fix(dev): source watcher ignores the package build's .compile- scratch dir (red main) - #669

Fixes red main (Verify (integration-2) at 7e56517756, route-invocation-dev-server.test.ts ×2).

Root cause

#656 made the package build compile into a second scratch sibling of the output root, .<output>.compile-XXXXXX, beside the existing .<output>.stage-XXXXXX. The agent-bundle dev source watcher (dev/watcher.ts, isOutputStagingPath) only knew the .stage- prefix, so the compile directory's creation and removal counted as a source change: every dist/ package build inside the dev server invalidated and republished the epoch it had just produced (same source revision, new epoch id). Anything pinned to the first epoch — the parity fixtures' operator .env, an invocation queued against it — then ran under, or was compared against, the second one (operator: 'missing', pluginRoot epoch mismatch).

Fix

isOutputStagingPath recognises both .<output>.stage- and .<output>.compile-. dev-watcher.test.ts emits addDir/add/unlinkDir for a .dist.compile-XXXXXX tree and asserts no invalidation (red without the fix: failedTests: 1, the compile paths appear in paths).

Gates (local merge gate, AGENTS.md #662; branch = origin/main 7e56517756 + this commit)

pnpm build && pnpm typecheck && pnpm lint      # ok
pnpm test:unit                                 # 4272 passed, 0 failed
AGENT_BUNDLE_WORKBENCH_PREBUILT=1 AGENT_BUNDLE_PACKAGE_PREBUILT=1 pnpm exec rstest --config rstest.integration.config.ts \
  packages/agent-bundle/tests/route-invocation-dev-server.test.ts packages/agent-bundle/tests/dev-workbench.test.ts \
  packages/agent-bundle/tests/dev-package-build.test.ts        # 37 passed, 0 failed

No website change (internal watcher rule). Changeset: patch.

Not fixed here

The same main run also fails route-register-typegen.test.ts ("Type 'false' does not satisfy the constraint 'true'") and three prepack.test.ts cases (zod/vendored dependency findings, document.files is not iterable) — these reproduce at 45beb54792 (#656) / 7e56517756 (#665) and are independent of this watcher rule; reported to their authors on #600.

Self-review

Reviewer: Claude Fable 5.1 Thinking High (read-only, diff vs origin/main). Findings: (1) prefix derivation matches package-build.ts:389-392/build.ts:695 for nested and default outputs — VERIFIED; (2) no other in-root scratch directory left unhandled (node_modules/.agent-bundle-dts- and .agent-bundle/** are excluded by directory name) — VERIFIED; (3) a shared prefix helper is a reasonable follow-up, not a blocker for a hotfix — accepted; (4) changeset ended in the literal (#PR) — fixed to (#669). Verdict: MERGE.