fix(mobile): merge-time fixes for the prompt composer (#444)

- styles.css: restate the composer overlay's own bottom gutter after the fold rules
  (the generic .paste-overlay longhand erased it: 0px flat, hinge strip replacing it
  folded) and subtract the fold strip from the dialog's max-height
- test/foldable-layout.test.ts: simulate the cascade for
  .paste-overlay.prompt-composer-overlay (fails without the CSS fix); pin the palette
  anchor by name instead of ELEMENTS.at(-1)
- keyboard-accessory.js: guard the app global in refreshForActiveSession() like the
  rest of the file
- keyboard-accessory.js: a whitespace-only draft is empty (Send no longer submits
  blank lines); the text still goes out untrimmed
- keyboard-accessory.js: derive _composerMaxLength and the frame refusal from one
  64 KiB frame limit minus both bracketed-paste markers so they cannot drift
- keyboard-accessory.js: translate the textarea placeholder and label at build time,
  since the DOM translator skips <textarea> subtrees
- i18n.js: zh-CN entries for the composer dialog copy
- docs/wiki/Mobile-Guide.md: describe the Compose key instead of a clipboard key
- CLAUDE.md: a "Mobile prompt composer" paragraph after the accessory bar one
- test/mobile-prompt-composer.test.ts: pin the whitespace rule and the derived budget

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
(cherry picked from commit f6725ba52da17b0bdbee8be3b5011e7cae514f69)

CLAUDE.md

@@ -344,6 +344,8 @@ Frontend JS modules have `@fileoverview` with `@dependency`/`@loadorder` tags. L
 
 **Shell keyboard accessory bar + one-shot Ctrl** (issue #262, `keyboard-accessory.js`): a **shell**-mode session automatically swaps the mobile accessory bar for terminal controls (Ctrl, Esc, Tab, four arrows, paste, dismiss); every other mode keeps the agent bar. `setMode()` now records the user's `extendedKeyboardBar` preference as the **base** layout and `refreshForActiveSession()` (called from `selectSession`) resolves base-vs-shell, so a settings save during a shell session cannot yank the bar away and switching back restores the user's choice. ⚠️ **Ctrl is a ONE-SHOT modifier applied in `terminal.onData`, not in a keydown handler**: a virtual keyboard emits no usable key events, so the character only exists as onData text. The hook sits AFTER `shouldSuppressTerminalQueryResponse` (xterm answers DA/CPR through onData too, and one of those would silently spend the modifier) and BEFORE every send path, so the control byte follows the normal control-char route. ⚠️ **Not every onData chunk is a keystroke**, and the query filter is not enough on its own: xterm ALSO emits mouse and focus reports on its own initiative, so the hook skips them via `isTerminalFocusOrMouseReport()` (they still reach the PTY, they just don't count as the next key). The mouse half is live — a shell session keeps the NARROW strip, so mouse DECSETs reach the browser and one tap while vim/htop runs spent the armed modifier silently (measured). The focus half is defense in depth: `FOCUS_ESCAPE_FILTER` in `session.ts` strips `\x1b[?1004h` from every PTY read, so `sendFocusMode` never turns on today; if it ever did, the bar's own post-key refocus would emit `\x1b[I` and eat the modifier before the user typed. ⚠️ It must disarm on ALL of: use, second tap, any other accessory key, session switch, keyboard dismissal, and a layout swap; a modifier left armed turns the next innocent keystroke into a control byte. ⚠️ **onData is not the only input path** — with `cjkInputEnabled` on, the CJK textarea owns the keyboard (onData returns early for everything it swallows, and the focus router sends `terminal.focus()` there, which is where the bar refocuses after every key), so `_handleCjkInput()` applies the modifier too. It is that module's single choke point to the PTY, so one call covers typed characters, IME flushes, Enter, backspace and arrows. Without it an armed modifier could neither fire NOR be spent, and survived to a later keystroke. Mapping is `ctrlByteFor()` (`code & 0x1f` over @A-Z[\]^_ and a-z, plus Ctrl+Space=NUL / Ctrl+?=DEL); characters with no control equivalent pass through unchanged, like a hardware keyboard. ⚠️ The armed style is `.accessory-btn.accessory-btn-ctrl.armed` (0,3,0) in BOTH stylesheets, and it cannot outrank mobile.css's light-skin repaint at **(0,3,1)** (`:is()` inherits its most specific argument, and that list holds `.btn-toolbar.btn-shell`) — so that rule excludes the state by hand as `.accessory-btn:not(.armed)`. Without the exclusion the armed button renders identically to a resting one on all four light skins, which is worse than no armed style at all.
 
+**Mobile prompt composer** (PR #444, the first slice of #359, `keyboard-accessory.js`): the agent bars' Paste key is now **Compose**, a dialog with a native multiline textarea (autocorrect, autocapitalize, spellcheck) where Enter adds a line and only **Send** submits; the shell bar keeps the direct Paste dialog, since shell input is not an agent prompt. Opening it ADOPTS the whole editable terminal prompt (`_takePendingLocalEcho`): the local-echo overlay's pending text has never reached the PTY, but the flushed prefix has, so that prefix is erased with backspaces counted in CODE POINTS (`Array.from(text).length`; measured on Claude Code 2.1.278, `a` + emoji + `b` takes three, and the UTF-16 count sent four and ate the neighbour; `clearTerminalInput()` in terminal-ui.js moved with it). ⚠️ **Drafts are per-session and in memory only** (`_composerDrafts`, never persisted: prompts routinely carry secrets, and persisting them would need the 0600 treatment the intent store gets). Every non-Send exit (Cancel, backdrop, Escape, "Use terminal keyboard") leaves the taken text ONLY in the draft, with the dot on the key (`has-draft`, kept in step by `_syncComposerDraftIndicator`) as the signal that the terminal prompt is empty on purpose, and `_cleanupSessionData` discards the draft with the session. ⚠️ **Delivery is a hand-built bracketed-paste frame** (`\x1b[200~` + the text with newlines mapped to `\r` + `\x1b[201~`, byte-identical to what `terminal.paste()` would emit) through `_sendInputAsync` WITHOUT `{ useMux: true }`, plus a SEPARATE Enter 120 ms later WITH it (codex drops keys that share a PTY read with a bracketed paste). Not `terminal.paste()`, for two reasons: xterm's `bracketedPasteMode` mirror is false for every session after a tab switch or reload (`terminal.reset()` in the replay re-clones the DEC modes, the tmux capture carries no `?2004h`, and tmux never forwards the pane's DECSET to a client after attach), so a paste through xterm would go out unbracketed and the CLI would submit at the first `\r`; and xterm's onData is where the local-echo paste branch flushes pending overlay text AHEAD of the block, text the composer has already taken and erased from the PTY, so the frame goes straight to the wire with the composer as the prompt's only owner. The unconditional frame is safe for a CLI that never enabled DECSET 2004 because tmux does the gating (measured against a live pane: markers stripped for a `cat -v` pane, forwarded intact to a process that had emitted `?2004h`). ⚠️ The frame must never take the mux fallback: `TmuxManager.sendInput()` strips every `\r` and `\n`, which welds the lines together and submits them. ⚠️ The size guard sits on the `MAX_INPUT_LENGTH` boundary (64 KiB of UTF-16 code units): `ws-routes.ts` drops a longer frame WITHOUT an ACK, which would wedge the durable queue, so `_composerMaxLength` is derived from that limit minus both markers and an oversized prompt stays a draft with a toast. ⚠️ `.prompt-composer-overlay` is a `.paste-overlay` with a gutter of its own (a `padding` shorthand whose bottom is 12px plus the safe area), and the unconditional `.paste-overlay` fold rule at the end of styles.css is a later longhand at the same specificity, so it ERASED that gutter (measured at 393x852: `padding-bottom: 0px` flat, and the hinge strip REPLACING the gutter with the fold variables set): the composer has its own restatement after the fold rules, the dialog's `max-height` subtracts `--fold-block-end`, and `test/foldable-layout.test.ts` lists the composer in `ELEMENTS` by hand, because its derived overlay list keys on rules that declare `position: fixed; inset: 0` themselves. Tests: `test/mobile-prompt-composer.test.ts` (in the CI gate, deliberately not under `test/mobile/**`).
+
 **Dismissing the on-screen keyboard** (PRs #279/#280, `terminal-ui.js`): the terminal parks focus on a hidden textarea that nothing used to release, so TWO gestures now blur it, and they own different regions. **(1)** `_installMobileKeyboardDismiss()` — a document-level `touchend` that fires only while the terminal input actually holds focus, **never inside `#terminalContainer`** (tap classification owns that) and **never on a control** (`MOBILE_KEYBOARD_DISMISS_EXEMPT_SELECTOR`, matched with `closest()` so an icon inside a button counts). Session tabs are covered by the selector's `[tabindex]:not([tabindex="-1"])` arm, which is what stops a tab tap from blurring and then being re-focused by `selectSession()`. **(2)** In `_handleMobileTerminalTap`, a second tap on **inert `content`** (`startedWithTerminalFocus`) blurs instead of re-focusing. ⚠️ Scoped to `content` on purpose: the prompt row (`input`) keeps focus-then-position so a second tap still places the caret, and actionable rows blur earlier via `_isActionableMobileTerminalTap`. ⚠️ **A scroll ends in `touchend` too** — dismissing there closes the keyboard and drops the composer mid-read, so travel is tracked from `touchstart` and multi-touch is never a tap. Both classifiers MUST share one threshold: `initTerminal`'s `TAP_THRESHOLD` reads `MOBILE_KEYBOARD_DISMISS_TAP_SLOP`, since a gesture the terminal calls a scroll and the dismiss handler calls a tap is exactly that bug. ⚠️ **The gate excludes `test/mobile/**`, so CI cannot see the only test covering (1)** — run `npm run test:mobile -- test/mobile/keyboard.test.ts` by hand and diff the FAIL list against master. (Not `npm test --`: the gate's config excludes that path, so a file filter pointing into it matches nothing and exits green having run zero tests.) That blind spot is why merging the two PRs, which conflicted semantically but not textually, produced a red suite with two green CI checks.
 
 **Phone toolbar: Enter replaces Shell** (post-1.8.0): inside `@media (max-width: 599px)` `btn-shell` is `display:none` and `btn-enter` takes its slot (`order: 4`); starting a shell moved into the Run dropdown (`Terminal / Shell` → `setRunMode('shell')` → `run()` → `runShell()`, button label "Run SH"). `runMode` is `z.string().max(20)` server-side, so new modes need no schema change. Desktop and tablet keep the green Run Shell button unchanged.