Advisor review found a critical stale-signal leak: if auto-compress
sets _compression_skipped_due_to_lock during a lock-skip, a subsequent
successful manual /compress will see the stale signal, falsely report
'Compression already in progress', and discard the compression results.
Fix:
- compress_context clears _compression_skipped_due_to_lock = None at
entry so each call's outcome alone determines the signal.
- Unified gateway 'holder: unknown' drift to match CLI/TUI pattern
(omit holder clause when not a descriptive string).
- Added MagicMock opt-outs in 3 sibling test files broken by the new
signal check (test_compress_here, test_compress_focus,
test_compress_plugin_engine).
- Added stale-signal-leak invariant test proving the fix.
e8000b42e7