[thekevinbot]

Fixes #1557

On inotify each directory gets its own watch. When a directory appears, the watcher walked it once and then watched what the walk found. A subdirectory created after that walk but before its parent's watch landed got no event and was never watched, so every later write inside it was lost. mkdir -p a/b/c racing the watcher's thread (easiest to hit pinned to one CPU) does exactly that.

Red commit first: watch_tree_watches_a_directory_created_before_its_parent_was_watched (unit test, packages/rust/src/watcher.rs).

The fix: watch_tree walks the new directory again after watching what it found, and stops once a walk finds nothing unwatched. A walk that finds nothing new costs one extra read of the new tree.

Hand test (dirsql server, all processes pinned to one CPU, mkdir -p dN/a/b/c/d/e/f/g then write r.json at the bottom, 200 times per run, 4 runs): before, 3 of 800 writes produced no event; after, 0 of 800.

E2E Verification

• Ran e2e suites locally for every affected SDK
• Python SDK e2e: watch_speed, jsonl_parse_speed, on_file_query, fanout -- 7 passed
• TypeScript SDK e2e: pnpm test:e2e -- passed
• Rust core e2e (if applicable): cargo test -p dirsql --features cli -- all passed
• packages/python/e2e-attestations/<branch>.json receipt written if packages/python changed (just e2e-attest-python)
• packages/ts/e2e-attestations/<branch>.json receipt written if packages/ts changed (just e2e-attest-ts)
• Command(s) run: testing-conventions e2e attest 'uv run python -m pytest tests/e2e/watch_speed_test.py tests/e2e/jsonl_parse_speed_test.py tests/e2e/on_file_query_test.py tests/e2e/fanout_test.py -q'; testing-conventions e2e attest 'pnpm test:e2e'
• Result summary: pass. watch_speed_test is flaky around its 1.1x bar on this host with and without this change (unfixed core failed 3 of 3, this branch passed 2 of 3); it measures writes to an existing file, a path this change does not touch.

Changelog / Migrations

• Changelog fragment added under <root>/<pkg>/changelog.d/ for each changed package (or: skip-changelog trailer on a commit with reason)
• Migration fragment with the same slug added under <root>/<pkg>/migrations.d/ for each changed package (every subsection but Summary _None._ when nothing breaks)