build: add ESLint to script/lint and containerize linting (closes #152)

TODO.md

@@ -32,17 +32,15 @@ The backlog lives on the
 [Gitea tracker](https://git.eeqj.de/sneak/AutistMask/issues), which is
 authoritative; this file does not duplicate it. Full policy file set present.
 Real-browser end-to-end suites (`make test-e2e` for Chrome,
-`make test-e2e-firefox` for Firefox) now sit alongside `make check`, which
-cannot see a runtime `ReferenceError` in a popup view, and
-`.gitea/workflows/e2e.yml` runs both of them on every push.
+`make test-e2e-firefox` for Firefox) sit alongside `make check`, which now does
+static analysis as well as formatting, and `.gitea/workflows/e2e.yml` runs both
+of them on every push.
 
 # Next Step
 
-Land [#152](https://git.eeqj.de/sneak/AutistMask/issues/152): add ESLint to
-`script/lint`. `make check` is `prettier --check` only today and cannot catch
-undefined identifiers, which is how
-[#150](https://git.eeqj.de/sneak/AutistMask/issues/150) and
-[#151](https://git.eeqj.de/sneak/AutistMask/issues/151) shipped.
+Pre-1.0 security review of the extension (key handling, DEBUG mode policy, RPC
+input validation) before any 1.0rc tag. Individual filed issues are parts of it,
+but the review is broader than any of them.
 
 # Completed Steps
 
@@ -143,6 +141,23 @@ undefined identifiers, which is how
   on the real clipboard, read back after a sentinel write. Each of the four was
   demonstrated failing against a deliberately broken build
   ([#188](https://git.eeqj.de/sneak/AutistMask/issues/188)).
+- 2026-08-14: `make check` does static analysis. `script/lint` ran
+  `prettier --check .`, byte-identical to `script/fmt-check`, so a wallet with
+  two shipped used-but-not-imported crashes behind it was green. ESLint is now
+  pinned in `package.json` with `@eslint/js` recommended as the base, flat
+  config in `eslint.config.js`, `no-undef` and `no-unused-vars` error-level, and
+  globals declared per tree — browser for the popup and content scripts, service
+  worker for `src/background/` and `src/shared/`, jest for `tests/`, node for
+  `build.js`. It found 41 unused bindings and 53 undefined identifiers; all are
+  fixed, and dropping a call to an unimported `foo()` into any `src/` file fails
+  `make lint`. Linting is also containerized now: `script/lint` builds the
+  Dockerfile's new `lint` stage, so the ESLint that decides whether this repo is
+  green is the pinned one and not the host's. The lint stage roughly doubles the
+  image build, so `script/test`'s hard timeout is now a bound on a hung suite
+  rather than a wall-clock budget: 30s on the host, where the suite runs in
+  about 8s, and `AUTISTMASK_TEST_TIMEOUT` raises it inside the image, where a
+  cold build pays install and contention costs the policy budget never described
+  ([#152](https://git.eeqj.de/sneak/AutistMask/issues/152)).
 - 2026-08-14: CI runs the browser end-to-end suites. `.gitea/workflows/e2e.yml`
   runs `script/test-e2e` and `script/test-e2e-firefox` as two jobs on every
   push, separate from `check`, so `make check` and its 20-second `make test` cap
@@ -481,8 +496,5 @@ undefined identifiers, which is how
 Only work that has no issue of its own belongs here; everything else is on the
 tracker.
 
-- Pre-1.0 security review of the extension (key handling, DEBUG mode policy, RPC
-  input validation) before any 1.0rc tag. Individual filed issues are parts of
-  it, but the review is broader than any of them.
 - Cut 1.0.0 once the milestone is empty, then continue tagging as milestones
   land.