fix(ui): Ctrl+O expands thinking blocks still in active_cell

After `ThinkingComplete` the finalized thinking entry sits in
`app.active_cell` with `streaming = false` until the active cell
flushes to history at end-of-turn. During that window the transcript
rendered the "thinking collapsed; press Ctrl+O for full text"
affordance from `render_thinking`, but `open_thinking_pager` only
searched `app.history` — so the handler surfaced "No thinking blocks
to expand" while pointing at the affordance. The affordance was
truthful; the handler was lying.

Routed the lookup through `cell_at_virtual_index` /
`virtual_cell_count`, the existing virtual-index API that
`open_tool_details_pager` already uses for the same active-cell
window. The selection-based path resolves through the virtual index
too, so dragging into an in-flight thinking block and pressing
Ctrl+O now works as well.

Regression guard: `open_thinking_pager_finds_thinking_in_active_cell`
drives the entry into active_cell, finalizes it so the "collapsed"
affordance is what render_thinking emits, then asserts Ctrl+O pushes
the Pager view instead of surfacing the "No thinking blocks" status.

CHANGELOG.md

@@ -86,6 +86,19 @@ coverage additions.
   `reasoning_content` replay, preventing second-turn HTTP 400s
   after tool calls when users keep the onboarding default model
   alias.
+- **`Ctrl+O` expands thinking blocks still in flight.**
+  `open_thinking_pager` only searched `app.history`, but after
+  `ThinkingComplete` the finalized thinking entry sits in
+  `app.active_cell` with `streaming = false` until the active cell
+  flushes at end-of-turn. During that window the transcript still
+  rendered the "thinking collapsed; press Ctrl+O for full text"
+  affordance from `render_thinking`, so the handler surfaced
+  "No thinking blocks to expand" while the affordance pointed at
+  it. Routed through the existing `cell_at_virtual_index` /
+  `virtual_cell_count` resolver that `open_tool_details_pager`
+  already uses; selection-based and most-recent lookups both reach
+  in-flight entries now. Regression-guarded by
+  `open_thinking_pager_finds_thinking_in_active_cell`.
 - **Skill completions no longer flood the top-level slash menu**
   (#1437, PR #1442 from **@reidliu41**). Installed skills now
   complete under `/skill <name>` while the root `/` menu stays

crates/tui/src/tui/ui.rs

@@ -8493,8 +8493,16 @@ fn open_pager_for_last_message(app: &mut App) -> bool {
 
 /// Open a pager showing the full thinking block. Targets the cell at the
 /// current selection if it's a Thinking cell; otherwise falls back to the
-/// most recent Thinking cell in history. Bound to Ctrl+O so users can read
-/// reasoning content that's been collapsed in calm-mode rendering.
+/// most recent Thinking cell across the virtual transcript (history +
+/// in-flight `active_cell`). Bound to Ctrl+O so users can read reasoning
+/// content that's been collapsed in calm-mode rendering.
+///
+/// The virtual-index lookup matters: after `ThinkingComplete` fires the
+/// finalized thinking entry sits in `active_cell` with `streaming = false`
+/// until the active cell flushes to history. During that window the
+/// transcript already renders the "thinking collapsed; press Ctrl+O for
+/// full text" affordance, so the handler must address active-cell entries
+/// or the affordance becomes a lie.
 fn open_thinking_pager(app: &mut App) -> bool {
     let selected_cell = app
         .viewport
@@ -8510,23 +8518,18 @@ fn open_thinking_pager(app: &mut App) -> bool {
         })
         .filter(|&idx| {
             matches!(
-                app.history.get(idx),
+                app.cell_at_virtual_index(idx),
                 Some(crate::tui::history::HistoryCell::Thinking { .. })
             )
         });
 
     let target_idx = selected_cell.or_else(|| {
-        app.history
-            .iter()
-            .enumerate()
-            .rev()
-            .find_map(|(idx, cell)| {
-                if matches!(cell, crate::tui::history::HistoryCell::Thinking { .. }) {
-                    Some(idx)
-                } else {
-                    None
-                }
-            })
+        (0..app.virtual_cell_count()).rev().find(|&idx| {
+            matches!(
+                app.cell_at_virtual_index(idx),
+                Some(crate::tui::history::HistoryCell::Thinking { .. })
+            )
+        })
     });
 
     let Some(idx) = target_idx else {
@@ -8534,13 +8537,18 @@ fn open_thinking_pager(app: &mut App) -> bool {
         return true;
     };
 
-    let cell = &app.history[idx];
     let width = app
         .viewport
         .last_transcript_area
         .map(|area| area.width)
         .unwrap_or(80);
-    let text = history_cell_to_text(cell, width);
+    let text = {
+        let Some(cell) = app.cell_at_virtual_index(idx) else {
+            app.status_message = Some("No thinking blocks to expand".to_string());
+            return true;
+        };
+        history_cell_to_text(cell, width)
+    };
     app.view_stack.push(PagerView::from_text(
         "Thinking",
         &text,

crates/tui/src/tui/ui/tests.rs

@@ -3948,6 +3948,42 @@ fn flush_active_cell_finalizes_unclosed_thinking_block() {
     );
 }
 
+#[test]
+fn open_thinking_pager_finds_thinking_in_active_cell() {
+    // After ThinkingComplete fires, the finalized thinking entry stays in
+    // `app.active_cell` with `streaming = false` until the active cell is
+    // flushed to history (end-of-turn, or when an assistant text arrives).
+    // During that window the transcript still renders the
+    // "thinking collapsed; press Ctrl+O for full text" affordance from
+    // `render_thinking`, so the handler must reach across the virtual
+    // transcript — not just `app.history` — or the promise is a lie.
+    // Regression guard for the v0.8.29 affordance/handler mismatch.
+    let mut app = create_test_app();
+    let _ = ensure_streaming_thinking_active_entry(&mut app);
+    append_streaming_thinking(&mut app, 0, "deliberating");
+    let finalized = finalize_streaming_thinking_active_entry(&mut app, Some(1.2), "");
+    assert!(finalized);
+    assert!(
+        app.history.is_empty(),
+        "thinking entry stays in active_cell until flush"
+    );
+    let active = app.active_cell.as_ref().expect("active cell present");
+    assert!(matches!(
+        active.entries().first(),
+        Some(HistoryCell::Thinking {
+            streaming: false,
+            ..
+        })
+    ));
+
+    assert!(open_thinking_pager(&mut app));
+    assert_eq!(
+        app.view_stack.top_kind(),
+        Some(ModalKind::Pager),
+        "pager must open for thinking entries still in active_cell"
+    );
+}
+
 #[test]
 fn engine_error_finalizes_active_thinking_block() {
     use crate::error_taxonomy::StreamError;