watch: cancel pending restart on shutdown

[trivikr]

Fixes a watch mode shutdown race where a pending debounced file change could still emit after FilesWatcher.clear() closed the active watchers. That allowed watch mode to restart the child process after shutdown had already started, which could leave out/Release/node --watch --inspect processes behind and fail CI’s leftover-process check.

This cancels the pending debounce timer during watcher cleanup and makes watched child exit handling stable across overlapping restart/shutdown paths.

Noticed while examining flaky tests in ubuntu2404_sharedlibs_shared_x64/56356

13:35:08 All tests passed.13:35:08 ps awwx | grep Release/node | grep -v grep | cat13:35:08 2405720 ? Sl 0:00 /home/iojs/build/workspace/node-test-commit-linux-containered/out/Release/node --inspect=0 --watch /home/iojs/build/workspace/node-test-commit-linux-containered/test/fixtures/watch-mode/inspect.js13:35:08 2405726 ? Sl 0:00 /home/iojs/build/workspace/node-test-commit-linux-containered/out/Release/node --inspect=0 /home/iojs/build/workspace/node-test-commit-linux-containered/test/fixtures/watch-mode/inspect.js13:35:08 make[1]: *** [Makefile:648: test-ci] Error 113:35:08 make: *** [Makefile:674: run-ci] Error 213:35:08 Build step 'Conditional steps (multiple)' marked build as failure

Testing

The updated unit tests were run before/after

Before

$ python3 tools/test.py -J --mode=release \ parallel/test-watch-mode-files_watcher-clear \ sequential/test-watch-mode-inspect \ parallel/test-watch-mode-files_watcher=== release test-watch-mode-files_watcher-clear ===Path: parallel/test-watch-mode-files_watcher-clearnode:assert:173 throw err; ^AssertionError [ERR_ASSERTION]: function should not have been called at file:///Users/trivikram/workspace/node/test/parallel/test-watch-mode-files_watcher-clear.mjs:45called with arguments: { owners: SafeSet(0) {}, eventType: 'change' } at FilesWatcher.mustNotCall (/Users/trivikram/workspace/node/test/common/index.js:567:12) at FilesWatcher.emit (node:events:509:20) at Timeout._onTimeout (node:internal/watch_mode/files_watcher:104:12) at listOnTimeout (node:internal/timers:605:17) at process.processTimers (node:internal/timers:541:7) { generatedMessage: false, code: 'ERR_ASSERTION', actual: undefined, expected: undefined, operator: 'fail', diff: 'simple'}Node.js v27.0.0-preCommand: out/Release/node --expose-internals /Users/trivikram/workspace/node/test/parallel/test-watch-mode-files_watcher-clear.mjs[00:03|% 100|+ 2|- 1]: DoneFailed tests:out/Release/node --expose-internals /Users/trivikram/workspace/node/test/parallel/test-watch-mode-files_watcher-clear.mjs

After

$ python3 tools/test.py -J --mode=release \ parallel/test-watch-mode-files_watcher-clear \ sequential/test-watch-mode-inspect \ parallel/test-watch-mode-files_watcher[00:03|% 100|+ 3|- 0]: DoneAll tests passed.

---

Assisted-by: openai:gpt-5.5

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.32%. Comparing base (c55b126) to head (2bff1af).
⚠️ Report is 120 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #63383 +/- ##
==========================================
+ Coverage 90.26% 90.32% +0.06% 
==========================================
Files 730 730 Lines 234004 234164 +160 Branches 43829 43913 +84 ==========================================
+ Hits 211223 211515 +292 + Misses 14502 14386 -116 + Partials 8279 8263 -16 

Files with missing lines	Coverage Δ
lib/internal/watch_mode/files_watcher.js	91.28% <100.00%> (+0.58%)	⬆️

... and 35 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/73818/

[trivikr]

Requested review from folks who'd recently contributed to watch mode.

[trivikr]

I'll request merge in a couple of days, if there's no additional feedback.

[nodejs-github-bot]

Landed in cb8eebf