Clean up the agent socket and working files when a signal ends the tool (closes #17)

Main ran the command tree on a background context, so SIGINT, SIGTERM or
SIGHUP killed the process before the deferred cleanup ran: the agent's
temporary directory and socket, and the install working directory, were
left behind.

Main now runs the tree on a signal.NotifyContext for those three signals.
A signal cancels the context, which ends the child ssh or sftp started
with exec.CommandContext, and the deferred cleanup then runs. The exit
status after a signal stays 1 unless ssh reported one of its own.

For "ssh to" the child is cancelled with SIGTERM rather than the default
kill, so ssh restores the terminal before it goes.

Model: opus-4-8

README.md

@@ -1,74 +1,16 @@
 # keyfunc
 
-`keyfunc` is a Go command-line tool by [@sneak](https://sneak.berlin) — its
+`keyfunc` turns a BIP-39 mnemonic into key pairs that can be recreated from
-license is not yet chosen
+that mnemonic at any time. The same mnemonic, key type and index always give the
-([#14](https://git.eeqj.de/sneak/keyfunc/issues/14)) — that turns a BIP-39
+same key.
-mnemonic into SSH keys, age 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 keys,
+Commands are grouped by what is derived: `keyfunc ssh ...` for ed25519 SSH
-`keyfunc age ...` for age identities and for encrypting and decrypting with
+keys, `keyfunc age ...` for age identities and for encrypting and decrypting
-them, and `keyfunc mnemonic ...` for child mnemonics derived from the main one.
+with them, and `keyfunc mnemonic ...` for child mnemonics derived from the
-
+main one.
-## Getting Started
-
-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, and `cli/ssh`, `cli/age`
-  and `cli/mnemonic` are the command groups.
-
-### 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
 
@@ -216,15 +158,6 @@ the same steps `sneak/secret` takes in its `agehd` package. `secret` derives at
 a vendor-specific path today; for its keys to equal this tool's it moves to
 this 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`
 
 Prints the recipient, the `age1...` public key, on one line.
@@ -257,65 +190,33 @@ not through step 4). Default 12 words. A child mnemonic is a full mnemonic in
 its own right: it can seed another `keyfunc`, another wallet, or `secret`, and
 it never has to be written down, since it can be derived again.
 
-Test vector: the child-mnemonic step is checked against BIP-85's own published
+## Adding a key type
-vectors, which derive from the specification's master key
-`xprv9s21ZrQH143K2LBWUUQRFXhucrQqBpKdRRxNVq2zBqsx8HVqFk2uYo8kmbaLLHRdqtQpUm98uKfu3vca1LqdGhUtyoFnCNkfmXRyPXLjbKb`.
-At key index 0 the 12-word English child mnemonic is:
 
-```
+Adding a key type is one package under `internal/` that turns the 32 derived
-girl mad pet galaxy egg matter matrix prison refuse sense ordinary nose
+bytes into that type's key, plus one cobra subcommand under `internal/cli/` that
-```
+groups its commands.
 
 ## Errors
 
 Errors go to standard error and the exit status is 1, except for `ssh to`,
 which passes through `ssh`'s own exit status.
 
-## Entrypoints
+## Building and running
 
-The repo adheres to the
+```
-[Scripts to Rule Them All](https://github.com/github/scripts-to-rule-them-all)
+make build    # produces ./keyfunc
-standard: most Makefile targets are thin shims over an executable in
+make check    # fmt-check, lint (golangci-lint) and tests
-`script/` (`build` and `clean` are the exceptions).
+```
 
-- `script/bootstrap` installs everything needed to build and develop (git, make,
+Examples:
-  Go), idempotently, from nix, apt, brew or apk; it does not install the linter,
-  which only runs inside Docker.
-- `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` runs `go vet` and then the test suite, rerunning verbosely if a
-  test fails.
-- `script/lint` runs the linter inside the image built from `Dockerfile.lint`
-  (which pins the linter by hash), so a complaint fails the build and leaves no
-  container behind.
-- `script/fmt` formats the Go source in place.
-- `script/fmt-check` checks that formatting without writing, failing if anything
-  is unformatted.
-- `script/check` runs `test`, `lint` and `fmt-check` and changes no files.
-- `script/docker` builds the Docker image tagged with the project name.
-- `script/cibuild` is the CI build the Gitea workflow calls: it runs the linter,
-  then `docker build`.
-- `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
+```
-
+keyfunc ssh pub -n 3 --mnemonic-command 'secret get foo'
-The open issues that stand between the tree and a 1.0 release:
+keyfunc ssh priv -n 3 > ~/.ssh/id_bip85_3
-
+keyfunc ssh install -n 3 user@example.com
-- [#14 Choose a license and add LICENSE](https://git.eeqj.de/sneak/keyfunc/issues/14)
+keyfunc ssh to -n 3 user@example.com uptime
-- [#15 Decide the Go module path before 1.0](https://git.eeqj.de/sneak/keyfunc/issues/15)
+keyfunc age pub -n 0
-- [#22 1.0 release readiness](https://git.eeqj.de/sneak/keyfunc/issues/22)
+keyfunc age encrypt -n 0 --armor -o notes.age notes.txt
-
+keyfunc age decrypt -n 0 notes.age
-## License
+keyfunc mnemonic -n 1 --words 24
-
+```
-Not yet chosen. The license is the owner's decision, still open on the tracker
-([#14](https://git.eeqj.de/sneak/keyfunc/issues/14)); the `LICENSE` file is added
-when that issue is answered.
-
-## Author
-
-[@sneak](https://sneak.berlin).