story-kit: start 160_story_constrain_thinking_trace_height_in_agent_stream_ui

.story_kit/work/2_current/160_story_constrain_thinking_trace_height_in_agent_stream_ui.md

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+---
+name: "Constrain thinking trace height in agent stream UI"
+---
+
+# Story 160: Constrain thinking trace height in agent stream UI
+
+## User Story
+
+As a user watching agent output in the web UI, I want thinking traces to be contained in a fixed-height scrolling viewport, so that I get a sense of thinking activity without excessive vertical noise.
+
+## Acceptance Criteria
+
+- [ ] Thinking tokens are visually distinct from regular text output in the streaming view
+- [ ] Thinking block has a fixed max-height (~80-100px) with overflow scrolling
+- [ ] Thinking block auto-scrolls to bottom as new tokens arrive (scrolls up in place)
+- [ ] Regular text output renders normally outside the thinking container
+- [ ] When thinking stops and text starts, the thinking block remains visible but stops growing
+
+## Out of Scope
+
+- TBD