fix(sessions): keep queued messages in queue when cancelling

[MattPua]

Problem

• Cancelling (Stop) an in-flight message dumps all queued messages back into the input box as combined text — they lose queued state.

Change

CleanShot.2026-06-16.at.11.59.48.2.mp4

• Stop now cancels only the in-flight turn; queued messages stay queued (still shown as cards, individually removable).
• New queuePaused flag on AgentSession, set by cancelPrompt, suppresses the auto-drain on the cancel-induced turn-end.
• Flag cleared on next user send, so kept messages resume after that turn.
• handleCancelPrompt no longer drains the queue into the editor.

Notes

• Resume is "on next send" — no new UI.
• Footer (N queued) hides after Stop (only shows while pending), but queued cards stay visible.

Testing

• shared / core / agent typecheck clean
• sessionServiceHost (116) + sessionStore (10) tests pass
• Biome lint clean

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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 a4556a4.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix(sessions): keep queued messages in q..." | Re-trigger Greptile}