fix: include untracked files in diff patch for working-tree runs

[dastratakos]

Summary

Fixes a bug where chapters referencing new/untracked files appeared in the table of contents but rendered empty on the detail page. The diff API endpoint now includes untracked file diffs for working-tree WORK scope runs, matching the behavior used during chapter import.

Changes

• Export hasStringStdout type guard from git.ts for reuse
• Add async buildUntrackedPatch() helper in the diff route that lists untracked files and generates their diffs
• Append untracked file patches to the response for WORKING_TREE/WORK runs

Testing

• pnpm typecheck, pnpm lint, and pnpm test all pass
• tested manually

---

[stage-review]

Ready to review this PR? Stage has broken it down into 3 individual chapters for you:

	Title
1	Export git stdout type guard
2	Implement untracked file patch generation
3	Include untracked files in working-tree diffs

_{Chapters generated by Stage for commit 179a4ef on May 14, 2026 1:43am UTC.}

[gemini-code-assist]

Code Review

This pull request introduces the ability to include untracked files in the diff output when the working tree is selected. It adds a new buildUntrackedPatch helper and updates the diff route to aggregate these patches. Feedback suggests several improvements to the new helper, including parallelizing the git commands for better performance, ensuring standard diff prefixes are used for consistency, and correctly capturing output when git exits with a zero status. There is also a recommendation to refactor this logic into the existing git utility module to reduce code duplication.

[chatgpt-codex-connector]

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