server: mirrored-pane typing is not cancelled by a detach or reattach before its queue drains #546

What

On a Windows mirror (terminalAttachKnown === false, or the first input before it is known), typed text goes through the mirror branch of the input handler in server/index.ts: it waits its turn in serialize(...), shapes the text with mirrorInput, checks that the connection still exists and authorizeSocket, then calls paneSendText. It never captures or re-checks the sender's attachment claim or membership, which the pty branch and the keys handler do since #508.

So on a mirrored pane: queue text behind another operation, detach the pane and switch, or detach and reattach, before the queue drains. The text still reaches the pane it was typed into.

Where

server/index.ts, case "input", the branch guarded by terminalAttachKnown === false || (!attachment && terminalAttachKnown === null).

Possible fix

Capture client.data.attached.get(pane_id) and the attachment before the queue, and apply the same claim, attachment identity and sender-membership checks inside the queued step, after the asynchronous shaping. The contract test can simulate the mirror on Linux as server/submit.contract.test.ts does.

Found by

Codex gpt-6.1-sol adversarial review of #508 at 471db0c (Medium). Pre-existing branch; #508 did not touch it.