fix(mobile): keep the keyboard up when an accessory key is pressed

An accessory key that acts on the terminal (arrows, Tab, Esc, Ctrl, scroll, clear input) took focus on press, so every tap blurred the terminal and the click handler had to focus it again: a blur/focus pair per tap that started a keyboard dismissal and shifted the toolbar each time. Such a key now cancels the mousedown default instead, the same pattern as the Attach input, so the terminal never loses focus on the press; the click-time refocus stays as the fallback. A first tap on clear/compact only arms the confirm and is treated the same way.

docs/architecture-invariants.md

@@ -1068,6 +1068,8 @@ Tests: `test/mobile-prompt-composer.test.ts` (in the CI gate, deliberately not u
 
 ⚠️ **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.
 
+⚠️ **An accessory key that keeps the keyboard up must not take focus on the press.** The keys that act on the terminal and leave the keyboard open (`ACCESSORY_REFOCUS_ACTIONS` in keyboard-accessory.js: scroll, arrows, Tab, Shift+Tab, Ctrl, Esc, clear input and the rest) cancel the `mousedown` default, the same pattern as the Attach input, so the hidden textarea keeps focus through the press; the `terminal.focus()` in the click handler stays as the fallback. Letting the tap blur the terminal and refocusing it afterwards made every such key start a keyboard dismissal, a blur/focus pair per tap that shifted the toolbar each time. A first tap on clear/compact only arms the confirm and is treated the same; the confirming tap, and keys that open a dialog or dismiss the keyboard on purpose, keep the default. Pinned against the real module by `test/accessory-keeps-terminal-focus.test.ts`.
+
 ⚠️ **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.
 
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