feat(tui): replace /diff command with persistent Diff tab

[kelsonpw]

What landed

• New src/ui/tui/components/DiffTab.tsx — persistent tab body in RunScreen. File list (newest-first, deduped by path) + colored unified diff for the selected file below. ↑↓ / j/k move selection; PgUp/PgDn scroll the diff body; ←→ still switch tabs.
• src/ui/tui/screens/RunScreen.tsx — wired the Diff tab between Events and Logs.

What was removed

• /diff slash command registration in src/ui/tui/console-commands.ts (and the parseDiffSlashInput helper).
• /diff dispatch case in src/ui/tui/components/ConsoleView.tsx (~80 lines of summary + detail branches).
• (kept) DiffViewer primitive — now consumed by the new tab and the existing outro "what changed" section.

Diff tab behavior

The tab subscribes narrowly to fileWritesTotal (a monotonic counter that climbs on every agent file write) and re-walks the canonical FileChangeLedger only when that counter advances. The DiffViewer primitive already windows the patch body to maxLines (default 30) around scrollOffset, so large diffs render at a constant ~30-line cost per frame. Outer Box uses overflow="hidden" (defense against the #779 overdraw bug). Empty state copy: no file changes yet — the agent hasn't edited anything. Discoverability hints in FileWritesPanel and DiffViewer summary mode now point to the Diff tab instead of the removed slash command.

Tests

• New: src/ui/tui/screens/__tests__/RunScreen.diffTab.test.tsx (6 tests + 2 snapshots at 80 / 60 cols). Covers tab visibility, tab ordering (Progress → Events → Diff → Logs), empty state, and content rendering with seeded ledger entries.
• Updated: console-commands.test.ts — replaced the old /diff registry assertions with a "removal" describe block that asserts /diff is absent and isKnownCommand('/diff') is false (the registry-doesn't-contain-/diff acceptance check).
• Updated: DiffViewer.test.tsx and FileWritesPanel.test.tsx for the new hint copy.

Test plan

• pnpm tsc --noEmit && pnpm lint && pnpm test — all green (4470 tests)
• src/utils/wizard-abort.ts untouched
• ← → tab switching still works
• /diff is gone from the slash palette (registry + isKnownCommand assertions)
• Snapshot tests at 80 cols + 60 cols

Deferred

The end-of-run "all changes summary" overlay that PR #599 also added is intentionally untouched — this PR only addresses the slash command → tab migration. No docs / skill prompts referenced /diff.

🤖 Generated with Claude Code

---

Note

Medium Risk
Medium risk because it changes a key navigation/workflow surface (removing /diff and adding a new RunScreen tab) and introduces new keyboard/scroll state that could regress TUI behavior, though it is isolated to UI and covered by new tests.

Overview
Adds a persistent RunScreen Diff tab that lists changed files (deduped, newest-first) and renders a colored unified diff for the selected file with keyboard navigation (↑↓/j/k) and paging scroll.

Removes the /diff slash command end-to-end (command registry, parsing/tests, and ConsoleView dispatch) and updates related UI copy/hints (e.g. DiffViewer summary footer, FileWritesPanel) to point users to the new tab. Adds an end-to-end RunScreen.diffTab test suite with snapshots to lock tab ordering, empty state, and narrow-width rendering.

^{Reviewed by Cursor Bugbot for commit a3fd2f7. Bugbot is set up for automated code reviews on this repo. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

Bugbot Autofix prepared fixes for both issues found in the latest run.

• ✅ Fixed: Stale scroll hint misguides DiffTab users
  • Updated the DiffViewer detail-mode hint from "press j/k or arrow keys to scroll" to "press PageUp/PageDown to scroll" to match DiffTab's actual key bindings.
• ✅ Fixed: useEffect clamp leaves render-time undefined access window
  • Added an inline clamp (Math.min(selectedIndex, files.length - 1)) at the render-time access site so files[clampedIndex] is always in bounds, closing the one-render gap before the useEffect fires.

Or push these changes by commenting:

@cursor push 813ab281f7

Preview (813ab281f7)

diff --git a/src/ui/tui/components/DiffTab.tsx b/src/ui/tui/components/DiffTab.tsx
--- a/src/ui/tui/components/DiffTab.tsx
+++ b/src/ui/tui/components/DiffTab.tsx
@@ -238,7 +238,8 @@
     return <EmptyState />;
   }
 
-  const selected = files[selectedIndex];
+  const clampedIndex = Math.min(selectedIndex, files.length - 1);
+  const selected = files[clampedIndex];
 
   return (
     // Outer Box uses `overflow="hidden"` — same defense the rest of the
@@ -247,7 +248,7 @@
     <Box flexDirection="column" flexGrow={1} overflow="hidden">
       <FileList
         files={files}
-        selectedIndex={selectedIndex}
+        selectedIndex={clampedIndex}
         installDir={store.session.installDir}
       />
       <Box marginTop={1} paddingX={1} flexDirection="column">

diff --git a/src/ui/tui/components/DiffViewer.tsx b/src/ui/tui/components/DiffViewer.tsx
--- a/src/ui/tui/components/DiffViewer.tsx
+++ b/src/ui/tui/components/DiffViewer.tsx
@@ -18,9 +18,9 @@
  *   - hunk header → `Colors.accent`
  *   - context    → `Colors.muted`
  *
- * Keyboard nav (detail mode): j/down to scroll forward, k/up to scroll
- * back, q/esc to exit. Owned by the parent surface — DiffViewer just
- * renders the slice given by `scrollOffset`.
+ * Keyboard nav (detail mode): PageDown to scroll forward, PageUp to scroll
+ * back. Owned by the parent surface — DiffViewer just renders the slice
+ * given by `scrollOffset`.
  */
 
 import { Box, Text } from 'ink';
@@ -159,7 +159,7 @@
             <Text color={Colors.muted}>
               {patchLines.length - scrollOffset - maxLines} more line
               {patchLines.length - scrollOffset - maxLines === 1 ? '' : 's'}{' '}
-              {Icons.dot} press j/k or arrow keys to scroll
+              {Icons.dot} press PageUp/PageDown to scroll
             </Text>
           </Box>
         )}

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[cursor]

Stale scroll hint misguides DiffTab users

Medium Severity

DiffViewer detail mode displays the hint "press j/k or arrow keys to scroll" (line 162), but DiffTab binds j/k and arrow keys to file selection, while PageUp/PageDown handle diff scrolling. Since this PR is the first production consumer of DiffViewer detail mode (OutroScreen only uses summary mode, and the old /diff command used plain-text feedback), the hint is now actively misleading for any diff longer than maxLines. Users following it will navigate the file list instead of scrolling.

Additional Locations (1)

• src/ui/tui/components/DiffViewer.tsx#L156-L165

 

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[cursor]

useEffect clamp leaves render-time undefined access window

Low Severity

The selectedIndex clamp lives in a useEffect (post-render), but files[selectedIndex] is accessed during render on line 241 and dereferenced as selected.path on line 256. If files ever shrinks between renders, one render will access an out-of-bounds index before the effect corrects it, causing a TypeError. The comment explicitly anticipates FIFO eviction, so clamping inline (e.g. Math.min(selectedIndex, files.length - 1)) at the access site would close the gap.

Additional Locations (1)

• src/ui/tui/components/DiffTab.tsx#L240-L241

 

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