fix(flows): don't bounce off a working flow on a partial load error

The flow detail query runs with errorPolicy:'all', so a failed sibling field
(the flow's log lists are separate, nullable root query fields — terminalLogs,
messageLogs, etc.) surfaces an Apollo error while `flow` itself resolves fine.
Both the redirect effect and the provider's load-error toast keyed off "any
error present", so one flaky log resolver would kick the user back to /flows
and toast "Failed to load flow" over a flow that had actually loaded.

Gate both on the flow genuinely being absent (`!flowData?.flow`) instead of on
the presence of an error. A missing/invalid flow still redirects and toasts
(its non-null `flow` field propagates to a null result); a partial failure now
renders the flow and lets the affected panel show its own empty state.

Reachability confirmed from the schema (sibling log fields are `[X!]`, nullable;
`flow` is `Flow!`, non-null) — end-to-end confirmation folded into the P2-S5
live run. 996 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/pages/flows/flow.tsx

@@ -79,7 +79,7 @@ function Flow() {
     const { isDesktop, isMobile } = useBreakpoint();
     const navigate = useNavigate();
 
-    const { flowData, flowError, flowId, isLoading: isFlowLoading } = useFlow();
+    const { flowData, flowId, isLoading: isFlowLoading } = useFlow();
     const { deleteFlow, finishFlow } = useFlows();
     const { isFavoriteFlow, toggleFavoriteFlow } = useFavorites();
 
@@ -108,10 +108,13 @@ function Flow() {
     const [renameFlowMutation, { loading: isRenameLoading }] = useMutation(RenameFlowDocument);
 
     useEffect(() => {
-        if (flowError || (!isFlowLoading && !flowData?.flow)) {
+        // errorPolicy:'all' surfaces a partial error while the flow itself
+        // loaded; leave only when the flow is genuinely absent, not on any error
+        // — else a failed sibling log query bounces the user off a working flow.
+        if (!isFlowLoading && !flowData?.flow) {
             navigate(routes.flows, { replace: true });
         }
-    }, [flowError, flowData, isFlowLoading, navigate]);
+    }, [flowData, isFlowLoading, navigate]);
 
     const handleFlowRenameSave = useCallback(async () => {
         const newTitle = editingInputRef.current?.value.trim();

frontend/src/providers/flow-provider.tsx

@@ -170,12 +170,11 @@ export function FlowProvider({ children }: FlowProviderProps) {
 
     const flowStatus = useMemo(() => flowData?.flow?.status, [flowData?.flow?.status]);
 
-    // A single Postgres "no rows in result set" surfaces here every time a sibling
-    // query/subscription retries against an invalid flow id; without a stable
-    // toast id Sonner would stack 8 copies of the same message before the page
-    // redirects. Surface a friendly message and drop the raw SQL detail entirely.
+    // errorPolicy:'all' surfaces a partial error while the flow loaded, so gate
+    // on `!flow` or a partial failure toasts over a flow that rendered fine. The
+    // stable id keeps the invalid-id "no rows" retries from stacking.
     useEffect(() => {
-        if (flowError) {
+        if (flowError && !flowData?.flow) {
             const raw = flowError.message ?? '';
             const isNotFound = /no rows in result set|not found/i.test(raw);
             toast.error(isNotFound ? 'Flow not found' : 'Failed to load flow', {
@@ -184,7 +183,7 @@ export function FlowProvider({ children }: FlowProviderProps) {
             });
             Log.error('Error loading flow:', flowError);
         }
-    }, [flowError]);
+    }, [flowError, flowData]);
 
     const submitAutomationMessage = useCallback(
         async (values: FlowFormValues) => {