fix(thread-startup): recover creation after reconnect

[chuks-qua]

What

• Count queued push bytes separately from RPC replies, so a large creation reply does not evict its own WebSocket.
• Replay agent.createAndSend with the original startup ID after reconnect. The server binds that ID to one task and rejects a changed request.
• Reconcile the preparing UI with the durable task, retain the submitted draft on a real failure, and add a repeatable lost-response worktree journey.

Why

Production logs showed the push guard closing sockets with 18–35 MiB buffered during task creation. A lost reply then made the UI report failure; Retry could start a second task with a fresh startup ID.

Evidence

• A controlled Electron run suppressed the first creation reply and closed the app socket. Before this patch, the UI briefly showed Failed to create thread and retained a separate Draft. After the patch, the app sent two RPCs on different sockets with the same startup ID, showed no false failure or extra Draft, and displayed one task and its fixture answer after reload.
• The public runtime worktree-setup --confirm-cleanup journey verified one startup, task, managed worktree, queued first turn, and persisted prompt after a lost reply. It cancelled Setup before any provider call and cleaned the owned fixture.
• The seven-task fixture completed 7/7 turns and delivered 3,458 ordered events without gaps or duplicates. This is a functional workload check, not a performance comparison.

UI Changes

The screenshots use only the repository fixture project. The first shows the extra Draft in the controlled pre-fix run. The second shows one task and its answer after reconnect and reload.

Review Notes

• Migration 0064 adds a nullable request fingerprint to startup records. Existing records remain readable.
• A process crash in the narrow managed-worktree interval between task insertion and startup binding can still leave an unbound task; the client asks for workspace inspection instead of silently creating another.
• Focused checks passed: 187 web tests, 77 server tests, 10 verification-script tests, both typechecks, targeted lint, and diff checks. No configuration change.