[chengyongru]

Summary

Fix the WebUI activity timer so live Working for ... duration is measured from the user turn start instead of the first activity row.

Root cause

The activity cluster only received reasoning/tool trace messages, so live duration started at the first trace createdAt. Transcript replay also regenerated message timestamps from the refresh time, which could reset activity timing after a reload.

Changes

• Carry the user turn start timestamp through activity timeline units.
• Use the turn start timestamp for live activity duration while preserving completed latencyMs replay behavior.
• Persist created_at_ms in WebUI transcript rows and replay it as UI createdAt.
• Add regression coverage for live timing and persisted replay timestamps.

Validation

• npm run test -- src/tests/thread-messages.test.tsx src/tests/agent-activity-cluster.test.tsx
• uv run --extra dev pytest tests\utils\test_webui_transcript.py tests\channels\test_websocket_channel.py::test_webui_message_envelope_marks_inbound_metadata tests\channels\test_websocket_channel.py::test_webui_message_envelope_appends_user_transcript -q
• npm run build
• uv run ruff check nanobot\webui\transcript.py tests\utils\test_webui_transcript.py tests\channels\test_websocket_channel.py
• Real gateway + Playwright check: seeded a pending activity turn and verified the page showed Working for 3m 50s, not Working for 10s.