fix(history): treat mid-turn absorption as delivery, not withdrawal

[Antisophy]

Recent Claude CLIs absorb queued messages into the running turn at a tool boundary instead of holding them for the next one. The queue entry is removed after delivery, and the delivery itself is recorded as a queued_command attachment rather than as a user line: the CLI's own absorption path removes the entry only once it has been folded into the running request, and marks each folded command's lifecycle as started. The queue-primary pipeline read every remove as "removed without being consumed", so absorbed messages were badged "not delivered" while the model demonstrably received them, and the delivery record was invisible because attachment lines were never translated.

This PR translates queued_command attachments into user messages and pairs each one strictly with a remove. The pair's records land in either order, so an attachment against a still-queued entry is held until the entry's fate is known: a remove completes the absorption and releases it; a dequeue discards it, since in that flow the echo carries the message and recent CLIs write the attachment as presentation only; one matching nothing renders nothing. An entry removed with no delivery record keeps the not-delivered outcome, so a genuine queue clear still reports honestly.

The delivery record becomes the visible message, so it anchors checkpoints like any user line, and undo truncation takes its queue records with it, matched by the text they carry because the enqueue is not adjacent to the delivery (the turn's own output sits between them). An absorbed delivery carries no file checkpoint, as there is no user record for the CLI to checkpoint at, so its boundary offers conversation-only undo instead of a file revert the CLI would reject with "not a user message in this session".

Covered by a replay unit test exercising both pairing orders, the dequeue-flow attachment, and an undelivered queue clear, plus reducer tests for the provisional handover. Full check set run; a handful of contention flakes passed on serial retry.

(Rebased onto 50cd0f9; the previously stacked undo fix is superseded by it and dropped.)

Update: real-world replay surfaced two hardening requirements now folded in. Queue records are matched resiliently rather than by content text alone (the CLI omits content for array-valued messages and texts can repeat): exact match, then empty-to-empty, and a remove finally settles the oldest unsettled entry. Echo pairing likewise prefers the awaiting entry whose text the echo carries, and a joined echo (several entries drained under one dequeue record, an older CLI behavior still present in long-lived sessions) settles every queued entry whose text appears in it. Without these, one stranded entry shifts every later pairing behind by one, and each turn opener renders twice after reload. The replay unit test covers the array-message flow and the pairing after it.