Refill composer when cancelling before the agent starts

[MattPua]

What

• When a turn is cancelled before the agent has produced any output, the just-sent message is refilled into the composer so a quick "oops" doesn't lose it.
• The message stays in conversation history — it's already committed to the agent's context and the persisted log, so removing it would desync the UI from what the model actually sees.
• Refill is skipped once the agent has started working, and when you're not focused on that chat.
• Attachments/mentions are restored as chips (via xmlToContent).

How

• New core method SessionService.hasAgentStartedCurrentTurn(taskId) owns the decision:
  • returns false while the prompt is still optimistic (echo not landed → no output possible → refill safe),
  • otherwise checks for agent output after the latest session/prompt, reusing the existing classifyTurnEventKind.
• Works for both local and cloud (reads store data both populate; avoids the local-only liveTurnContent).
• useSessionCallbacks just captures the serialized text and applies the queued-wins / focus gating.

Test plan

• Instant cancel (Stop and Escape) before output → message refilled + stays in history
• Cancel after agent emits text/tool call → no refill
• Queued message present → queued restore wins
• Steer send → no refill
• Cancel while viewing a different task → that composer untouched
• Local and cloud behave the same

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Created with PostHog Code

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 85e1a5d.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "feat(sessions): refill composer when can..." | Re-trigger Greptile}

[greptile-apps]

lastSentTextRef populated before sendPrompt resolves

lastSentTextRef.current is assigned before the await, so it is set even when sendPrompt ultimately rejects (e.g., network error). On a brand-new task with no previous events, hasAgentStartedCurrentTurn returns false, so a subsequent cancel would refill the failed-send's text. For existing sessions the refill is suppressed because the backwards-scan sees a prior agent event and returns true, which limits the blast radius. The current behaviour is arguably fine (user gets back what they tried to send), but it is worth confirming this is intentional rather than accidental — moving the assignment to after the await and inside the try block would make the intent explicit.