chore(worker): Improve git operation perf

[brendan-kellam]

This PR updates the repo indexing path to generate a commit-graph on clone / fetch to accelerate commit traversal operations. The commit-graph is a pre-computed file that stores commit metadata (OIDs, parent pointers, timestamps, generation numbers) in a format optimized for sequential reads. This speeds up operations like rev-list --count, log, and merge-base significantly on large repositories.

See: https://git-scm.com/docs/commit-graph

NOTE: Local repositories will not have a commit graph generated for them.

Summary by CodeRabbit

• Performance
  • Commit graph generation is now triggered after cloning and during fetch to speed up operations that traverse commit history.
• Documentation
  • Added guidance on creating and updating commit graphs for local repositories and clarified related examples.

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[coderabbitai]

Caution

Review failed

The pull request is closed.

Walkthrough

Adds Git commit-graph generation: graphs are written after cloning, fetch now requests commit-graph updates, and a new exported writeCommitGraph utility allows manual graph creation with non-fatal error handling. (47 words)

Changes

Cohort / File(s)	Summary
Changelog CHANGELOG.md	Added "Changed" entry noting commit graph generation for commit traversal performance.
Git operations packages/backend/src/git.ts	After clone, invoke commit-graph generation; add --write-commit-graph to fetch; export writeCommitGraph() which runs git commit-graph write --reachable with debug-logged, non-fatal errors.
Docs docs/docs/connections/local-repos.mdx	New "Optimizing git operations" section describing commit-graph usage and manual commands for local repos; minor formatting cleanup.

Sequence Diagram(s)

mermaid
sequenceDiagram
participant Cloner as Cloner
participant GitCLI as Git CLI
participant RepoFS as Repository (FS)
Cloner->>GitCLI: git clone
GitCLI-->>RepoFS: write repository data
Cloner->>GitCLI: writeCommitGraph(path)
GitCLI-->>RepoFS: git commit-graph write --reachable
Note over GitCLI,RepoFS: Errors logged as debug; non-fatal

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• chore(worker): Improve git operation perf #791 — Adds writeCommitGraph and updates clone/fetch to generate/update Git commit-graph (same code-level change).

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'chore(worker): Improve git operation perf' accurately reflects the main change in the changeset - adding commit-graph generation to improve performance for git operations, particularly commit traversal.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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