feat: set DM_BASE_PATH so the viz-app serves under its Ingress sub-path

operator/handlers.py

@@ -178,13 +178,22 @@ def build_environment(
 
     DM_PROJECT_DIR is mandatory (the app exits without it); the remaining DM_*
     variables provide instance metadata.
+
+    When an instance id is known we also set DM_BASE_PATH to '/<instance-id>'.
+    The viz-app uses this to serve under the Ingress sub-path (its assets,
+    client-side routes and API calls are then resolved relative to the prefix);
+    without it the app would serve from '/' and render a blank page behind the
+    path-based Ingress. It is omitted when no instance id is available.
     """
-    return [
+    env: List[Dict[str, str]] = [
         {"name": "DM_PROJECT_DIR", "value": project_mount_path},
         {"name": "DM_PROJECT_ID", "value": str(project_id)},
         {"name": "DM_INSTANCE_ID", "value": str(instance_id)},
         {"name": "DM_INSTANCE_OWNER", "value": str(instance_owner)},
     ]
+    if instance_id:
+        env.append({"name": "DM_BASE_PATH", "value": f"/{instance_id}"})
+    return env
 
 
 def build_deployment_body(

tests/test_handlers.py

@@ -132,6 +132,27 @@ def test_build_environment_exposes_dm_metadata() -> None:
     assert by_name["DM_INSTANCE_OWNER"] == "dlister"
 
 
+def test_build_environment_sets_dm_base_path_from_instance_id() -> None:
+    # The viz-app serves under a sub-path when DM_BASE_PATH is set; the operator
+    # mirrors the instance id (prefixed with '/') so assets, client-side routes
+    # and API calls resolve under the Ingress prefix.
+    env = _example_environment()
+    by_name = {item["name"]: item["value"] for item in env}
+    assert by_name["DM_BASE_PATH"] == "/instance-111"
+
+
+def test_build_environment_omits_dm_base_path_when_instance_id_absent() -> None:
+    # Without an instance id there is no sub-path; the app then serves at '/'.
+    env = handlers.build_environment(
+        project_id="project-000",
+        instance_id="",
+        instance_owner="dlister",
+        project_mount_path=PROJECT_MOUNT_PATH,
+    )
+    by_name = {item["name"]: item["value"] for item in env}
+    assert "DM_BASE_PATH" not in by_name
+
+
 # --- service ----------------------------------------------------------------