watch: detect files replaced via unlink and create

[marcopiraccini]

Fixes: #51621
Refs: #54774

On Linux, --watch stopped restarting after the first time a watched file was replaced via unlink+create or rename (atomic saves, docker compose watch, bind mounts), so it appeared to "only reload the first time".

filterFile watched each file directly, which binds the inotify watch to the file's inode.
On replacement the old inode is unlinked: the watch fires once, then dies; the new file's inode is never watched.

Fix: on Linux, watch the parent directory non-recursively instead of the file. The directory inode is stable across replacements, and unrelated siblings are still discarded by the filter-mode check in #onChange. macOS/Windows already watched the directory and were unaffected.

Other platforms without recursive watching (AIX, SmartOS, BSDs) keep watching the file itself: a directory watch there does not report the changed entry, which made the test time out on AIX and SmartOS.

[mstaicu]

When can we expect this to be merged?

[trivikr]

CI is failing on aix and smartos

not ok 5496 parallel/test-watch-mode-files_watcher
  ---
  duration_ms: 120070.78700
  severity: fail
  exitcode: -15
  stack: |-
    timeout
  ...

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.38%. Comparing base (66f26d3) to head (f8e34b1).
⚠️ Report is 27 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #63888      +/-   ##
==========================================
- Coverage   90.38%   90.38%   -0.01%     
==========================================
  Files         790      790              
  Lines      274497   274508      +11     
  Branches    52557    52566       +9     
==========================================
+ Hits       248100   248101       +1     
- Misses      16879    16883       +4     
- Partials     9518     9524       +6     

Files with missing lines	Coverage Δ
lib/internal/watch_mode/files_watcher.js	90.55% <100.00%> (-0.89%)	⬇️

... and 31 files with indirect coverage changes

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[marcopiraccini]

@ShogunPanda @trivikr the request-ci label added on 2026-09-21 was never picked up: auto-start-ci only starts PRs with an approval, and the previous one was dismissed by the rebase. Could you re-review so Jenkins runs on AIX and SmartOS?

NOTE: make lint-js currently fails until #66307 lands

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/77950/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/77980/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/77992/

[nodejs-github-bot]

Landed in 3641c36