[kamath]

Summary

Adds Biome 2.5 as the repo's linter and formatter and fixes everything it reports. Also adds a CI workflow, so pull requests are linted, built, type-checked, and unit-tested.

Biome runs in three places, and warnings fail all three:

• pnpm check runs pnpm lint (which is biome check --error-on-warnings .) before type-checking each package.
• A pre-push hook, installed by pnpm install through simple-git-hooks, runs pnpm lint. Set SKIP_SIMPLE_GIT_HOOKS=1 to bypass it.
• CI: see below.

CI (.github/workflows/ci.yml)

Runs on pull requests and on pushes to main, with two parallel jobs:

• biome (about 7s): biomejs/setup-biome installs the Biome version pinned in pnpm-lock.yaml, then runs biome ci --error-on-warnings ..
• check (about 70s): pnpm/setup@v3 installs the pnpm version from packageManager plus the latest Node 22.x, then runs pnpm install --frozen-lockfile with a cached store. After that it runs pnpm build, pnpm -r check, and pnpm test.
  • The build has to run first because the web app's type-check imports routeTree.gen.ts, which only the Vite build generates.
  • The tests run .ts files directly, so they need Node 22.18 or newer. Node 22.x satisfies that.

Commits

1. Add Biome: biome.json, root scripts, and a README note.
2. Apply Biome formatting and safe lint fixes: generated output only.
3. Fix Biome lint diagnostics: hand fixes for the 74 remaining diagnostics.
4. Pre-push hook and fail on warnings.
5. CI: Biome job.
6. CI: build, type-check, and unit tests job.

Config choices

• 2-space indent, double quotes, and a 100-column line width. The code is already written in this style, and 100 columns gave a roughly net-neutral diff.
• Uses the recommended rules with no rules turned off.
• worker-configuration.d.ts is excluded because Wrangler generates it (about 15.7k lines).
• CSS tailwindDirectives is enabled so @source in styles.css parses.
• simple-git-hooks is declined in allowBuilds. Its own postinstall is not needed because the root prepare script installs the hook.

Hand-written lint fixes

• noNonNullAssertion (54): replaced with explicit narrowing. Examples: a type guard for ownsSession, tab lookups that check their result, a CDP Quad tuple type, and assert.ok narrowing in tests.
• noExplicitAny (13): added AXNode and FrameTreeNode interfaces for the CDP payloads that snapshots read. evaluate, evaluateIn, and Locator.apply are now generic with an unknown default. The remaining raw CDP JSON goes through a single documented CdpPayload alias.
• React: added type="button". Message parts render through a MessagePart component, so the index key appears in one place.
• Other: noAssignInExpressions and noImplicitAnyLet.

The repo has exactly three biome-ignore comments, each with a reason: the CdpPayload alias, the message part index key, and the scroll effect's trigger dependencies.

Two small behavior changes:

• tab.close now throws "No tab is open." instead of crashing on undefined.
• The tools package's temporary-session shutdown skips browser.stop when a handle has no sessionId.

Testing

• Both CI jobs pass on this PR. The check job ran 62/62 unit tests.
• Locally, against headless Chrome: test:runtime passes and pnpm test:e2e passes 14/14.
• The pre-push hook blocked a push with a lint warning, blocked one with a lint error, and allowed a clean push.

Not changed

The engines fields and the README still say Node 22.13+. That is enough to run pnpm 11, but running the .ts sources directly (for example pnpm test or pnpm cli) needs 22.18+. I left it as is because the published packages may really support 22.13.