Report how long a run has been going, not just how long it took

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UytviPMJbXzD8P84nLvXcq

backend/tests/api/routes/test_observability.py

@@ -266,6 +266,21 @@ def test_runs_narrow_to_one_minute(
     assert [run["id"] for run in runs["data"]] == ["minute-in"]
 
 
+def test_a_running_cascade_reports_how_long_it_has_been_going(
+    client: TestClient, superuser_token_headers: dict[str, str], db: Session
+) -> None:
+    """The collector writes a duration at the end; until then, time since."""
+    started = datetime.now(UTC) - timedelta(seconds=30)
+    db.add(FlowRun(id="in-flight", flow=FLOW, started_at=started, status="running"))
+    db.commit()
+
+    runs = client.get(
+        f"{PREFIX}/runs", headers=superuser_token_headers, params={"status": "running"}
+    ).json()
+
+    assert runs["data"][0]["duration_ms"] >= 30_000
+
+
 def test_events_narrow_to_one_minute(
     client: TestClient, superuser_token_headers: dict[str, str], db: Session
 ) -> None:

backend/tests/api/routes/test_runs.py

@@ -5,7 +5,7 @@ The pipeline half — what a hit restores and what a key is made of — is in
 """
 
 import json
-from datetime import UTC, datetime
+from datetime import UTC, datetime, timedelta
 
 import pytest
 from sqlmodel import Session, col, select
@@ -286,6 +286,31 @@ def test_the_overview_counts_a_flow_the_list_page_would_not_reach(
     assert (row["runs"], row["running"], row["queued"]) == (3, 1, 0)
 
 
+def test_a_running_run_reports_how_long_it_has_been_going(
+    client, superuser_token_headers
+):
+    """A duration is only written at the end; until then, time since it began."""
+    with Session(db_engine) as session:
+        session.add(
+            Run(
+                id="in-flight",
+                flow="timed",
+                status="running",
+                created_at=datetime.now(UTC),
+                started_at=datetime.now(UTC) - timedelta(seconds=30),
+            )
+        )
+        session.commit()
+
+    rows = client.get(
+        f"{settings.API_V1_STR}/runs",
+        headers=superuser_token_headers,
+        params={"flow": "timed"},
+    ).json()
+
+    assert rows[0]["duration_ms"] >= 30_000
+
+
 def test_overview_is_not_read_as_a_run_id(client, superuser_token_headers):
     """`/overview` is declared before `/{run_id}`, which would swallow it."""
     answer = client.get(