fix(ui): fill the review stream on first paint (0.20.x)

[benvinegar]

Summary

Backports #922 onto the 0.20.x maintenance branch.

• estimate the viewport while OpenTUI layout is still unmeasured so nowrap file windowing fills the first frame
• render edge-jump destinations before moving the native viewport
• stabilize viewport resize subscriptions and equivalent line-cursor identity
• add unit, interaction, and PTY regression coverage

The runtime changes applied cleanly apart from App.tsx, where the backport retains the 0.20.x transient-notice implementation. PTY conflicts were resolved against the maintenance branch test layout without bringing unrelated main-only coverage.

Verification

• bun run typecheck
• bun run lint
• bun run format:check
• bun run deps:check
• focused viewport, windowing, interaction, and component tests: 199 passed
• first-frame PTY regression: passed
• bun run test: both shards passed (1,547 + 1,510 tests)
• bun run test:integration: 130 passed
• bun run test:tty-smoke: 9 passed
• real-TTY source smoke against origin/0.20.x, including first paint and G
• bun run changeset:status -- --since=origin/0.20.x: patch bump for hunkdiff

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
hunk-web	Ignored	Preview	Aug 30, 2026 9:31pm

[greptile-apps]

Greptile Summary

This backport estimates the initial review viewport, pre-renders edge-jump destinations, stabilizes viewport and cursor identities, and adds regression coverage.

• Adds first-paint viewport estimation for nowrap file windowing.
• Routes top/bottom commands through render-first edge requests.
• Revises viewport subscriptions and equivalent line-cursor reuse.
• Adds unit, interaction, component, and PTY coverage.

Confidence Score: 3/5

The PR should not merge until viewport measurement uses the actual OpenTUI event contract and edge jumps supersede pending selection-reveal retries.

The initial geometry callback can be missed because it subscribes to an undocumented event name, and a recently scheduled hunk-reveal retry can override an explicit top or bottom jump.

Files Needing Attention: src/ui/components/panes/DiffPane.tsx

Important Files Changed

Filename	Overview
src/ui/App.tsx	Converts content-edge scrolling into monotonic render-first requests passed to DiffPane.
src/ui/components/panes/DiffPane.tsx	Adds initial viewport estimation, edge-jump rendering, viewport subscription changes, and cursor identity reuse; the new event subscription and pending-reveal interaction need correction.
src/ui/lib/viewportTiming.ts	Adds bounded initial-height estimation and measured-height fallback helpers.
src/ui/lib/lineCursors.ts	Reuses cursor arrays only when every navigation field remains equivalent.
test/pty/layout.test.ts	Adds real-terminal regression coverage for filling a tall first nowrap frame.

Sequence Diagram

sequenceDiagram
  participant U as User
  participant A as App
  participant D as DiffPane
  participant O as OpenTUI viewport
  U->>A: G or gg
  A->>D: scrollEdgeRequest
  D->>D: Render destination rows
  D->>O: scrollTo(edge)
  O-->>D: Viewport geometry event
  D->>D: Refresh windowed rows

Loading

Prompt To Fix All With AI

### Issue 1
src/ui/components/panes/DiffPane.tsx:831
**Viewport resize event is misnamed**

When the scrollbox publishes its measured geometry, this listener waits for `resize` instead of OpenTUI's documented `resized` event, leaving `scrollViewport.height` at zero or stale and causing windowing to leave blank review rows until another scroll triggers a read.

```suggestion
      scrollBox.viewport.on("resized", handleViewportResize);
```

### Issue 2
src/ui/components/panes/DiffPane.tsx:972-995
**Pending reveal overrides edge jumps**

When G or gg is pressed during the 120 ms selected-hunk settling period, this effect moves to the requested edge without cancelling the pending reveal; the later reveal observes the pinned-header change and scrolls back to the selected hunk, so the command lands at the wrong position.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "fix(ui): stabilize viewport startup timi..." | Re-trigger Greptile}