fix(pi): forward the wheel from cliMouseTracking so scrolling survives replay

pi 1.4.0 is an alt-screen TUI that 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 stayed dead until a resize made pi redraw.

Same shape as copilot: altScreen strip-mux-and-mouse (the server records
the stripped DECSETs as cliMouseTracking, which survives the replay),
wheelForward always, transcriptPageKeys (PageUp/PageDown fallback for a
stale flag, measured on pi 1.4.0). _shouldForwardWheelToApp treats pi like
copilot. Registry pins and docs updated.

Tests: 2 new in terminal-scroll-routing (red before). Full run: 12989
passed, 5 red from the de_DE locale / XDG env (custom-model-run-menu-ui,
git-worktrees, edit-history-sync), all green under LANG=C.UTF-8.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
(cherry picked from commit 53e4136d9f4401e9250ac6a122599ffcb2a57e8a)

docs/architecture-invariants.md

@@ -231,14 +231,16 @@ Further detail: the `<prefix>: <title>` form (`w3-myapp: fix the login redirect`
 
 ### Terminal scrollback: strip flavors and wheel/touch forwarding
 
-**Three strip flavors, one carry** (#205, `session.ts:_handleTerminalOutput`): the FULL strip (`isAltScreenStripMode` = codex/claude/gemini) removes alt-screen toggles, `3J`, and mouse-tracking DECSETs. The MOUSE strip (`isMuxMouseStripMode` = opencode and copilot) removes alt-screen toggles AND the mouse DECSETs but KEEPS `3J` — the middle case, for a mouse-capable full-screen TUI: its tracking DECSETs reach the browser (tmux `mouse off` passes the pane's modes through to the client), xterm obeys them, and then every DRAG is reported to the TUI instead of selecting text — so mark-and-copy silently did nothing (measured 62 `none` / 18 `any` over 16s, 5/5 dead drags while `any`) and the obvious fallback, Ctrl+C, is opencode's `app_exit`. Copilot is the same shape (measured on 1.0.95: alt screen, mouse reporting on): left on the narrow strip, Auto Copy and copy-on-select did nothing and only Shift+drag selected. `3J` stays because a TUI is not a `clear` consumer. Every other mode (shell/antigravity/pi/grok/deepseek/omp) gets the NARROW strip (`isMuxAltScreenOnlyStripMode`) — alt-screen toggles ONLY — and only when tmux-backed (`useMux`). Rationale: the tmux CLIENT emits `smcup` as its first bytes at attach, before any program runs, parking xterm in the scrollback-less alternate buffer for the whole session (touch scrolling no-ops; xterm's own wheel handler converts the wheel to Up/Down arrows = readline history cycling — both #205 symptoms). tmux never forwards a pane program's alt-screen toggles to its client (it repaints instead; measured — vim/less inside a pane emit zero to the client), so the only thing the narrow strip ever removes is tmux's own smcup. It keeps `3J` (a user's `clear` is a deliberate scrollback wipe) and the mouse DECSETs (tmux passes those through even with `mouse off`; stripping them would break htop/vim mouse support — which is exactly why the mouse strip is opt-in per CLI and not part of the narrow flavour). ⚠️ The `useMux` gate is load-bearing: `startShell()`/`startInteractive()` fall back to a DIRECT PTY when mux creation fails, and there the inner program's own `?1049h` really does reach xterm — stripping it would break vim/less/htop for real. The replay path (`session-routes.ts`, via `session.usesMux`) applies the same three branches; the frontend gate (`_shouldReportMouseToCli()`) keeps no mode list at all: it reads only the published `cliMouseTracking`, which the server sets solely in a DECSET-stripping branch (full or mouse), so it can only be true for a mode whose DECSETs are stripped — the modes where the browser's hand-encoded tap (`_sendSyntheticSgrTap`) is the only way a click still reaches the CLI. Whichever modes the registry strips, the browser follows (pinned in `test/claude-scrollback-strip.test.ts`). The chunk-boundary carry (`_altScreenSeqCarry`) runs for all three flavors. Tests: `test/claude-scrollback-strip.test.ts`, `test/terminal-touch-tap.test.ts`.
+**Three strip flavors, one carry** (#205, `session.ts:_handleTerminalOutput`): the FULL strip (`isAltScreenStripMode` = codex/claude/gemini) removes alt-screen toggles, `3J`, and mouse-tracking DECSETs. The MOUSE strip (`isMuxMouseStripMode` = opencode, copilot and pi) removes alt-screen toggles AND the mouse DECSETs but KEEPS `3J` — the middle case, for a mouse-capable full-screen TUI: its tracking DECSETs reach the browser (tmux `mouse off` passes the pane's modes through to the client), xterm obeys them, and then every DRAG is reported to the TUI instead of selecting text — so mark-and-copy silently did nothing (measured 62 `none` / 18 `any` over 16s, 5/5 dead drags while `any`) and the obvious fallback, Ctrl+C, is opencode's `app_exit`. Copilot is the same shape (measured on 1.0.95: alt screen, mouse reporting on): left on the narrow strip, Auto Copy and copy-on-select did nothing and only Shift+drag selected. `3J` stays because a TUI is not a `clear` consumer. Every other mode (shell/antigravity/pi/grok/deepseek/omp) gets the NARROW strip (`isMuxAltScreenOnlyStripMode`) — alt-screen toggles ONLY — and only when tmux-backed (`useMux`). Rationale: the tmux CLIENT emits `smcup` as its first bytes at attach, before any program runs, parking xterm in the scrollback-less alternate buffer for the whole session (touch scrolling no-ops; xterm's own wheel handler converts the wheel to Up/Down arrows = readline history cycling — both #205 symptoms). tmux never forwards a pane program's alt-screen toggles to its client (it repaints instead; measured — vim/less inside a pane emit zero to the client), so the only thing the narrow strip ever removes is tmux's own smcup. It keeps `3J` (a user's `clear` is a deliberate scrollback wipe) and the mouse DECSETs (tmux passes those through even with `mouse off`; stripping them would break htop/vim mouse support — which is exactly why the mouse strip is opt-in per CLI and not part of the narrow flavour). ⚠️ The `useMux` gate is load-bearing: `startShell()`/`startInteractive()` fall back to a DIRECT PTY when mux creation fails, and there the inner program's own `?1049h` really does reach xterm — stripping it would break vim/less/htop for real. The replay path (`session-routes.ts`, via `session.usesMux`) applies the same three branches; the frontend gate (`_shouldReportMouseToCli()`) keeps no mode list at all: it reads only the published `cliMouseTracking`, which the server sets solely in a DECSET-stripping branch (full or mouse), so it can only be true for a mode whose DECSETs are stripped — the modes where the browser's hand-encoded tap (`_sendSyntheticSgrTap`) is the only way a click still reaches the CLI. Whichever modes the registry strips, the browser follows (pinned in `test/claude-scrollback-strip.test.ts`). The chunk-boundary carry (`_altScreenSeqCarry`) runs for all three flavors. Tests: `test/claude-scrollback-strip.test.ts`, `test/terminal-touch-tap.test.ts`.
 
 ⚠️ **What a mouse-DECSET strip (full or mouse) removes, it must REMEMBER.** Stripping the mouse DECSETs means xterm's `modes.mouseTrackingMode` is permanently `'none'` for those modes, so the browser hand-encodes click reports to compensate (`_sendSyntheticSgrTap`). With no state to consult it did that on EVERY click, which delivered mouse reports to programs that never asked for them: the same pane runs a plain shell whenever the CLI has exited or a `shell` was started inside a claude-mode session, and a shell prints the report as literal text (`[<0;88;20M`), garbling the next line typed. `_recordStrippedMouseMode()` therefore records each stripped sequence as it goes and publishes `cliMouseTracking` through `toState()`, and `_shouldReportMouseToCli()` requires it. ⚠️ Only the TRACKING modes count (1000/1001/1002/1003): 1005/1006 select an ENCODING and 1007 is alt-scroll, and counting those would put the stray reports straight back. ⚠️ The change broadcasts IMMEDIATELY rather than through `broadcastSessionStateDebounced`, because the flag flips when a dialog opens and the user can click that dialog inside the 500ms debounce window. Measured on a live claude 2.x: the CLI holds a tracking mode on continuously in fullscreen (so clicks keep being reported exactly as before; the default inline renderer holds none, measured on 2.1.283 even with `/model` open), while a bash prompt in the same stripped mode reports nothing. Fails toward silence: after a server restart the flag is false until the CLI re-emits, which tmux does at client attach.
 
-**Wheel forwarding requires observed mouse tracking: Claude ≥ 2.1.187, tracked Codex or tracked Copilot** (`terminal-ui.js:_shouldForwardWheelToApp`). The original #227 measurement remains valid for **Codex 0.147.0 inline**: `alternate_on=0`, `mouse_any_flag=0`, growing tmux history, and SGR wheel reports do nothing. Claude 2.1.280 inline similarly reports `alternate_on=0`, `mouse_any_flag=0`; forwarding there swallows gestures, so it keeps local scrollback. Fullscreen Claude (`CLAUDE_CODE_NO_FLICKER=1` or `"tui": "fullscreen"`) enables mouse tracking and accepts reports. **Fresh Codex 0.163.0 fullscreen measurement (2026-10-18, isolated local tmux pane)**: `alternate_on=1`, `mouse_any_flag=1`; one `\x1b[<64;10;10M` report moves the transcript one row upward, and `\x1b[<65;10;10M` restores the original screen. This is capability evidence, not a minimum-version promise: untracked Codex (including a 0.162.0 measurement (2026-10) with `mouse_any_flag=0`) keeps local history or the hollow-pane paging fallback. Codex does not publish the Claude-only CLI version field, so its gate requires the observed flag rather than a Claude version. The registry records this as `wheelForward.mode: 'always'` (observed mouse tracking is still required); Claude remains `version-gated`. A stale/false flag after startup cannot authorize forwarding. ⚠️ A strip mode alone is not evidence that a CLI consumes SGR reports. Verify with a real `\x1b[<64;c;rM` write into a live pane before adding a mode here. Hand-encoded SGR taps remain independently gated by `_shouldReportMouseToCli()`; the older #325 no-op measurement describes untracked inline Codex and must not be generalized to newer tracked fullscreen renderers. Shift/local-history opt-outs and xterm's native mouse/alternate-screen handling remain intact.
+**Wheel forwarding requires observed mouse tracking: Claude ≥ 2.1.187, tracked Codex, tracked Copilot or tracked Pi** (`terminal-ui.js:_shouldForwardWheelToApp`). The original #227 measurement remains valid for **Codex 0.147.0 inline**: `alternate_on=0`, `mouse_any_flag=0`, growing tmux history, and SGR wheel reports do nothing. Claude 2.1.280 inline similarly reports `alternate_on=0`, `mouse_any_flag=0`; forwarding there swallows gestures, so it keeps local scrollback. Fullscreen Claude (`CLAUDE_CODE_NO_FLICKER=1` or `"tui": "fullscreen"`) enables mouse tracking and accepts reports. **Fresh Codex 0.163.0 fullscreen measurement (2026-10-18, isolated local tmux pane)**: `alternate_on=1`, `mouse_any_flag=1`; one `\x1b[<64;10;10M` report moves the transcript one row upward, and `\x1b[<65;10;10M` restores the original screen. This is capability evidence, not a minimum-version promise: untracked Codex (including a 0.162.0 measurement (2026-10) with `mouse_any_flag=0`) keeps local history or the hollow-pane paging fallback. Codex does not publish the Claude-only CLI version field, so its gate requires the observed flag rather than a Claude version. The registry records this as `wheelForward.mode: 'always'` (observed mouse tracking is still required); Claude remains `version-gated`. A stale/false flag after startup cannot authorize forwarding. ⚠️ A strip mode alone is not evidence that a CLI consumes SGR reports. Verify with a real `\x1b[<64;c;rM` write into a live pane before adding a mode here. Hand-encoded SGR taps remain independently gated by `_shouldReportMouseToCli()`; the older #325 no-op measurement describes untracked inline Codex and must not be generalized to newer tracked fullscreen renderers. Shift/local-history opt-outs and xterm's native mouse/alternate-screen handling remain intact.
 
 **Copilot also receives forwarded reports** (1.0.95 measured in tmux: alt screen, `mouse_any_flag=1`): its mouse DECSETs are stripped so a drag selects, which also stops xterm encoding the wheel for it, so `_shouldForwardWheelToApp` sends the same SGR reports by hand while `cliMouseTracking` is true; six `\x1b[<64;…M` reports moved its transcript 18 lines, a phone swipe takes the same gate, and there is NO version gate.
 
+**Pi is the same shape, and the reason it moved to the mouse strip** (1.4.0 measured in tmux, default settings: `alternate_on=1`, `history_size=0`, `mouse_any_flag=1`, SGR): pi enables mouse tracking ONCE at start. Left on the narrow strip, the wheel worked only until Codeman replayed the buffer (tab switch, reload): the replay carries no DECSETs, xterm's `mouseTrackingMode` fell to `'none'` with `baseY` 0, and the wheel hit an empty local buffer until a resize made pi redraw. Measured on a fresh session: `drag` right after the first select, `none` after a tab switch and after a reload. With the mouse strip the server records the tracking (`cliMouseTracking`), which survives the replay; `_shouldForwardWheelToApp` forwards by hand while it is true. One SGR wheel report moves pi's transcript one row; PageUp/PageDown page it (the `transcriptPageKeys` fallback for a stale flag). Not measured: pi versions before 1.4.0.
+
 Codex 0.163.0 approval check in that isolated read-only/on-request session: the "Would you like to run the following command?" prompt remained on `1. Yes, proceed` after SGR wheel-up and wheel-down over both the transcript and approval option rows 36/37; the requested marker file was not created. The background transcript can scroll while the approval prompt remains fixed. Codeman does alert on this prompt: `src/web/screen-blocked.ts` reads Codex dialogs off the pane (`capabilities.workDetect.blockedLine`) and broadcasts `hook:permission_prompt`, which `_onHookPermissionPrompt` (settings-ui.js) records and `updateTabAlertFromHooks` (app.js) turns into the `'action'` tab alert, and both page-key fallbacks check it. The SGR wheel path deliberately does not consult that alert, because this measurement showed wheel reports leave the approval selection unchanged. Native Codex owns its approval selection; do not mistake a hook-only unit fixture for approval-dialog evidence.
 
 Native wheel travel retains upstream pixel/line/page units (100 px = 4 lines; Firefox 3-line events = 3 lines); no one-tick-per-event policy is introduced here. A fresh native gesture at or above 0.1 row (2.5px) rounds its opening travel to at least one tick (subject to the per-event cap), so an isolated 4px mouse click responds, 40px sends two ticks and 120px sends five. The signed remainder is carried forward; travel discarded by the per-event cap does not become a backlog. The signed remainder is debt repaid by subsequent same-direction events: ten 2.5px events still total one tick. Debt/fractions expire after a 150ms gap; a reversal inside that gap discards the old debt without another pre-payment. Sub-threshold jitter does not pre-pay. The first native report of each tab visit bypasses the 40 ms batching timer; later reports coalesce and only unsent bytes can be cancelled on reversal. Every queued batch belongs to its originating session, so switching tabs cannot send its bytes into the newly selected pane. Zero-delta events leave pending movement untouched. Tiles use the same helpers and their own queue/session.