fix: preserve stage Airflow failures

packages/hflow-server/src/hflow_server/_graph.py

@@ -64,6 +64,7 @@
 from hflow_server._runtime import (
     ResolvedRuntime,
     RuntimeResolver,
+    RuntimeSource,
     airflow_failure_refusal,
     optional_string,
     resolved_runtime_or_refuse,
@@ -449,11 +450,13 @@ def create_graph_router(pipeline_state: PipelineState, resolver: RuntimeResolver
     router = APIRouter(prefix="/api/v1")
 
     def stage_task_instances(
-        client: AirflowClient, dag_id: str, dag_run_id: str
+        client: AirflowClient, dag_id: str, dag_run_id: str, *, source: RuntimeSource
     ) -> list[dict[str, Any]]:
         try:
             return client.task_instances(dag_id, dag_run_id)
-        except AirflowClientError:
+        except AirflowClientError as error:
+            if error.status != 404:
+                raise airflow_failure_refusal(error, source=source) from error
             # A stage sub-DAG that vanished (or a run Airflow expired) leaves
             # that lane without task detail; the master's own state -- the
             # page's point -- is already in hand, so this is a thinner
@@ -523,7 +526,9 @@ def read_run_graph(dag_run_id: str) -> RunGraphResponse:
                 stage_runs = runtime.client.dag_runs(
                     stage_dag_id, limit=_STAGE_RUN_SEARCH_LIMIT, order_by="-id"
                 )
-            except AirflowClientError:
+            except AirflowClientError as error:
+                if error.status != 404:
+                    raise airflow_failure_refusal(error, source=runtime.source) from error
                 # An unregistered stage sub-DAG (a partial profile, or a
                 # bundle mid-render) is a stage that never ran here.
                 stage_runs = []
@@ -534,7 +539,9 @@ def read_run_graph(dag_run_id: str) -> RunGraphResponse:
             stage_run_id = optional_string(matched.run.get("dag_run_id"))
             stage_tasks = (
                 _sorted_task_instances(
-                    stage_task_instances(runtime.client, stage_dag_id, stage_run_id),
+                    stage_task_instances(
+                        runtime.client, stage_dag_id, stage_run_id, source=runtime.source
+                    ),
                     stage_topology.dag,
                 )
                 if stage_run_id is not None

packages/hflow-server/src/hflow_server/_runtime.py

@@ -396,7 +396,9 @@ def list_runtime_runs(
                     recent_runs = runtime.client.dag_runs(
                         stage_dag_id, limit=_RECENT_STAGE_RUN_LIMIT, order_by="-id"
                     )
-                except AirflowClientError:
+                except AirflowClientError as error:
+                    if error.status != 404:
+                        raise airflow_failure_refusal(error, source=runtime.source) from error
                     # A stage sub-DAG that has not registered (or errored) is
                     # an empty strip, not a failed page.
                     recent_runs = []

packages/hflow-server/tests/test_server_run_graph.py

@@ -433,6 +433,72 @@ def stage_runs_404(
     assert all(stage["dag_run_id"] is None for stage in payload["stages"])
 
 
+def test_run_graph_maps_stage_dag_listing_failures_to_502(
+    bundle_api: TestClient, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    _stubbed_airflow(
+        monkeypatch,
+        master_run={
+            "dag_run_id": MASTER_RUN_ID,
+            "state": "success",
+            "start_date": MASTER_STARTED_AT,
+        },
+        stage_runs={},
+        task_instances={(MASTER_DAG_ID, MASTER_RUN_ID): []},
+    )
+
+    def failing_stage_runs(
+        self: AirflowClient, dag_id: str, *, limit: int = 100, order_by: str | None = None
+    ) -> list[dict[str, Any]]:
+        if dag_id != MASTER_DAG_ID:
+            raise AirflowClientError(
+                "GET /dagRuns failed with HTTP 503: scheduler down", status=503
+            )
+        return []
+
+    monkeypatch.setattr(AirflowClient, "dag_runs", failing_stage_runs)
+    response = bundle_api.get(f"/api/v1/runtime/runs/{MASTER_RUN_ID}/graph")
+    assert response.status_code == 502
+    assert "scheduler down" in response.json()["detail"]
+
+
+def test_run_graph_maps_stage_task_listing_failures_to_502(
+    bundle_api: TestClient, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    _stubbed_airflow(
+        monkeypatch,
+        master_run={
+            "dag_run_id": MASTER_RUN_ID,
+            "state": "success",
+            "start_date": MASTER_STARTED_AT,
+        },
+        stage_runs={
+            "demo_pipeline_sync": [
+                {
+                    "dag_run_id": "sync__run",
+                    "state": "success",
+                    "start_date": "2026-08-21T10:00:05+00:00",
+                }
+            ]
+        },
+        task_instances={(MASTER_DAG_ID, MASTER_RUN_ID): []},
+    )
+
+    def failing_task_instances(
+        self: AirflowClient, dag_id: str, dag_run_id: str
+    ) -> list[dict[str, Any]]:
+        if dag_id != MASTER_DAG_ID:
+            raise AirflowClientError(
+                "GET /taskInstances failed with HTTP 401: unauthorized", status=401
+            )
+        return []
+
+    monkeypatch.setattr(AirflowClient, "task_instances", failing_task_instances)
+    response = bundle_api.get(f"/api/v1/runtime/runs/{MASTER_RUN_ID}/graph")
+    assert response.status_code == 502
+    assert "unauthorized" in response.json()["detail"]
+
+
 def test_run_graph_unknown_run_is_a_404(
     bundle_api: TestClient, monkeypatch: pytest.MonkeyPatch
 ) -> None:

packages/hflow-server/tests/test_server_runtime.py

@@ -275,6 +275,22 @@ def fake_dag_runs(
     assert all(stage["recent"] == [] for stage in payload["stages"])
 
 
+def test_runs_maps_stage_dag_listing_failures_to_502(
+    bundle_api: TestClient, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    def failing_dag_runs(
+        self: AirflowClient, dag_id: str, *, limit: int = 100, order_by: str | None = None
+    ) -> list[dict[str, Any]]:
+        if dag_id == "demo_pipeline_ingest":
+            return []
+        raise AirflowClientError("GET /dagRuns failed with HTTP 429: rate limited", status=429)
+
+    monkeypatch.setattr(AirflowClient, "dag_runs", failing_dag_runs)
+    response = bundle_api.get("/api/v1/runtime/runs")
+    assert response.status_code == 502
+    assert "rate limited" in response.json()["detail"]
+
+
 def test_runs_without_a_runtime_is_a_clear_409(
     runtime_free_cwd: Path, tmp_path: Path, unbuilt_assets_dir: Path
 ) -> None: