunc turns a BIP-39 mnemonic into key pairs that can " +
 			"be recreated from that mnemonic at any time. The same " +
 			"mnemonic, key type and index always give the same key.",
-		Version:       Version,
+		Version:       resolveVersion(Version, info),
 		SilenceUsage:  true,
 		SilenceErrors: true,
 	}
@@ -37,19 +62,38 @@ func Root() *cobra.Command {
 	return root
 }
 
+// init keeps the command on the main thread. Linux hands a signal sent
+// to the tool to that thread first, and a thread runs a pending signal
+// handler before its own code, so when "age encrypt -o" or "age
+// decrypt -o" checks for a signal as its input ends, one sent before
+// then, as by Ctrl-C on a pipeline, has been received.
+//
+//nolint:gochecknoinits // only an init can keep main on the main thread
+func init() {
+	runtime.LockOSThread()
+}
+
 // Main runs the tool and returns the status the process should exit
 // with. An error ends the tool with status 1, except when it carries a
 // status of its own, which "ssh to" uses to hand on the status ssh
 // ended with. ssh has already said whatever it had to say in that
 // case, so nothing more is printed.
+//
+// SIGINT, SIGTERM and SIGHUP end the tool at once, as they end any Go
+// program, so a command waiting at the mnemonic prompt or reading what
+// it encrypts or decrypts goes no further. The exceptions catch the
+// signals to clean up first: "ssh to" and "ssh install" while they
+// have ssh or sftp running, so the child ends and their own cleanup
+// still runs, and "age encrypt -o" and "age decrypt -o" while they
+// write a new file to rename over the named one, so the unfinished file
+// is removed.
 func Main() int {
 	err := Root().Execute()
 	if err == nil {
 		return 0
 	}
 
-	var passed ssh.StatusError
+	if passed, ok := errors.AsType[ssh.StatusError](err); ok {
-	if errors.As(err, &passed) {
 		return passed.Status
 	}
 

internal/cli/cli_test.go

@@ -5,13 +5,13 @@ import (
 	"strings"
 	"testing"
 
-	"git.eeqj.de/sneak/keyfunc/internal/childmnemonic"
-	"git.eeqj.de/sneak/keyfunc/internal/cli"
-	"git.eeqj.de/sneak/keyfunc/internal/derive"
-	"git.eeqj.de/sneak/keyfunc/internal/mnemonic"
 	"github.com/stretchr/testify/require"
-	bip39 "github.com/tyler-smith/go-bip39"
 	"golang.org/x/crypto/ssh"
+	"sneak.berlin/go/keyfunc/internal/bip39"
+	"sneak.berlin/go/keyfunc/internal/childmnemonic"
+	"sneak.berlin/go/keyfunc/internal/cli"
+	"sneak.berlin/go/keyfunc/internal/derive"
+	"sneak.berlin/go/keyfunc/internal/mnemonic"
 )
 
 // The two lines the README says the example mnemonic produces.
@@ -22,6 +22,11 @@ const (
 		"0I4FKs+eVUulTPHfk9VtXw1tMF"
 )
 
+// The child mnemonic the README says the example mnemonic gives at
+// index 0.
+const childZero = "prosper short ramp prepare exchange stove life " +
+	"snack client enough purpose fold"
+
 // The two child mnemonic lengths the tests ask for.
 const (
 	twelve     = 12
@@ -45,6 +50,28 @@ func TestTheReadmeTestVectors(t *testing.T) {
 		vectorOne+" keyfunc/ssh/1",
 		strings.TrimSpace(run(t, "ssh", "pub", "-n", "1")),
 	)
+	require.Equal(t,
+		childZero, strings.TrimSpace(run(t, "mnemonic", "-n", "0")),
+	)
+}
+
+func TestTheSpacingBetweenTheWordsDoesNotChangeTheKeys(t *testing.T) {
+	words := strings.Fields(example())
+
+	for name, spaced := range map[string]string{
+		"one word per line": strings.Join(words, "\n"),
+		"double spaces":     strings.Join(words, "  "),
+		"tabs":              strings.Join(words, "\t"),
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Setenv(mnemonic.Variable, spaced)
+
+			require.Equal(t,
+				vectorZero+" keyfunc/ssh/0",
+				strings.TrimSpace(run(t, "ssh", "pub", "-n", "0")),
+			)
+		})
+	}
 }
 
 func TestTheCommentCanBeChosen(t *testing.T) {

internal/cli/mnemonic/mnemonic.go

@@ -4,10 +4,10 @@ package mnemonic
 import (
 	"fmt"
 
-	"git.eeqj.de/sneak/keyfunc/internal/childmnemonic"
-	"git.eeqj.de/sneak/keyfunc/internal/cli/options"
-	"git.eeqj.de/sneak/keyfunc/internal/derive"
 	"github.com/spf13/cobra"
+	"sneak.berlin/go/keyfunc/internal/childmnemonic"
+	"sneak.berlin/go/keyfunc/internal/cli/options"
+	"sneak.berlin/go/keyfunc/internal/derive"
 )
 
 // Command returns the mnemonic command.

internal/cli/options/options.go

@@ -5,8 +5,8 @@ package options
 import (
 	"fmt"
 
-	"git.eeqj.de/sneak/keyfunc/internal/mnemonic"
 	"github.com/spf13/cobra"
+	"sneak.berlin/go/keyfunc/internal/mnemonic"
 )
 
 // Add gives a command the flags that every command has. They are

internal/cli/signals/signals.go

@@ -0,0 +1,53 @@
+// Package signals catches the signals that end the tool, for the
+// commands that clean up before they end.
+package signals
+
+import (
+	"context"
+	"os"
+	"os/signal"
+	"syscall"
+)
+
+// Context is signal.NotifyContext for SIGINT, SIGTERM and SIGHUP: the
+// context it returns is cancelled when one of them arrives, and stop
+// stops catching them. It leaves out any of the three the tool was
+// started with set to be ignored, as nohup does with SIGHUP, because
+// catching a signal turns an ignored one back on and would end a run
+// that was meant to survive it.
+func Context(parent context.Context) (context.Context, context.CancelFunc) {
+	endings := caught()
+
+	// Given no signals at all, NotifyContext would catch every one.
+	if len(endings) == 0 {
+		return context.WithCancel(parent)
+	}
+
+	return signal.NotifyContext(parent, endings...)
+}
+
+// Notify is signal.Notify for the signals Context catches: each one
+// that arrives is sent to c, until signal.Stop(c).
+func Notify(c chan<- os.Signal) {
+	endings := caught()
+
+	// Given no signals at all, Notify would catch every one.
+	if len(endings) > 0 {
+		signal.Notify(c, endings...)
+	}
+}
+
+// caught returns those of SIGINT, SIGTERM and SIGHUP that the tool was
+// not started with set to be ignored.
+func caught() []os.Signal {
+	endings := []os.Signal{syscall.SIGINT, syscall.SIGTERM, syscall.SIGHUP}
+	kept := make([]os.Signal, 0, len(endings))
+
+	for _, ending := range endings {
+		if !signal.Ignored(ending) {
+			kept = append(kept, ending)
+		}
+	}
+
+	return kept
+}

internal/cli/ssh/install.go

@@ -4,14 +4,18 @@ import (
 	"bytes"
 	"crypto/rand"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"slices"
 	"strings"
+	"syscall"
+	"time"
 
 	"github.com/spf13/cobra"
+	"sneak.berlin/go/keyfunc/internal/cli/signals"
 )
 
 // Where the key goes on the host and what the file it arrives in is
@@ -32,6 +36,33 @@ const (
 	localMode     = 0o600
 )
 
+// waitDelay is the WaitDelay sftp runs with: from a signal, or from sftp
+// ending, how long the tool waits for sftp to end and its output to
+// close before it kills sftp and stops reading. That is ample for sftp
+// to stop the ssh it started, and short enough that a signal still ends
+// the tool within a second.
+const waitDelay = 250 * time.Millisecond
+
+// ErrCannotEnter is the refusal of a host whose .ssh is there but
+// cannot be entered, so that nothing in it can be read or written.
+var ErrCannotEnter = errors.New(
+	"~/.ssh is there on the host but cannot be entered",
+)
+
+// ErrSymlink is the refusal of a host whose authorized_keys is a
+// symlink: the rename that puts the new file in place would replace the
+// link itself, and the file it points at would never get the key.
+var ErrSymlink = errors.New(
+	"~/.ssh/authorized_keys on the host is a symlink, which the tool " +
+		"leaves alone",
+)
+
+// ErrStrayArgument is the refusal of anything but the host before --,
+// which would otherwise be handed to sftp in front of the host.
+var ErrStrayArgument = errors.New(
+	"only the host goes before --; options for sftp go after --",
+)
+
 // install returns the command that adds the public key to a host.
 func install() *cobra.Command {
 	cmd := &cobra.Command{
@@ -43,7 +74,22 @@ func install() *cobra.Command {
 			"beside it which is then renamed over it. Nothing is run " +
 			"on the host. Anything after -- is given to sftp " +
 			"unchanged, which is where the port goes (-P).",
-		Args: cobra.MinimumNArgs(1),
+		Args: cobra.MatchAll(
+			cobra.MinimumNArgs(1),
+			func(cmd *cobra.Command, args []string) error {
+				// ArgsLenAtDash is -1 when there is no --.
+				before := cmd.ArgsLenAtDash()
+				if before == -1 {
+					before = len(args)
+				}
+
+				if before != 1 {
+					return ErrStrayArgument
+				}
+
+				return nil
+			},
+		),
 		RunE: func(cmd *cobra.Command, args []string) error {
 			key, comment, err := derived(cmd)
 			if err != nil {
@@ -55,6 +101,14 @@ func install() *cobra.Command {
 				return err
 			}
 
+			// From here on a signal cancels the context, which
+			// sftp runs under, instead of ending the tool, so sftp
+			// ends and the working directory is still removed.
+			ctx, stop := signals.Context(cmd.Context())
+			defer stop()
+
+			cmd.SetContext(ctx)
+
 			return add(cmd, args[0], args[1:], line)
 		},
 	}
@@ -76,7 +130,7 @@ func add(cmd *cobra.Command, host string, options []string, line string) error {
 
 	defer func() { _ = os.RemoveAll(work) }()
 
-	content, err := fetch(cmd, host, options,
+	content, present, err := fetch(cmd, host, options,
 		filepath.Join(work, "authorized_keys"),
 	)
 	if err != nil {
@@ -88,16 +142,18 @@ func add(cmd *cobra.Command, host string, options []string, line string) error {
 		return write(cmd, "already present\n")
 	}
 
-	return upload(cmd, host, options, work, merged)
+	return upload(cmd, host, options, work, merged, present)
 }
 
 // upload writes the new file to the host and renames it over
 // authorized_keys, which is the step that either happens or does not.
 // Nothing is removed when a step fails: the file left behind is named
-// so that it can be looked at and cleared away by hand.
+// so that it can be looked at and cleared away by hand. The directory
+// is made and set to its mode only when the read found none: an .ssh
+// that was already there is left with the mode it had.
 func upload(
 	cmd *cobra.Command, host string, options []string,
-	work, merged string,
+	work, merged string, present bool,
 ) error {
 	local := filepath.Join(work, "authorized_keys.merged")
 
@@ -111,14 +167,24 @@ func upload(
 		return err
 	}
 
-	// The mkdir may fail: the directory is usually there already.
+	var batch []string
-	said, err := session(cmd, host, options, []string{
+
-		"-mkdir " + directory,
+	if !present {
-		"chmod " + directoryMode + " " + directory,
+		// The mkdir is allowed to fail in case the directory appeared
-		"put " + quoted(local) + " " + sidecar,
+		// between the read and now; the chmod then sets its mode.
-		"chmod " + fileMode + " " + sidecar,
+		batch = append(batch,
-		"rename " + sidecar + " " + authorized,
+			"-mkdir "+directory,
-	})
+			"chmod "+directoryMode+" "+directory,
+		)
+	}
+
+	batch = append(batch,
+		"put "+quoted(local)+" "+sidecar,
+		"chmod "+fileMode+" "+sidecar,
+		"rename "+sidecar+" "+authorized,
+	)
+
+	said, err := session(cmd, host, options, batch)
 	if err != nil {
 		// sftp echoes each command as it runs it and stops at the
 		// first that fails, so the name is in what it said only once
@@ -154,12 +220,29 @@ func session(
 
 	//nolint:gosec // the options are the user's own, meant for sftp
 	command := exec.CommandContext(cmd.Context(), "sftp", argv...)
+	command.Env = childEnv()
 	command.Stdin = strings.NewReader(strings.Join(batch, "\n") + "\n")
 	command.Stdout = &said
 	command.Stderr = &said
 
+	// A cancelled context means a signal arrived. Send sftp a SIGTERM
+	// rather than the default kill, so it stops the ssh it started
+	// before it goes. Anything sftp started that still holds its output
+	// keeps the tool waiting no longer than waitDelay.
+	command.Cancel = func() error {
+		return command.Process.Signal(syscall.SIGTERM)
+	}
+	command.WaitDelay = waitDelay
+
 	err := command.Run()
 
+	// sftp ended well and only something it started, such as the
+	// master ssh leaves running for ControlPersist under -v, still held
+	// its output: the session worked.
+	if errors.Is(err, exec.ErrWaitDelay) {
+		err = nil
+	}
+
 	_, _ = cmd.ErrOrStderr().Write(said.Bytes())
 
 	if err != nil {
@@ -185,31 +268,116 @@ func merge(content, line string) (string, bool) {
 }
 
 // fetch brings the host's authorized_keys into the given path and
-// returns what is in it. A host that has no such file reads as empty,
+// returns what is in it, and whether the .ssh directory was already
-// but only when that is what sftp said about it: a file that is there
+// there. The one session lists .ssh, then .ssh/., and then gets the
-// and cannot be read fails the run, because writing back over it
+// file, so the listings settle the state of the directory before the
-// would leave the host with the new key and nothing else.
+// get is read.
+//
+// The file reads as empty in just two cases: sftp reported .ssh itself
+// as not there, or both listings succeeded and the get then reported
+// the file as not there. Anything else — a listing refused, the file
+// there but unreadable, the connection down — fails the run and writes
+// nothing, because writing back over what was not read would leave the
+// host with the new key and nothing else. sftp cannot tell a missing
+// file from one in a directory it cannot enter, so the listings do: a
+// directory that is there but cannot be read fails the first, and one
+// that can be read but not entered fails the second, because nothing in
+// it can be looked up, not even ".". The first listing of such a
+// directory comes up empty, as the server leaves out every name it
+// cannot look up.
+//
+// The first listing is a long one, which shows an authorized_keys that
+// is a symlink as one. That is refused before anything else sftp said
+// is read, so a link the get could not follow is refused in the same
+// words.
 func fetch(
 	cmd *cobra.Command, host string, options []string, into string,
-) (string, error) {
+) (string, bool, error) {
 	said, err := session(cmd, host, options, []string{
+		"ls -n " + directory,
+		"ls -1 " + directory + "/.",
 		"get " + authorized + " " + quoted(into),
 	})
+	if symlinked(said) {
+		return "", false, ErrSymlink
+	}
+
 	if err != nil {
-		if absent(said) {
+		if listingNotFound(said, directory) {
-			return "", nil
+			return "", false, nil
 		}
 
-		return "", err
+		if listingNotFound(said, directory+"/.") {
+			return "", false, ErrCannotEnter
+		}
+
+		if absent(said) {
+			return "", true, nil
+		}
+
+		return "", false, err
 	}
 
 	//nolint:gosec // the path is a temporary file of the tool's own
 	content, err := os.ReadFile(into)
 	if err != nil {
-		return "", fmt.Errorf("reading the fetched file: %w", err)
+		return "", false, fmt.Errorf("reading the fetched file: %w", err)
 	}
 
-	return string(content), nil
+	return string(content), true, nil
+}
+
+// listingNotFound says whether sftp reported the path it was asked to
+// list as not being there. For .ssh that is the one listing failure
+// read as a host that has no authorized_keys yet; for .ssh/., once .ssh
+// itself has been listed, it is a .ssh that is there but cannot be
+// entered. The reading is taken only from the line in which sftp
+// reports on that path: any other failure of a listing, in particular a
+// directory that is there but cannot be read, is left as a failure, so
+// that no key is written to a host whose keys were never read.
+func listingNotFound(said, path string) bool {
+	for line := range strings.Lines(said) {
+		named, is := reportedCannotList(strings.TrimSpace(line))
+		if is && (named == path || strings.HasSuffix(named, "/"+path)) {
+			return true
+		}
+	}
+
+	return false
+}
+
+// reportedCannotList returns the path an sftp line reports it cannot
+// list for want of it, and whether the line is such a report. The
+// client writes this one wording when it cannot look up the path a
+// listing names, giving the path the server expanded.
+func reportedCannotList(line string) (string, bool) {
+	const (
+		before = `Can't ls: "`
+		after  = `" not found`
+	)
+
+	if !strings.HasPrefix(line, before) ||
+		!strings.HasSuffix(line, after) {
+		return "", false
+	}
+
+	return strings.TrimSuffix(strings.TrimPrefix(line, before), after), true
+}
+
+// symlinked says whether the long listing of .ssh shows authorized_keys
+// as a symlink. With -n the client writes each line itself, as ls -l
+// does, whatever the server: the type comes first, "l" for a symlink,
+// and the path as the listing named it comes last.
+func symlinked(said string) bool {
+	for line := range strings.Lines(said) {
+		fields := strings.Fields(line)
+		if len(fields) > 0 && strings.HasPrefix(fields[0], "l") &&
+			fields[len(fields)-1] == authorized {
+			return true
+		}
+	}
+
+	return false
 }
 
 // absent says whether sftp reported the file that was asked for as

internal/cli/ssh/install_test.go

@@ -10,6 +10,7 @@ import "testing"
 const (
 	echoed = `sftp> get .ssh/authorized_keys "/tmp/keyfunc/authorized_keys"
 `
+	listed  = "sftp> ls -n .ssh\n"
 	warning = `Warning: Identity file /gone not accessible: ` +
 		"No such file or directory.\n"
 )
@@ -76,3 +77,65 @@ func TestAbsenceIsReadOnlyFromWhatSFTPSaidAboutAuthorizedKeys(t *testing.T) {
 		})
 	}
 }
+
+// TestTheDirectoryIsReadAsAbsentOnlyFromTheListingSayingSo holds the
+// wordings the OpenSSH client was seen to use when a listing fails: a
+// directory it cannot find is reported one way, and one it cannot read
+// another, and only the first is read as a host with no .ssh yet. A
+// .ssh that can be read but not entered lists as empty, and the
+// listing of .ssh/. that follows reports that path, not .ssh, as not
+// found.
+func TestTheDirectoryIsReadAsAbsentOnlyFromTheListingSayingSo(t *testing.T) {
+	t.Parallel()
+
+	listings := map[string]struct {
+		said string
+		want bool
+	}{
+		"the directory is not there": {
+			said: listed + `Can't ls: "/home/someone/.ssh" not found` + "\n",
+			want: true,
+		},
+		"the directory is not there, named as it was asked for": {
+			said: listed + `Can't ls: ".ssh" not found` + "\n",
+			want: true,
+		},
+		"the directory is not there and an identity file is not either": {
+			said: warning + listed +
+				`Can't ls: "/home/someone/.ssh" not found` + "\n",
+			want: true,
+		},
+		"the directory is there and cannot be read": {
+			said: listed +
+				`remote readdir("/home/someone/.ssh/"): Permission denied` + "\n",
+			want: false,
+		},
+		"the directory is there and cannot be entered": {
+			said: listed + "sftp> ls -1 .ssh/.\n" +
+				`Can't ls: "/home/someone/.ssh/." not found` + "\n",
+			want: false,
+		},
+		"some other directory is not there": {
+			said: listed + `Can't ls: "/home/someone/.config" not found` + "\n",
+			want: false,
+		},
+		"the connection did not come up": {
+			said: "ssh: connect to host example.com port 22: " +
+				"Connection refused\nConnection closed\n",
+			want: false,
+		},
+	}
+
+	for name, listing := range listings {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			if listingNotFound(listing.said, directory) != listing.want {
+				t.Errorf(
+					"read as absent: %t, wanted %t, from:\n%s",
+					!listing.want, listing.want, listing.said,
+				)
+			}
+		})
+	}
+}

internal/cli/ssh/ssh.go

@@ -3,11 +3,14 @@ package ssh
 
 import (
 	"fmt"
+	"os"
+	"strings"
 
-	"git.eeqj.de/sneak/keyfunc/internal/cli/options"
-	"git.eeqj.de/sneak/keyfunc/internal/derive"
-	"git.eeqj.de/sneak/keyfunc/internal/sshkey"
 	"github.com/spf13/cobra"
+	"sneak.berlin/go/keyfunc/internal/cli/options"
+	"sneak.berlin/go/keyfunc/internal/derive"
+	"sneak.berlin/go/keyfunc/internal/mnemonic"
+	"sneak.berlin/go/keyfunc/internal/sshkey"
 )
 
 // Command returns the ssh command and everything under it.
@@ -84,6 +87,26 @@ func write(cmd *cobra.Command, text string) error {
 	return nil
 }
 
+// childEnv is the tool's environment with the mnemonic variables taken
+// out, for the ssh and sftp children it starts. "ssh to" exists so the
+// private key never leaves the tool; the mnemonic, from either variable,
+// must not leave it either.
+func childEnv() []string {
+	environ := os.Environ()
+	kept := make([]string, 0, len(environ))
+
+	for _, entry := range environ {
+		name, _, _ := strings.Cut(entry, "=")
+		if name == mnemonic.Variable || name == mnemonic.CommandVariable {
+			continue
+		}
+
+		kept = append(kept, entry)
+	}
+
+	return kept
+}
+
 // addComment gives a command its comment flag.
 func addComment(cmd *cobra.Command) {
 	cmd.Flags().String(

internal/cli/ssh/to.go

@@ -7,8 +7,10 @@ import (
 	"os"
 	"os/exec"
 	"slices"
+	"syscall"
 
 	"github.com/spf13/cobra"
+	"sneak.berlin/go/keyfunc/internal/cli/signals"
 )
 
 // StatusError says the tool should end with the status ssh ended with.
@@ -41,7 +43,14 @@ func to() *cobra.Command {
 				return err
 			}
 
-			served, err := key.Serve(cmd.Context(), comment)
+			// From here until the agent is taken down, a signal
+			// cancels the context instead of ending the tool, so
+			// ssh ends and the socket and its directory are still
+			// removed.
+			ctx, stop := signals.Context(cmd.Context())
+			defer stop()
+
+			served, err := key.Serve(ctx, comment)
 			if err != nil {
 				return err
 			}
@@ -52,7 +61,7 @@ func to() *cobra.Command {
 				"-o", "IdentityAgent=" + served.Socket(),
 			}, args)
 
-			return connect(cmd.Context(), argv)
+			return connect(ctx, argv)
 		},
 	}
 
@@ -70,17 +79,24 @@ func to() *cobra.Command {
 func connect(ctx context.Context, argv []string) error {
 	//nolint:gosec // the arguments are the user's own, meant for ssh
 	command := exec.CommandContext(ctx, "ssh", argv...)
+	command.Env = childEnv()
 	command.Stdin = os.Stdin
 	command.Stdout = os.Stdout
 	command.Stderr = os.Stderr
 
+	// A cancelled context means a signal arrived. Send ssh a
+	// SIGTERM rather than the default kill, so it puts the terminal
+	// back the way it found it before it goes.
+	command.Cancel = func() error {
+		return command.Process.Signal(syscall.SIGTERM)
+	}
+
 	err := command.Run()
 	if err == nil {
 		return nil
 	}
 
-	var ended *exec.ExitError
+	if ended, ok := errors.AsType[*exec.ExitError](err); ok {
-	if errors.As(err, &ended) {
 		status := ended.ExitCode()
 		if status < 0 {
 			// A signal ended ssh, and a signal has no status of its

internal/cli/ssh_test.go

@@ -3,18 +3,38 @@ package cli_test
 import (
 	"bytes"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"slices"
 	"strconv"
 	"strings"
+	"syscall"
 	"testing"
+	"time"
 
-	"git.eeqj.de/sneak/keyfunc/internal/cli"
-	"git.eeqj.de/sneak/keyfunc/internal/cli/ssh"
-	"git.eeqj.de/sneak/keyfunc/internal/mnemonic"
 	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/keyfunc/internal/cli"
+	"sneak.berlin/go/keyfunc/internal/cli/ssh"
+	"sneak.berlin/go/keyfunc/internal/mnemonic"
 )
 
+// runAsTool, set in the environment of a re-executed test binary, tells
+// TestMain to run the tool through Main rather than the suite, so the
+// signal tests can drive the real signal path in a process they can
+// send a signal to.
+const runAsTool = "KEYFUNC_TEST_RUN_AS_TOOL"
+
+// TestMain re-executes the test binary as the tool when runAsTool is
+// set, and otherwise runs the suite. The signal tests start the tool
+// this way, as a subprocess they can signal and watch end.
+func TestMain(m *testing.M) {
+	if os.Getenv(runAsTool) == "1" {
+		os.Exit(cli.Main())
+	}
+
+	os.Exit(m.Run())
+}
+
 // The modes the host is supposed to end up with, and the mode the
 // stand-ins need so that they can be run at all.
 const (
@@ -32,7 +52,7 @@ const (
 )
 
 // notADirectory is what a test puts where the .ssh directory belongs
-// to make a step of the write session fail.
+// to make a .ssh that is listed but cannot be entered.
 const notADirectory = "a file where the directory belongs\n"
 
 // missingIdentity is a path with no file at it, handed to sftp after
@@ -47,6 +67,9 @@ const (
 	keptIn    = "authorized_keys"
 )
 
+// remoteCommand is the command the "to" tests hand ssh after the host.
+const remoteCommand = "uptime"
+
 // The tool's own name, as it stands in the arguments a test hands to
 // Main, the ssh subcommand both commands the tests here drive live
 // under, and the one of those two these tests name most.
@@ -60,22 +83,38 @@ const (
 // an authorized_keys file.
 const keyLine = vectorZero + " keyfunc/ssh/0\n"
 
+// marker is a variable set beside the mnemonic ones and expected to
+// reach the stand-in, so a scrubbed environment is told apart from an
+// empty one.
+const marker = "KEYFUNC_TEST_MARKER"
+
 // installer is a stand-in for the system sftp for the install
 // command. It writes down the arguments and every command of the
-// batch it is given, echoes each command as sftp does, and carries
+// batch it is given, echoes each command as sftp does, writes down its
-// the commands out against a directory standing in for the host's
+// own environment when a test asks for it, and carries the commands out
-// home directory, so that what keyfunc sends can be watched doing its
+// against a directory standing in for the host's home directory, so that
-// work. A command that begins with a dash may fail; any other failure
+// what keyfunc sends can be watched doing its work. A command that
-// ends the session, as it does in sftp's own batch mode.
+// begins with a dash may fail; any other failure ends the session, as it
+// does in sftp's own batch mode.
 //
-// The two ways a get can fail are worded as the OpenSSH client words
+// The listing and the two ways a get can fail are worded as the
-// them, both naming the path the server expanded: a file that is not
+// OpenSSH client words them, each naming the path the server expanded.
-// there, which is the one failure the tool reads as an empty file, and
+// A long listing (-n) writes each entry as the client does, its type
-// a file that is there and cannot be read, which is not. An -i naming
+// first, so that a symlink shows as one.
-// a file that is not here draws the warning ssh writes for it, which
+// A listing fails one way when .ssh is not there and another when it is
+// there but shut to the user; the first is the only failure read as a
+// host with no file. A get fails one way for a file that is not there,
+// which after a listing that came up empty is also read as no file, and
+// another for a file that is there and cannot be read, which is a
+// failure. A directory shut to the user is stood in for by mode 000,
+// which the listing reads off the mode itself so that the test does not
+// turn on the user it runs as, and one the user can enter but not write
+// to by mode 500, which the put reads off the same way. An -i naming a
+// file that is not here draws the warning ssh writes for it, which
 // carries the wording of a missing file into a session that goes on to
 // authenticate.
 const installer = `
+[ -n "$KEYFUNC_TEST_ENVIRONMENT" ] && env > "$KEYFUNC_TEST_ENVIRONMENT"
 previous=
 for argument in "$@"; do
 	printf '%s\n' "$argument" >> "$KEYFUNC_TEST_ARGUMENTS"
@@ -99,6 +138,28 @@ while IFS= read -r line; do
 	eval "set -- $line"
 	worked=yes
 	case "$1" in
+	ls)
+		dir=$3
+		if [ ! -e "$home/$dir" ]; then
+			worked=no
+			printf 'Can'\''t ls: "%s" not found\n' "$home/$dir" >&2
+		elif [ -d "$home/$dir" ] && [ "$(stat -c '%a' "$home/$dir")" = 0 ]; then
+			worked=no
+			printf 'remote readdir("%s/"): Permission denied\n' \
+				"$home/$dir" >&2
+		else
+			for entry in "$home/$dir"/*; do
+				[ -e "$entry" ] || continue
+				name="$dir/$(basename "$entry")"
+				if [ "$2" = -n ]; then
+					printf '%s    ? someone  users  0 Oct  4 15:44 %s\n' \
+						"$(stat -c '%A' "$entry")" "$name"
+				else
+					printf '%s\n' "$name"
+				fi
+			done
+		fi
+		;;
 	get)
 		if [ ! -e "$home/$2" ]; then
 			worked=no
@@ -108,7 +169,13 @@ while IFS= read -r line; do
 			printf 'remote open "%s": Permission denied\n' "$home/$2" >&2
 		fi
 		;;
-	put) cp "$2" "$home/$3" 2>/dev/null || worked=no ;;
+	put)
+		if [ "$(stat -c '%a' "$(dirname "$home/$3")")" = 500 ]; then
+			worked=no
+		else
+			cp "$2" "$home/$3" 2>/dev/null || worked=no
+		fi
+		;;
 	mkdir) mkdir "$home/$2" 2>/dev/null || worked=no ;;
 	chmod) chmod "$2" "$home/$3" 2>/dev/null || worked=no ;;
 	rename) mv "$home/$2" "$home/$3" 2>/dev/null || worked=no ;;
@@ -122,9 +189,11 @@ done
 
 // caller is a stand-in for the system ssh for the to command. It
 // writes down the arguments it was given, notes the agent socket if
-// there really is one at the path it was handed, and ends with the
+// there really is one at the path it was handed, writes down its own
-// status the test asked for.
+// environment when a test asks for it, and ends with the status the
+// test asked for.
 const caller = `
+[ -n "$KEYFUNC_TEST_ENVIRONMENT" ] && env > "$KEYFUNC_TEST_ENVIRONMENT"
 for argument in "$@"; do
 	printf '%s\n' "$argument" >> "$KEYFUNC_TEST_ARGUMENTS"
 done
@@ -135,6 +204,30 @@ fi
 exit "$KEYFUNC_TEST_STATUS"
 `
 
+// sleeper is a stand-in for the system ssh that notes the agent socket
+// and then blocks, so a test can cancel the context while it is running
+// and watch the tool take the agent down. The wait ends on its own only
+// as a backstop, well after the test has cancelled and looked.
+const sleeper = `
+socket=${2#IdentityAgent=}
+if [ -S "$socket" ]; then
+	printf '%s\n' "$socket" > "$KEYFUNC_TEST_SOCKET"
+fi
+sleep 5
+`
+
+// stalled is a stand-in for the system sftp that starts a child, notes
+// it has started, and then blocks, so a test can signal the tool while
+// sftp is running. The child holds the output the tool reads sftp
+// through, as the ssh that sftp starts does, and is started before the
+// note so that it is there when the signal ends the shell and still
+// holds that output afterwards.
+const stalled = `
+sleep 5 &
+touch "$KEYFUNC_TEST_STARTED"
+wait
+`
+
 // pretended is where a stand-in writes down what it was asked to do.
 type pretended struct {
 	// home stands in for the home directory on the host.
@@ -176,8 +269,8 @@ func TestAKeyThatIsAlreadyThereIsLeftAlone(t *testing.T) {
 	require.Equal(t, "already present\n", install(t, host))
 	require.Equal(t, "somebody else\n"+keyLine, read(t, path))
 
-	// The fetch and nothing after it: the tool did not connect again.
+	// The read and nothing after it: the tool did not connect again.
-	require.Len(t, recorded(t, pretend.batch), 1)
+	require.Equal(t, 1, connections(t, pretend))
 }
 
 func TestAnEmptyFileGetsTheKeyAndNoBlankLineBeforeIt(t *testing.T) {
@@ -218,7 +311,9 @@ func TestTheFileIsUploadedBesideTheOldOneAndThenRenamedOverIt(t *testing.T) {
 		strings.HasPrefix(beside, ".ssh/authorized_keys.keyfunc-"),
 	)
 
-	require.True(t, strings.HasPrefix(sent[0], "get .ssh/authorized_keys "))
+	// The listing fails on a host with no .ssh, so the get never runs;
+	// the write session then makes the directory and puts the file.
+	require.Equal(t, "ls -n .ssh", sent[0])
 	require.Equal(t, "-mkdir .ssh", sent[1])
 	require.Equal(t, "chmod 700 .ssh", sent[2])
 	require.Equal(t, "put", strings.Fields(sent[3])[0])
@@ -237,12 +332,133 @@ func TestAFileThatCannotBeReadIsNotWrittenOver(t *testing.T) {
 	require.Empty(t, printed)
 	require.Contains(t, said, "Permission denied")
 
-	// The fetch and nothing after it, and what was on the host is
+	// The read and nothing after it, and what was on the host is
 	// still what is on the host.
-	require.Len(t, recorded(t, pretend.batch), 1)
+	require.Equal(t, 1, connections(t, pretend))
 	require.DirExists(t, unreadable)
 }
 
+func TestAnUnreadableDirectoryIsNotWrittenInto(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	pretend := pretendHost(t)
+	unlistable(t, pretend)
+
+	// The listing is refused, which is not the same as no directory, so
+	// the tool writes nothing rather than treat a directory it cannot
+	// enter as a host with no file.
+	printed, said, err := attempt(t, host)
+	require.Error(t, err)
+	require.Empty(t, printed)
+	require.Contains(t, said, "Permission denied")
+
+	// The read and nothing after it: no second connection wrote a key.
+	require.Equal(t, 1, connections(t, pretend))
+}
+
+func TestADirectoryThatCannotBeEnteredIsRefusedBeforeAnyUpload(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	pretend := pretendHost(t)
+
+	// A file where .ssh belongs is listed and cannot be entered, which is
+	// how sftp sees a directory that can be read but not entered: the
+	// listing of .ssh comes up and the listing of .ssh/. finds nothing.
+	inTheWay := filepath.Join(pretend.home, keptUnder)
+	require.NoError(t,
+		os.WriteFile(inTheWay, []byte(notADirectory), fileMode),
+	)
+
+	printed, _, err := attempt(t, host)
+	require.ErrorIs(t, err, ssh.ErrCannotEnter)
+	require.Empty(t, printed)
+
+	// The read and nothing after it: no upload was tried, and what was
+	// on the host is still what is on the host.
+	require.Equal(t, 1, connections(t, pretend))
+	require.Equal(t, notADirectory, read(t, inTheWay))
+}
+
+func TestASymlinkedFileIsRefusedBeforeAnyUpload(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	pretend := pretendHost(t)
+
+	// The file the link points at, which the key would never reach.
+	target := filepath.Join(pretend.home, "keys")
+	require.NoError(t,
+		os.WriteFile(target, []byte("somebody else\n"), fileMode),
+	)
+
+	directory := filepath.Join(pretend.home, keptUnder)
+	require.NoError(t, os.Mkdir(directory, directoryMode))
+
+	link := filepath.Join(directory, keptIn)
+	require.NoError(t, os.Symlink(target, link))
+
+	printed, _, err := attempt(t, host)
+	require.ErrorIs(t, err, ssh.ErrSymlink)
+	require.Empty(t, printed)
+
+	// The read and nothing after it: no upload was tried, the link
+	// still points where it did, and what it points at is unchanged.
+	require.Equal(t, 1, connections(t, pretend))
+
+	pointsAt, err := os.Readlink(link)
+	require.NoError(t, err)
+	require.Equal(t, target, pointsAt)
+	require.Equal(t, "somebody else\n", read(t, target))
+}
+
+func TestAnArgumentBesideTheHostIsRefusedBeforeAnyConnection(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	pretend := pretendHost(t)
+
+	runs := [][]string{
+		{host, "frank@example.com"},
+		{host, "2222"},
+		{host, "frank@example.com", "--", "-P", "2222"},
+		{"--", host},
+	}
+
+	for _, args := range runs {
+		printed, _, err := attempt(t, args...)
+		require.ErrorIs(t, err, ssh.ErrStrayArgument)
+		require.Empty(t, printed)
+	}
+
+	// sftp was never started, so nothing was uploaded.
+	require.NoFileExists(t, pretend.arguments)
+}
+
+func TestAnExistingDirectoryKeepsItsModeAndIsNotRemade(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	pretend := pretendHost(t)
+
+	// A directory that is there but holds no file yet, made with a mode
+	// of its own so that a stray chmod would show.
+	const ownMode = 0o755
+
+	directory := filepath.Join(pretend.home, keptUnder)
+	require.NoError(t, os.Mkdir(directory, ownMode))
+
+	require.Equal(t, "added\n", install(t, host))
+
+	// The key is added and the directory keeps the mode it had: the
+	// write session neither made it nor set its mode.
+	require.Equal(t, keyLine, read(t, filepath.Join(directory, keptIn)))
+
+	kept, err := os.Stat(directory)
+	require.NoError(t, err)
+	require.Equal(t, os.FileMode(ownMode), kept.Mode().Perm())
+
+	sent := recorded(t, pretend.batch)
+	require.NotContains(t, sent, "-mkdir .ssh")
+	require.NotContains(t, sent, "chmod 700 .ssh")
+}
+
 func TestAWarningAboutAnotherFileIsNotTakenForTheOneAskedFor(t *testing.T) {
 	t.Setenv(mnemonic.Variable, example())
 
@@ -259,7 +475,7 @@ func TestAWarningAboutAnotherFileIsNotTakenForTheOneAskedFor(t *testing.T) {
 	require.Contains(t, said, "No such file or directory")
 	require.Contains(t, said, "Permission denied")
 
-	require.Len(t, recorded(t, pretend.batch), 1)
+	require.Equal(t, 1, connections(t, pretend))
 	require.DirExists(t, unreadable)
 
 	// The same run again, this way for the status it ends with.
@@ -279,27 +495,30 @@ func TestAFailedStepNamesTheUploadedFileAndChangesNothing(t *testing.T) {
 
 	pretend := pretendHost(t)
 
-	// A file where the .ssh directory belongs: nothing is there to
+	// A .ssh that can be listed and entered but not written to: the
-	// fetch, and then the put has nowhere to put anything, so the
+	// fetch finds no file in it, and then the put has nowhere to put
-	// write session ends at the put.
+	// anything, so the write session ends at the put.
-	inTheWay := filepath.Join(pretend.home, keptUnder)
+	const unwritable = 0o500
-	require.NoError(t,
+
-		os.WriteFile(inTheWay, []byte(notADirectory), fileMode),
+	directory := filepath.Join(pretend.home, keptUnder)
-	)
+	require.NoError(t, os.Mkdir(directory, unwritable))
 
 	printed, said, err := attempt(t, host)
 	require.Error(t, err)
 	require.Empty(t, printed)
 	require.Contains(t, said, "put failed")
 
-	// The put is the last command the session got to, and the file it
+	// The put, after the three commands of the fetch, is the first and
-	// was uploading is the one the message names.
+	// last command the write session got to, and the file it was
+	// uploading is the one the message names.
 	sent := recorded(t, pretend.batch)
 	require.Len(t, sent, 4)
 	require.Equal(t, "put", strings.Fields(sent[3])[0])
 	require.Contains(t, err.Error(), strings.Fields(sent[3])[2])
 
-	require.Equal(t, notADirectory, read(t, inTheWay))
+	left, err := os.ReadDir(directory)
+	require.NoError(t, err)
+	require.Empty(t, left)
 
 	// The same run again, this way for the status it ends with.
 	given := os.Args
@@ -338,12 +557,28 @@ func TestWhatComesAfterTheDashesIsGivenToSFTP(t *testing.T) {
 	)
 }
 
+func TestAProcessSFTPLeavesBehindDoesNotFailTheRun(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	pretend := pretendHost(t)
+
+	// A session that works ends by leaving a child behind that holds
+	// sftp's output, as the master ssh leaves running for ControlPersist
+	// does under -v.
+	standIn(t, "sftp", installer+"sleep 5 &\n")
+
+	require.Equal(t, "added\n", install(t, host))
+	require.Equal(t, keyLine,
+		read(t, filepath.Join(pretend.home, keptUnder, keptIn)),
+	)
+}
+
 func TestSSHIsPointedAtTheAgentAndItsStatusIsHandedOn(t *testing.T) {
 	t.Setenv(mnemonic.Variable, example())
 
 	arguments, noted := pretendCall(t)
 
-	_, err := execute(t, subcommand, "to", host, "uptime")
+	_, err := execute(t, subcommand, "to", host, remoteCommand)
 
 	var passed ssh.StatusError
 
@@ -352,7 +587,7 @@ func TestSSHIsPointedAtTheAgentAndItsStatusIsHandedOn(t *testing.T) {
 
 	given := recorded(t, arguments)
 	require.Equal(t, "-o", given[0])
-	require.Equal(t, []string{host, "uptime"}, given[2:])
+	require.Equal(t, []string{host, remoteCommand}, given[2:])
 
 	// The stand-in wrote the path down only because there really was
 	// a socket there while it ran.
@@ -370,11 +605,186 @@ func TestTheToolEndsWithTheStatusSSHEndedWith(t *testing.T) {
 
 	t.Cleanup(func() { os.Args = given })
 
-	os.Args = []string{tool, subcommand, "to", host, "uptime"}
+	os.Args = []string{tool, subcommand, "to", host, remoteCommand}
 
 	require.Equal(t, failingStatus, cli.Main())
 }
 
+func TestASignalTakesTheAgentDirectoryDown(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	// The three signals the tool handles, checked one after another.
+	signals := []struct {
+		name   string
+		signal os.Signal
+	}{
+		{"SIGTERM", syscall.SIGTERM},
+		{"SIGINT", syscall.SIGINT},
+		{"SIGHUP", syscall.SIGHUP},
+	}
+
+	for _, ending := range signals {
+		signalEndsTheTool(t, ending.name, ending.signal)
+	}
+}
+
+// signalEndsTheTool runs the tool as a subprocess against a stand-in
+// ssh that blocks, waits until the agent is up and ssh is running
+// against it, sends the tool the signal, and requires the agent socket
+// and its directory to be gone once the tool has ended. The subprocess
+// goes through Main and the command's signal handling, so with that handling
+// removed the signal kills the tool outright, no deferred cleanup runs,
+// the directory is left behind, and the check fails.
+func signalEndsTheTool(t *testing.T, name string, signal os.Signal) {
+	t.Helper()
+
+	noted := filepath.Join(t.TempDir(), "socket")
+	t.Setenv("KEYFUNC_TEST_SOCKET", noted)
+	standIn(t, "ssh", sleeper)
+
+	//nolint:gosec // the binary is this test's own, re-run as the tool
+	command := exec.CommandContext(
+		t.Context(), os.Args[0], subcommand, "to", host, remoteCommand,
+	)
+
+	command.Env = append(os.Environ(), runAsTool+"=1")
+	require.NoError(t, command.Start())
+
+	// The stand-in notes the socket only once the agent is up and ssh
+	// is running against it, so this is where the signal lands.
+	socket := waitForSocket(t, noted)
+
+	require.NoError(t, command.Process.Signal(signal))
+	waitForTool(t, name, command)
+
+	// The signal ended the tool, and its deferred cleanup still ran:
+	// the agent socket and its directory are gone.
+	require.NoDirExists(t, filepath.Dir(socket), name)
+}
+
+// waitForTool waits for the subprocess to end, and fails the test if it
+// does not end in time.
+func waitForTool(t *testing.T, name string, command *exec.Cmd) {
+	t.Helper()
+
+	done := make(chan error, 1)
+	go func() { done <- command.Wait() }()
+
+	select {
+	case <-done:
+	case <-time.After(10 * time.Second):
+		t.Fatalf("the tool did not end after %s", name)
+	}
+}
+
+// waitForSocket waits for the stand-in to write down the agent socket
+// and gives back the path, which means the agent is up and ssh is
+// running against it.
+func waitForSocket(t *testing.T, noted string) string {
+	t.Helper()
+
+	var socket string
+
+	require.Eventually(t, func() bool {
+		content, err := os.ReadFile(noted) //nolint:gosec // test path
+		if err != nil {
+			return false
+		}
+
+		socket = strings.TrimSpace(string(content))
+
+		return socket != ""
+	}, 5*time.Second, 5*time.Millisecond)
+
+	return socket
+}
+
+func TestASignalTakesTheInstallWorkingDirectoryDown(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	for _, ending := range []os.Signal{
+		syscall.SIGTERM, syscall.SIGINT, syscall.SIGHUP,
+	} {
+		signalEndsTheInstall(t, ending.String(), ending)
+	}
+}
+
+// signalEndsTheInstall runs "ssh install" as a subprocess against a
+// stand-in sftp that blocks, with a temporary directory of the test's
+// own, waits until sftp is running, sends the tool the signal, and
+// requires the tool to end within a second with status 1 and the
+// working directory it made there to be gone.
+func signalEndsTheInstall(t *testing.T, name string, signal os.Signal) {
+	t.Helper()
+
+	temporary := t.TempDir()
+	started := filepath.Join(t.TempDir(), "started")
+	t.Setenv("KEYFUNC_TEST_STARTED", started)
+	standIn(t, "sftp", stalled)
+
+	//nolint:gosec // the binary is this test's own, re-run as the tool
+	command := exec.CommandContext(
+		t.Context(), os.Args[0], subcommand, installing, host,
+	)
+
+	command.Env = append(os.Environ(), runAsTool+"=1", "TMPDIR="+temporary)
+	require.NoError(t, command.Start())
+
+	// sftp is started only once the working directory has been made.
+	require.Eventually(t, func() bool {
+		_, err := os.Stat(started)
+
+		return err == nil
+	}, 5*time.Second, 5*time.Millisecond)
+
+	working, err := os.ReadDir(temporary)
+	require.NoError(t, err)
+	require.Len(t, working, 1, name)
+
+	sent := time.Now()
+
+	require.NoError(t, command.Process.Signal(signal))
+	waitForTool(t, name, command)
+
+	// The child sftp started would hold sftp's output for seconds yet.
+	require.Less(t, time.Since(sent), time.Second, name)
+	require.Equal(t, failedStatus, command.ProcessState.ExitCode(), name)
+
+	left, err := os.ReadDir(temporary)
+	require.NoError(t, err)
+	require.Empty(t, left, name)
+}
+
+func TestTheMnemonicIsNotHandedToSFTP(t *testing.T) {
+	t.Setenv(mnemonic.CommandVariable, "echo "+example())
+	t.Setenv(mnemonic.Variable, example())
+	t.Setenv(marker, "reaches the stand-in")
+
+	pretendHost(t)
+	environment := recordEnvironment(t)
+
+	install(t, host)
+
+	mnemonicWithheld(t, read(t, environment))
+}
+
+func TestTheMnemonicIsNotHandedToSSH(t *testing.T) {
+	t.Setenv(mnemonic.CommandVariable, "echo "+example())
+	t.Setenv(mnemonic.Variable, example())
+	t.Setenv(marker, "reaches the stand-in")
+
+	pretendCall(t)
+	environment := recordEnvironment(t)
+
+	_, err := execute(t, subcommand, "to", host, remoteCommand)
+
+	var passed ssh.StatusError
+
+	require.ErrorAs(t, err, &passed)
+
+	mnemonicWithheld(t, read(t, environment))
+}
+
 // pretendHost puts the install stand-in on the path and gives back the
 // places it writes to.
 func pretendHost(t *testing.T) pretended {
@@ -455,6 +865,38 @@ func unfetchable(t *testing.T, pretend pretended) string {
 	return path
 }
 
+// unlistable puts a .ssh on the stand-in host that is there but shut to
+// the user, a directory of mode 000, and gives back its path. Its mode
+// is put back before the temporary directory is cleared so that it can
+// be.
+func unlistable(t *testing.T, pretend pretended) string {
+	t.Helper()
+
+	directory := filepath.Join(pretend.home, keptUnder)
+	require.NoError(t, os.Mkdir(directory, directoryMode))
+	require.NoError(t, os.Chmod(directory, 0))
+
+	t.Cleanup(func() { _ = os.Chmod(directory, directoryMode) })
+
+	return directory
+}
+
+// connections returns how many times the tool ran sftp, counted from
+// the -b that opens each session's arguments.
+func connections(t *testing.T, pretend pretended) int {
+	t.Helper()
+
+	count := 0
+
+	for _, argument := range recorded(t, pretend.arguments) {
+		if argument == "-b" {
+			count++
+		}
+	}
+
+	return count
+}
+
 // pretendCall puts the to stand-in on the path and gives back the file
 // the arguments are written down in and the file the agent socket is
 // noted in.
@@ -491,6 +933,28 @@ func standIn(t *testing.T, name, body string) {
 	)
 }
 
+// recordEnvironment asks the stand-in to write its environment down and
+// gives back the file it writes it to.
+func recordEnvironment(t *testing.T) string {
+	t.Helper()
+
+	path := filepath.Join(t.TempDir(), "environment")
+	t.Setenv("KEYFUNC_TEST_ENVIRONMENT", path)
+
+	return path
+}
+
+// mnemonicWithheld requires that neither mnemonic variable reached the
+// stand-in and that the marker set beside them did, so an empty
+// environment does not pass for a scrubbed one.
+func mnemonicWithheld(t *testing.T, environment string) {
+	t.Helper()
+
+	require.NotContains(t, environment, mnemonic.Variable+"=")
+	require.NotContains(t, environment, mnemonic.CommandVariable+"=")
+	require.Contains(t, environment, marker+"=")
+}
+
 // read returns what is in a file.
 func read(t *testing.T, path string) string {
 	t.Helper()

internal/cli/version_internal_test.go

@@ -0,0 +1,37 @@
+package cli
+
+import (
+	"runtime/debug"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestResolveVersion(t *testing.T) {
+	t.Parallel()
+
+	release := &debug.BuildInfo{Main: debug.Module{Version: "v1.2.3"}}
+	local := &debug.BuildInfo{Main: debug.Module{Version: "(devel)"}}
+	empty := &debug.BuildInfo{}
+
+	t.Run("stamped value wins over build info", func(t *testing.T) {
+		t.Parallel()
+		require.Equal(t, "v0.1.0", resolveVersion("v0.1.0", release))
+	})
+
+	t.Run("go install reports the module version", func(t *testing.T) {
+		t.Parallel()
+		require.Equal(t, "v1.2.3", resolveVersion(devVersion, release))
+	})
+
+	t.Run("a local build stays dev", func(t *testing.T) {
+		t.Parallel()
+		require.Equal(t, devVersion, resolveVersion(devVersion, local))
+	})
+
+	t.Run("no version anywhere stays dev", func(t *testing.T) {
+		t.Parallel()
+		require.Equal(t, devVersion, resolveVersion(devVersion, empty))
+		require.Equal(t, devVersion, resolveVersion(devVersion, nil))
+	})
+}

internal/derive/derive.go

@@ -8,7 +8,7 @@ import (
 	"git.eeqj.de/sneak/secret/pkg/bip85"
 	"github.com/btcsuite/btcd/btcutil/hdkeychain"
 	"github.com/btcsuite/btcd/chaincfg"
-	bip39 "github.com/tyler-smith/go-bip39"
+	"sneak.berlin/go/keyfunc/internal/bip39"
 )
 
 const (

internal/derive/derive_test.go

@@ -5,8 +5,8 @@ import (
 	"strings"
 	"testing"
 
-	"git.eeqj.de/sneak/keyfunc/internal/derive"
 	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/keyfunc/internal/derive"
 )
 
 // application is the number the SSH key type uses.

internal/mnemonic/mnemonic.go

@@ -10,8 +10,8 @@ import (
 	"os/exec"
 	"strings"
 
-	bip39 "github.com/tyler-smith/go-bip39"
 	"golang.org/x/term"
+	"sneak.berlin/go/keyfunc/internal/bip39"
 )
 
 const (
@@ -104,10 +104,11 @@ func ask() (string, error) {
 	return checked(string(typed))
 }
 
-// checked drops the surrounding whitespace and refuses a mnemonic that
+// checked joins the words with single spaces, whatever whitespace
-// does not pass the BIP-39 checksum.
+// separated them, since the seed is computed over the string itself,
+// and refuses a mnemonic that does not pass the BIP-39 checksum.
 func checked(words string) (string, error) {
-	words = strings.TrimSpace(words)
+	words = strings.Join(strings.Fields(words), " ")
 
 	if !bip39.IsMnemonicValid(words) {
 		return "", ErrChecksum

internal/mnemonic/mnemonic_test.go

@@ -4,8 +4,8 @@ import (
 	"strings"
 	"testing"
 
-	"git.eeqj.de/sneak/keyfunc/internal/mnemonic"
 	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/keyfunc/internal/mnemonic"
 )
 
 // Two more mnemonics that pass the checksum, so a test can tell which

internal/sshkey/sshkey_test.go

@@ -7,11 +7,11 @@ import (
 	"strings"
 	"testing"
 
-	"git.eeqj.de/sneak/keyfunc/internal/derive"
-	"git.eeqj.de/sneak/keyfunc/internal/sshkey"
 	"github.com/stretchr/testify/require"
 	"golang.org/x/crypto/ssh"
 	"golang.org/x/crypto/ssh/agent"
+	"sneak.berlin/go/keyfunc/internal/derive"
+	"sneak.berlin/go/keyfunc/internal/sshkey"
 )
 
 // agentDirectoryMode is what the directory holding the agent socket

package.json

@@ -0,0 +1,6 @@
+{
+  "license": "MIT",
+  "devDependencies": {
+    "prettier": "3.8.1"
+  }
+}

script/bootstrap

@@ -3,13 +3,35 @@
 # repo. Idempotent: every install is guarded by a check, so tools that
 # are already there are left alone. Base tooling comes from nix, apt,
 # brew, or apk, detected in that order, and nothing is assumed to be
-# present. The linter is not installed here: it only ever runs inside
+# present. Go is installed at the version the Dockerfile's Go image
-# the image built from Dockerfile.lint, so Docker is what is needed for
+# carries, from the official release archive, into ~/.local/go. Node is
-# it, and that is checked for rather than installed.
+# used directly if installed; otherwise it is installed at a pinned
+# version via nvm (installing nvm itself first, from a hash-verified
+# release archive, never curl | sh). The linter is not installed here:
+# linting and testing run only as phases of the Dockerfile, so Docker is
+# what is needed for them, and that is checked for rather than
+# installed.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
+# Must match the Go in the Dockerfile's golang image; the sha256 of each
+# archive is in install_go.
+GO_VERSION="1.26.8"
+
+# This script cannot change its caller's PATH, so script/fmt,
+# script/fmt-check, script/precommit and the Makefile put this directory
+# first on their own PATH, as is done here.
+GO_DIR="$HOME/.local/go"
+PATH="$GO_DIR/bin:$PATH"
+
+# Pinned versions, 2026-07-06
+NODE_VERSION="22.17.0"
+NVM_VERSION="0.40.3"
+# sha256 of https://github.com/nvm-sh/nvm/archive/refs/tags/v0.40.3.tar.gz
+NVM_SHA256="5f4d6aaa04a177dc93c985e31dbc411ab6b8c6e1e21d8015dbc1372625fcd1d0"
+YARN_VERSION="1.22.22"
+
 PKGMGR=""
 SUDO=""
 
@@ -32,6 +54,9 @@ detect_pkgmgr() {
         if [ "$(id -u)" != "0" ]; then
             SUDO="sudo"
         fi
+        # This runs once, before the first install: a fresh host or
+        # runner image has no package lists yet.
+        $SUDO apt-get update
     fi
 }
 
@@ -50,17 +75,139 @@ missing() {
     ! command -v "$1" >/dev/null 2>&1
 }
 
+# verify_sha256 <file> <expected-hash>
+verify_sha256() {
+    if command -v sha256sum >/dev/null 2>&1; then
+        actual="$(sha256sum "$1" | cut -d' ' -f1)"
+    else
+        actual="$(shasum -a 256 "$1" | cut -d' ' -f1)"
+    fi
+    if [ "$actual" != "$2" ]; then
+        echo "bootstrap: sha256 mismatch for $1" >&2
+        echo "  expected: $2" >&2
+        echo "  actual:   $actual" >&2
+        exit 1
+    fi
+}
+
+# True when the go first on PATH reports exactly GO_VERSION. No go, a go
+# that fails, or any other output is a mismatch.
+go_version_matches() {
+    out="$(go version 2>/dev/null)" || return 1
+    case "$out" in
+        "go version go$GO_VERSION "*) return 0 ;;
+        *) return 1 ;;
+    esac
+}
+
+install_go() {
+    # sha256 of the go1.26.8 archives at https://go.dev/dl/, 2026-10-04
+    case "$(uname -s)-$(uname -m)" in
+        Linux-x86_64)
+            platform="linux-amd64"
+            sha256="d0f743b33e8d8945e6b1f432edd15785c70507121d6e2a723b21285eddf8b57b"
+            ;;
+        Linux-aarch64)
+            platform="linux-arm64"
+            sha256="211ffced9dcb9633a55eac6364816ec0ddd951389a740e88fa8b3337971bdda0"
+            ;;
+        Darwin-x86_64)
+            platform="darwin-amd64"
+            sha256="186be014105aa6542b767d2c6ed5cca10a0214bdff809ef1724022a8c7894150"
+            ;;
+        Darwin-arm64)
+            platform="darwin-arm64"
+            sha256="a012b25b571bd0138a03dcd25375ceba866fe5ca822f426d2c66a4de56fd3f4b"
+            ;;
+        *)
+            echo "bootstrap: no Go archive pinned for $(uname -s) $(uname -m)" >&2
+            exit 1
+            ;;
+    esac
+    if missing curl; then pkg_install curl curl curl curl; fi
+    tmp="$(mktemp -d)"
+    curl -fsSL -o "$tmp/go.tar.gz" \
+        "https://go.dev/dl/go${GO_VERSION}.${platform}.tar.gz"
+    verify_sha256 "$tmp/go.tar.gz" "$sha256"
+    # An archive unpacked over an older Go leaves a broken tree.
+    rm -rf "$GO_DIR"
+    mkdir -p "$GO_DIR"
+    tar -xzf "$tmp/go.tar.gz" -C "$GO_DIR" --strip-components=1
+    rm -rf "$tmp"
+}
+
+# nvm is a bash script; run a command in a bash with nvm loaded
+nvm_sh() {
+    bash -c ". \"\$HOME/.nvm/nvm.sh\" && $*"
+}
+
+ensure_nvm() {
+    [ -s "$HOME/.nvm/nvm.sh" ] && return 0
+    # nvm prerequisites; nvm itself requires bash
+    if missing bash; then pkg_install bash bash bash bash; fi
+    if missing curl; then pkg_install curl curl curl curl; fi
+    if missing git; then pkg_install git git git git; fi
+    tmp="$(mktemp -d)"
+    curl -fsSL -o "$tmp/nvm.tar.gz" \
+        "https://github.com/nvm-sh/nvm/archive/refs/tags/v${NVM_VERSION}.tar.gz"
+    verify_sha256 "$tmp/nvm.tar.gz" "$NVM_SHA256"
+    mkdir -p "$HOME/.nvm"
+    tar -xzf "$tmp/nvm.tar.gz" -C "$HOME/.nvm" --strip-components=1
+    rm -rf "$tmp"
+}
+
+ensure_node() {
+    if ! missing node; then return 0; fi
+    ensure_nvm
+    nvm_sh "nvm install $NODE_VERSION"
+}
+
+ensure_yarn() {
+    if ! missing yarn; then return 0; fi
+    if ! missing corepack; then
+        corepack enable
+        corepack prepare "yarn@$YARN_VERSION" --activate
+    elif [ -s "$HOME/.nvm/nvm.sh" ]; then
+        nvm_sh "nvm use $NODE_VERSION >/dev/null && corepack enable && \
+            corepack prepare yarn@$YARN_VERSION --activate"
+    else
+        npm install -g "yarn@$YARN_VERSION"
+    fi
+}
+
+install_js_deps() {
+    if missing yarn && [ -s "$HOME/.nvm/nvm.sh" ]; then
+        nvm_sh "nvm use $NODE_VERSION >/dev/null && cd \"$ROOT\" && \
+            yarn install --frozen-lockfile"
+    else
+        yarn install --frozen-lockfile
+    fi
+}
+
 main() {
     cd "$ROOT"
 
     if missing git; then pkg_install git git git git; fi
     if missing make; then pkg_install gnumake make make make; fi
-    if missing go; then pkg_install go golang go go; fi
+
+    if ! go_version_matches; then
+        install_go
+        hash -r
+        if ! go_version_matches; then
+            echo "bootstrap: $(command -v go) is not go$GO_VERSION after installing it" >&2
+            exit 1
+        fi
+    fi
+    go version
 
     go mod download
 
+    ensure_node
+    ensure_yarn
+    install_js_deps
+
     if missing docker; then
-        echo "bootstrap: docker is not installed; make lint needs it" >&2
+        echo "bootstrap: docker is not installed; make lint and make test need it" >&2
     fi
 
     echo "bootstrap complete"

script/cibuild

@@ -1,8 +1,10 @@
 #!/bin/sh
-# script/cibuild: run the CI build. The linter needs an image of its
+# script/cibuild: run the CI build. It bootstraps first: a CI runner
-# own, so it runs first; the Dockerfile then runs the formatting check,
+# checks out and runs this and nothing else, and script/fmt-check runs
-# the tests and the build, so a green run here means make check is
+# the formatter on the host, which a pristine checkout cannot do.
-# green.
+# --no-cache for the same reason as script/docker: the gate phases the
+# final stage depends on are RUN steps, and a cached one is a check that
+# did not run.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
@@ -10,8 +12,17 @@ ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    "$SCRIPT_DIR/lint"
+    "$SCRIPT_DIR/bootstrap"
-    docker build .
+    "$SCRIPT_DIR/check"
+    # Own line: a failing command substitution inside an argument does
+    # not trip `set -e`, so the inline form degrades silently to an
+    # empty constant. The VERSION build argument takes precedence over
+    # the version a build stage derives from the .git in the context.
+    version="$(git describe --tags --always --dirty 2>/dev/null || true)"
+    [ -n "$version" ] || version="unknown"
+    docker build --no-cache \
+        --build-arg VERSION="$version" \
+        -t "$("$SCRIPT_DIR/projectname")" .
 }
 
 main "$@"

script/docker

@@ -1,6 +1,8 @@
 #!/bin/sh
 # script/docker: build the Docker image tagged with the project name.
 # Identical in all repos; the tag comes from script/projectname.
+# --no-cache because the gate phases the final stage depends on are RUN
+# steps, and a cached one is a check that did not run.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
@@ -8,7 +10,15 @@ ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    docker build -t "$("$SCRIPT_DIR/projectname")" .
+    # Own line: a failing command substitution inside an argument does
+    # not trip `set -e`, so the inline form degrades silently to an
+    # empty constant. The VERSION build argument takes precedence over
+    # the version a build stage derives from the .git in the context.
+    version="$(git describe --tags --always --dirty 2>/dev/null || true)"
+    [ -n "$version" ] || version="unknown"
+    docker build --no-cache \
+        --build-arg VERSION="$version" \
+        -t "$("$SCRIPT_DIR/projectname")" .
 }
 
 main "$@"

script/fmt

@@ -1,12 +1,36 @@
 #!/bin/sh
-# script/fmt: format all files (writes).
+# script/fmt: format all files (writes): the Go source with go fmt, then
+# the Markdown files with prettier.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
+# Where script/bootstrap installs Go; it cannot put it on our PATH.
+PATH="$HOME/.local/go/bin:$PATH"
+
+# Must match the pin in script/bootstrap.
+NODE_VERSION="22.17.0"
+
+# script/bootstrap installs node and yarn under nvm and leaves neither
+# on the PATH of the shell that called it, so resolve the pinned
+# toolchain here the way bootstrap's own install step does. nvm is a
+# bash script, hence the subshell.
+run_yarn() {
+    if command -v yarn >/dev/null 2>&1; then
+        exec yarn "$@"
+    fi
+    if [ ! -s "$HOME/.nvm/nvm.sh" ]; then
+        echo "fmt: no yarn; run script/bootstrap first" >&2
+        exit 1
+    fi
+    exec bash -c '. "$HOME/.nvm/nvm.sh" && nvm use "$1" >/dev/null &&
+        shift && exec yarn "$@"' bash "$NODE_VERSION" "$@"
+}
+
 main() {
     cd "$ROOT"
     go fmt ./...
+    run_yarn run prettier --write '**/*.md' --tab-width 4 --prose-wrap always
 }
 
 main "$@"

script/fmt-check

@@ -5,6 +5,28 @@ set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
+# Where script/bootstrap installs Go; it cannot put it on our PATH.
+PATH="$HOME/.local/go/bin:$PATH"
+
+# Must match the pin in script/bootstrap.
+NODE_VERSION="22.17.0"
+
+# script/bootstrap installs node and yarn under nvm and leaves neither
+# on the PATH of the shell that called it, so resolve the pinned
+# toolchain here the way bootstrap's own install step does. nvm is a
+# bash script, hence the subshell.
+run_yarn() {
+    if command -v yarn >/dev/null 2>&1; then
+        exec yarn "$@"
+    fi
+    if [ ! -s "$HOME/.nvm/nvm.sh" ]; then
+        echo "fmt-check: no yarn; run script/bootstrap first" >&2
+        exit 1
+    fi
+    exec bash -c '. "$HOME/.nvm/nvm.sh" && nvm use "$1" >/dev/null &&
+        shift && exec yarn "$@"' bash "$NODE_VERSION" "$@"
+}
+
 main() {
     cd "$ROOT"
     if [ -n "$(gofmt -l .)" ]; then
@@ -12,6 +34,7 @@ main() {
         gofmt -l .
         exit 1
     fi
+    run_yarn run prettier --check '**/*.md' --tab-width 4 --prose-wrap always
 }
 
 main "$@"

script/lint

@@ -1,9 +1,13 @@
 #!/bin/sh
-# script/lint: run the linter. Linting only ever happens inside the
+# script/lint: run the linter. Linting is a phase of the Dockerfile and
-# image built from Dockerfile.lint, which pins the linter by hash, so
+# this builds that phase alone; the linter is never installed or run on
-# the answer is the same on every machine and in CI. The linter runs as
+# a developer host, where a shared result cache and a host-global lock
-# a build step of that image, so a complaint fails the build and no
+# make its answer untrustworthy.
-# container is left behind.
+#
+# The phase is not the last stage in the file, so it is built only when
+# --target names it. --no-cache because a cached lint layer is a lint
+# that did not run. The tag makes each build replace the previous image
+# instead of leaving a dangling one behind.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
@@ -11,7 +15,8 @@ ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    docker build --progress=plain -f Dockerfile.lint \
+    docker build --no-cache \
+        --target lint \
         -t "$("$SCRIPT_DIR/projectname")-lint" .
 }
 

script/precommit

@@ -7,6 +7,9 @@ set -eu
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
 ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
+# Where script/bootstrap installs Go; it cannot put it on our PATH.
+PATH="$HOME/.local/go/bin:$PATH"
+
 main() {
     cd "$ROOT"
     go mod tidy

script/test

@@ -1,13 +1,19 @@
 #!/bin/sh
-# script/test: run the test suite (vet first, verbose rerun on failure).
+# script/test: run the test suite. Testing is a phase of the Dockerfile
+# and this builds that phase alone, on the same terms as script/lint:
+# --target because a phase that is not the last stage is built only when
+# named, --no-cache because a cached test layer is a test that did not
+# run, and a tag so each build replaces the previous image.
 set -eu
 
-ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
+ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    go vet ./...
+    docker build --no-cache \
-    go test -timeout 90s ./... || go test -timeout 90s -v ./...
+        --target test \
+        -t "$("$SCRIPT_DIR/projectname")-test" .
 }
 
 main "$@"

yarn.lock

@@ -0,0 +1,8 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+
+prettier@3.8.1:
+  version "3.8.1"
+  resolved "https://registry.yarnpkg.com/prettier/-/prettier-3.8.1.tgz#edf48977cf991558f4fcbd8a3ba6015ba2a3a173"
+  integrity sha512-UOnG6LftzbdaHZcKoPFtOcCKztrQ57WkHDeRD9t/PTQtmT0NHSeWWepj6pS0z/N7+08BHFDQVUrfmfMRcZwbMg==