Route mouse wheel scroll to the chat transcript instead of the prompt

docs/tui-cutover-readiness.md

@@ -99,12 +99,14 @@ performed.
    the shell's key handler), but the reported real-terminal failure is not
    reproduced or explained. Until someone pastes into a real TTY, treat text paste
    as unverified.
-2. **Mouse selection policy (CL-5540).** DEC mouse reporting is moving to
-   off-by-default (`mouseCapture` in `src/tui-opentui/product-host.ts:101`) so the
-   terminal owns drag-select and copy. The cost is that click-to-expand and
-   drag-scroll are off unless the user presses `Alt+M`
-   (`src/tui-opentui/shell.ts:3392`). This is a deliberate trade, but it is a
-   visible regression for mouse users and the default is not settled.
+2. **Mouse selection policy (CL-5540).** DEC mouse reporting defaults on in
+   the main shell (`useMouse` in `src/tui-opentui/product-host.ts:218`), so
+   wheel scroll and click-to-expand work out of the box. The cost is native
+   text selection, which the terminal cannot perform while reporting is on;
+   `Alt+M` (`toggleMouseCapture` in `src/tui-opentui/shell.ts:4006`) hands the
+   mouse back for that. The satellite pickers (`list-modal.ts`,
+   `provider-setup.ts`) keep reporting off and are unaffected. This is the
+   settled decision, not a pending tradeoff.
 3. **Shift+Enter does not insert a newline on terminals that do not report the
    modifier.** `Ctrl+Enter` and `Ctrl+J` are the working newline chords and the
    help catalog says so (`src/tui-opentui/keybindings.ts`). The kitty keyboard

src/tui-opentui/keybindings.ts

@@ -25,7 +25,7 @@ export const SHELL_SHORTCUTS: readonly ShellShortcut[] = [
   { keys: "Ctrl+C", description: "interrupt the run, or clear the prompt when idle; press twice to exit" },
   { keys: "Ctrl+O", description: "open the command palette; press again to close it" },
   { keys: "Alt+C", description: "copy mode: pick a message, tool output, or diff; press again to close it" },
-  { keys: "Alt+M", description: "take the mouse for click-to-expand and drag-scroll; off by default so drag-select and copy work" },
+  { keys: "Alt+M", description: "release the mouse to the terminal for native drag-select and copy; on by default for wheel scroll and click-to-expand" },
   { keys: "Alt+E", description: "expand or collapse every collapsible row (tool call, diff, skill, reasoning)" },
   { keys: "Tab", description: "move focus between the prompt and the transcript" },
   { keys: "Esc", description: "close the open overlay, or leave subagent observe" },

src/tui-opentui/list-modal.ts

@@ -44,9 +44,8 @@ export async function runListModal(
     : await createCliRenderer({
         exitOnCtrlC: false,
         targetFps: 30,
-        // Same trade as the product host (CL-5540): reporting off by default
-        // so the terminal owns drag-select and its own copy in these satellite
-        // pickers too.
+        // Reporting stays off in this satellite picker, unlike the main
+        // shell, so the terminal owns drag-select and its own copy here.
         useMouse: false,
         enableMouseMovement: false,
       })

src/tui-opentui/mouse-reporting-disabled.test.ts

@@ -1,10 +1,11 @@
 /**
  * CL-5540: the onboarding provider picker and the satellite list modals
  * (session resume, session mode) mount their own renderer and must disable
- * DEC mouse reporting the same way the product host does, or the terminal
- * never gets button-1 drags to run its own text selection. These tests mock
- * `@opentui/core` so the real (non-test-injected) `createCliRenderer` branch
- * runs, and assert on the options it was actually called with.
+ * DEC mouse reporting, unlike the main shell, or the terminal never gets
+ * button-1 drags to run its own text selection in these pickers. These
+ * tests mock `@opentui/core` so the real (non-test-injected)
+ * `createCliRenderer` branch runs, and assert on the options it was
+ * actually called with.
  */
 import { afterAll, describe, expect, mock, test } from "bun:test"
 import type { Harness } from "./harness.js"

src/tui-opentui/palette.ts

@@ -171,7 +171,7 @@ export const DEFAULT_PALETTE_COMMANDS: readonly PaletteCommand[] = [
   },
   {
     id: "toggle_mouse",
-    label: "Toggle mouse capture (off by default so you can drag-select)",
+    label: "Toggle mouse capture (on by default; release it to drag-select)",
     keywords: ["mouse", "select", "selection", "copy", "drag"],
     dispatch: "residual",
     category: "view",

src/tui-opentui/product-host.ts

@@ -116,9 +116,10 @@ export type ProductHostConfig = {
   /** First-run telemetry disclosure, shown on the landing screen. */
   readonly telemetryNotice?: string
   /**
-   * Take DEC mouse reporting. Default false: while it is on the terminal hands
-   * drags to us and cannot select text, which breaks copy with the mouse.
-   * Alt+M flips it at runtime for click-to-expand and drag-scroll.
+   * Take DEC mouse reporting. Default true: wheel/trackpad scroll only
+   * reaches OpenTUI when the terminal is told to report it, otherwise the
+   * terminal's own alternate-scroll mode resends it as arrow keys. Alt+M
+   * hands the mouse back to the terminal for native drag-select.
    */
   readonly useMouse?: boolean
 }
@@ -206,11 +207,15 @@ export async function mountProductHost(
     : await createCliRenderer({
         exitOnCtrlC: false,
         targetFps: 30,
-        // Mouse reporting off by default: any of DEC 1000/1002/1003/1006 makes
-        // the terminal forward drags to us instead of selecting text, so the
-        // user cannot copy with the mouse. Alt+M takes the mouse when
-        // click-to-expand or drag-scroll is wanted.
-        useMouse: config.useMouse ?? false,
+        // Mouse reporting on by default: without it, wheel/trackpad scroll
+        // never reaches OpenTUI — the terminal's own alternate-scroll mode
+        // swallows it and resends it as arrow keys, which the prompt then
+        // reads as history navigation instead of the transcript scrolling.
+        // Cost accepted: this suppresses the terminal's native drag-select
+        // in the main shell. Alt+M hands the mouse back when that is wanted.
+        // enableMouseMovement stays off (no ?1003): only clicks and wheel
+        // are needed.
+        useMouse: config.useMouse ?? true,
         enableMouseMovement: false,
         // A plain terminal sends a bare CR for both Enter and Shift+Enter, so
         // the modifier only arrives once the kitty keyboard protocol is

src/tui-opentui/provider-setup.ts

@@ -586,8 +586,8 @@ export async function runProviderSetup(
     : await createCliRenderer({
         exitOnCtrlC: false,
         targetFps: 30,
-        // Same trade as the product host (CL-5540): reporting off by default
-        // so the terminal owns drag-select and its own copy during onboarding.
+        // Reporting stays off during onboarding, unlike the main shell, so
+        // the terminal owns drag-select and its own copy here.
         useMouse: false,
         enableMouseMovement: false,
       })

src/tui-opentui/shell.test.ts

@@ -159,6 +159,49 @@ describe("createAppShell", () => {
     )
   })
 
+  test("wheel scroll landing on the prompt moves the transcript, not the prompt", async () => {
+    await withTestRenderer(
+      async (h) => {
+        const shell = createAppShell(h.renderer, {
+          terminal: { columns: 80, rows: 24 },
+          wireKeys: false,
+        })
+        try {
+          for (let i = 0; i < 50; i++) {
+            appendTranscript(shell, `seed-${i}`)
+          }
+          await h.renderOnce()
+          await h.renderOnce()
+          expect(isTranscriptFollowing(shell)).toBe(true)
+          const followingTop = shell.transcript.scrollTop
+
+          // Locate the prompt's interior on screen and scroll through the
+          // renderer's real SGR-mouse parse + hit-test dispatch, the same
+          // path a live terminal drives — not a direct method call, which
+          // would pass even if the renderer never routed the event here.
+          const rows = h.captureCharFrame().split("\n")
+          const borderRow = rows.findIndex((r) => r.includes("╭"))
+          const promptX = rows[borderRow]!.indexOf("╭") + 2
+          const promptY = borderRow + 1
+
+          for (let i = 0; i < 5; i++) {
+            await h.mockMouse.scroll(promptX, promptY, "up")
+          }
+          await h.renderOnce()
+
+          // The wheel event landed on the prompt, but the transcript moved
+          // and pinned — the prompt's own (empty) buffer never scrolled.
+          expect(shell.transcript.scrollTop).toBeLessThan(followingTop)
+          expect(isTranscriptFollowing(shell)).toBe(false)
+          expect(stickyMode(shell)).toBe("PINNED")
+        } finally {
+          shell.dispose()
+        }
+      },
+      { width: 80, height: 24 },
+    )
+  })
+
   test("focus lease: prompt vs transcript", async () => {
     await withTestRenderer(
       async (h) => {

src/tui-opentui/shell.ts

@@ -20,6 +20,7 @@ import {
   type BaseRenderable,
   type CliRenderer,
   type KeyEvent,
+  type MouseEvent,
   type TextChunk,
 } from "@opentui/core"
 
@@ -3998,8 +3999,8 @@ export function copyAllTargets(shell: AppShell): boolean {
 
 /**
  * Alt+M: take DEC mouse reporting, or hand it back to the terminal.
- * Reporting is off by default so drag-select and the terminal's own copy keep
- * working; taking it enables click-to-expand and drag-scroll at that cost.
+ * Reporting is on by default so wheel scroll and click-to-expand work;
+ * releasing it restores the terminal's own drag-select and copy.
  * Returns the new enabled state, or null when the host exposes no control.
  */
 export function toggleMouseCapture(shell: AppShell): boolean | null {
@@ -4497,6 +4498,33 @@ export function handleCtrlC(
   })
 }
 
+/**
+ * Wheel/trackpad scroll landing on the prompt scrolls the chat instead.
+ *
+ * The prompt textarea is an editable buffer with its own `scrollY`, so
+ * OpenTUI's default routing — whichever renderable the wheel event hits, or
+ * the focused renderable when the hit misses — happily scrolls the prompt's
+ * own (usually one-screen, nothing-to-scroll) content. The prompt also holds
+ * keyboard focus for the whole session, so it is the fallback target for any
+ * wheel event that lands off the transcript's hit-tested rows. Overriding the
+ * scroll case here — rather than teaching the transcript's own scroll lease
+ * about wheel events — keeps the fix to exactly where wheel input actually
+ * arrives, without touching transcript viewport internals.
+ */
+function routePromptWheelToTranscript(
+  prompt: BaseRenderable,
+  transcript: ScrollBoxRenderable,
+): void {
+  ;(prompt as unknown as { onMouseEvent: (event: MouseEvent) => void }).onMouseEvent = (
+    event: MouseEvent,
+  ) => {
+    if (event.type !== "scroll") return
+    ;(
+      transcript as unknown as { onMouseEvent: (event: MouseEvent) => void }
+    ).onMouseEvent(event)
+  }
+}
+
 /**
  * Build the app shell frame on an OpenTUI renderer.
  * Mounts sticky transcript / overlay host / transient notice / prompt box.
@@ -4727,6 +4755,7 @@ export function createAppShell(
     cursorColor: UI.text,
     placeholderColor: UI.textFaint,
   })
+  routePromptWheelToTranscript(prompt, transcript)
   promptField.add(prompt)
   promptBox.add(promptTopRule)
   promptBox.add(promptField)