feat: annotatable diff view

[backnotprop]

Summary

Adds annotation support to the plan diff view using block-level hover. Users hover over added/removed/modified diff sections and annotate entire blocks — same pattern as code block hover in the normal Viewer.

What we tried and why we pivoted

Attempt 1: Text-selection via web-highlighter. Copied ~250 lines of annotation plumbing from Viewer.tsx into PlanCleanDiffView. Worked for basic cases but was fragile — findTextInDOM broke across diff boundaries, unchanged text got orphaned on toggle, cross-section selections picked wrong contexts, and highlights vanished on re-render due to unstable callback dependencies.

Attempt 2: Extracted useAnnotationHighlighter hook. Deduplicated the shared logic between Viewer and PlanCleanDiffView. Fixed the re-render teardown bug and added auto-restore for persisted annotations. But the core fragility remained — text-search restoration in a fragmented diff DOM is inherently unreliable.

Final approach: Block-level hover annotation. Replaced text-selection entirely. Hovering a diff section shows the annotation toolbar anchored to that block. No web-highlighter, no DOM marks, no findTextInDOM. Annotations live purely in React state. Delete just removes from state. Toggle is trivial — nothing to restore.

What shipped

• Block-level diff annotation — hover added/removed/modified sections to annotate
• useAnnotationHighlighter hook — extracted from Viewer.tsx, used by Viewer only (not diff view)
• View isolation — diff annotations filtered to diff view, normal annotations filtered to normal view, no bleed-through
• diff badge in AnnotationPanel for all diff annotations
• [In diff content] label in exported feedback
• diffContext field on Annotation type, flows through sharing and draft persistence

Known limitations

• Pinpoint input mode not integrated in diff view
• No scroll-to-selected for diff annotations (clicking in panel doesn't scroll to the block)
• Unchanged sections are not annotatable (by design — nothing changed)

Test plan

• Enter diff mode → hover a green (added) section → toolbar appears at top-right
• Click Comment → popover opens → submit → annotation in panel with diff badge
• Hover a red (removed) section → same flow
• Modified section: hover old half and new half independently
• Unchanged section: no toolbar on hover
• Delete annotation from panel → removed cleanly (no stale DOM marks)
• Toggle diff off/on → annotations persist in panel, no highlights to restore
• Normal annotations don't appear in diff mode; diff annotations don't appear in normal mode
• Deny with diff annotations → feedback includes [In diff content] labels
• Toolstrip modes (Redline, Comment, Quick Label) all work in diff view
• bun run build:hook → production build succeeds

🤖 Generated with Claude Code

[backnotprop]

Code review

No issues found above the confidence threshold. Checked for bugs, CLAUDE.md compliance, and dead/stale code from refactoring.

Note: Several cleanup opportunities were identified at moderate confidence (scored 75/100 each, below the 80 threshold for flagging). These are all dead code from the multi-iteration refactoring on this branch — not bugs, but worth a cleanup pass:

• resolveContext extension point in useAnnotationHighlighter has no callers (designed for text-selection iteration, superseded by block-level hover)
• Hook header comment and CLAUDE.md both claim the hook is shared with PlanCleanDiffView, which no longer uses it
• 'unchanged' variant in diffContext type union is never set (unchanged blocks have no hover handlers)
• No-op useEffect for scroll-to-selected in PlanCleanDiffView (runs a DOM query, does nothing with the result)
• CLAUDE.md says per-context labels like [In newly added content] but code emits generic [In diff content]
• annotations prop accepted by PlanDiffViewer but never passed through (silently dropped)

🤖 Generated with Claude Code

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