[Mohamed Mansour (mohamedmansour)]

markdown-state-serve.test.ts fails intermittently in the E2E (Ubuntu) job (example). A Markdown edit that starts referencing a missing stateFile never triggers a rebuild, so the test times out after 30 s. This is a real dev-server bug, not a test problem.

Root cause

After every rebuild, Press created a new file watcher and dropped the old one. Dropping a notify-debouncer-mini watcher discards events still inside its 50 ms debounce window, and the replacement only sees writes made after it registers. An edit made right after a rebuild finished could fall into that gap and be lost silently. The test hits the gap because it edits as soon as new output appears.

Fix

• Add WatcherHandle::retarget to webui-dev-server. It updates a running watcher's roots, exact files, and ignore list in place. The debouncer and unchanged recursive roots stay registered, so events observed during a refresh are still delivered. Content baselines reset the way a new watcher's would, so no-op-save filtering is unchanged.
• Exact-file parents (generated stateFile directories, projection manifests) are still re-registered on every retarget. Some backends drop a watch silently when its directory is deleted, and generators routinely recreate these directories. They use a separate notify backend: FSEvents applies each subscription change by restarting its stream, which would otherwise interrupt source-root events on macOS.
• If one path cannot be watched, retarget still registers the rest and returns the first error.
• Press now retargets its single watcher after each rebuild instead of replacing it. The existing re-check of included JSON against the bytes used for rendering still runs once the new subscriptions are active.

spawn_watcher is now built on retarget, so webui serve --watch uses the same registration path. Nested roots are deduplicated, which does not change which files are covered.

Review notes

• Unchanged recursive roots are no longer re-registered on every rebuild. A source root (content, config, or public directory) deleted and recreated between two rebuilds may not be watched again on Windows, where notify drops the watch without an event. This matches Press before stateFile support and current webui serve. Generated include directories keep per-rebuild re-registration.
• watch.rs was already over 700 lines, so the backend wrapper and subscription bookkeeping live in watch_backend.rs and watch_subscriptions.rs.

Validation

• Reproduced before the fix:
  • A minimal repro (edit, then replace the watcher) lost the edit 5/5 times on Windows and 5/5 on Linux (WSL, inotify).
  • The E2E test failed 3/60 runs under parallel CPU load, including the CI symptom and a lost final Markdown edit.
• With the fix:
  • The E2E test passed 210/210 runs under the same load.
  • The full Press E2E suite passed 118/118.
  • Dev-server and Press Rust tests pass on Windows and Linux.
• New regression tests:
  • source_edits_during_a_watch_refresh_still_rebuild (Press): failed 5/5 before the fix, passes 10/10 after.
  • Dev-server: retarget_delivers_edits_observed_before_it, retarget_moves_exact_file_subscriptions, and a filter-reset test.
  • Subscription-diff unit tests, including best-effort registration after a failure.
• cargo xtask check passes.

The E2E test itself is unchanged. It is the only end-to-end coverage of serve watching generated JSON includes, atomic replacements, and newly referenced missing files.

[Copilot]

🟡 Changes recommended

Root deduplication can leave a still-requested child directory unwatched when its ancestor cannot be registered, breaking best-effort recovery.

1 open issue

• Retain nested roots when ancestor watch registration fails · New

What changed in this PR

This PR fixes lost dev-server rebuild events by letting Press update a running watcher instead of replacing it after each build.

Changes:

• Add in-place watch retargeting while preserving the debouncer and unchanged recursive roots.
• Separate exact-file watches from recursive-root watches and add subscription bookkeeping.
• Update Press integration, regression tests, and watcher API documentation.

File	Description
crates/​webui-press/​src/​serve.rs	Retargets the existing watcher and tests edits during refresh.
crates/​webui-dev-server/​src/​watch.rs	Adds retargeting, shared event filtering, and regression tests.
crates/​webui-dev-server/​src/​watch_subscriptions.rs	Manages subscription changes, root deduplication, and registration failures.
crates/​webui-dev-server/​src/​watch_backend.rs	Separates recursive-root and exact-file notification backends.
crates/​webui-dev-server/​src/​lib.rs	Exports WatchTargets and documents retargeting.
crates/​webui-dev-server/​README.md	Explains why callers should retarget rather than replace watchers.

_{Review effort: Balanced}

[mddinbox]

Target: 6ceba63...cf9179d | Coverage: complete; CI: Desktop npm native (x86_64-apple-darwin) and Desktop npm native (x86_64-pc-windows-msvc) in progress
Challenge: 1 revised after independent challenge; rechecked on pinned code | Compatibility: none
Action: COMMENT | Pending explicit-file changes can leave served output stale.

[mddinbox]

[Medium] reset re-hashes every explicit file before the debouncer flushes. If a configured projection manifest changes after this build reads it but its event is still pending when retarget runs, the new hash is seeded here and the queued event is dropped as unchanged; source_targets watches these manifests as explicit files, while StateDependencies::changed_paths() does not track them. The just-finished output can therefore remain stale until another watched change. Preserve/forward changes against the prior explicit-file baseline across retarget, and add an explicit-file debounce-window regression test.