FE-665: Show per-patch diffs in the staged-changes overlay

[kostandinang]

What

Drops <ContentDiff> into PatchListOverlay so the diff is visible even when the side-chat panel is closed.

Stacked on #107. Second FE-665 slice.

Linear: FE-665.

How

• EditPatch gains optional currentContent?: string so the overlay can render diffs without re-querying.
• Overlay's N pending changes label becomes click-to-expand. Expanded state renders a per-patch list with summary + word-level diff. Auto-collapses when staged count returns to 0.

╭ N pending changes · Undo · Apply ╮     ← collapsed
              ↓ click
╭ ▾ N pending changes · Undo · Apply ╮
│ • Edit C1 — soften wording          │
│   Use ⎯⎯SQLite⎯⎯ Postgres for…    │   ← diff inline
│ • Annotate C2 — clarify exclusion   │

Out of scope

Per-patch actions (Discard, Apply-one) in the overlay; new mutation paths.

Test plan

• Close the side-chat with staged edits; click N pending changes in the overlay; see diffs inline

[cursor]

PR Summary

Medium Risk
Medium risk because it changes the core staged-changes overlay UI/state behavior and extends the staged patch data shape (EditPatch.currentContent, anchorReferenceCode), which could affect patch staging/rendering across surfaces.

Overview
Adds an expand-to-detail mode to PatchListOverlay: the N pending changes label becomes an aria-expanded toggle that reveals a per-patch list under the sticky bar and auto-collapses when the staged count returns to 0.

Expanded rows render a kind-tinted reference badge (anchorReferenceCode), an ImpactChip, and—for edit patches only—a word-level ContentDiff when currentContent is available and differs from newContent (otherwise summary-only).

Extends patch staging to capture more snapshot data: EditPatch gains optional currentContent, and side-chat-host now stages patches with anchorReferenceCode and currentContent so the overlay can render diffs without extra store lookups. Includes a shared ImpactChip component (moved out of side-chat-popover) and adds comprehensive RTL coverage for the new overlay toggle/diff behavior.

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[augmentcode]

🤖 Augment PR Summary

Summary: Expands the staged-change overlay into an expandable, per-patch detail list so users can inspect diffs even with the side-chat panel closed.

Changes:

• Adds optional `anchorReferenceCode` + `currentContent` snapshots to staged patches to avoid re-querying the entity store in overlay consumers.
• Updates `SideChatHost` staging paths to populate these snapshots for edit/annotate/edge/drill-down patches.
• Extracts a shared `ImpactChip` component and reuses it in both the side-chat popover and overlay.
• Makes the “N pending changes” label a toggle button (`aria-expanded`) that reveals a per-patch `
  ` detail view.
  • Renders a word-level `` inline for edit patches when `currentContent` + `newContent` are both present and differ; otherwise summary-only.
  • Auto-collapses the expanded list when staged count returns to 0 after apply/undo.
  • Moves `PatchListOverlay` mounting into the structured-list scroll area to keep the sticky behavior scoped to the workspace scroller.
  • Adds RTL coverage for expand/collapse behavior, multi-patch rendering, diff spans, reference badge, and impact chip.

  Technical Notes: Non-edit patches (and edit patches without currentContent) intentionally render summary-only to keep overlay rendering deterministic without additional data fetches.

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[kostandinang]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• FE-674: Agent classifier UI on pending review rows #124
• FE-674: Side-chat polish + DiffPopover + saved-toast move #121
• FE-674: Inline source diff + edit-target on pending review rows #120
• FE-674: Plan V3.1 verification strategy + node-edit cards #119
• FE-674: Suppress no-op Undo on hard apply + V3.0 polish #118
• FE-674: Resolve pending review rows #117
• FE-674: Show pending review rows in the patch overlay #116
• FE-674: Open downstream-review rows on hard-impact edit #115
• FE-657: Direct in-place editing on the structured-list view #109
• FE-665: Show per-patch diffs in the staged-changes overlay #108 👈 (View in Graphite)
• FE-665: Show word-level diff on staged edits in side-chat #107
• FE-673: Side-chat Edit mode — edit, link, and drill-down patches #105
• main

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