External rotation (logrotate, manual `mv gateway.log gateway.log.1`,
another process rotating the file) leaves `_ManagedRotatingFileHandler`'s
open fd pinned to the renamed inode. All subsequent writes go to the
rotated backup instead of the file every operator expects to read,
producing the symptom 'gateway.log frozen mid-write while agent.log
keeps growing with gateway.* records'.
PR #16229 fixed the original CLI->gateway init-order bug (#8404) so the
handler attaches in the first place. This is the sibling fix for what
happens after attach, when something external rotates underneath us.
Adds a WatchedFileHandler-style inode check on emit(): if baseFilename
no longer matches the open stream's (dev,ino), close the stale fd and
reopen at the expected path. doRollover() refreshes the snapshot so our
own rollover isn't misidentified as external.
Five regression tests cover the matrix: external rename, external
unlink, external truncate (must NOT trigger reopen — inode unchanged),
normal doRollover() (must still work), and the end-to-end
Allen-reproduction (rotate + re-call setup_logging).
55/55 tests in tests/test_hermes_logging.py pass; 5972/5972 in
tests/gateway/ pass.
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