refactor: simplify rewrite operations with unified handle_rewrite_event

[svarlamov]

Summary

Replaces the per-operation-type rewrite machinery with a single unified algorithm (handle_rewrite_event) that normalizes all commit-rewriting operations into Vec<(source, new)> mappings before applying diff-tree-based hunk shifts. This is a major architectural simplification targeting the rewrite operations subsystem.

Net change: +3,741 / -15,633 lines (net reduction of ~11,900 lines)

Key changes:

• Unified entrypoint: handle_rewrite_event(repo, RewriteEvent) handles all rewrite types (rebase, amend, cherry-pick, reset, squash) through one code path
• Core algorithm: shift_authorship_notes uses git diff-tree to compute hunk shifts between source and target commits, adjusting line-level attestation entries
• Range-diff mapping: derive_mappings_from_range_diff pairs old/new commits via git range-diff, with squash detection and merge-commit mapping
• Cherry-pick matching: Two-pass algorithm (patch-id anchoring + positional gap-fill) for pairing source commits with cherry-picked results
• Non-FF detection: Daemon detects non-fast-forward ref moves on refs/heads/* and fires the unified handler
• Amend fix: New post_commit_amend_with_final_state uses blame-based VirtualAttributions to preserve AI attribution on unchanged lines
• Note protection: shift_authorship_notes skips target commits that already have authorship notes

Deleted modules (~15,600 lines):

• src/authorship/rebase_authorship.rs (4,786 lines)
• src/git/rewrite_log.rs (710 lines)
• src/commands/squash_authorship.rs (361 lines)
• ~3,850 lines gutted from daemon.rs (rewrite_events_from_semantic_events, apply_rewrite_side_effect, pending state, replay/recovery helpers)
• Dead functions: convert_to_checkpoints_for_squash, restore_stashed_va, _serialize_to_writer, _deserialize_from_reader
• Dead test infrastructure in daemon_mode.rs

Test results:

• 25 previously-failing tests now pass (amend, pull-rebase, sessions_cutover)
• 0 regressions introduced
• ~210 remaining failures are all pre-existing on main (rebase-with-conflicts, reset working-log reconstruction, stash — these require deeper architectural changes beyond this PR's scope)

Files still referenced (NOT deletable yet):

• git_handlers.rs — test infrastructure (GIT_AI=git proxy mode)
• git_ai_handlers.rs — subcommand dispatch center
• install_hooks.rs — active git-ai install feature
• range_authorship.rs — git-ai stats feature
• push_hooks.rs / stash_hooks.rs — daemon still calls these

Test plan

• task build passes
• task lint passes (no clippy warnings)
• task fmt passes
• Integration tests: 2719 passed, ~210 failed (all pre-existing), 82 ignored
• Verified 0 regressions vs base branch (all new failures are flaky, pass in isolation)
• Ubuntu CI jobs pass
• Review Devin feedback

🤖 Generated with Claude Code

[devin-ai-integration]

Devin Review found 2 new potential issues.

View 21 additional findings in Devin Review.

[devin-ai-integration]

🔴 save_stash_attributions ignores pathspecs, causing attribution loss on partial stash pop to different HEAD

In save_stash_attributions at src/authorship/rewrite_stash.rs:150, the _pathspecs parameter is unused (note the underscore prefix). The function copies the ENTIRE working log directory as the stash backup instead of filtering to only the pathspec-matching files. While same-HEAD restore (restore_stash_attributions) mitigates this via merge_initial_files using or_insert, the different-HEAD restore path (restore_stash_attributions_with_shift at line 210) processes ALL files from the unfiltered backup, builds a full InitialAttributions, and writes it via working_log.write_initial(initial) at line 373 — which overwrites the target HEAD's existing INITIAL file entirely. This means if a user does git stash push -- src/file.rs (partial stash), switches branches where there's existing uncommitted AI attribution, then pops, all non-stashed file attributions at the current HEAD are silently lost.

Prompt for agents

The save_stash_attributions function at src/authorship/rewrite_stash.rs:146 takes a _pathspecs parameter but ignores it, copying the entire working log directory. This causes the restore_stash_attributions_with_shift path (line 210) to overwrite the target HEAD's INITIAL file with ALL attributions from the backup (including non-stashed files), destroying any existing attributions at the target HEAD.

Two approaches to fix:

1. Filter the saved backup: Instead of copying the entire working log directory, read the INITIAL file, filter files/file_blobs to only those matching pathspecs (using path_matches_any), and write a filtered copy to the stash backup directory. This ensures the backup only contains stashed file attributions.

2. Merge on restore: In restore_stash_attributions_with_shift, instead of calling working_log.write_initial(initial) which overwrites, first read the existing INITIAL at current_head, then merge the stash attributions into it (similar to how merge_initial_files works), preserving existing entries.

Approach 1 is cleaner since it fixes the root cause and keeps both restore paths simpler. The _pathspecs parameter should be used to filter initial.files and initial.file_blobs before writing to the stash backup directory.

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[devin-ai-integration]

🟡 shift_authorship_notes silently skips mappings when target has unparseable note

In shift_authorship_notes at src/authorship/rewrite.rs:255-263, when the target commit (new_sha) has an existing note that fails AuthorshipLog::deserialize_from_string, the else { continue; } branch causes the entire mapping to be skipped. This means the source commit's valid note is never shifted to the target — the attribution data is silently lost. The intent of the check is to avoid overwriting a valid target note, but an unparseable target note should not block the source note from being written. This could happen if the target has a note from an older schema version or corrupted data.

Suggested change

	if let Some(existing_raw) = notes_map.get(new_sha) {
	if let Ok(existing_log) = AuthorshipLog::deserialize_from_string(existing_raw) {
	if !existing_log.attestations.is_empty() {
	continue;
	}
	} else {
	continue;
	}
	}
	if let Some(existing_raw) = notes_map.get(new_sha) {
	if let Ok(existing_log) = AuthorshipLog::deserialize_from_string(existing_raw) {
	if !existing_log.attestations.is_empty() {
	continue;
	}
	}
	// If existing note is unparseable, allow overwriting with shifted source note
	}

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[devin-ai-integration]

Devin Review found 1 new potential issue.

View 20 additional findings in Devin Review.

[devin-ai-integration]

🟡 Stash restore with shift drops entire multi-line attribution if either boundary line was modified

In restore_stash_attributions_with_shift, the line-mapping shift at src/authorship/rewrite_stash.rs:340-352 requires BOTH attr.start_line and attr.end_line to be present in line_map (i.e., both must fall within Equal diff regions). If a LineAttribution spans lines 5-10 and lines 5-8 are unchanged but lines 9-10 were modified, line_map.get(&attr.end_line) returns None, causing the entire 5-10 attribution to be dropped — losing the correctly-mapped lines 5-8. This over-drops attribution when popping a stash onto a different HEAD where file content changed. The hunk_shift.rs segment-based algorithm correctly handles partial overlaps by splitting ranges, but this stash-specific code path does not.

Prompt for agents

In restore_stash_attributions_with_shift (rewrite_stash.rs:340-352), the filter_map requires both start_line and end_line to be in line_map for the attribution to survive. This drops the entire range if the boundary line was modified. Instead, for each LineAttribution, iterate through each line in the range (start_line..=end_line) and collect only the lines that ARE in line_map. Then compress the surviving mapped lines back into contiguous LineAttribution ranges. This matches the behavior of build_preserved_segments in hunk_shift.rs which correctly handles partial overlaps by splitting ranges at hunk boundaries. The key change is: instead of checking only boundary lines, check each line individually and build new ranges from the surviving mapped lines.

---

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[devin-ai-integration]

Devin Review found 1 new potential issue.

View 22 additional findings in Devin Review.

[devin-ai-integration]

🔴 restore_stash_attributions_with_shift overwrites INITIAL instead of merging, losing current HEAD attributions

When git stash pop or git stash apply is invoked on a HEAD different from the stash's base commit, restore_stash_attributions_with_shift calls working_log.write_initial(initial) at src/authorship/rewrite_stash.rs:373, which completely overwrites the INITIAL file for the current HEAD. Any AI attributions accumulated at the current HEAD (e.g., from checkpoints created between stash push and pop) are silently lost.

By contrast, the same-HEAD path (restore_stash_attributions at src/authorship/rewrite_stash.rs:167) correctly merges INITIAL files via merge_initial_files at line 200. This asymmetry means that stash pop on the same branch works correctly, but stash pop after switching branches (a common workflow) can lose attribution data.

Prompt for agents

In restore_stash_attributions_with_shift (src/authorship/rewrite_stash.rs around line 372-373), the code calls working_log.write_initial(initial) which completely overwrites any existing INITIAL attributions at current_head. This causes data loss when the user has accumulated AI attributions at current_head between stash push and stash pop.

The fix should mirror what restore_stash_attributions does (line 199-200): check if an INITIAL file already exists at the destination and merge the two InitialAttributions structs, using the merge_initial_files function or equivalent merge logic. Specifically, after building the InitialAttributions struct at line 364, check if an INITIAL already exists at current_head's working log. If so, read the existing one and merge both (using or_insert for files, prompts, humans, sessions, file_blobs), then write the merged result. If no existing INITIAL exists, write_initial is fine as-is.

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