Inline file diff in review pane (git mode)

[jwaldrip]

Summary

When the provider is git and we have file history, surface a markdown-aware diff in the review screen so reviewers can see what changed — not just that something closed. Most useful in two contexts:

1. Closed feedback resolution. When a closed FB carries a commit SHA in iterations[], expand the FeedbackItem to show a unified diff of the file the fix-hat touched. Connects directly to the iteration history we just shipped (feat(builder): add version-aware building with rollback guidance #95-adjacent — Task feat(planner): add relevance-ranked learning search #94 in the local tracker; FeedbackItem renders the chain but the commit pill is currently display-only).
2. "What changed since I last signed?" When a slot has signed_at: <ISO> + body_sha256, the artifact pane could offer a "show changes since I signed" toggle. We already have gitLogSinceTimestamp in packages/haiku/src/orchestrator/workflow/drift-sweep.ts:63 and git show <commit>:<path> for retrieving body-at-commit; the missing piece is the renderer.

Why this isn't trivial

Markdown is paragraph-flow, not line-flow. A naive line diff produces visual noise where prose got reflowed but didn't actually change meaning.

Three approach families:

• diff (npm) → unified line diff inside <MarkdownViewer>. Smallest blast radius. Works fine for code blocks and structural edits; ugly for prose reflows.
• markdown-diff (npm). Markdown-aware; outputs markdown-flavored unified diff. Lighter weight, last published Apr 2024.
• Custom remark-based renderer. We already have remark + remark-gfm + remark-html in packages/haiku-ui/package.json. Could AST-diff with token-level granularity. Highest fidelity, most work.

Suggested scope (minimum viable)

• Add diff package to packages/haiku-ui.

• Build <UnifiedDiff body=\"...\" since=\"...\" /> component that renders a unified-diff block with +/- lines + minimal syntax highlighting.

• In FeedbackItem.tsx expanded view, when:

  • the FB is closed
  • iterations[] has at least one entry with a commit SHA
  • the host runtime is git-mode (a new gitMode: boolean prop threaded from session data)

  …surface a "Show changes" expander next to the iteration row. Click → fetch the diff via a new /api/diff/:commit/:path endpoint that shells git show <commit>:<path> against the previous parent and returns the raw bodies for the renderer to diff client-side.

Out of scope for v1

• Side-by-side view (unified is enough for prose).
• Multi-file diff per iteration (one commit = one rendered file path).
• Image diff (fileSha256 outputs are already covered by the drift sweep; image diff is a separate UX surface).

References

• packages/haiku/src/orchestrator/workflow/drift-sweep.ts:63 — gitLogSinceTimestamp exists for git enrichment.
• packages/haiku/src/state-tools.ts:1036 — isGitRepo() is the runtime gate.
• packages/haiku-api/src/schemas/feedback.ts:127 — iterations[] schema; commit: z.string().max(64).optional() is the field to consume.
• packages/haiku-ui/src/organisms/FeedbackItem.tsx — the iteration commit pill is already rendered (truncated to 7 chars). Diff expander hooks here.

Tracking

Filed as a followup to the review-screen UX bundle that landed Task #94 (iterations chain rendering) and Task #95 (agent excerpts via inline_anchor).