story-kit: start 155_story_queue_messages_while_agent_is_busy

.story_kit/work/2_current/155_story_queue_messages_while_agent_is_busy.md

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+---
+name: "Queue messages while agent is busy"
+---
+
+# Story 155: Queue messages while agent is busy
+
+## User Story
+
+As a user, I want to type and submit messages while an agent is busy, so that they queue up and send automatically when the agent is ready — like Claude Code CLI does.
+
+## Acceptance Criteria
+
+- [ ] When loading is true, user can still submit a message via Enter or the send button
+- [ ] Submitted message is shown in the input area as 'queued' with visual indication (e.g. muted styling, label)
+- [ ] User can edit or cancel the queued message before it sends
+- [ ] When the agent response completes (loading becomes false), the queued message auto-submits
+- [ ] Only one message can be queued at a time — subsequent submissions replace the queued message
+- [ ] If the user cancels the current generation, the queued message does not auto-submit
+
+## Out of Scope
+
+- TBD