Land the commit diff view as its own branch

[Defmon3]

Seen on: component/git-history

What it fixes

The details pane lists a commit's changed files but cannot show what changed. This piece adds the diff view for a whole commit or one file, reached from the details pane, with a visible note when the server cut a large patch.

Why we need it

It is PR 8 of the series in the Git History series issue (#8), the last History-only piece. It is small and self-contained.

How to fix it

Cut a fresh branch on top of the details pane carrying the diff component and its test. The PR description states the end state from the series issue. Nothing deferred.

[Defmon3]

Technical appendix: Land the commit diff view as its own branch

Investigated on branch component/git-history at commit 821fc7f, base upstream/main at a6797b3.

Findings

• apps/web/src/components/git-history/GitHistoryCommitDiff.tsx (132 lines, new): the diff view for a commit or a single file, fed by vcs.getCommitDiff. GitHistoryCommitDiff.test.tsx (new).
• GitHistoryPanel.tsx opens the view through its commitDiffRequest state, set from the details pane's file rows.
• The server caps the patch and returns a truncated flag (getCommitDiff in apps/server/src/vcs/GitVcsDriverCore.ts, part of the file and diff reads piece).
• Size: about 150 source lines plus tests.

The problem

Observed: the diff view is inseparable from the panel today.

Once done: a branch on top of the details pane lets a user open a commit's diff, or one file's diff, from the details pane, with a note when the server truncated it.