fix(terminal): stop forwarding the wheel to codex, it ignores SGR reports

DodgyBadger reported a completely dead wheel in codex tabs (#227 comment)
while the scrollbar drag worked, and the [scroll] line confirmed the
branch: forward-sgr with 967 rows of healthy local scrollback unused.

Measured against codex-cli 0.147.0 in a bare tmux: codex never enables
mouse tracking (mouse_any_flag=0), runs an inline viewport
(alternate_on=0) and pushes its transcript into the terminal's own
scrollback (history_size grows), and SGR wheel reports written to its
pane change nothing at all. Hand-encoded SGR taps are no-ops too, so
they stay (harmless), which means click-to-position is merely
unavailable there rather than damaging.

_shouldForwardWheelToApp now returns true for claude >= 2.1.187 and
nothing else; codex falls to the local-scrollback path like
shell/gemini/opencode, which is the same history the scrollbar drag was
already reaching. The claude-only PageUp fallback is untouched.

Verified in Chromium against a live codex session on an isolated
instance: routing logs local-scrollback, the viewport moves 39 -> 4 and
zero bytes go to the PTY.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/architecture-invariants.md

@@ -80,7 +80,9 @@ Implementation detail extracted from `CLAUDE.md` so that file stays small enough
 
 **Two strip flavors, one carry** (#205, `session.ts:_handleTerminalOutput`): the FULL strip (`isAltScreenStripMode` = codex/claude/gemini) removes alt-screen toggles, `3J`, and mouse-tracking DECSETs. Every other mode (shell/opencode/antigravity) 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). ⚠️ 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 narrow branch; the frontend `_sessionUsesServerMouseStrip()` mirror stays claude/codex/gemini because only the FULL strip touches mouse DECSETs. The chunk-boundary carry (`_altScreenSeqCarry`) runs for both flavors. Tests: `test/claude-scrollback-strip.test.ts`.
 
-**Wheel/touch forwarding is NOT gated on viewport-at-bottom** (#205, `terminal-ui.js:_shouldForwardWheelToApp`): for sessions verified to scroll their own transcript on SGR wheel reports (codex, claude ≥ 2.1.187 — version via the local/docker/remote `--version` probes), the plain wheel AND touch drags forward as coalesced SGR reports (`_forwardScrollToApp` → `_sendSyntheticSgrWheel`, 40ms batches, 5-tick cap, 512-byte queue bound). It used to gate on the viewport being at the bottom so both scrollbacks stayed reachable, but a repaint-mode CLI keeps NO terminal scrollback of its own — xterm's buffer holds only replayed repaint frames, so local scrolling drags the CLI's pinned prompt box up the screen over stale frames; and `scrollToLastNonEmptyLine()` routinely parked the viewport off-bottom, silently pinning the wheel to local. Forwarding now snaps the viewport home first (SGR coordinates address the LIVE screen — a report computed from a scrolled-up viewport would hit-test the wrong row). Local scrollback remains on Shift+wheel and the `terminalWheelLocalScrollback` opt-out (both also cover touch via the shared gate; touch has no Shift, so the setting is its only local pin). `_wheelScrollLines()` normalizes `deltaMode` (Firefox fires LINE deltas ≈3/notch — read as pixels that rounded to 0 and fell to the ±1 fallback, ~4× too slow; PAGE deltas scale by `terminal.rows`) while keeping the #154 Shift-axis trap (macOS trackpads put Shift+scroll magnitude on deltaX). Tests: `test/terminal-touch-tap.test.ts`.
+**Only claude ≥ 2.1.187 forwards the wheel; every other mode scrolls local scrollback** (#227 follow-up, `terminal-ui.js:_shouldForwardWheelToApp`). Codex was in the forward list until a reporter hit a completely dead wheel in codex tabs while the scrollbar drag worked. Measured against codex-cli 0.147.0 in a bare tmux: it never enables mouse tracking (`mouse_any_flag=0`) and SGR wheel reports fed to its PTY change nothing on screen, because it runs an INLINE viewport (`alternate_on=0`) and pushes its transcript into the terminal's own scrollback (tmux `history_size` grows) instead of paging in-app. So for codex, local scrollback IS the transcript and forwarding swallowed every tick. ⚠️ "The TUI is a strip mode" is NOT evidence that it consumes wheel reports — verify with a real `\x1b[<64;c;rM` write into a live pane before adding a mode here. Hand-encoded SGR TAPS stay enabled for codex (`_sessionUsesServerMouseStrip`); measured, they are no-ops that insert nothing, so click-to-position is simply unavailable there rather than harmful.
+
+**Wheel/touch forwarding is NOT gated on viewport-at-bottom** (#205, `terminal-ui.js:_shouldForwardWheelToApp`): for sessions verified to scroll their own transcript on SGR wheel reports (claude ≥ 2.1.187 — version via the local/docker/remote `--version` probes), the plain wheel AND touch drags forward as coalesced SGR reports (`_forwardScrollToApp` → `_sendSyntheticSgrWheel`, 40ms batches, 5-tick cap, 512-byte queue bound). It used to gate on the viewport being at the bottom so both scrollbacks stayed reachable, but a repaint-mode CLI keeps NO terminal scrollback of its own — xterm's buffer holds only replayed repaint frames, so local scrolling drags the CLI's pinned prompt box up the screen over stale frames; and `scrollToLastNonEmptyLine()` routinely parked the viewport off-bottom, silently pinning the wheel to local. Forwarding now snaps the viewport home first (SGR coordinates address the LIVE screen — a report computed from a scrolled-up viewport would hit-test the wrong row). Local scrollback remains on Shift+wheel and the `terminalWheelLocalScrollback` opt-out (both also cover touch via the shared gate; touch has no Shift, so the setting is its only local pin). `_wheelScrollLines()` normalizes `deltaMode` (Firefox fires LINE deltas ≈3/notch — read as pixels that rounded to 0 and fell to the ±1 fallback, ~4× too slow; PAGE deltas scale by `terminal.rows`) while keeping the #154 Shift-axis trap (macOS trackpads put Shift+scroll magnitude on deltaX). Tests: `test/terminal-touch-tap.test.ts`.
 
 **A false gate on a Claude session must not mean a DEAD gesture** (#205 round 2, `_maybePageCliTranscript`): every way `_shouldForwardWheelToApp()` returns false leaves a repaint-mode pane scrolling a buffer that has nothing in it (`baseY === 0`) — the version probe came back empty, the CLI really is older than 2.1.187, or the user turned on `terminalWheelLocalScrollback`. The 1.12.0 retest reported exactly that: a wheel that did nothing at all while Fn+Up (PageUp) paged back through intact text, which is the proof that the CLI's own history and the PTY input path were both fine. So under the triple guard (claude mode + gate false + `baseY === 0`) wheel and touch travel is translated into coalesced `\x1b[5~` / `\x1b[6~` through the same 40ms queue as the SGR reports, at half a screen of travel per page key (the key jumps a whole screen; a 1:1 mapping was unusably slow with a discrete wheel). ⚠️ Shift is excluded on purpose — it is the explicit "give me local scrollback" gesture and must keep that meaning. ⚠️ `terminalWheelLocalScrollback` is deliberately NOT scoped away from repaint-mode CLIs even though it is a footgun there: that would silently override an explicit user choice, so the fallback catches it instead. **Server-side counterpart**: `getClaudeCliVersion()` caches SUCCESS for the process lifetime but must never cache FAILURE — it used to, so one timed-out or PATH-starved probe at the first Claude session start disabled wheel-forwarding for every Claude session until the server restarted (a dead wheel on phone, tablet and laptop at once, the signature of a server-side cause). Failures now retry with a 1/2/4…15min backoff; the policy is the pure `resolveClaudeCliVersion()`. Tests: `test/terminal-scroll-routing.test.ts`, `test/claude-cli-version-cache.test.ts`.
 

docs/scrollback-fix-plan.md

@@ -163,6 +163,57 @@ both self-reporting, so the retest ask is now "open the console and paste the `[
 - iPhone: Claude or shell session, and whether a full tab kill changes anything.
 - Browser console: `app.terminalUi?.terminal?.modes?.mouseTrackingMode` (false-path 4).
 
+## ROUND 3 (2026-08-09): Codex wheel dead — CONFIRMED AND FIXED
+
+DodgyBadger (Codex latest, Chrome, Windows 11): mouse wheel does nothing in a CODEX session
+while working fine in shell and web tabs; DRAGGING THE SCROLLBAR WORKS, so xterm's local
+buffer demonstrably has content for their codex pane. Analysis against the shipped code:
+
+- `_shouldForwardWheelToApp` returns true UNCONDITIONALLY for `codex` (no version gate, unlike
+  claude's `>= 2.1.187`), so every plain wheel tick is sent as SGR reports to Codex.
+- The "verified to scroll its transcript on SGR wheel reports" claim for codex predates
+  current Codex builds; if Codex latest ignores SGR wheel, forwarding eats the gesture while
+  the healthy local scrollback (proven by the working scrollbar) sits unused.
+- The #227 PageUp fallback cannot rescue this: it is gated to `claude` mode AND `baseY === 0`,
+  and codex here has real local scrollback. The `[scroll]` diagnostic will still say
+  `forward-sgr (mode=codex, ...)`, confirming the branch, worth asking the reporter to paste.
+
+**CONFIRMED by the reporter's `[scroll]` line (2026-08-09, PR #227 comment)**:
+`forward-sgr (mode=codex, cliVersion=unknown, localScrollbackOptOut=false, mouseTracking=none,
+localScrollbackRows=967)`. Forwarding branch active, 967 rows of healthy local scrollback
+unused, Codex ignoring the SGR reports. Environment: Codex latest, Chrome, Windows 11.
+
+**Measured against codex-cli 0.147.0** (isolated `tmux -L codexwheel`, fake `CODEX_HOME/auth.json`,
+history built with 401ing prompts), which settles it without needing a version gate at all:
+
+| Probe                                          | Result                                          |
+| ---------------------------------------------- | ----------------------------------------------- |
+| `#{mouse_any_flag}` once the TUI is up         | `0`: codex never enables mouse tracking         |
+| `#{alternate_on}`                              | `0`: inline viewport, not an alt-screen pager   |
+| `#{history_size}` while prompting              | grows 3 → 32: the transcript goes to scrollback |
+| 6 × `\x1b[<64;10;10M` written to the pane      | pane capture byte-identical, nothing happens    |
+| control: literal `zz`                          | pane changes, so the probe can see changes      |
+| `\x1b[<0;12;5M` + release (the click-tap path) | no change either: taps are no-ops, not garbage  |
+
+Codex has no in-app pager to drive: its history lives in the terminal's own scrollback, which is
+exactly what forwarding was stealing the gesture from. A version gate would be the wrong fix (and
+`cliVersion=unknown` means there is no codex probe to gate on anyway).
+
+**Fix (shipped):** `_shouldForwardWheelToApp` now returns true for `claude >= 2.1.187` and nothing
+else. Codex falls to the normal local-scrollback path like shell/gemini/opencode, so wheel and touch
+scroll the same history the scrollbar drag was already scrolling. The claude-only PageUp fallback is
+untouched: codex never needs it, its local buffer is real. Taps stay hand-encoded for codex
+(`_sessionUsesServerMouseStrip`), measured harmless, so click-to-position is merely unavailable
+there rather than damaging. Lesson for the next mode added to the forward list: "it is a strip mode"
+proves nothing, write a real SGR report into a live pane and diff the capture first.
+
+Verified end-to-end in Chromium against a live codex session on an isolated instance
+(`CODEMAN_INSTANCE=codexwheel`, port 5055, `envOverrides.CODEX_HOME` pointing at the fake auth
+dir): trusted `page.mouse.wheel` up now logs
+`[scroll] … → local-scrollback (mode=codex, …, localScrollbackRows=43)`, moves the viewport
+39 → 4 (back to the Codex banner), and sends ZERO bytes to the PTY. Unit coverage:
+`test/terminal-touch-tap.test.ts` ("only claude forwards — codex and gemini keep the local wheel").
+
 Original plan follows.
 
 ## Reports