Act on a run, and read Home top-down

Runs: a run can now be deleted (DELETE /runs/{id}, cancelling a live one
first), exported as csv from the screen's own filters, and its flow label
opens the flow. Its "Parameters" panel became "Inputs" and lists every
input the flow declares, marking the ones that took the flow's own value
rather than the run's — the comparison table resolves the same defaults
instead of printing "unset".

Home reads brain, dashboards, health, flows: the mosaic is one full-width
scrolling strip, and the flows list and the flow-activity rollups merged
into a single left-joined table so a flow's state and its numbers sit on
one row.

Charts take a drag to narrow the x window and a double click or tap to
come back out. UplotChart holds the scale and passes resetScales:false
while a window is held, which is what the old comment said made this
impossible.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019LrWVRguqbk33YzfEeUx5W

backend/tests/api/routes/test_runs.py

@@ -432,6 +432,99 @@ def test_overview_is_not_read_as_a_run_id(client, superuser_token_headers):
     assert isinstance(answer.json(), list)
 
 
+# -----------------------------------------------------------------------------
+# Deleting a run
+#
+# The route owns the four statements; what these guard is that it takes the
+# children with it and refuses a run the driver is still writing to.
+# -----------------------------------------------------------------------------
+
+
+@pytest.fixture
+def deletable_run():
+    """One finished run with a node, a number and an artifact row hanging off it."""
+    run_id = "del-1"
+    with Session(db_engine) as session:
+        session.add(
+            Run(id=run_id, flow="deleted", status="ok", created_at=datetime.now(UTC))
+        )
+        session.add(RunNode(run_id=run_id, node="deleted.a", status="ok"))
+        session.add(RunMetric(run_id=run_id, name="deleted.loss", step=0, value=1.0))
+        session.add(
+            RunArtifact(
+                run_id=run_id,
+                name="deleted.out",
+                filename="out.bin",
+                node="a",
+                digest="d" * 64,
+                size=7,
+            )
+        )
+        session.commit()
+    yield run_id
+    with Session(db_engine) as session:
+        run = session.get(Run, run_id)
+        if run is not None:
+            session.delete(run)
+            session.commit()
+
+
+def test_deleting_a_run_takes_its_children_with_it(
+    client, superuser_token_headers, deletable_run
+):
+    """No foreign key cascades here, so the route has to do it itself."""
+    answer = client.delete(
+        f"{settings.API_V1_STR}/runs/{deletable_run}", headers=superuser_token_headers
+    )
+
+    assert answer.status_code == 204
+    with Session(db_engine) as session:
+        assert session.get(Run, deletable_run) is None
+        for table in (RunNode, RunMetric, RunArtifact):
+            left = session.exec(
+                select(table).where(col(table.run_id) == deletable_run)
+            ).all()
+            assert left == [], f"{table.__name__} rows outlived the run"
+
+
+def test_deleting_a_run_that_is_not_there_is_a_404(client, superuser_token_headers):
+    answer = client.delete(
+        f"{settings.API_V1_STR}/runs/nope-1", headers=superuser_token_headers
+    )
+
+    assert answer.status_code == 404
+
+
+def test_a_running_run_is_refused_rather_than_raced(client, superuser_token_headers):
+    """The driver writes its nodes back at the end; they would have no run."""
+    run_id = "del-live"
+    with Session(db_engine) as session:
+        session.add(
+            Run(
+                id=run_id,
+                flow="deleted",
+                status="running",
+                created_at=datetime.now(UTC),
+            )
+        )
+        session.commit()
+    try:
+        answer = client.delete(
+            f"{settings.API_V1_STR}/runs/{run_id}", headers=superuser_token_headers
+        )
+
+        assert answer.status_code == 409
+        assert "Cancel it" in answer.json()["detail"]
+        with Session(db_engine) as session:
+            assert session.get(Run, run_id) is not None
+    finally:
+        with Session(db_engine) as session:
+            run = session.get(Run, run_id)
+            if run is not None:
+                session.delete(run)
+                session.commit()
+
+
 # -----------------------------------------------------------------------------
 # A cached node's curve
 #