Run lint and tests as Dockerfile phases built with --no-cache (closes #202)

script/check, cibuild, docker, lint, test, setup and install-precommit
are now the sneak/prompts main copies, unchanged: lint and test each
build their Dockerfile phase with --no-cache. The lint phase runs
golangci-lint from the image REPO_POLICIES.md names, with libvips-dev
from apt-get; the test phase runs the tests with a 90-second timeout;
the build stage depends on both. script/bootstrap installs the C
compiler and image libraries only with --cgo, which the test phase and
build stage pass, and refreshes the apt lists before its first apt
install. Dockerfile.lint and CHECK_EPOCH are gone, and make
docker-versioned and docker-test call the scripts. Without VERSION the
build stage still uses git describe, per issue 166.

Model: opus-5-5

README.md

@@ -92,8 +92,11 @@ another part of pixa failed to stop. A request not finished by then is cut off.
 
 Outside Docker, pixa needs libvips (the image has 8.15) and libheif to run, as
 it uses libvips through CGO; building it also needs their development files,
-`pkg-config` and a C compiler. `script/bootstrap` installs all of these with
-nix, apt, brew or apk.
+`pkg-config` and a C compiler. `script/bootstrap --cgo` installs all of these,
+as the `Dockerfile` does where it compiles pixa. Plain `script/bootstrap`, which
+`script/setup` and `script/cibuild` run, installs only git, make and Go: the
+checks compile pixa in Docker, so the host needs none of the C libraries. Docker
+itself must already be installed.
 
 ## Running under upaas
 
@@ -565,28 +568,38 @@ standard: normalized scripts in `script/` are the entrypoints for the
 development workflow, and the Makefile targets are thin shims that call
 them. We provide:
 
-- `script/bootstrap` — install all dependencies (idempotent)
+- `script/bootstrap` — install git, make and Go and download the Go modules
+  (idempotent); with `--cgo`, also the C compiler and the libvips and libheif
+  libraries that compiling pixa needs
 - `script/setup` — make a fresh clone ready for development
   (bootstrap, then install-precommit)
 - `script/projectname` — output the project name ("pixa")
-- `script/test` — run the test suite
-- `script/lint` — run golangci-lint, always in a container (builds
-  `Dockerfile.lint` when run outside one)
+- `script/test` — run the test suite: build the `test` phase of the
+  `Dockerfile`, tagged `pixa-test`
+- `script/lint` — run golangci-lint: build the `lint` phase of the `Dockerfile`,
+  tagged `pixa-lint`; the linter never runs on the host
 - `script/fmt` — format all code (writes)
-- `script/fmt-check` — check formatting (read-only)
+- `script/fmt-check` — check formatting (read-only), on the host
 - `script/check` — run test, lint, and fmt-check
-- `script/docker` — build the Docker image tagged via `script/projectname`
+- `script/docker` — build the Docker image tagged via `script/projectname`, with
+  the version from `git describe`; the image's build stage depends on the `lint`
+  and `test` phases, so this runs them too
 - `script/docker-smoke` — build the image, start it, wait for it to be healthy
 - `script/loadtest` — measure pixad's throughput, latency and peak memory; a
   benchmark, not part of `script/check` (see Load Test)
-- `script/cibuild` — CI entrypoint: `docker build .` with a new
-  `CHECK_EPOCH` on every run, so the Dockerfile's checks run instead of
-  coming from the build cache, and a green run implies a green repo
+- `script/cibuild` — CI entrypoint: run `script/bootstrap` (without `--cgo`),
+  then `script/check`, then build the image as `script/docker` does
 - `script/precommit` — pre-commit checks (`go mod tidy` guard, then
   `script/check`)
 - `script/install-precommit` — install the git pre-commit hook that
   runs `script/precommit`
 
+Every `docker build` in these scripts passes `--no-cache`, so the lint and test
+phases run on every build instead of coming from the build cache.
+`script/check`, `script/cibuild`, `script/docker`, `script/lint`, `script/test`,
+`script/setup` and `script/install-precommit` are the standard copies from
+`sneak/prompts`, kept identical to them.
+
 ## Load Test
 
 `script/loadtest` (or `make loadtest`) measures how fast pixad answers and how