chore: re-vendor canonical files from prompts at dd4027b (closes #472)

Copies .dockerignore, .gitignore, .prettierignore, check.yml and
REPO_POLICIES.md from sneak/prompts at dd4027b. The repo's own entries
(dist/, release/, yarn files) are kept after the canonical content.

The Dockerfile gets separate lint and test phases. Its last stage
depends on both, checks the git describe version and runs make build.
script/lint, test, check, cibuild and docker are the canonical models.
check-censored moves into the lint phase and test-verify-build into the
test phase. fmt and fmt-check fall back to the nvm-installed node. The
e2e image builds are uncached. Comments that cited the old 20-second
test cap now say 60.

Model: opus-5-5

Dockerfile

@@ -1,41 +1,80 @@
+# Lint phase: ESLint, prettier --check, and script/check-censored. The tools
+# are invoked directly rather than through `make lint` or `script/lint`, which
+# are themselves a docker build and would recurse into a daemon that does not
+# exist in a build step.
+#
 # node:22-slim (22.x LTS), 2026-02-24
-FROM node@sha256:5373f1906319b3a1f291da5d102f4ce5c77ccbe29eb637f072b6c7b70443fc36 AS base
+FROM node@sha256:5373f1906319b3a1f291da5d102f4ce5c77ccbe29eb637f072b6c7b70443fc36 AS lint
 
 WORKDIR /app
 
-# Marks "already inside the lint container" for script/lint, which otherwise
-# shells out to docker to build the lint stage below. Nothing outside this
-# image sets it.
-ENV AUTISTMASK_LINT_NATIVE=1
-
-# script/test's default 30s bound is the host figure. In here the same suite
-# starts on a cold jest cache and shares the runner with the rest of the build,
-# so 30s is too tight — it killed a healthy suite at 30.6s on a cold CI cache.
-# 180s still catches a hang in three minutes and cannot be tripped by a suite
-# that is merely running on contended hardware.
-ENV AUTISTMASK_TEST_TIMEOUT=180
-
-# script/bootstrap installs all prerequisites (make via apt here; node
-# is already in the base image, yarn comes via corepack) and runs
-# yarn install --frozen-lockfile. Dependency manifests are copied first
-# so the bootstrap layer is cached until they change.
 COPY script/ script/
 COPY package.json yarn.lock ./
 RUN script/bootstrap
 
 COPY . .
 
-# Lint stage — fail fast on static analysis and formatting, before the tests
-# and the build. This is also the stage script/lint builds from a host, which
-# is how linting stays on the pinned ESLint rather than the host's.
-FROM base AS lint
-RUN make lint
+RUN yarn run lint
+RUN script/check-censored
+
+# Test phase, same shape and for the same reason: the jest suite (its worker
+# cap is in package.json), rerun verbose on failure, then
+# script/test-verify-build.
+#
+# node:22-slim (22.x LTS), 2026-02-24
+FROM node@sha256:5373f1906319b3a1f291da5d102f4ce5c77ccbe29eb637f072b6c7b70443fc36 AS test
+
+WORKDIR /app
+
+COPY script/ script/
+COPY package.json yarn.lock ./
+RUN script/bootstrap
+
+COPY . .
+
+RUN timeout 90 yarn run test || \
+    { echo "--- Rerunning with --verbose for details ---"; \
+      timeout 90 yarn run test:verbose; exit 1; }
+RUN script/test-verify-build
+
+# Development environment with the extension built, and the last stage: a
+# plain `docker build .` names no target and so builds this one. Nothing is
+# wanted from the two phases above; the copies are what make BuildKit build
+# them first, so this image cannot be produced unless lint and test passed. A
+# stage appended after this one would drop all three out of a plain build.
+#
+# node:22-slim (22.x LTS), 2026-02-24
+FROM node@sha256:5373f1906319b3a1f291da5d102f4ce5c77ccbe29eb637f072b6c7b70443fc36
+
+WORKDIR /app
 
-# Full check and build. The COPY --from is a no-op file copy whose only job is
-# to make BuildKit finish the lint stage before this one starts; without it the
-# stages run in parallel and a lint failure would not fail the build early.
-FROM base AS check
 COPY --from=lint /app/package.json /dev/null
+COPY --from=test /app/package.json /dev/null
 
-RUN make check
-RUN make build
+# script/bootstrap installs all prerequisites, git included. Manifests are
+# copied first so that layer stays cached until dependencies change.
+COPY script/ script/
+COPY package.json yarn.lock ./
+RUN script/bootstrap
+# A tar-stream context keeps the sender's file owners, which git refuses.
+RUN git config --system --add safe.directory /app
+
+COPY . .
+
+# 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, and build.js, which stamps the
+# extension with the commit it was built from, would stamp "unknown".
+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; \
+    make build
+# A LABEL cannot run git, so it carries the build argument alone; a plain
+# `docker build .` leaves it empty.
+LABEL org.opencontainers.image.version="${VERSION}"