chore(lint): cover tools/ in the lint gate; attach cause in dev-proxy rebuild() (#718)

[debugmcpdev]

Closes #718.

What

pnpm lint — and so .husky/pre-push and all three CI jobs that run it — linted src/, packages/*/src/ and scripts/ but not tools/. The dev-proxy supervisor under tools/dev-proxy/ starts, stops and proxies the backend; it sat outside the gate with two preserve-caught-error errors in BackendManager.rebuild() (lines 366 and 375 on current main — the issue's 355/364 are from an older revision) that nothing reported.

• package.json — lint gains "tools/**/*.{js,mjs,cjs}". A superset of the issue's tools/dev-proxy/**: tools/ contains only the dev-proxy today, so the findings are identical, and a future tools/ directory is covered by default. Experimental probes belong in scripts/experiments/, which eslint.config.js already ignores. No ESLint config change: the **/*.{js,mjs,cjs} block already configures .mjs with node globals, and preserve-caught-error comes from js.configs.recommended.
• lint:fix now runs the same four globs with --fix instead of src/**/*.ts alone, so the hook's "run pnpm run lint:fix for auto-fixes" hint is true for everything lint reports. (Running it over the widened globs on this tree changes nothing.)
• tools/dev-proxy/dev-proxy.mjs — both rebuild() rethrows attach the caught execSync error as cause. Safe with respect to dev-proxy forwards backend stderr verbatim with naive chunk splitting #154's sanitization: every consumer of that error serializes err.message alone (handleDevTool's two catches, the fatal handler), so the raw build output on cause never reaches a tool response or a log line.
• tests/integration/dev-proxy-startup.test.ts — rebuild() and its catch blocks had no coverage. A new case sets DEV_PROXY_BUILD_CMD to a failing command and calls dev_rebuild_and_restart: the payload is exactly { success: false, error: "Build failed: …boom…" } with no cause, and the old backend keeps serving because the build failed before the restart.
• Docs — CONTRIBUTING.md (Dev-Loop Gate + Setup), AGENTS.md, and the adapter guide's checklist (which already omitted scripts/**) state the new glob set and drop the lint/lint:fix asymmetry note.

Verification

• pnpm exec eslint "tools/**/*.{js,mjs,cjs}": 2 errors before, 0 after.
• pnpm run lint (now covering tools/) clean; typecheck:all, changelog:check, check:docs clean.
• tests/integration/dev-proxy-startup.test.ts: 6/6 (the new case 1.2 s).
• Pre-push gate passed.

🤖 Generated with Claude Code

Review round (4aa0f41)

The /code-review on the first commit looked at what the newly-covered catch blocks actually said, and three of its findings were real defects in those lines:

• A buffer overflow was reported as a timeout. err.killed || err.signal === 'SIGTERM' was the timeout test, but execSync never sets killed, and an output-buffer overflow (ENOBUFS, 1 MiB default) arrives with the same SIGTERM — probed on this box: timeout → code: 'ETIMEDOUT', overflow → code: 'ENOBUFS', both signal: 'SIGTERM'. The timeout branch now keys on ETIMEDOUT, and maxBuffer is 64 MiB so an over-chatty build is not killed at all.
• A timed-out build discarded the output it had produced. The timeout message now carries the same sanitized tail the failure message does, so "where was it when it hung" is answered.
• A failed build sent a spurious tools/list_changed. The build fails before restart() runs, so the backend — and its tool inventory — is untouched, yet both handlers announced a change. Build and restart are now sequenced by one helper (rebuildThenRestart) that notifies only for a restart failure; BackendManager.rebuildAndRestart() is gone, and a rejected env update no longer notifies either.
• lint:fix is pnpm run lint --fix — one glob list instead of a second copy that could drift again (the drift class this issue is about).
• The integration case is renamed to what it can observe (it cannot see cause), asserts that no notification is added past the initial start's own, and a second case drives a hanging build through DEV_PROXY_BUILD_TIMEOUT_MS=1000. Both fail on the previous dev-proxy.mjs.

Declined here: making rebuild() async (execSync blocks the supervisor for the length of the build) is a concurrency-model change rather than a lint-gate fix — filed as #748. Attaching a slimmed cause instead of the raw execSync error would defeat preserve-caught-error's purpose; the message-only contract is documented at the throw site and locked by the tests.

Verification after the round: tests/integration/dev-proxy-startup.test.ts 7/7; lint (tools/ included), typecheck:all, changelog:check, check:docs clean; pre-push gate passed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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