fix(git): disable external diff for patch output

[stromseng]

What Changed

Appended --no-ext-diff to git diff --patch calls

Why

Having an external diff tool set in git breaks the diff display.
Closes #927

UI Changes

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

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Note

Low Risk
Low risk: only tweaks git diff invocation flags for patch output, with no changes to business logic or data handling.

Overview
Ensures patch output is generated using Git’s built-in diff by appending --no-ext-diff to the git diff --patch calls used for commit preparation (prepareCommitContext) and range context (readRangeContext), preventing external diff tools from breaking diff display.

^{Reviewed by Cursor Bugbot for commit 0c857f8. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Disable external diff tools in git diff calls for patch generation

Adds --no-ext-diff to the git diff invocations in prepareCommitContext and readRangeContext in GitVcsDriverCore.ts. This ensures staged and range diff patches always use git's built-in diff output, ignoring any external diff tool configured in the user's git config.

^{Macroscope summarized 0c857f8.}

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[macroscopeapp]

Approvability

Verdict: Approved

Simple bug fix adding --no-ext-diff to git diff commands, ensuring consistent patch output regardless of user's external diff configuration. This is a standard defensive fix with no behavioral side effects.

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[Copilot]

Pull request overview

Updates server-side Git diff invocations to ensure patch output remains in standard unified diff format even when users have configured an external diff tool (e.g., via diff.external), addressing issue #927.

Changes:

• Add --no-ext-diff to git diff --patch calls used for commit-context patch generation.
• Add --no-ext-diff to range diff patch generation for context reads.
• Add --no-ext-diff to checkpoint diff patch generation.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
apps/server/src/vcs/GitVcsDriverCore.ts	Ensures unified patch output for staged and range diffs by disabling external diff tools.
apps/server/src/checkpointing/Layers/CheckpointStore.ts	Ensures checkpoint diff patch output stays parseable by disabling external diff tools.

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Dismissing prior approval to re-evaluate 0c857f8