Pin tailwindcss and check the committed stylesheet against it (closes #231)

make css ran whatever tailwindcss binary was on the host's PATH, so the committed stylesheet depended on the machine that built it, and nothing noticed when a template used a class the stylesheet lacked. make css now runs the standalone tailwindcss v4.2.1, pinned by sha256, in a Dockerfile stage, and a check stage, run by make check and required by the image build, fails when the committed static/css/tailwind.css differs from what the templates need, showing the differing rules. input.css names its sources. The unused .btn-text is removed and the stylesheet regenerated, dropping only unused rules. The README has a Stylesheet section.

Model: opus-5-5

Dockerfile

@@ -29,14 +29,51 @@ RUN script/assets
 RUN --network=none golangci-lint config verify --config .golangci.yml
 RUN --network=none golangci-lint run --config .golangci.yml --build-tags browser ./...
 
+# Stylesheet stages. static/css/tailwind.css is generated, by this pinned
+# tailwindcss, from static/css/input.css and the files its @source lines
+# name. `make css` (script/css) writes it out from the css-output stage.
+# The css-check stage fails when the committed file differs from what is
+# generated; `make check` runs it, and so does the build stage below.
+#
+# tailwindcss v4.2.1 standalone CLI, released 2026-02-23: one binary per
+# architecture, each pinned by its sha256 from the release's sha256sums.txt.
+# debian:bookworm-slim, 2026-10-02: the binary needs glibc.
+FROM debian:bookworm-slim@sha256:3783cc01769c7b2b1b83a5c5ad96c815348e28ed7da68e2e3687004faa906251 AS tailwind-amd64
+ADD --checksum=sha256:39e8d4e24b3c83b0a6e69e100a972fbc75d5fef8dce47b3ddac3cf92dea81fe3 --chmod=755 \
+    https://github.com/tailwindlabs/tailwindcss/releases/download/v4.2.1/tailwindcss-linux-x64 /usr/local/bin/tailwindcss
+
+FROM debian:bookworm-slim@sha256:3783cc01769c7b2b1b83a5c5ad96c815348e28ed7da68e2e3687004faa906251 AS tailwind-arm64
+ADD --checksum=sha256:d87e6486bb3f70b04ef1dcaacc4ee6548a5a15fbf521b31bc24d2c774f68a951 --chmod=755 \
+    https://github.com/tailwindlabs/tailwindcss/releases/download/v4.2.1/tailwindcss-linux-arm64 /usr/local/bin/tailwindcss
+
+# TARGETARCH, set by docker, is the architecture being built for.
+FROM tailwind-${TARGETARCH} AS css
+WORKDIR /src
+COPY . .
+RUN tailwindcss -i static/css/input.css -o /out/tailwind.css --minify
+
+FROM scratch AS css-output
+COPY --from=css /out/tailwind.css /
+
+# Both files are split after each "}", one rule per line, so that when they
+# differ the diff shows the rules that differ.
+FROM css AS css-check
+RUN sed 's/}/}\n/g' static/css/tailwind.css > /tmp/committed.css \
+    && sed 's/}/}\n/g' /out/tailwind.css > /tmp/generated.css \
+    && diff -U0 /tmp/committed.css /tmp/generated.css || { \
+        echo "static/css/tailwind.css is not what make css generates; run make css" >&2; \
+        exit 1; \
+    }
+
 # Build stage
 # golang:1.26.1-bookworm (Debian-based), 2026-03-17
 # Using Debian-based image because gorm.io/driver/sqlite pulls in
 # mattn/go-sqlite3 (CGO), which does not compile on Alpine musl.
 FROM golang:1.26.1-bookworm@sha256:4465644228bc2857a954b092167e12aa59c006a3492282a6c820bf4755fd64a4 AS builder
 
-# Depend on lint stage passing
+# Depend on the lint and stylesheet check stages passing
 COPY --from=lint /src/go.sum /dev/null
+COPY --from=css-check /out/tailwind.css /dev/null
 
 # jq is a runtime dependency of script/ci-mark-superseded, which the test
 # suite executes. git is what script/version derives the version with.