fix: tolerate rewritten HEAD reflog during commit finalization

[peckfly]

Summary

• keep raw worktree HEAD reflog regression errors visible at the low level
• during commit trace finalization, ignore only rewritten worktree HEAD reflog offsets when branch ref changes or stable pre/post HEAD snapshots already prove the commit movement
• preserve errors for non-commit commands, missing evidence, and amend-without-ref-change cases
• add unit and daemon regression coverage

Testing

• cargo fmt -- --check
• cargo test worktree_head_reflog -- --test-threads 12
• cargo test trace_normalizer --lib -- --test-threads 12
• cargo test daemon_commit_writes_note_when_worktree_head_reflog_is_rewritten_before_finalization --test daemon_mode -- --test-threads 1

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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[svarlamov]

Thank you for the contribution @peckfly -- what bug/issue is this fixing?

[peckfly]

Thank you for the contribution @peckfly -- what bug/issue is this fixing?

This fixes a daemon post-commit attribution bug.

I hit a case where an AI edit was checkpointed correctly, but after git commit the commit had no refs/notes/ai note, so stats/blame treated the added lines as unknown. The daemon log showed:

worktree HEAD reflog cut regressed (1889 < 19738)

The issue is that commit trace finalization reads the worktree HEAD reflog delta using offsets captured at trace start/end. If .git/logs/HEAD is rewritten or truncated during the commit, that supplemental reflog read fails. Previously that failure aborted normalization for the whole commit, so the post-commit authorship note was never written.

The fix keeps the low-level error intact, but narrowly tolerates it for ordinary git commit only when branch ref changes or stable pre/post HEAD snapshots already prove the commit movement. Other cases still return the error.

I added unit tests for the allowed and disallowed cases, plus a daemon regression test that reproduces the bug by truncating .git/logs/HEAD in a post-commit hook and verifies the authorship note/blame still preserve the AI attribution.