Move the command line from cmd/bsdaily into internal/cli (closes #8)

cmd/bsdaily/main.go now only passes Version to cli.Main and exits with
the status it returns, as REPO_POLICIES.md requires of cmd/. The cobra
command, the flag rules and the date parsing moved unchanged into
internal/cli, so flags, help text, error messages, exit status and the
first log line stay as they were. The fallback to dev for an empty
version moved with them into cli.Main.

parseTargetDates is exported as ParseTargetDates so that a table test
outside the package can reach it; the test never touches the filesystem
or runs the extraction. README describes the new layout and TODO.md
records the step.

Model: opus-5-5

.prettierignore

@@ -0,0 +1,2 @@
+node_modules/
+yarn.lock

.prettierrc

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

Dockerfile

@@ -47,7 +47,9 @@ FROM golang:1.26.4-alpine@sha256:3ad57304ad93bbec8548a0437ad9e06a455660655d9af01
 COPY --from=lint /src/go.sum /dev/null
 COPY --from=test /src/go.sum /dev/null
 
-ARG VERSION=dev
+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
 
@@ -58,8 +60,22 @@ RUN go mod download
 # Copy source code
 COPY . .
 
-# Build (pure Go, no CGO required since we use modernc.org/sqlite)
-RUN CGO_ENABLED=0 go build -o /bsdaily ./cmd/bsdaily
+# Build (pure Go, no CGO required since we use modernc.org/sqlite).
+# 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 /bsdaily ./cmd/bsdaily
 
 # Runtime stage
 # alpine:3.21, 2026-06-28

Makefile

@@ -1,7 +1,9 @@
 .PHONY: all bootstrap setup check test lint fmt fmt-check build clean deps test-coverage test-integration install release release-snapshot docker hooks
 
-# Version number
-VERSION := 0.1.0-dev
+# Stamped into the binary: the same `git describe` a plain `docker build .`
+# runs, or dev when it prints nothing (outside a git checkout, or where git is
+# missing). ?= so that a VERSION already in the environment takes precedence.
+VERSION ?= $(or $(shell git describe --tags --always 2>/dev/null),dev)
 
 # Default target
 all: bsdaily
@@ -36,7 +38,7 @@ lint:
 
 # Build binary (pure Go; no CGO required since we use modernc.org/sqlite).
 bsdaily: internal/*/*.go cmd/bsdaily/*.go
-	CGO_ENABLED=0 go build -o $@ ./cmd/bsdaily
+	CGO_ENABLED=0 go build -ldflags "-X main.Version=$(VERSION)" -o $@ ./cmd/bsdaily
 
 # Clean build artifacts.
 clean:

README.md

@@ -1,28 +1,26 @@
 # bsdaily
 
-[bsdaily](https://git.eeqj.de/sneak/bsdaily) is a command-line utility
-written in [Go](https://golang.org) that carves a single day (or a range of
-days) of [Bluesky](https://bsky.app) firehose data out of a large,
-continuously-growing SQLite database and writes it out as a self-contained,
+[bsdaily](https://git.eeqj.de/sneak/bsdaily) is a command-line utility written
+in [Go](https://golang.org) that carves a single day (or a range of days) of
+[Bluesky](https://bsky.app) firehose data out of a large, continuously-growing
+SQLite database and writes it out as a self-contained,
 [zstd](https://facebook.github.io/zstd/)-compressed SQL dump. The dumps are
-named by date (e.g. `2026-06-27.sql.zst`), organized into per-month
-directories, and are designed to be published, archived, mirrored, and later
-re-merged back into a single database.
+named by date (e.g. `2026-06-27.sql.zst`), organized into per-month directories,
+and are designed to be published, archived, mirrored, and later re-merged back
+into a single database.
 
 The source database is read from a read-only [ZFS](https://openzfs.org)
-snapshot, so extraction never contends with the live firehose ingester that
-is writing to the original database. The tool is operationally
-conservative: it checks free disk space before starting, copies the snapshot
-to fast scratch storage, processes one day at a time to avoid SQLite lock
-contention, verifies every compressed output before publishing it, and
-writes output atomically via a temp-file-and-rename so a partial run never
-leaves a corrupt `.sql.zst` behind.
+snapshot, so extraction never contends with the live firehose ingester that is
+writing to the original database. The tool is operationally conservative: it
+checks free disk space before starting, copies the snapshot to fast scratch
+storage, processes one day at a time to avoid SQLite lock contention, verifies
+every compressed output before publishing it, and writes output atomically via a
+temp-file-and-rename so a partial run never leaves a corrupt `.sql.zst` behind.
 
-This project was written by [@sneak](https://sneak.berlin) to produce a
-daily, mergeable, publicly-mirrorable archive of the Bluesky firehose. It is
-currently a one-person effort. The current version is pre-1.0 and there has
-not yet been a versioned release; [SemVer](https://semver.org) will be used
-for releases.
+This project was written by [@sneak](https://sneak.berlin) to produce a daily,
+mergeable, publicly-mirrorable archive of the Bluesky firehose. It is currently
+a one-person effort. The current version is pre-1.0 and there has not yet been a
+versioned release; [SemVer](https://semver.org) will be used for releases.
 
 # Build Status
 
@@ -33,14 +31,14 @@ branch must always be green.
 
 Primary development happens on a privately-run Gitea instance at
 [https://git.eeqj.de/sneak/bsdaily](https://git.eeqj.de/sneak/bsdaily) and
-issues are [tracked
-there](https://git.eeqj.de/sneak/bsdaily/issues).
+issues are [tracked there](https://git.eeqj.de/sneak/bsdaily/issues).
 
-Changes must always be formatted with a standard `go fmt`, syntactically
-valid, and must pass the linting defined in the repository (the shared
-`.golangci.yml` from `sneak/prompts`), which can be run with a `make lint`.
-The `main` branch is protected and all changes must be made via [pull
-requests](https://git.eeqj.de/sneak/bsdaily/pulls) and pass CI to be merged.
+Changes must always be formatted with `make fmt` (`go fmt` for Go, prettier for
+Markdown), syntactically valid, and must pass the linting defined in the
+repository (the shared `.golangci.yml` from `sneak/prompts`), which can be run
+with a `make lint`. The `main` branch is protected and all changes must be made
+via [pull requests](https://git.eeqj.de/sneak/bsdaily/pulls) and pass CI to be
+merged.
 
 See [`REPO_POLICIES.md`](REPO_POLICIES.md) for detailed coding standards,
 tooling requirements, and workflow conventions.
@@ -50,55 +48,55 @@ tooling requirements, and workflow conventions.
 This repository adheres to the
 [Scripts to Rule Them All](https://github.com/github/scripts-to-rule-them-all)
 standard: normalized scripts in `script/` are the entrypoints for the
-development workflow, and the Makefile targets are thin shims that call
-them. We provide:
+development workflow, and the Makefile targets are thin shims that call them. We
+provide:
 
-- `script/bootstrap` — install all development dependencies (go, Go
-  module download); the linter is not installed on the host
+- `script/bootstrap` — install all development dependencies (go, Go module
+  download, node and yarn at pinned versions when absent, and the prettier
+  pinned in `package.json` and `yarn.lock`); a node or yarn already installed is
+  used whatever its version; the linter is not installed on the host
 - `script/setup` — make a fresh clone ready for development: runs
   `script/bootstrap`, then `script/install-precommit`
-- `script/projectname` — print the project name (used for the Docker
-  image tags)
-- `script/test` — build the Dockerfile's `test` phase, which runs the
-  test suite with `-race` (verbose rerun on failure)
+- `script/projectname` — print the project name (used for the Docker image tags)
+- `script/test` — build the Dockerfile's `test` phase, which runs the test suite
+  with `-race` (verbose rerun on failure)
 - `script/lint` — build the Dockerfile's `lint` phase, which runs
   `golangci-lint run ./...`
-- `script/fmt` — format the Go code with `go fmt` (writes)
-- `script/fmt-check` — check the Go formatting with `gofmt` (read-only)
-- `script/check` — run `script/test`, `script/lint`, and
-  `script/fmt-check`
-- `script/docker` — build the Docker image tagged via
-  `script/projectname`; the build runs the `lint` and `test` phases
-  first
-- `script/cibuild` — CI entrypoint: runs `script/bootstrap` and
-  `script/check`, then builds the Docker image tagged via
-  `script/projectname`
-- `script/precommit` — pre-commit gate: `go mod tidy` (must not change
-  `go.mod` or `go.sum`) and `go fmt`, then `script/check`
-- `script/install-precommit` — install the git pre-commit hook that
-  runs `script/precommit`
+- `script/fmt` — format the Go code with `go fmt` and every Markdown file with
+  prettier (writes)
+- `script/fmt-check` — check the Go formatting with `gofmt` and the Markdown
+  formatting with prettier (read-only)
+- `script/check` — run `script/test`, `script/lint`, and `script/fmt-check`
+- `script/docker` — build the Docker image tagged via `script/projectname`; the
+  build runs the `lint` and `test` phases first
+- `script/cibuild` — CI entrypoint: runs `script/bootstrap` and `script/check`,
+  then builds the Docker image tagged via `script/projectname`
+- `script/precommit` — pre-commit gate: `go mod tidy` (must not change `go.mod`
+  or `go.sum`) and `go fmt`, then `script/check`
+- `script/install-precommit` — install the git pre-commit hook that runs
+  `script/precommit`
 
-Every Docker build in `script/` is uncached, so the `lint` and `test`
-phases always run rather than being served from the build cache.
+Every Docker build in `script/` is uncached, so the `lint` and `test` phases
+always run rather than being served from the build cache.
 
 # Problem Statement
 
-A Bluesky firehose ingester writes every observed post (and associated
-users, hashtags, URLs, and media references) into a single ever-growing
-SQLite database, `firehose.db`. This database has several properties that
-make it awkward to publish or archive directly:
+A Bluesky firehose ingester writes every observed post (and associated users,
+hashtags, URLs, and media references) into a single ever-growing SQLite
+database, `firehose.db`. This database has several properties that make it
+awkward to publish or archive directly:
 
-- It is **large and always growing**, so re-publishing the whole thing every
-  day is wasteful.
+- It is **large and always growing**, so re-publishing the whole thing every day
+  is wasteful.
 - It is **continuously written**, so reading from it directly risks lock
   contention with the live ingester and inconsistent reads.
-- It is **monolithic**, so there is no natural unit at which to mirror,
-  share, or distribute "just yesterday's posts".
+- It is **monolithic**, so there is no natural unit at which to mirror, share,
+  or distribute "just yesterday's posts".
 
-What is wanted instead is a stable, immutable, per-day artifact: a small
-file containing exactly one calendar day of firehose data, cheap to publish,
-cheap to mirror, and trivially re-mergeable into a full database by anyone
-who collects a set of them.
+What is wanted instead is a stable, immutable, per-day artifact: a small file
+containing exactly one calendar day of firehose data, cheap to publish, cheap to
+mirror, and trivially re-mergeable into a full database by anyone who collects a
+set of them.
 
 # Proposed Solution
 
@@ -108,81 +106,86 @@ A tool, `bsdaily`, that:
   filesystem, so it reads from a consistent point-in-time copy that the live
   ingester cannot be writing to;
 - copies the snapshot's database files to fast scratch storage;
-- **extracts** a single day's `posts` (and all rows reachable from them) into
-  a fresh, minimal per-day SQLite database;
-- **dumps** that per-day database to SQL and pipes it through multithreaded
-  zstd compression;
-- **verifies** the compressed output (zstd integrity check plus a sanity
-  check that the decompressed stream actually looks like SQL);
+- **extracts** a single day's `posts` (and all rows reachable from them) into a
+  fresh, minimal per-day SQLite database;
+- **dumps** that per-day database to SQL and pipes it through multithreaded zstd
+  compression;
+- **verifies** the compressed output (zstd integrity check plus a sanity check
+  that the decompressed stream actually looks like SQL);
 - **publishes** the result atomically as
   `DailiesBase/YYYY-MM/YYYY-MM-DD.sql.zst`.
 
 Each daily dump is emitted with `INSERT` statements over the full schema
-(including the deduplicated `users`, `hashtags`, and `urls` lookup tables),
-so any collection of daily dumps can be merged into a single database by
-rewriting `INSERT INTO` to `INSERT OR IGNORE INTO` and replaying them in
-sequence. Two helper scripts ([`merge_daily_dumps.sh`](merge_daily_dumps.sh)
-and [`regenerate_auxiliary_tables.sql`](regenerate_auxiliary_tables.sql)) are
+(including the deduplicated `users`, `hashtags`, and `urls` lookup tables), so
+any collection of daily dumps can be merged into a single database by rewriting
+`INSERT INTO` to `INSERT OR IGNORE INTO` and replaying them in sequence. Two
+helper scripts ([`merge_daily_dumps.sh`](merge_daily_dumps.sh) and
+[`regenerate_auxiliary_tables.sql`](regenerate_auxiliary_tables.sql)) are
 included to do exactly this and to rebuild the aggregate statistics
 (`use_count`, `first_seen`, user `resolved_at`/`updated_at`) afterward.
 
 # Design Goals
 
-- **Never disturb the live ingester.** All reads come from a ZFS snapshot,
-  never the live database.
+- **Never disturb the live ingester.** All reads come from a ZFS snapshot, never
+  the live database.
 - **Crash-safe, idempotent runs.** Output is written to a temp file and
   atomically renamed; a day whose final output already exists is skipped, so
   re-running a range is safe and resumable.
-- **Mergeable output.** Daily dumps re-combine losslessly into a full
-  database via `INSERT OR IGNORE`.
+- **Mergeable output.** Daily dumps re-combine losslessly into a full database
+  via `INSERT OR IGNORE`.
 - **Operationally cautious.** Free-space preflight checks on both scratch and
   output filesystems; explicit verification of every artifact before it is
   published.
 - **Fast where it's free.** Large snapshot copies use a 256MiB buffer,
   pre-allocate the destination, and (on Linux) issue `posix_fadvise`
-  sequential/willneed hints; extraction uses aggressive,
-  crash-unsafe-by-design SQLite pragmas because the working data lives only
-  in disposable scratch space.
+  sequential/willneed hints; extraction uses aggressive, crash-unsafe-by-design
+  SQLite pragmas because the working data lives only in disposable scratch
+  space.
 
 # Non-Goals
 
-- **Real-time export.** `bsdaily` operates on daily snapshots; the freshest
-  day it can produce is the snapshot date minus one.
-- **Schema ownership.** The schema is defined by the upstream firehose
-  ingester; [`schema.sql`](schema.sql) is included for reference only.
-  `bsdaily` copies whatever table and index DDL it finds in the source.
-- **Cross-platform deployment.** It is built and run on Linux (the
-  free-space check and fadvise hints use `golang.org/x/sys/unix`; a non-Linux
-  build compiles but is a no-op for the fadvise hints). The hard-coded paths
-  assume the production host's ZFS layout.
+- **Real-time export.** `bsdaily` operates on daily snapshots; the freshest day
+  it can produce is the snapshot date minus one.
+- **Schema ownership.** The schema is defined by the upstream firehose ingester;
+  [`schema.sql`](schema.sql) is included for reference only. `bsdaily` copies
+  whatever table and index DDL it finds in the source.
+- **Cross-platform deployment.** It is built and run on Linux (the free-space
+  check and fadvise hints use `golang.org/x/sys/unix`; a non-Linux build
+  compiles but is a no-op for the fadvise hints). The hard-coded paths assume
+  the production host's ZFS layout.
 
 # How It Works
 
+`cmd/bsdaily/main.go` only passes the version to `internal/cli` and exits with
+the status it returns. `internal/cli` holds the command line: the flags, the
+rules for combining them and the parsing of the dates they name.
+`internal/bsdaily` does the extraction.
+
 A single run proceeds as follows:
 
 1. **Find the snapshot.** Scan `SnapshotBase` for directories matching
-   `zfs-auto-snap_daily-YYYY-MM-DD-NNNN`, pick the most recent, and confirm
-   it contains `firehose.db`.
-2. **Determine target days.** Default to the snapshot date minus one day;
-   or use `--date`, or every day in the inclusive `--from`/`--to` range.
+   `zfs-auto-snap_daily-YYYY-MM-DD-NNNN`, pick the most recent, and confirm it
+   contains `firehose.db`.
+2. **Determine target days.** Default to the snapshot date minus one day; or use
+   `--date`, or every day in the inclusive `--from`/`--to` range.
 3. **Preflight disk space.** Require at least 500GiB free on the scratch
    filesystem and 20GiB free on the output filesystem.
 4. **Copy the database to scratch.** Copy `firehose.db`, its `-wal`, and (if
    present) its `-shm` from the snapshot into a fresh temp directory under
    `TmpBase`.
 5. **Per day**, processed strictly one at a time to avoid SQLite contention:
-   - skip the day if its final output file already exists;
-   - `ATTACH` the copied source DB to a new empty per-day DB, recreate the
-     table DDL, and `INSERT ... SELECT` the target day's `posts` plus all
-     rows reachable from them (`posts_hashtags`, `posts_urls`, `hashtags`,
-     `urls`, `users`, and `media` if that table exists);
-   - abort the day cleanly if there are zero posts (`ErrNoPosts`), rather
-     than emitting an empty dump;
-   - recreate indexes, detach the source, and verify the inserted row count;
-   - `sqlite3 .dump | zstdmt` into a hidden temp file;
-   - run a zstd integrity check and confirm the decompressed head looks like
-     SQL;
-   - atomically rename into place and delete the per-day scratch DB.
+    - skip the day if its final output file already exists;
+    - `ATTACH` the copied source DB to a new empty per-day DB, recreate the
+      table DDL, and `INSERT ... SELECT` the target day's `posts` plus all rows
+      reachable from them (`posts_hashtags`, `posts_urls`, `hashtags`, `urls`,
+      `users`, and `media` if that table exists);
+    - abort the day cleanly if there are zero posts (`ErrNoPosts`), rather than
+      emitting an empty dump;
+    - recreate indexes, detach the source, and verify the inserted row count;
+    - `sqlite3 .dump | zstdmt` into a hidden temp file;
+    - run a zstd integrity check and confirm the decompressed head looks like
+      SQL;
+    - atomically rename into place and delete the per-day scratch DB.
 6. **Clean up** the temp directory and log a processed/skipped/total summary.
 
 # Usage
@@ -191,6 +194,7 @@ A single run proceeds as follows:
 bsdaily                          # extract the snapshot date minus one day
 bsdaily --date 2026-06-27        # extract a single specific day
 bsdaily --from 2026-06-01 --to 2026-06-27   # extract an inclusive range
+bsdaily --version                # print the version and exit
 ```
 
 Flags:
@@ -199,9 +203,24 @@ Flags:
   `--from`/`--to`.
 - `--from YYYY-MM-DD` — start of an inclusive range (requires `--to`).
 - `--to YYYY-MM-DD` — end of an inclusive range (requires `--from`).
+- `-v`, `--version` — print the version and exit.
 
 With no flags, the tool extracts the day before the latest snapshot. All
-progress is logged as structured `slog` text to stderr.
+progress is logged as structured `slog` text to stderr; the first line of every
+run carries the version.
+
+The version is set at link time and depends on how the binary was built:
+
+- `docker build .` takes it from the `VERSION` build argument when one is given,
+  otherwise from `git describe --tags --always` on the `.git` in the build
+  context. The build fails if `.git` is there and the version still comes out
+  empty, `dev` or `unknown`. With neither `.git` nor `VERSION`, the binary
+  reports `dev`.
+- `script/docker`, `script/cibuild` and `make docker` pass the host's
+  `git describe --tags --always --dirty` as `VERSION`, so on a modified tree the
+  version ends in `-dirty`. When that prints nothing, they pass `unknown`.
+- `make` stamps the host's `git describe --tags --always`, without `-dirty`, or
+  `dev` when that prints nothing.
 
 ## Merging dumps back into a database
 
@@ -219,9 +238,9 @@ sqlite3 merged.db < regenerate_auxiliary_tables.sql
 - **Go** (see [`go.mod`](go.mod) for the toolchain version) to build.
 - **Linux** for production use (ZFS snapshots, `statfs` free-space checks,
   `posix_fadvise` hints).
-- The **`sqlite3`** and **`zstdmt`** (multithreaded zstd) binaries on
-  `PATH`; `zstdcat` is used for verification. SQLite reads/writes during
-  extraction use the pure-Go [`modernc.org/sqlite`](https://pkg.go.dev/modernc.org/sqlite)
+- The **`sqlite3`** and **`zstdmt`** (multithreaded zstd) binaries on `PATH`;
+  `zstdcat` is used for verification. SQLite reads/writes during extraction use
+  the pure-Go [`modernc.org/sqlite`](https://pkg.go.dev/modernc.org/sqlite)
   driver, so no cgo is required for that part.
 
 # Configuration
@@ -241,21 +260,21 @@ elsewhere.
 
 # Data Model
 
-The firehose schema (reference copy in [`schema.sql`](schema.sql)) centers
-on a `posts` table, with `users` keyed by DID and many-to-many junction
-tables linking posts to deduplicated `hashtags` and `urls`. An optional
-`media` table tracks downloaded blobs by content hash. `bsdaily` does not
-own this schema; it reflects whatever DDL exists in the source snapshot and
-selects forward from `posts` along the foreign-key relationships to produce a
-referentially-complete per-day slice.
+The firehose schema (reference copy in [`schema.sql`](schema.sql)) centers on a
+`posts` table, with `users` keyed by DID and many-to-many junction tables
+linking posts to deduplicated `hashtags` and `urls`. An optional `media` table
+tracks downloaded blobs by content hash. `bsdaily` does not own this schema; it
+reflects whatever DDL exists in the source snapshot and selects forward from
+`posts` along the foreign-key relationships to produce a referentially-complete
+per-day slice.
 
 # Use Cases
 
 ## Daily public archive
 
-Publish one small, immutable file per day to static HTTP (or IPFS, or a
-mirror network) so that anyone can fetch exactly the day(s) they want and
-re-merge them locally.
+Publish one small, immutable file per day to static HTTP (or IPFS, or a mirror
+network) so that anyone can fetch exactly the day(s) they want and re-merge them
+locally.
 
 ## Backfilling a range
 
@@ -265,16 +284,17 @@ safe to re-run.
 
 ## Reconstituting a full database
 
-Collect any set of daily dumps and merge them with `INSERT OR IGNORE` to
-rebuild a complete, queryable SQLite database, then regenerate the aggregate
-statistics tables.
+Collect any set of daily dumps and merge them with `INSERT OR IGNORE` to rebuild
+a complete, queryable SQLite database, then regenerate the aggregate statistics
+tables.
 
 # See Also
 
 ## Links
 
 - Repo: [https://git.eeqj.de/sneak/bsdaily](https://git.eeqj.de/sneak/bsdaily)
-- Issues: [https://git.eeqj.de/sneak/bsdaily/issues](https://git.eeqj.de/sneak/bsdaily/issues)
+- Issues:
+  [https://git.eeqj.de/sneak/bsdaily/issues](https://git.eeqj.de/sneak/bsdaily/issues)
 - Bluesky: [https://bsky.app](https://bsky.app)
 - zstd: [https://facebook.github.io/zstd/](https://facebook.github.io/zstd/)
 

TODO.md

@@ -1,12 +1,12 @@
 # Workflow
 
-* branch (from `main`)
-* do the work in Next Step
-* move Next Step to the top of Completed Steps
-* move the top item of Future Steps into Next Step
-* commit (`TODO.md` changes in the same commit as the work)
-* merge to `main` if the branch is not protected, otherwise open a PR
-* push
+- branch (from `main`)
+- do the work in Next Step
+- move Next Step to the top of Completed Steps
+- move the top item of Future Steps into Next Step
+- commit (`TODO.md` changes in the same commit as the work)
+- merge to `main` if the branch is not protected, otherwise open a PR
+- push
 
 # Status
 
@@ -14,35 +14,46 @@ pre-1.0
 
 # Next Step
 
-Format Markdown with prettier in `script/fmt` and `script/fmt-check`
-(https://git.eeqj.de/sneak/bsdaily/issues/7).
+Expand the `internal/bsdaily` tests beyond the compilation smoke test: unit
+tests for the extraction, verification, and atomic-publish paths.
 
 # Completed Steps
 
+- 2026-10-06: Moved the command line (flags, the rules for combining them, date
+  parsing) from `cmd/bsdaily` into `internal/cli`, with unit tests for the flag
+  rules and the dates; `cmd/bsdaily/main.go` is now a single call into it
+  (https://git.eeqj.de/sneak/bsdaily/issues/8).
+- 2026-10-06: A plain `docker build .` and a host `make` build stamp the git tag
+  or short commit into the binary, which `bsdaily` logs on the first line of
+  every run and prints with `--version`
+  (https://git.eeqj.de/sneak/bsdaily/issues/4).
 - 2026-10-06: Added the canonical `.golangci.yml`, moved the lint phase to
   golangci-lint v2.14.0, and fixed the code to pass it
   (https://git.eeqj.de/sneak/bsdaily/issues/6).
+- 2026-10-06: Formatted Markdown with prettier: `script/fmt` writes and
+  `script/fmt-check` checks every Markdown file; prettier pinned in
+  `package.json` and `yarn.lock`, installed by `script/bootstrap`, which
+  installs node and yarn at pinned versions when absent and otherwise uses the
+  ones already installed; existing Markdown reformatted.
 - 2026-10-05: Brought the repo up to the standard layout: canonical
-  `.gitignore`, `.dockerignore` and `.editorconfig`; `lint` and `test`
-  phases in the `Dockerfile`, built by `script/lint` and `script/test`;
-  canonical `script/cibuild`, `script/docker` and CI workflow; no linter
-  installed on the host; re-vendored `REPO_POLICIES.md`.
-- 2026-07-07 Adopted scripts-to-rule-them-all: `script/` entrypoints,
-  Makefile shims, README Entrypoints section
-- 2026-06-28: Fixed errcheck lint failures; added compilation smoke test;
-  tidied go.mod.
-- 2026-06-28: Added repo scaffolding: README, LICENSE, Makefile,
-  Dockerfile, REPO_POLICIES.md, and Gitea CI.
-- 2026-02-12: Fixed SQLite database locking by removing parallel
-  processing; fixed Linux build via golang.org/x/sys/unix Fadvise.
-- 2026-02-12: Optimized file copy for large databases; moved temp
-  directory to NVMe scratch storage.
+  `.gitignore`, `.dockerignore` and `.editorconfig`; `lint` and `test` phases in
+  the `Dockerfile`, built by `script/lint` and `script/test`; canonical
+  `script/cibuild`, `script/docker` and CI workflow; no linter installed on the
+  host; re-vendored `REPO_POLICIES.md`.
+- 2026-07-07 Adopted scripts-to-rule-them-all: `script/` entrypoints, Makefile
+  shims, README Entrypoints section
+- 2026-06-28: Fixed errcheck lint failures; added compilation smoke test; tidied
+  go.mod.
+- 2026-06-28: Added repo scaffolding: README, LICENSE, Makefile, Dockerfile,
+  REPO_POLICIES.md, and Gitea CI.
+- 2026-02-12: Fixed SQLite database locking by removing parallel processing;
+  fixed Linux build via golang.org/x/sys/unix Fadvise.
+- 2026-02-12: Optimized file copy for large databases; moved temp directory to
+  NVMe scratch storage.
 - 2026-02-11: Added date range support.
 - 2026-02-09: Initial implementation: single-day extraction, specific-date
   targeting, faster pruning of throwaway database copies.
 
 # Future Steps
 
-- Expand tests beyond the compilation smoke test: unit tests for the
-  extraction, verification, and atomic-publish paths.
 - Cut a first SemVer release once compliance and test coverage land.

cmd/bsdaily/main.go

@@ -3,123 +3,18 @@
 package main
 
 import (
-	"errors"
-	"fmt"
-	"log/slog"
 	"os"
-	"time"
 
-	"git.eeqj.de/sneak/bsdaily/internal/bsdaily"
-	"github.com/spf13/cobra"
+	"git.eeqj.de/sneak/bsdaily/internal/cli"
 )
 
-var (
-	errDateExclusive  = errors.New("--date and --from/--to are mutually exclusive")
-	errFromRequiresTo = errors.New("--from requires --to")
-	errToRequiresFrom = errors.New("--to requires --from")
-	errFromAfterTo    = errors.New("--from is after --to")
-)
+// Version is the git tag or short commit, set at link time with
+// -X main.Version=... by the Dockerfile and the Makefile. A build that sets
+// nothing, or sets it empty, reports dev.
+//
+//nolint:gochecknoglobals // -X can only set a package-level variable
+var Version string
 
 func main() {
-	logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{
-		Level: slog.LevelInfo,
-	}))
-	slog.SetDefault(logger)
-
-	var dateFlag, fromFlag, toFlag string
-
-	rootCmd := &cobra.Command{
-		Use:          "bsdaily",
-		Short:        "Extract a single day's data from the latest daily snapshot",
-		SilenceUsage: true,
-		RunE: func(_ *cobra.Command, _ []string) error {
-			targetDates, err := parseTargetDates(dateFlag, fromFlag, toFlag)
-			if err != nil {
-				return err
-			}
-
-			err = bsdaily.Run(targetDates)
-			if err != nil {
-				return err
-			}
-
-			slog.Info("completed successfully")
-
-			return nil
-		},
-	}
-
-	rootCmd.Flags().StringVarP(&dateFlag, "date", "d", "",
-		"target date to extract (YYYY-MM-DD); "+
-			"defaults to snapshot date minus one day")
-	rootCmd.Flags().StringVar(&fromFlag, "from", "",
-		"start of date range to extract (YYYY-MM-DD, inclusive); use with --to")
-	rootCmd.Flags().StringVar(&toFlag, "to", "",
-		"end of date range to extract (YYYY-MM-DD, inclusive); use with --from")
-
-	err := rootCmd.Execute()
-	if err != nil {
-		os.Exit(1)
-	}
-}
-
-// parseTargetDates turns the --date, --from and --to flags into the days
-// to extract. It returns nil when none of them is set, which Run takes
-// to mean the snapshot date minus one day.
-func parseTargetDates(dateFlag, fromFlag, toFlag string) ([]time.Time, error) {
-	hasDate := dateFlag != ""
-	hasFrom := fromFlag != ""
-	hasTo := toFlag != ""
-
-	// Validate mutual exclusivity
-	if hasDate && (hasFrom || hasTo) {
-		return nil, errDateExclusive
-	}
-
-	if hasFrom != hasTo {
-		if hasFrom {
-			return nil, errFromRequiresTo
-		}
-
-		return nil, errToRequiresFrom
-	}
-
-	if hasDate {
-		t, err := time.Parse("2006-01-02", dateFlag)
-		if err != nil {
-			return nil, fmt.Errorf(
-				"invalid --date %q (expected YYYY-MM-DD): %w", dateFlag, err)
-		}
-
-		return []time.Time{t}, nil
-	}
-
-	if !hasFrom {
-		return nil, nil
-	}
-
-	from, err := time.Parse("2006-01-02", fromFlag)
-	if err != nil {
-		return nil, fmt.Errorf(
-			"invalid --from %q (expected YYYY-MM-DD): %w", fromFlag, err)
-	}
-
-	to, err := time.Parse("2006-01-02", toFlag)
-	if err != nil {
-		return nil, fmt.Errorf(
-			"invalid --to %q (expected YYYY-MM-DD): %w", toFlag, err)
-	}
-
-	if from.After(to) {
-		return nil, fmt.Errorf("%w (--from %s, --to %s)",
-			errFromAfterTo, fromFlag, toFlag)
-	}
-
-	var targetDates []time.Time
-
-	for d := from; !d.After(to); d = d.AddDate(0, 0, 1) {
-		targetDates = append(targetDates, d)
-	}
-
-	return targetDates, nil
+	os.Exit(cli.Main(Version))
 }

internal/bsdaily/copy.go

@@ -6,7 +6,6 @@ import (
 	"io"
 	"log/slog"
 	"os"
-	"path/filepath"
 	"time"
 )
 
@@ -26,7 +25,8 @@ func CopyFile(src, dst string) (err error) {
 
 	slog.Info("copying file", "src", src, "dst", dst)
 
-	srcFile, err := os.Open(filepath.Clean(src))
+	//nolint:gosec // src is a path this package built
+	srcFile, err := os.Open(src)
 	if err != nil {
 		return fmt.Errorf("opening source %s: %w", src, err)
 	}
@@ -48,7 +48,8 @@ func CopyFile(src, dst string) (err error) {
 		applyFileAdvice(srcFile, srcInfo.Size())
 	}
 
-	dstFile, err := os.Create(filepath.Clean(dst))
+	//nolint:gosec // dst is a path this package built
+	dstFile, err := os.Create(dst)
 	if err != nil {
 		return fmt.Errorf("creating destination %s: %w", dst, err)
 	}

internal/bsdaily/disk.go

@@ -21,7 +21,8 @@ func CheckFreeSpace(path string, minBytes uint64, label string) error {
 		return fmt.Errorf("statfs %s (%s): %w", path, label, err)
 	}
 
-	free := stat.Bavail * uint64(stat.Bsize) //nolint:gosec // Bsize is never negative
+	//nolint:gosec,unconvert // Bsize is never negative; Bavail is signed on FreeBSD
+	free := uint64(stat.Bavail) * uint64(stat.Bsize)
 	freeGB := float64(free) / float64(bytesPerGB)
 	minGB := float64(minBytes) / float64(bytesPerGB)
 

internal/bsdaily/dump.go

@@ -29,7 +29,8 @@ func DumpAndCompress(dbPath, outputPath string) (err error) {
 		return err
 	}
 
-	outFile, err := os.Create(filepath.Clean(outputPath))
+	//nolint:gosec // outputPath is a path this package built
+	outFile, err := os.Create(outputPath)
 	if err != nil {
 		return fmt.Errorf("creating output file: %w", err)
 	}

internal/bsdaily/extract.go

@@ -55,7 +55,7 @@ func ExtractDay(srcDBPath, dstDBPath string, targetDay time.Time) error {
 		return fmt.Errorf("attaching source database: %w", err)
 	}
 
-	err = copyTables(ctx, db)
+	err = createTables(ctx, db)
 	if err != nil {
 		return err
 	}
@@ -94,9 +94,9 @@ func ExtractDay(srcDBPath, dstDBPath string, targetDay time.Time) error {
 	return nil
 }
 
-// copyTables creates every table of the attached source database, empty,
+// createTables creates every table of the attached source database, empty,
 // in the destination database.
-func copyTables(ctx context.Context, db *sql.DB) error {
+func createTables(ctx context.Context, db *sql.DB) error {
 	// Copy table DDL from source
 	slog.Info("copying table DDL from source")
 

internal/cli/cli.go

@@ -0,0 +1,67 @@
+// Package cli is the bsdaily command line: the command, its flags, the
+// rules for combining them and the dates they name. The extraction itself
+// is in package bsdaily.
+package cli
+
+import (
+	"log/slog"
+	"os"
+
+	"git.eeqj.de/sneak/bsdaily/internal/bsdaily"
+	"github.com/spf13/cobra"
+)
+
+// Main runs the bsdaily command on the program's command-line arguments
+// and returns the status for the process to exit with. version is the
+// build's version; an empty one is reported as dev.
+func Main(version string) int {
+	if version == "" {
+		version = "dev"
+	}
+
+	logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	}))
+	slog.SetDefault(logger)
+
+	var dateFlag, fromFlag, toFlag string
+
+	rootCmd := &cobra.Command{
+		Use:          "bsdaily",
+		Short:        "Extract a single day's data from the latest daily snapshot",
+		Version:      version,
+		SilenceUsage: true,
+		RunE: func(_ *cobra.Command, _ []string) error {
+			slog.Info("starting", "version", version)
+
+			targetDates, err := ParseTargetDates(dateFlag, fromFlag, toFlag)
+			if err != nil {
+				return err
+			}
+
+			err = bsdaily.Run(targetDates)
+			if err != nil {
+				return err
+			}
+
+			slog.Info("completed successfully")
+
+			return nil
+		},
+	}
+
+	rootCmd.Flags().StringVarP(&dateFlag, "date", "d", "",
+		"target date to extract (YYYY-MM-DD); "+
+			"defaults to snapshot date minus one day")
+	rootCmd.Flags().StringVar(&fromFlag, "from", "",
+		"start of date range to extract (YYYY-MM-DD, inclusive); use with --to")
+	rootCmd.Flags().StringVar(&toFlag, "to", "",
+		"end of date range to extract (YYYY-MM-DD, inclusive); use with --from")
+
+	err := rootCmd.Execute()
+	if err != nil {
+		return 1
+	}
+
+	return 0
+}

internal/cli/dates.go

@@ -0,0 +1,74 @@
+package cli
+
+import (
+	"errors"
+	"fmt"
+	"time"
+)
+
+var (
+	errDateExclusive  = errors.New("--date and --from/--to are mutually exclusive")
+	errFromRequiresTo = errors.New("--from requires --to")
+	errToRequiresFrom = errors.New("--to requires --from")
+	errFromAfterTo    = errors.New("is after --to")
+)
+
+// ParseTargetDates turns the --date, --from and --to flags into the days
+// to extract. It returns nil when none of them is set, which bsdaily.Run
+// takes to mean the snapshot date minus one day.
+func ParseTargetDates(dateFlag, fromFlag, toFlag string) ([]time.Time, error) {
+	hasDate := dateFlag != ""
+	hasFrom := fromFlag != ""
+	hasTo := toFlag != ""
+
+	// Validate mutual exclusivity
+	if hasDate && (hasFrom || hasTo) {
+		return nil, errDateExclusive
+	}
+
+	if hasFrom != hasTo {
+		if hasFrom {
+			return nil, errFromRequiresTo
+		}
+
+		return nil, errToRequiresFrom
+	}
+
+	if hasDate {
+		t, err := time.Parse("2006-01-02", dateFlag)
+		if err != nil {
+			return nil, fmt.Errorf(
+				"invalid --date %q (expected YYYY-MM-DD): %w", dateFlag, err)
+		}
+
+		return []time.Time{t}, nil
+	}
+
+	if !hasFrom {
+		return nil, nil
+	}
+
+	from, err := time.Parse("2006-01-02", fromFlag)
+	if err != nil {
+		return nil, fmt.Errorf(
+			"invalid --from %q (expected YYYY-MM-DD): %w", fromFlag, err)
+	}
+
+	to, err := time.Parse("2006-01-02", toFlag)
+	if err != nil {
+		return nil, fmt.Errorf(
+			"invalid --to %q (expected YYYY-MM-DD): %w", toFlag, err)
+	}
+
+	if from.After(to) {
+		return nil, fmt.Errorf("--from %s %w %s", fromFlag, errFromAfterTo, toFlag)
+	}
+
+	var targetDates []time.Time
+
+	for d := from; !d.After(to); d = d.AddDate(0, 0, 1) {
+		targetDates = append(targetDates, d)
+	}
+
+	return targetDates, nil
+}

internal/cli/dates_test.go

@@ -0,0 +1,127 @@
+package cli_test
+
+import (
+	"slices"
+	"strings"
+	"testing"
+
+	"git.eeqj.de/sneak/bsdaily/internal/cli"
+)
+
+func TestParseTargetDates(t *testing.T) {
+	t.Parallel()
+
+	const oneDay = "2026-05-14"
+
+	// want lists the expected days as YYYY-MM-DD.
+	tests := []struct {
+		name string
+		date string
+		from string
+		to   string
+		want []string
+	}{
+		{name: "no flags"},
+		{name: "single date", date: "2026-06-27", want: []string{"2026-06-27"}},
+		{
+			name: "range across a month end", from: "2026-06-29", to: "2026-07-02",
+			want: []string{"2026-06-29", "2026-06-30", "2026-07-01", "2026-07-02"},
+		},
+		{name: "range of one day", from: oneDay, to: oneDay, want: []string{oneDay}},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			got, err := cli.ParseTargetDates(tt.date, tt.from, tt.to)
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+
+			days := make([]string, 0, len(got))
+			for _, day := range got {
+				days = append(days, day.Format("2006-01-02"))
+			}
+
+			if !slices.Equal(days, tt.want) {
+				t.Errorf("days = %v, want %v", days, tt.want)
+			}
+		})
+	}
+}
+
+func TestParseTargetDatesErrors(t *testing.T) {
+	t.Parallel()
+
+	const dateExclusive = "--date and --from/--to are mutually exclusive"
+
+	// wantErr is the whole error message. With startsWith set it is only how
+	// the message starts: for a malformed date, the date parser's own
+	// explanation follows it.
+	tests := []struct {
+		name       string
+		date       string
+		from       string
+		to         string
+		wantErr    string
+		startsWith bool
+	}{
+		{
+			name: "from after to", from: "2026-03-02", to: "2026-03-01",
+			wantErr: "--from 2026-03-02 is after --to 2026-03-01",
+		},
+		{name: "from without to", from: "2026-04-01", wantErr: "--from requires --to"},
+		{name: "to without from", to: "2026-04-02", wantErr: "--to requires --from"},
+		{
+			name: "date with from", date: "2026-01-05", from: "2026-01-06",
+			wantErr: dateExclusive,
+		},
+		{
+			name: "date with to", date: "2026-01-13", to: "2026-01-14",
+			wantErr: dateExclusive,
+		},
+		{
+			name: "date with from and to", date: "2026-01-07",
+			from: "2026-01-08", to: "2026-01-09",
+			wantErr: dateExclusive,
+		},
+		{
+			name: "malformed date", date: "27.06.2026",
+			wantErr:    `invalid --date "27.06.2026" (expected YYYY-MM-DD): `,
+			startsWith: true,
+		},
+		{
+			name: "date that does not exist", date: "2026-02-30",
+			wantErr:    `invalid --date "2026-02-30" (expected YYYY-MM-DD): `,
+			startsWith: true,
+		},
+		{
+			name: "malformed from", from: "2026-1-10", to: "2026-01-11",
+			wantErr:    `invalid --from "2026-1-10" (expected YYYY-MM-DD): `,
+			startsWith: true,
+		},
+		{
+			name: "malformed to", from: "2026-01-12", to: "tomorrow",
+			wantErr:    `invalid --to "tomorrow" (expected YYYY-MM-DD): `,
+			startsWith: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			_, err := cli.ParseTargetDates(tt.date, tt.from, tt.to)
+
+			switch {
+			case err == nil:
+				t.Errorf("no error, want %q", tt.wantErr)
+			case tt.startsWith && !strings.HasPrefix(err.Error(), tt.wantErr):
+				t.Errorf("error = %q, want one starting %q", err, tt.wantErr)
+			case !tt.startsWith && err.Error() != tt.wantErr:
+				t.Errorf("error = %q, want %q", err, tt.wantErr)
+			}
+		})
+	}
+}

package.json

@@ -0,0 +1,5 @@
+{
+  "devDependencies": {
+    "prettier": "3.8.1"
+  }
+}

script/bootstrap

@@ -3,11 +3,20 @@
 # this repo. Idempotent: every install is guarded by a check so already
 # installed tools are skipped. Base tooling comes from nix, apt, brew,
 # or apk (detected in that order); assumes NOTHING is present (not git,
-# make, or go).
+# make, go, or node). Node is 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).
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
+# 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=""
 APT_UPDATED=""
@@ -56,6 +65,69 @@ 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
+}
+
+# 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"
 
@@ -68,6 +140,12 @@ main() {
 
     go mod download
 
+    # Node and yarn, then the prettier pinned in package.json and
+    # yarn.lock, which script/fmt and script/fmt-check run
+    ensure_node
+    ensure_yarn
+    install_js_deps
+
     echo "bootstrap complete"
 }
 

script/fmt

@@ -1,12 +1,34 @@
 #!/bin/sh
-# script/fmt: format all files (writes).
+# script/fmt: format all files (writes): the Go code with go fmt and
+# every Markdown file with prettier.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
+# 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 replaces this shell, so it stays the last step.
+    run_yarn run prettier --write '**/*.md' --tab-width 4 --prose-wrap always
 }
 
 main "$@"

script/fmt-check

@@ -1,10 +1,30 @@
 #!/bin/sh
 # script/fmt-check: check formatting (read-only). Same scope as
-# script/fmt, but fails instead of writing.
+# script/fmt, the Go code and every Markdown file, but fails instead of
+# writing.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
+# 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 "$ROOT"
     unformatted="$(gofmt -l .)"
@@ -13,6 +33,8 @@ main() {
         echo "$unformatted" >&2
         exit 1
     fi
+    # run_yarn replaces this shell, so it stays the last step.
+    run_yarn run prettier --check '**/*.md' --tab-width 4 --prose-wrap always
 }
 
 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==