fix(webui): correct activity timer duration (#4649)

tests/utils/test_webui_transcript.py

@@ -25,6 +25,17 @@ def test_append_and_read_roundtrip(tmp_path, monkeypatch) -> None:
     assert lines[0]["text"] == "hello"
 
 
+def test_append_stamps_created_at_ms(tmp_path, monkeypatch) -> None:
+    monkeypatch.setattr("nanobot.config.paths.get_data_dir", lambda: tmp_path)
+    monkeypatch.setattr("nanobot.webui.transcript.time.time", lambda: 1_700_000_000.0)
+    key = "websocket:t-created-at"
+
+    append_transcript_object(key, {"event": "user", "chat_id": "t-created-at", "text": "hello"})
+
+    lines = read_transcript_lines(key)
+    assert lines[0]["created_at_ms"] == 1_700_000_000_000
+
+
 def _force_small_transcript_budget(monkeypatch, *, limit: int = 520, target: int = 260) -> None:
     monkeypatch.setattr("nanobot.webui.transcript._MAX_TRANSCRIPT_FILE_BYTES", limit)
     monkeypatch.setattr("nanobot.webui.transcript._TARGET_ACTIVE_TRANSCRIPT_BYTES", target)
@@ -291,6 +302,31 @@ def test_replay_delta_and_turn_end(tmp_path, monkeypatch) -> None:
     assert msgs[1]["latencyMs"] == 42
 
 
+def test_replay_uses_persisted_created_at_ms() -> None:
+    msgs = replay_transcript_to_ui_messages(
+        [
+            {
+                "event": "user",
+                "chat_id": "t-created-at",
+                "text": "q",
+                "created_at_ms": 1_700_000_000_000,
+            },
+            {
+                "event": "message",
+                "chat_id": "t-created-at",
+                "kind": "tool_hint",
+                "text": "exec()",
+                "created_at_ms": 1_700_000_230_000,
+            },
+        ],
+    )
+
+    assert [message["createdAt"] for message in msgs] == [
+        1_700_000_000_000,
+        1_700_000_230_000,
+    ]
+
+
 def test_thread_response_does_not_mark_completed_message_tool_tail_pending(
     tmp_path,
     monkeypatch,