Steer composed messages with modified Enter

[hamzamerzic]

Summary

• make Cmd/Ctrl+Enter queue the current draft durably and then steer exactly that confirmed row into a live turn
• fall back to ordinary submit when no steerable turn is active
• reuse the existing per-row steer state machine so racing turn completion leaves the message safely queued
• retain plain Enter and Shift+Enter behavior across desktop and touch-primary input

Provenance

Reviewed from production-local commit d74b6a5c and replayed cleanly onto current main 41a3809 without depending on the attachment-draft patch.

Validation

• focused shortcut, queue-race, and build-rail tests: 28 passed
• full reviewed UI stack: 1,765 frontend library tests and 47 hook tests passed
• production frontend build passed
• includes a Playwright regression for the durable queue-to-steer request sequence

[hamzamerzic]

Review follow-up: the stable send callback now dereferences the current per-row steer implementation after the queue acknowledgement instead of capturing a render-local closure. Modified-Enter also synchronously guards the full queue-to-steer operation, so repeated keydowns before the acknowledgement cannot enqueue twice; structural and delayed-ack browser regressions cover both properties. Focused tests: 28 passed. Clean combined UI stack: 1,768 library + 47 hook tests passed; production build passed.

[hamzamerzic]

Round 2 complete on exact head 1451383f15d274332d760f6bbac59d89df3fde02. Rechecked the queue acknowledgement boundary, stable callback dereference, repeated-keydown guard, attachment preservation, pending-question behavior, and fallback to ordinary queueing. No new finding. All hosted checks are green; recommendation: merge.

[hamzamerzic]

Landed on protected main through reviewed integration #147 (merge 226106c). The integrated patch matches this PR's reviewed head; closing the superseded source PR to keep the queue truthful.