Use standard git diff output even when diff.external is configured

[marvin-bitterlich]

Why?

T3 Code uses git diff output to build patch and stat views in the app. When a user has diff.external configured, those commands can return tool-specific output instead of standard unified diffs, which breaks parsing and rendering.

How?

Added a small shared helper for machine-readable git diff invocations and used it for the server-side diff, stat, and numstat calls that feed status details, commit context, range context, and checkpoint diffs.

Added regression tests that configure diff.external and verify the app still receives standard diff output.

Decisions

• Applied --no-ext-diff only to diff commands where T3 Code expects machine-readable output.

• Closes External diff tool breaks diff display #927

Note

Add --no-ext-diff to all git diff invocations to ignore configured external diff tools

• Introduces machineReadableGitDiffArgs helper in diffArgs.ts that prepends "diff" and "--no-ext-diff" to any provided git diff arguments.
• Updates GitCore (statusDetails, prepareCommitContext, readRangeContext) and CheckpointStore (diffCheckpoints) to use this helper, ensuring diff.external config is ignored.
• Adds integration tests in GitCore.test.ts that configure an external diff script and assert it is not invoked by prepareCommitContext or readRangeContext.

^{Macroscope summarized 115cf97.}

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on this repository. Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 779b3522-f109-416f-a1e2-bcad1e5e1009

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

📝 Coding Plan

• Generate coding plan for human review comments

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

Tip

CodeRabbit can enforce grammar and style rules using `languagetool`.

Configure the reviews.tools.languagetool setting to enable/disable rules and categories. Refer to the LanguageTool Community to learn more.

[Noojuno]

I don't think this helper really provides value since it increases the overall complexity by making you need to go to a different file to figure out what we're actually calling

imo you should just add the --no-ext-diff flag to the existing diff command call sites rather than trying to decrease duplication with a helper