Replace O(n) go-git tree walks with git diff-tree in post-commit hook

[khaong]

Summary

• Add cmd/entire/cli/gitops/ package with DiffTreeFiles/DiffTreeFileList wrappers around git diff-tree --no-commit-id -r -z
• Replace filesChangedInCommit go-git tree walk with git diff-tree (703ms → ~25ms on 58k-file repos)
• Replace getAllChangedFilesBetweenTrees in attribution with git diff-tree (4685ms → ~36ms), keeping go-git fallback for CondenseSessionByID (doctor command)
• Remove timing instrumentation added during investigation

Before/after (58k-file repo)

origin/main:  5.95s
this branch:  0.30s  (20x faster)

Test plan

• New cmd/entire/cli/gitops/diff_test.go — tests DiffTreeFiles with real git repos (normal commit, initial commit, multi-commit range, deleted files, no changes, subdirectory files)
• TestGetAllChangedFilesBetweenTreesSlow — preserved coverage for go-git fallback path (nil trees, identical trees, add/delete scenarios)
• All existing CalculateAttributionWithAccumulated tests updated and passing (exercise slow fallback via empty commit hashes)
• TestFilesChangedInCommit / TestFilesChangedInCommit_InitialCommit updated for new signature
• mise run fmt && mise run lint && mise run test:ci all green

🤖 Generated with Claude Code

[cursor]

PR Summary

Medium Risk
Medium risk because post-commit condensation/attribution correctness now depends on executing/parsing git diff-tree; failures degrade to warnings/empty results (and attribution may be skipped), potentially affecting which sessions/files are condensed and reported.

Overview
Introduces a new gitops helper (DiffTreeFiles/DiffTreeFileList) that shells out to git diff-tree -r -z and parses its null-delimited output (including rename/copy paths).

Switches post-commit’s filesChangedInCommit and attribution’s “changed files between base and head” enumeration to this fast path when commit hashes are available, threading headCommitHash/attributionBaseCommit through condensation/attribution plumbing; keeps the prior go-git tree-walk logic as an explicit slow fallback for flows without commit hashes (e.g. doctor/force-condense).

Adds comprehensive tests for diff-tree parsing and real-repo scenarios, updates existing attribution and post-commit tests for the new signatures, and removes a now-irrelevant cache-equivalence test.

^{Written by Cursor Bugbot for commit 2fc6033. Configure here.}

[khaong]

bugbot run

[Copilot]

Pull request overview

This PR improves post-commit hook performance by replacing expensive go-git tree walks with a new git diff-tree-based implementation for changed-file detection, while retaining a go-git fallback for doctor/CondenseSessionByID paths.

Changes:

• Add a new cli/gitops package that wraps git diff-tree --no-commit-id -r -z and parses its output.
• Switch post-commit “files changed in commit” detection to use git diff-tree instead of go-git tree diffs.
• Switch attribution’s “non-agent changed files” detection to git diff-tree when commit hashes are available, keeping a slow go-git fallback and updating tests accordingly.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
cmd/entire/cli/gitops/diff.go	Adds DiffTreeFiles / DiffTreeFileList wrappers and output parser for git diff-tree -z.
cmd/entire/cli/gitops/diff_test.go	Adds real-repo tests for diff-tree behavior plus parser unit tests.
cmd/entire/cli/strategy/manual_commit_hooks.go	Replaces filesChangedInCommit implementation to use gitops.DiffTreeFiles; threads ctx through.
cmd/entire/cli/strategy/phase_postcommit_test.go	Updates post-commit tests for new filesChangedInCommit(ctx, commit) signature and removes prior cache-equivalence coverage.
cmd/entire/cli/strategy/manual_commit_attribution.go	Introduces a fast path via DiffTreeFileList for non-agent file detection with a slow go-git fallback.
cmd/entire/cli/strategy/manual_commit_attribution_test.go	Updates attribution tests for the new function signature; renames and parallelizes the slow-path test.
cmd/entire/cli/strategy/manual_commit_condensation.go	Plumbs commit hashes into attribution options to enable the new fast path when available.

Comments suppressed due to low confidence (1)

cmd/entire/cli/strategy/manual_commit_hooks.go:2124

• filesChangedInCommit drops all committed file detection if gitops.DiffTreeFiles returns an error (returns an empty map) and the error is silently ignored. That can cause incorrect overlap checks / carry-forward decisions when the git CLI is unavailable or diff-tree fails; consider logging at least a debug/warn and falling back to the prior go-git tree diff (or propagating an error up to PostCommit so the hook can take a safe default).

			slog.String("session_id", state.SessionID),
		)
	}

	// Clear turn checkpoint IDs. Do NOT update CheckpointTranscriptStart here — it was
	// already set correctly by PostCommit: condenseAndUpdateState sets it to the total
	// transcript lines when condensing, and carryForwardToNewShadowBranch resets it to 0
	// when carry-forward is active. Overwriting here would break carry-forward by making
	// sessionHasNewContent think the transcript is fully consumed (no growth).

[cursor]

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[khaong]

bugbot run

[khaong]

bugbot run

[cursor]

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

[khaong]

git diff-tree output coverage verification

Verified the parser handles all possible status codes from git diff-tree -r -z:

Status	Paths	Appears without flags?	Parser	Verified
A (add)	1	Yes	✅	unit + integration test
D (delete)	1	Yes	✅	unit + integration test
M (modify)	1	Yes	✅	unit + integration test
M (chmod-only)	1	Yes (mode fields differ, same status)	✅	manual test
T (type change, e.g. file→symlink)	1	Yes	✅	manual test
R (rename)	2	No (needs -M flag)	✅	unit + integration test
C (copy)	2	No (needs -C flag)	✅	unit test
U (unmerged)	1	No (index-only, not between commits)	✅	n/a
X (unknown/git bug)	1	Theoretically	✅	n/a

Since we don't pass -M or -C, renames always appear as D+A pairs in practice. The R/C handling is defensive.