fix(pi): leave page keys out, and pin the strip that makes the wheel work

transcriptPageKeys applied to every pi, and a pi in `tuiMode: regular` binds
PageUp/PageDown to its editor. It emits no mouse enable, so the flag stays
false, and on a fresh pane the buffer is hollow: the wheel sent PageUp, the
caret of a multi-line draft moved, and the next keystroke landed on the wrong
line. Measured on real pi 1.1.0, 1.4.0 and 1.5.0. Regular mode is not exotic,
it only takes one line in pi's settings. Telling the two modes apart would
need a new capability, since the paging gate takes no id, so pi has no
fallback: a fullscreen pi with "Wheel scrolls local history" on stays where
master left it.

altScreen, the half of the fix that does the work, was pinned by nothing:
reverting it left 1328 tests green. The strip decision table reads its
expected value from the same registry entry. pi now has its own block using
the bytes it really emits, which also pins that focus reporting survives.

The fullscreen default dates from pi 1.0.0, not 1.4.0, so the comments say
that, and the sites still calling pi narrow-strip or main-screen by default
are corrected. Where a comment listed CLIs it now names the capability.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/claude-scrollback-strip.test.ts

@@ -102,7 +102,7 @@ describe('isMuxAltScreenOnlyStripMode', () => {
       expect(isMuxAltScreenOnlyStripMode(mode, false)).toBe(false);
     }
     // The full strip and the mouse strip already own their modes; never double-gate.
-    for (const mode of ['claude', 'codex', 'gemini', 'opencode', 'copilot'] as const) {
+    for (const mode of ['claude', 'codex', 'gemini', 'opencode', 'copilot', 'pi'] as const) {
       expect(isMuxAltScreenOnlyStripMode(mode, true)).toBe(false);
     }
   });
@@ -372,6 +372,44 @@ describe('strip decision table: live stream = replay, for every stock CLI', () =
  * on itself. Left in, xterm reports a plain drag to the TUI instead of selecting, so Auto Copy and
  * copy-on-select did nothing (only Shift+drag selected). Same strip, same reason.
  */
+describe('pi: alt-screen + mouse DECSETs stripped, 3J kept (#758)', () => {
+  // What fullscreen pi really emits on entering its TUI, read off a pane on 1.1.0, 1.4.0 and 1.5.0.
+  // Tracking comes on once, here, so a replay that drops it leaves the wheel dead unless the
+  // server remembers it. ?1004h (focus reporting) is not a mouse mode and stays.
+  const ENTER = '\x1b[?1049h\x1b[?7l\x1b[?1000h\x1b[?1002h\x1b[?1004h\x1b[?1006h';
+
+  it('is a mouse-strip mode under tmux, and only there', () => {
+    expect(isMuxMouseStripMode('pi', true)).toBe(true);
+    expect(isMuxMouseStripMode('pi', false)).toBe(false);
+  });
+
+  it('drops the alt-screen and mouse enables, and keeps focus reporting and 3J', () => {
+    const session = new Session({ workingDir: '/tmp', mode: 'pi' as never, useMux: true });
+    handleOutput(session, `${ENTER}\x1b[3JTUI`);
+    expect(session.terminalBuffer).toBe('\x1b[?7l\x1b[?1004h\x1b[3JTUI');
+  });
+
+  it('publishes cliMouseTracking so the wheel survives a replay', () => {
+    const session = new Session({ workingDir: '/tmp', mode: 'pi' as never, useMux: true });
+    handleOutput(session, `${ENTER}TUI`);
+    expect(session.toState().cliMouseTracking).toBe(true);
+    handleOutput(session, '\x1b[?1006l\x1b[?1004l\x1b[?1003l\x1b[?1002l\x1b[?1000l');
+    expect(session.toState().cliMouseTracking).toBeFalsy();
+  });
+
+  it('never sets the flag for an inline pi, which emits no mouse enable', () => {
+    const session = new Session({ workingDir: '/tmp', mode: 'pi' as never, useMux: true });
+    handleOutput(session, '\x1b[?2004hpi');
+    expect(session.toState().cliMouseTracking).toBeFalsy();
+  });
+
+  it('leaves a direct-PTY pi pane untouched', () => {
+    const session = new Session({ workingDir: '/tmp', mode: 'pi' as never, useMux: false });
+    handleOutput(session, '\x1b[?1049h\x1b[?1002hTUI');
+    expect(session.terminalBuffer).toBe('\x1b[?1049h\x1b[?1002hTUI');
+  });
+});
+
 describe('copilot: alt-screen + mouse DECSETs stripped, 3J kept', () => {
   it('is a mouse-strip mode under tmux, and only there', () => {
     expect(isMuxMouseStripMode('copilot', true)).toBe(true);

test/cli-registry-schema.test.ts

@@ -633,7 +633,7 @@ describe('capability shapes', () => {
 
   it('declares which CLIs get the wheel forwarded, and whether a version gates it', () => {
     // Claude forwards from 2.1.187 (fullscreen only); tracked Codex and Copilot
-    // forward without a version gate, and so does pi (1.4.0 measured). Unmeasured entries stay 'never'.
+    // forward without a version gate, and so does pi. Unmeasured entries stay 'never'.
     const mode = (id: string) => STOCK_CLIS.find((e) => (e.id as string) === id)?.capabilities.wheelForward;
     expect(mode('copilot')).toEqual({ mode: 'always' });
     expect(mode('claude')).toEqual({ mode: 'version-gated', minVersion: '2.1.187' });
@@ -645,10 +645,12 @@ describe('capability shapes', () => {
   });
 
   it('declares transcriptPageKeys for exactly the CLIs measured to page on PageUp/PageDown', () => {
-    // claude (repaint mode), codex, opencode, copilot and pi (all on the alternate screen) were
+    // claude (repaint mode), codex, opencode and copilot (all on the alternate screen) were
     // measured paging their own transcript on PageUp/PageDown; no other stock entry has been.
+    // pi pages too when fullscreen, and stays out on purpose: in `tuiMode: regular` the same keys
+    // move the caret of a multi-line draft.
     const paging = STOCK_CLIS.filter((e) => e.capabilities.transcriptPageKeys === true).map((e) => e.id as string);
-    expect(paging.sort()).toEqual(['claude', 'codex', 'copilot', 'opencode', 'pi']);
+    expect(paging.sort()).toEqual(['claude', 'codex', 'copilot', 'opencode']);
   });
 });
 

test/terminal-scroll-routing.test.ts

@@ -898,7 +898,7 @@ describe('GitHub Copilot wheel forwarding', () => {
   });
 });
 
-describe('pi wheel forwarding (1.4.0: alt-screen TUI with mouse tracking)', () => {
+describe('pi wheel forwarding (fullscreen by default since 1.0.0)', () => {
   // pi enables mouse tracking once at start. Codeman's replay (tab switch, reload) drops that
   // mode in xterm (`mouseTrackingMode` none, baseY 0), so the wheel hit an empty local buffer
   // and went dead until a redraw. Like Copilot, the server strips the DECSETs and publishes
@@ -908,13 +908,22 @@ describe('pi wheel forwarding (1.4.0: alt-screen TUI with mouse tracking)', () =
     expect(app._shouldForwardWheelToApp({ shiftKey: false })).toBe(true);
   });
 
-  it('keeps Shift+wheel local and falls back to paging when the flag is stale', () => {
+  it('keeps Shift+wheel local', () => {
     expect(hollowApp({ mode: 'pi', cliMouseTracking: true }).app._shouldForwardWheelToApp({ shiftKey: true })).toBe(
       false
     );
-    const { app } = hollowApp({ mode: 'pi', cliMouseTracking: false });
+  });
+
+  it('sends nothing to an inline pi: page keys there move the caret of a multi-line draft', () => {
+    // `tuiMode: regular`, and every pi below 1.0.0, emits no mouse enable, so the flag stays false
+    // over a buffer that is hollow on a fresh pane. pi binds PageUp to its editor in that mode:
+    // measured on real pi, the wheel moved the caret and the next X landed on the first line.
+    const { app, sent } = hollowApp({ mode: 'pi', cliMouseTracking: false });
+
     expect(app._shouldForwardWheelToApp({ shiftKey: false })).toBe(false);
-    expect(app._localScrollbackIsHollow()).toBe(true);
+    expect(app._maybePageCliTranscript({ shiftKey: false }, -18)).toBe(false);
+    app._flushWheelSgrQueue();
+    expect(sent).toEqual([]);
   });
 });