feat(ui): add mouse-drag text selection and clipboard copy

[raulk]

Hunk is very cool, but it's missing some basic features. Chipping in this PR to add selections via OpenTUI's OSC 52 support.

Concretely, this adds:

Mouse-drag text selection. Click anywhere on a diff row and drag to select a range of text. The selection spans multiple rows when you drag across them, and a character-level visual highlight follows the pointer. Releasing the drag copies the selected text to your clipboard via OSC 52.

Double-click and triple-click. Double-click expands the selection to word boundaries within the clicked line. Triple-click copies the entire line.

Split mode awareness. Triple-click and drag selection automatically stay within the side you started on. When copy decorations are enabled, column offsets are computed relative to the correct pane, so what you see highlighted is exactly what lands on the clipboard.

Copy decorations toggle. A View > Copy decorations menu item (off by default, or set copy_decorations in config) controls whether copied text includes diff rails, line numbers, gutters, and file headers. When off, only the changed code text is copied.

[greptile-apps]

Greptile Summary

This PR adds mouse-drag text selection to Hunk's diff views, with OSC 52 clipboard copy on drag release, double/triple-click word and line selection, split-pane side awareness, and a View > Copy decorations toggle that controls whether the clipboard payload includes diff rails, gutters and line numbers or only the changed code text.

• copySelection.ts + renderRows.tsx: New 560-line module handles hit-testing mouse events to selection points, text rendering (decorated vs. code-only), column-range computation for per-character visual highlights, and double/triple-click expansion. renderInlineSpans is significantly refactored to split spans at selection boundaries.
• DiffPane.tsx + App.tsx: Wire drag-start/move/end handlers, expose a cancelCopySelectionRef for cross-pane cancellation, route OSC 52 copy through the renderer, and surface a transient status-bar notice for unsupported terminals.
• Config / types plumbing: copy_decorations added throughout CommonOptions, PersistedViewPreferences, AppBootstrap, and loadAppBootstrap. Well-covered by new unit tests in copySelection.test.ts and additions to pierre.test.ts.

Confidence Score: 3/5

The copy path works end-to-end and is well tested, but the default value for copyDecorations is set to true in DEFAULT_VIEW_PREFERENCES while the PR description and menu label say the feature ships as off by default; merging as-is means new users receive decorated clipboard output without enabling any option.

The default value in config.ts contradicts the documented and intended out-of-box behaviour. It is a single-character fix, but without it the feature ships with the opposite default from what was designed and communicated. The rest of the implementation—hit-testing, rendering, split-side awareness, OSC 52 wiring—is thorough and backed by good test coverage.

src/core/config.ts — the copyDecorations default in DEFAULT_VIEW_PREFERENCES needs to flip from true to false.

Important Files Changed

Filename	Overview
src/core/config.ts	Adds copyDecorations to CommonOptions, PersistedViewPreferences, config resolution and merge logic. The default value is true (on) which contradicts the PR description's "off by default" intent.
src/ui/components/panes/copySelection.ts	New 563-line module implementing the full copy-selection logic: hit-testing mouse events to selection points, text rendering for both decorated and code-only modes, column-range computation for visual highlights, and double/triple-click expansion. Minor edge case: double-click on whitespace returns an inverted column range before normalization.
src/ui/components/panes/DiffPane.tsx	Core integration: adds drag-start/update/end handlers, OSC 52 copy path, cancelCopySelectionRef exposure for cross-pane cancellation, and passes selection ranges down to per-file views. First drag event stale-closure means native selection may flash briefly.
src/ui/diff/renderRows.tsx	Large refactor of renderInlineSpans to support character-level selection highlights by splitting spans at selection boundaries. Adds renderDecoratedPlannedRowText and renderCodeOnlyPlannedRowText for clipboard rendering. Logic is complex but well-covered by tests.
src/ui/App.tsx	Wires copyDecorations state, toggleCopyDecorations, showTransientNotice, and cancelCopySelectionRef into the component tree. showTransientNotice schedules a bare setTimeout without cleanup.
src/ui/lib/diffSectionGeometry.ts	Extends DiffSectionGeometry to carry lineNumberDigits and plannedRows so the clipboard renderer can re-use the already-measured plan without rebuilding it; also extracts buildPlannedSectionRows helper.
src/ui/diff/rowStyle.ts	Adds selectionHighlightBg blending helper and splitGutterText extractor (shared between TUI and clipboard renderers). Theme selectedHunk colours bumped for better contrast under the new blend ratio.
src/ui/components/panes/copySelection.test.ts	New 518-line test file covering all public functions in copySelection.ts, including split/stack layout, side filtering, pinned-header selection, and row-key building. Good coverage.
src/ui/lib/appMenus.ts	Adds copyDecorations / toggleCopyDecorations to BuildAppMenusOptions and inserts the "Copy decorations" menu item into the View menu. Clean.

Sequence Diagram

sequenceDiagram
    participant User
    participant DiffPane
    participant copySelection
    participant renderRows
    participant OSC52

    User->>DiffPane: onMouseDown (drag start)
    DiffPane->>copySelection: resolveCopySelectionPoint(event)
    copySelection-->>DiffPane: CopySelectionPoint (anchor)
    DiffPane->>DiffPane: "setCopySelectionDrag({anchor, focus, moved:false})"

    User->>DiffPane: onMouseDrag (pointer moves)
    DiffPane->>copySelection: resolveCopySelectionPoint(event)
    copySelection-->>DiffPane: CopySelectionPoint (focus)
    DiffPane->>DiffPane: "setCopySelectionDrag({anchor, focus, moved:true})"
    DiffPane->>renderRows: buildCopySelectedRowKeys (visual highlight)

    User->>DiffPane: onMouseUp / onMouseDragEnd
    DiffPane->>copySelection: normalizeCopySelectionRange(anchor, focus)
    copySelection-->>DiffPane: "{start, end}"
    DiffPane->>renderRows: renderCopySelectionText(context, start, end, side)
    renderRows-->>DiffPane: clipboard text string
    DiffPane->>OSC52: copyToClipboardOSC52(text)
    DiffPane->>App: onCopyFeedback("Copied selection to clipboard")
    App->>User: StatusBar transient notice

Loading

Comments Outside Diff (2)

1. src/ui/components/panes/copySelection.ts, line 1774-1791 (link)

   Double-click on whitespace produces an inverted column range

   When the user double-clicks on a space or tab character, wordStart and wordEnd both remain at localCol (neither loop advances), giving startCol = localCol + globalContentStart and endCol = localCol - 1 + globalContentStart. endCol < startCol. normalizeCopySelectionRange corrects the ordering, but the resulting selection highlights only the character immediately before the clicked space rather than the space itself or nothing—a confusing UX that mismatches what other editors do on a whitespace double-click.

   Prompt To Fix With AI

   This is a comment left during a code review.
   Path: src/ui/components/panes/copySelection.ts
   Line: 1774-1791
   
   Comment:
   **Double-click on whitespace produces an inverted column range**
   
   When the user double-clicks on a space or tab character, `wordStart` and `wordEnd` both remain at `localCol` (neither loop advances), giving `startCol = localCol + globalContentStart` and `endCol = localCol - 1 + globalContentStart`. `endCol < startCol`. `normalizeCopySelectionRange` corrects the ordering, but the resulting selection highlights only the character immediately before the clicked space rather than the space itself or nothing—a confusing UX that mismatches what other editors do on a whitespace double-click.
   
   How can I resolve this? If you propose a fix, please make it concise.

2. src/ui/App.tsx, line 148-153 (link)

   setTimeout without cleanup can fire after unmount

   showTransientNotice schedules a bare setTimeout with no cleanup path. If the App component is unmounted before the timer fires (e.g. in tests or hot-reload) the callback will try to call setTransientNoticeText on an unmounted component. This is low-severity in production (there is only one App instance), but it can produce spurious React state-update warnings in tests. The timer's id should be stored in a ref and cleared in a companion useEffect.

   Prompt To Fix With AI

   This is a comment left during a code review.
   Path: src/ui/App.tsx
   Line: 148-153
   
   Comment:
   **`setTimeout` without cleanup can fire after unmount**
   
   `showTransientNotice` schedules a bare `setTimeout` with no cleanup path. If the `App` component is unmounted before the timer fires (e.g. in tests or hot-reload) the callback will try to call `setTransientNoticeText` on an unmounted component. This is low-severity in production (there is only one `App` instance), but it can produce spurious React state-update warnings in tests. The timer's `id` should be stored in a ref and cleared in a companion `useEffect`.
   
   How can I resolve this? If you propose a fix, please make it concise.

Prompt To Fix All With AI

Fix the following 5 code review issues. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 5
src/core/config.ts:15
**Default value contradicts documented behavior**

The PR description and UI label both say "Copy decorations" is _off by default_, but `DEFAULT_VIEW_PREFERENCES.copyDecorations: true` initialises it as on. This flows through `resolveConfiguredCliInput` → `loadAppBootstrap` → `App`, so new users without a config file will start with decorations enabled, copying diff rails, line numbers and gutters instead of bare code text. The value should be `false` to match the documented default.

### Issue 2 of 5
src/core/config.ts:17-19
Set `copyDecorations` to `false` so the out-of-the-box experience copies only code text, matching the PR description and menu label ("off by default").

```suggestion
  showAgentNotes: false,
  copyDecorations: false,
};
```

### Issue 3 of 5
src/ui/components/panes/copySelection.ts:1774-1791
**Double-click on whitespace produces an inverted column range**

When the user double-clicks on a space or tab character, `wordStart` and `wordEnd` both remain at `localCol` (neither loop advances), giving `startCol = localCol + globalContentStart` and `endCol = localCol - 1 + globalContentStart`. `endCol < startCol`. `normalizeCopySelectionRange` corrects the ordering, but the resulting selection highlights only the character immediately before the clicked space rather than the space itself or nothing—a confusing UX that mismatches what other editors do on a whitespace double-click.

### Issue 4 of 5
src/ui/App.tsx:148-153
**`setTimeout` without cleanup can fire after unmount**

`showTransientNotice` schedules a bare `setTimeout` with no cleanup path. If the `App` component is unmounted before the timer fires (e.g. in tests or hot-reload) the callback will try to call `setTransientNoticeText` on an unmounted component. This is low-severity in production (there is only one `App` instance), but it can produce spurious React state-update warnings in tests. The timer's `id` should be stored in a ref and cleared in a companion `useEffect`.

### Issue 5 of 5
src/ui/components/panes/DiffPane.tsx:596-601
**Stale `copySelectionDrag` on the first drag event**

Inside `updateCopySelection`, `event.preventDefault()` / `event.stopPropagation()` are gated on the closed-over `copySelectionDrag` value. On the very first `onMouseDrag` event that fires immediately after `beginCopySelection` sets the drag state, React has not yet re-rendered, so `copySelectionDrag` is still `null` and the two calls are skipped. The state-setter path (functional update inside `setCopySelectionDrag`) correctly sees the latest value, but the native-selection suppression fires a render cycle late. The consequence is a brief native-selection flash on drag start.

_{Reviews (1): Last reviewed commit: "feat(ui): add mouse-drag text selection ..." | Re-trigger Greptile}

[greptile-apps]

Default value contradicts documented behavior

The PR description and UI label both say "Copy decorations" is off by default, but DEFAULT_VIEW_PREFERENCES.copyDecorations: true initialises it as on. This flows through resolveConfiguredCliInput → loadAppBootstrap → App, so new users without a config file will start with decorations enabled, copying diff rails, line numbers and gutters instead of bare code text. The value should be false to match the documented default.

Prompt To Fix With AI

This is a comment left during a code review.
Path: src/core/config.ts
Line: 15

Comment:
**Default value contradicts documented behavior**

The PR description and UI label both say "Copy decorations" is _off by default_, but `DEFAULT_VIEW_PREFERENCES.copyDecorations: true` initialises it as on. This flows through `resolveConfiguredCliInput` → `loadAppBootstrap` → `App`, so new users without a config file will start with decorations enabled, copying diff rails, line numbers and gutters instead of bare code text. The value should be `false` to match the documented default.

How can I resolve this? If you propose a fix, please make it concise.

[greptile-apps]

Set copyDecorations to false so the out-of-the-box experience copies only code text, matching the PR description and menu label ("off by default").

Suggested change

	showAgentNotes: false,
	copyDecorations: true,
	};
	showAgentNotes: false,
	copyDecorations: false,
	};

Prompt To Fix With AI

This is a comment left during a code review.
Path: src/core/config.ts
Line: 17-19

Comment:
Set `copyDecorations` to `false` so the out-of-the-box experience copies only code text, matching the PR description and menu label ("off by default").

```suggestion
  showAgentNotes: false,
  copyDecorations: false,
};
```

How can I resolve this? If you propose a fix, please make it concise.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

[greptile-apps]

Stale copySelectionDrag on the first drag event

Inside updateCopySelection, event.preventDefault() / event.stopPropagation() are gated on the closed-over copySelectionDrag value. On the very first onMouseDrag event that fires immediately after beginCopySelection sets the drag state, React has not yet re-rendered, so copySelectionDrag is still null and the two calls are skipped. The state-setter path (functional update inside setCopySelectionDrag) correctly sees the latest value, but the native-selection suppression fires a render cycle late. The consequence is a brief native-selection flash on drag start.

Prompt To Fix With AI

This is a comment left during a code review.
Path: src/ui/components/panes/DiffPane.tsx
Line: 596-601

Comment:
**Stale `copySelectionDrag` on the first drag event**

Inside `updateCopySelection`, `event.preventDefault()` / `event.stopPropagation()` are gated on the closed-over `copySelectionDrag` value. On the very first `onMouseDrag` event that fires immediately after `beginCopySelection` sets the drag state, React has not yet re-rendered, so `copySelectionDrag` is still `null` and the two calls are skipped. The state-setter path (functional update inside `setCopySelectionDrag`) correctly sees the latest value, but the native-selection suppression fires a render cycle late. The consequence is a brief native-selection flash on drag start.

How can I resolve this? If you propose a fix, please make it concise.