Thanks for picking this up — the shape is right and the diff is small. Three things I'd want fixed before merging, plus a couple of small notes.

1. Doesn't match the issue spec — current input silently disappears (blocker)

#1438 says: "if message has been stashed, exchange stash and input". The PR doesn't exchange — when the input is non-empty and the stash already has content, the current input is dropped and replaced by the stash:

} else {  // input.length > 0
  if (stashRef.current) {
    setInput(stashRef.current);   // current input is lost
    stashRef.current = "";
    ...

This is the deviation noted in your PR description ("current input is replaced by the stash"). It means an accidental Alt+S in the middle of a half-typed message destroys the message without any recovery path. The point of a stash register is that one extra Alt+S brings it back. Please make it a true swap:

const recalled = stashRef.current;
stashRef.current = input;
setInput(recalled);

2. No gating — fires under modals and while busy

The handler is placed above if (busy) return; and above the whole !pendingShell && !pendingPath && !pendingSessionsPicker && !pendingCheckpointPicker && !pendingMcpHub && !walkthroughActive && !pendingChoice && !pendingReviseEditor && !pendingEditReview && !stagedInput && !pendingRevision guard set that every other composer-targeting shortcut in this file uses. Consequences:

• Pressing Alt+S during a running turn mutates composer state the user can't see, and pushes a "Stashed" / "Recalled" row into the log out of nowhere.
• Same thing under shell/path confirms, session picker, walkthrough, edit-review, etc.

Copy the same guard block that Ctrl+O and the Space-toggle-undo blocks above it use.

3. composer.hintStash is a dead i18n key

hintStash: "stash" / "暂存" is declared in EN, zh-CN, and types.ts, but never rendered anywhere — no composer hint bar references it. Either wire it into the bottom hint strip alongside hintClear / hintHistory / hintAbort, or drop the key. As-is it'll confuse the next person grepping for unused strings.

Smaller notes

• key.input === "s" || key.input === "S" also catches Alt+Shift+S. Fine if intentional, but worth aligning with the rest of the shortcut handlers (which mostly stick to the lowercase form).
• The test only covers that the i18n keys are exposed. After fixing feat: Allow user to press tab and add aditional context when denying. #1 and feat: event-log kernel — durable Event sidecar + replay-capable consumer #2, it'd be worth one behaviour test for the full state machine: empty + no stash → "Nothing to stash"; non-empty + no stash → input cleared + stash set; non-empty + existing stash → swap; gated off when busy or a modal is up.
• The two if (stashRef.current) { setInput(...); stashRef.current = ""; pushInfo(stashRecall) } branches in the original layout collapse into one once feat: Allow user to press tab and add aditional context when denying. #1 is in.

Leaving this open — push a fixup and I'll take another look.

done

Thanks — fixup looks right, swap + gating + dead key all addressed. Merging.