diff --git a/src/Web/autopilot-monitor-web/app/analyze-rules/page.tsx b/src/Web/autopilot-monitor-web/app/analyze-rules/page.tsx
index 150ca481..8d010215 100644
--- a/src/Web/autopilot-monitor-web/app/analyze-rules/page.tsx
+++ b/src/Web/autopilot-monitor-web/app/analyze-rules/page.tsx
@@ -42,12 +42,10 @@ export default function AnalyzeRulesPage() {
 
   const { data: rules, loading, execute: fetchRulesExec, setData: setRules } = useAuthenticatedFetch<AnalyzeRule[]>({
     onError: (err) => showError(err.message),
-    onTokenExpired: (err) => showError(err.message),
   });
 
   const { execute: mutate } = useAuthenticatedFetch({
     onError: (err) => showError(err.message),
-    onTokenExpired: (err) => showError(err.message),
   });
 
   // Filter state
diff --git a/src/Web/autopilot-monitor-web/app/apps/components/InstallsTab.tsx b/src/Web/autopilot-monitor-web/app/apps/components/InstallsTab.tsx
index 13fc25a4..9ef6cabf 100644
--- a/src/Web/autopilot-monitor-web/app/apps/components/InstallsTab.tsx
+++ b/src/Web/autopilot-monitor-web/app/apps/components/InstallsTab.tsx
@@ -7,8 +7,7 @@ import { useTenant } from "../../../contexts/TenantContext";
 import { useAuth } from "../../../contexts/AuthContext";
 import { useNotifications } from "../../../contexts/NotificationContext";
 import { scopedApi } from "@/lib/scopedApi";
-import { authenticatedFetch, TokenExpiredError } from "@/lib/authenticatedFetch";
-import { apiErrorFromResponse, describeApiError } from "@/lib/scopedFetch";
+import { fetchJson } from "@/lib/apiClient";
 import { formatBytes, formatDuration } from "@/lib/formatting";
 import DoBreakdownBar from "@/components/DoBreakdownBar";
 import { CalculatingInline } from "@/components/CalculatingCard";
@@ -82,7 +81,7 @@ export default function InstallsTab({ scope, timeRange }: InstallsTabProps) {
   const router = useRouter();
   const { tenantId } = useTenant();
   const { getAccessToken } = useAuth();
-  const { addNotification } = useNotifications();
+  const { notifyError } = useNotifications();
   const { isGlobalAdmin, scopeInitialized, scopeKey } = scope;
 
   const [data, setData] = useState<AppsListResponse | null>(null);
@@ -110,32 +109,26 @@ export default function InstallsTab({ scope, timeRange }: InstallsTabProps) {
         const listUrl = scopedApi.appsList(scope, days);
         const metricsUrl = scopedApi.appMetrics(scope, days);
 
-        const [listRes, metricsRes] = await Promise.all([
-          authenticatedFetch(listUrl, getAccessToken, { signal: AbortSignal.timeout(APPS_FETCH_TIMEOUT_MS) }),
-          authenticatedFetch(metricsUrl, getAccessToken, { signal: AbortSignal.timeout(APPS_FETCH_TIMEOUT_MS) }),
+        // The list is the page; the DO rollup is decoration — its failure stays silent.
+        const [listRes, metricsRes] = await Promise.allSettled([
+          fetchJson<AppsListResponse>(listUrl, getAccessToken, { signal: AbortSignal.timeout(APPS_FETCH_TIMEOUT_MS) }),
+          fetchJson<AppMetricsResponse>(metricsUrl, getAccessToken, { signal: AbortSignal.timeout(APPS_FETCH_TIMEOUT_MS) }),
         ]);
 
         if (cancelled) return;
-        if (listRes.ok) {
-          setData((await listRes.json()) as AppsListResponse);
+        if (listRes.status === "fulfilled") {
+          setData(listRes.value);
           succeeded = true;
         } else {
-          // Error envelope: the backend's message plus the correlation id as a quotable reference.
-          const { message, reference } = describeApiError(await apiErrorFromResponse(listRes));
-          addNotification("error", "Backend Error", `Failed to load apps: ${message}`, "apps-list-error", undefined, reference ?? undefined);
+          notifyError("Backend Error", listRes.reason, "apps-list-error", "Failed to load apps.");
         }
-        if (metricsRes.ok) {
-          const m = (await metricsRes.json()) as AppMetricsResponse;
-          setDoRollup(m.deliveryOptimization ?? null);
+        if (metricsRes.status === "fulfilled") {
+          setDoRollup(metricsRes.value.deliveryOptimization ?? null);
         }
       } catch (err) {
         if (cancelled) return;
-        if (err instanceof TokenExpiredError) {
-          addNotification("error", "Session Expired", err.message, "session-expired-error");
-        } else {
-          console.error("Failed to fetch app installs", err);
-          addNotification("error", "Backend Not Reachable", "Unable to load app dashboard data.", "apps-list-error");
-        }
+        console.error("Failed to fetch app installs", err);
+        notifyError("Backend Not Reachable", err, "apps-list-error", "Unable to load app dashboard data.");
       } finally {
         progressFinish(succeeded);
         if (!cancelled) setLoading(false);
diff --git a/src/Web/autopilot-monitor-web/app/dashboard/hooks/useTenantSecurityConfig.ts b/src/Web/autopilot-monitor-web/app/dashboard/hooks/useTenantSecurityConfig.ts
index 78397b16..f21ef1c9 100644
--- a/src/Web/autopilot-monitor-web/app/dashboard/hooks/useTenantSecurityConfig.ts
+++ b/src/Web/autopilot-monitor-web/app/dashboard/hooks/useTenantSecurityConfig.ts
@@ -3,17 +3,11 @@
 import { useEffect, useState } from "react";
 import { api } from "@/lib/api";
 import { TokenExpiredError } from "@/lib/authenticatedFetch";
-import { dedupedAuthFetch } from "@/lib/dedupedAuthFetch";
-import type { NotificationType } from "@/contexts/NotificationContext";
+import { dedupedFetchJson } from "@/lib/dedupedAuthFetch";
 import { missingContactProfileParts } from "@/lib/edition";
 
-type AddNotification = (
-  type: NotificationType,
-  title: string,
-  message: string,
-  key?: string,
-  href?: string,
-) => void;
+/** NotificationContext.notifyError, injected so the hook stays free of the provider. */
+type NotifyError = (title: string, err: unknown, key?: string, fallback?: string) => void;
 
 /** The subset of the feature-flags response the dashboard banners read. */
 export interface TenantConfigurationSummary {
@@ -79,7 +73,7 @@ export function useTenantSecurityConfig(
   tenantId: string | null | undefined,
   user: User | null | undefined,
   getAccessToken: (forceRefresh?: boolean) => Promise<string | null>,
-  addNotification: AddNotification,
+  notifyError: NotifyError,
 ): TenantSecuritySummary {
   const [summary, setSummary] = useState<TenantSecuritySummary>(EMPTY_SUMMARY);
 
@@ -95,19 +89,12 @@ export function useTenantSecurityConfig(
       if (!user.isTenantAdmin && !user.isGlobalAdmin && user.role == null) return;
 
       try {
-        const response = await dedupedAuthFetch(api.config.featureFlags(tenantId), getAccessToken);
-
-        if (!response.ok) {
-          setSummary(EMPTY_SUMMARY);
-          return;
-        }
-
-        const data: TenantConfigurationSummary = await response.json();
+        const data = await dedupedFetchJson<TenantConfigurationSummary>(api.config.featureFlags(tenantId), getAccessToken);
         setSummary(summarizeTenantSecurityConfig(data));
       } catch (error) {
-        if (error instanceof TokenExpiredError) {
-          addNotification('error', 'Session Expired', error.message, 'session-expired-error');
-        }
+        // Fail-soft on a backend refusal (the banners just stay quiet); a token expiry is the
+        // one failure the user must hear about.
+        if (error instanceof TokenExpiredError) notifyError('Session Expired', error);
         setSummary(EMPTY_SUMMARY);
       }
     };
diff --git a/src/Web/autopilot-monitor-web/app/dashboard/page.tsx b/src/Web/autopilot-monitor-web/app/dashboard/page.tsx
index 62bfccbb..5829daf6 100644
--- a/src/Web/autopilot-monitor-web/app/dashboard/page.tsx
+++ b/src/Web/autopilot-monitor-web/app/dashboard/page.tsx
@@ -99,7 +99,7 @@ function HomeContent() {
     ? "w-full px-4 sm:px-6 lg:px-8 py-4"
     : "max-w-7xl mx-auto py-4 sm:px-6 lg:px-8";
   const { user, getAccessToken, isActivationPending, hasGlobalScope } = useAuth();
-  const { addNotification } = useNotifications();
+  const { addNotification, notifyError } = useNotifications();
   // `?tenant=<id>` deep-links a cross-tenant view onto one tenant — used by the /fleet card grid to drill
   // a managed tenant into this dashboard. Ignored for non-cross-tenant users (the filter is unused there).
   const initialTenantFilter = searchParams?.get("tenant") ?? "";
@@ -262,7 +262,7 @@ function HomeContent() {
     }
   }, [user, router]);
 
-  const { serialValidationEnabled, proContactMissing, proContactMissingParts, appHomingFunnelActive } = useTenantSecurityConfig(tenantId, user, getAccessToken, addNotification);
+  const { serialValidationEnabled, proContactMissing, proContactMissingParts, appHomingFunnelActive } = useTenantSecurityConfig(tenantId, user, getAccessToken, notifyError);
 
   // Disable global-scope mode for users without platform scope. A read-only Global Reader keeps it
   // (their cross-tenant view is read-only-safe; writes are gated separately + backend-enforced).
diff --git a/src/Web/autopilot-monitor-web/app/fleet-health/page.tsx b/src/Web/autopilot-monitor-web/app/fleet-health/page.tsx
index d47dfcd7..adc4fad0 100644
--- a/src/Web/autopilot-monitor-web/app/fleet-health/page.tsx
+++ b/src/Web/autopilot-monitor-web/app/fleet-health/page.tsx
@@ -10,7 +10,7 @@ import { useTenant } from "../../contexts/TenantContext";
 import { useAuth } from "../../contexts/AuthContext";
 import { useNotifications } from "../../contexts/NotificationContext";
 import { scopedApi } from "@/lib/scopedApi";
-import { fetchJson } from "@/lib/scopedFetch";
+import { fetchJson } from "@/lib/apiClient";
 import { authenticatedFetch, TokenExpiredError } from "@/lib/authenticatedFetch";
 import FleetStatCard from "./components/FleetStatCard";
 import TimeAttributionSection, { TimeAttributionResponseDto } from "./components/TimeAttributionSection";
diff --git a/src/Web/autopilot-monitor-web/app/gather-rules/page.tsx b/src/Web/autopilot-monitor-web/app/gather-rules/page.tsx
index 9960a068..d0109f45 100644
--- a/src/Web/autopilot-monitor-web/app/gather-rules/page.tsx
+++ b/src/Web/autopilot-monitor-web/app/gather-rules/page.tsx
@@ -28,12 +28,10 @@ export default function GatherRulesPage() {
 
   const { data: rules, loading, execute: fetchRulesExec, setData: setRules } = useAuthenticatedFetch<GatherRule[]>({
     onError: (err) => showError(err.message),
-    onTokenExpired: (err) => showError(err.message),
   });
 
   const { execute: mutate } = useAuthenticatedFetch({
     onError: (err) => showError(err.message),
-    onTokenExpired: (err) => showError(err.message),
   });
 
   // Filter state
diff --git a/src/Web/autopilot-monitor-web/app/ime-log-patterns/page.tsx b/src/Web/autopilot-monitor-web/app/ime-log-patterns/page.tsx
index 7ae52845..e5fa410f 100644
--- a/src/Web/autopilot-monitor-web/app/ime-log-patterns/page.tsx
+++ b/src/Web/autopilot-monitor-web/app/ime-log-patterns/page.tsx
@@ -28,12 +28,10 @@ export default function ImeLogPatternsPage() {
 
   const { data: patterns, loading, execute: fetchPatternsExec, setData: setPatterns } = useAuthenticatedFetch<ImeLogPattern[]>({
     onError: (err) => showError(err.message),
-    onTokenExpired: (err) => showError(err.message),
   });
 
   const { execute: mutate } = useAuthenticatedFetch({
     onError: (err) => showError(err.message),
-    onTokenExpired: (err) => showError(err.message),
   });
 
   // Filters
diff --git a/src/Web/autopilot-monitor-web/app/sessions/hooks/useSessionTenantConfig.ts b/src/Web/autopilot-monitor-web/app/sessions/hooks/useSessionTenantConfig.ts
index f455f29a..c6624b59 100644
--- a/src/Web/autopilot-monitor-web/app/sessions/hooks/useSessionTenantConfig.ts
+++ b/src/Web/autopilot-monitor-web/app/sessions/hooks/useSessionTenantConfig.ts
@@ -2,7 +2,8 @@
 
 import { useCallback, useEffect, useState } from "react";
 import { api } from "@/lib/api";
-import { dedupedAuthFetch } from "@/lib/dedupedAuthFetch";
+import { dedupedFetchJson } from "@/lib/dedupedAuthFetch";
+import type { TenantFeatureFlagsResponse } from "@/utils/wire-types.generated";
 
 interface UseSessionTenantConfigReturn {
   showScriptOutput: boolean;
@@ -36,9 +37,7 @@ export function useSessionTenantConfig(
         // These flags are exposed via the member-readable feature-flags endpoint so that
         // Operators and Viewers can load session details without 403'ing on the admin-only
         // full /api/config/{tenantId} response.
-        const res = await dedupedAuthFetch(api.config.featureFlags(sessionTenantId), getAccessToken);
-        if (!res.ok || cancelled) return;
-        const cfg = await res.json();
+        const cfg = await dedupedFetchJson<TenantFeatureFlagsResponse>(api.config.featureFlags(sessionTenantId), getAccessToken);
         if (cancelled) return;
         setShowScriptOutput(cfg.showScriptOutput ?? true);
         setEnableSoftwareInventoryAnalyzer(cfg.enableSoftwareInventoryAnalyzer ?? false);
diff --git a/src/Web/autopilot-monitor-web/contexts/NotificationContext.tsx b/src/Web/autopilot-monitor-web/contexts/NotificationContext.tsx
index f0c0315e..c367be18 100644
--- a/src/Web/autopilot-monitor-web/contexts/NotificationContext.tsx
+++ b/src/Web/autopilot-monitor-web/contexts/NotificationContext.tsx
@@ -1,6 +1,7 @@
 "use client";
 
 import React, { createContext, useContext, useState, useCallback, useMemo } from 'react';
+import { apiErrorNotification } from '@/lib/apiClient';
 
 export type NotificationType = 'error' | 'warning' | 'info' | 'success';
 
@@ -20,6 +21,11 @@ interface NotificationContextType {
   notifications: Notification[];
   unreadCount: number;
   addNotification: (type: NotificationType, title: string, message: string, key?: string, href?: string, reference?: string) => void;
+  /**
+   * The error toast for a failed API call: message and reference from the error envelope
+   * (describeApiError); a token expiry renders as "Session Expired" whatever the title.
+   */
+  notifyError: (title: string, err: unknown, key?: string, fallback?: string) => void;
   markAsRead: (id: string) => void;
   markAllAsRead: () => void;
   removeNotification: (id: string) => void;
@@ -101,6 +107,11 @@ export function NotificationProvider({ children }: { children: React.ReactNode }
     }
   }, []);
 
+  const notifyError = useCallback((title: string, err: unknown, key?: string, fallback?: string) => {
+    const n = apiErrorNotification(title, err, key, fallback);
+    addNotification(n.type, n.title, n.message, n.key, undefined, n.reference);
+  }, [addNotification]);
+
   const markAsRead = useCallback((id: string) => {
     setNotifications(prev =>
       prev.map(n => n.id === id ? { ...n, read: true } : n)
@@ -130,11 +141,12 @@ export function NotificationProvider({ children }: { children: React.ReactNode }
     notifications,
     unreadCount,
     addNotification,
+    notifyError,
     markAsRead,
     markAllAsRead,
     removeNotification,
     clearAll,
-  }), [notifications, unreadCount, addNotification, markAsRead, markAllAsRead, removeNotification, clearAll]);
+  }), [notifications, unreadCount, addNotification, notifyError, markAsRead, markAllAsRead, removeNotification, clearAll]);
 
   return (
     <NotificationContext.Provider value={value}>
diff --git a/src/Web/autopilot-monitor-web/hooks/useAuthenticatedFetch.ts b/src/Web/autopilot-monitor-web/hooks/useAuthenticatedFetch.ts
index 32d1fa4d..7212e4be 100644
--- a/src/Web/autopilot-monitor-web/hooks/useAuthenticatedFetch.ts
+++ b/src/Web/autopilot-monitor-web/hooks/useAuthenticatedFetch.ts
@@ -4,16 +4,15 @@ import { useState, useCallback, useRef } from "react";
 import { useLatest } from "@/hooks/useLatest";
 import { useAuth } from "@/contexts/AuthContext";
 import { useNotifications } from "@/contexts/NotificationContext";
-import {
-  authenticatedFetch,
-  TokenExpiredError,
-} from "@/lib/authenticatedFetch";
+import { TokenExpiredError } from "@/lib/authenticatedFetch";
+import { apiErrorText, fetchJson } from "@/lib/apiClient";
 
 export interface UseAuthenticatedFetchOptions {
-  /** Called on non-TokenExpiredError failures. If not set, only the error state is updated. */
+  /**
+   * Called on every failure (ApiError, TokenExpiredError, network). If not set, only the error
+   * state is updated — except a token expiry, which the notification bell reports.
+   */
   onError?: (error: Error) => void;
-  /** Called on TokenExpiredError. Default: addNotification via NotificationContext. */
-  onTokenExpired?: (error: TokenExpiredError) => void;
 }
 
 export interface ExecuteOptions<T> {
@@ -41,7 +40,7 @@ export function useAuthenticatedFetch<T = unknown>(
   options?: UseAuthenticatedFetchOptions,
 ): UseAuthenticatedFetchReturn<T> {
   const { getAccessToken } = useAuth();
-  const { addNotification } = useNotifications();
+  const { notifyError } = useNotifications();
 
   const [data, setData] = useState<T | null>(null);
   const [loading, setLoading] = useState(false);
@@ -78,25 +77,7 @@ export function useAuthenticatedFetch<T = unknown>(
         }
         setError(null);
 
-        const response = await authenticatedFetch(url, getAccessToken, init);
-
-        if (!response.ok) {
-          // Try to extract error message from response body (API returns { message: "..." })
-          let message = `Failed: ${response.statusText}`;
-          try {
-            const errorData = await response.json();
-            if (errorData.message) message = errorData.message;
-          } catch {
-            /* response body wasn't JSON */
-          }
-          throw new Error(message);
-        }
-
-        if (response.status === 204) {
-          return null;
-        }
-
-        const json = await response.json();
+        const json = await fetchJson<unknown>(url, getAccessToken, init);
         const result = executeOptions?.transform
           ? executeOptions.transform(json)
           : (json as T);
@@ -111,26 +92,13 @@ export function useAuthenticatedFetch<T = unknown>(
           return null;
         }
         const opts = optionsRef.current;
-        if (err instanceof TokenExpiredError) {
-          if (opts?.onTokenExpired) {
-            opts.onTokenExpired(err);
-          } else {
-            addNotification(
-              "error",
-              "Session Expired",
-              err.message,
-              "session-expired",
-            );
-          }
-        } else if (opts?.onError) {
-          opts.onError(
-            err instanceof Error ? err : new Error(String(err)),
-          );
+        if (opts?.onError) {
+          opts.onError(err instanceof Error ? err : new Error(String(err)));
+        } else if (err instanceof TokenExpiredError) {
+          notifyError("Session Expired", err);
         }
 
-        const message =
-          err instanceof Error ? err.message : "An unknown error occurred";
-        setError(message);
+        setError(apiErrorText(err, "An unknown error occurred"));
         return null;
       } finally {
         // Only the spinner's owner may clear it — a superseded request finishing early
@@ -140,7 +108,7 @@ export function useAuthenticatedFetch<T = unknown>(
         }
       }
     },
-    [getAccessToken, addNotification, optionsRef],
+    [getAccessToken, notifyError, optionsRef],
   );
 
   return { data, loading, error, execute, clearError, setData };
diff --git a/src/Web/autopilot-monitor-web/hooks/useEditionInfo.ts b/src/Web/autopilot-monitor-web/hooks/useEditionInfo.ts
index 155000c5..1f8c254b 100644
--- a/src/Web/autopilot-monitor-web/hooks/useEditionInfo.ts
+++ b/src/Web/autopilot-monitor-web/hooks/useEditionInfo.ts
@@ -3,7 +3,7 @@
 import { useEffect, useState } from "react";
 import { useAuth } from "@/contexts/AuthContext";
 import { api } from "@/lib/api";
-import { dedupedAuthFetch } from "@/lib/dedupedAuthFetch";
+import { dedupedFetchJson } from "@/lib/dedupedAuthFetch";
 import { parseEditionInfo, type EditionInfo } from "@/lib/edition";
 
 /**
@@ -30,9 +30,7 @@ export function useEditionInfo(): EditionInfo | null {
     let cancelled = false;
     const run = async () => {
       try {
-        const res = await dedupedAuthFetch(api.config.featureFlags(tenantId), getAccessToken);
-        if (!res.ok) return;
-        const parsed = parseEditionInfo(await res.json());
+        const parsed = parseEditionInfo(await dedupedFetchJson<unknown>(api.config.featureFlags(tenantId), getAccessToken));
         if (!cancelled) setInfo(parsed);
       } catch {
         // Leave null — chrome renders nothing rather than a guessed edition.
diff --git a/src/Web/autopilot-monitor-web/lib/__tests__/apiClient.guard.baseline.ts b/src/Web/autopilot-monitor-web/lib/__tests__/apiClient.guard.baseline.ts
new file mode 100644
index 00000000..2296c381
--- /dev/null
+++ b/src/Web/autopilot-monitor-web/lib/__tests__/apiClient.guard.baseline.ts
@@ -0,0 +1,273 @@
+// Ratchet baseline for lib/__tests__/apiClient.guard.test.ts — per-file counts of the legacy
+// call-site patterns on 2026-09-06. Only ever shrinks: a migrated file lowers or drops its entry,
+// a new raw site anywhere fails the guard. Regenerate a shrunken map by hand, never by script over
+// the whole tree (the guard's stale check tells you which entries to lower).
+
+/** Files that keep a raw site for a stated reason; they never leave the baseline. */
+export const PERMANENT: Record<string, string> = {
+  "contexts/AuthContext.tsx": "auth/me bootstrap runs before the auth context exists — raw fetch by design",
+  "components/landing/StatsBand.tsx": "unauthenticated public blob manifest, not the API",
+  "app/health-check/page.tsx": "/version.json of the SWA itself, not the API",
+  "app/settings/TenantConfigContext.tsx": "consent return path routes on TokenExpiredError (router.replace) — the one non-message handling",
+};
+
+export const AUTHENTICATEDFETCH_BASELINE: Record<string, number> = {
+  "app/admin/AdminConfigContext.tsx": 8,
+  "app/admin/backups/components/RestoreRowDiffModal.tsx": 1,
+  "app/admin/backups/detail/page.tsx": 2,
+  "app/admin/backups/page.tsx": 3,
+  "app/admin/components/ConfigReseedSection.tsx": 4,
+  "app/admin/components/DeviceBlockSection.tsx": 6,
+  "app/admin/components/DistressReportsSection.tsx": 1,
+  "app/admin/components/FeedbackSection.tsx": 1,
+  "app/admin/components/IdentityBindingsSection.tsx": 3,
+  "app/admin/components/IgnoredSoftwareTab.tsx": 4,
+  "app/admin/components/MaintenanceTriggerSection.tsx": 2,
+  "app/admin/components/MappedSoftwareTab.tsx": 3,
+  "app/admin/components/OpsEventsSection.tsx": 1,
+  "app/admin/components/SessionExportSection.tsx": 1,
+  "app/admin/components/SessionReportsSection.tsx": 3,
+  "app/admin/components/TenantAdminSection.tsx": 5,
+  "app/admin/components/TenantManagementSection.tsx": 10,
+  "app/admin/components/UnmappedSoftwareTab.tsx": 5,
+  "app/admin/components/VersionBlockSection.tsx": 3,
+  "app/admin/components/VulnerabilityDataSection.tsx": 11,
+  "app/admin/customs-archive/detail/page.tsx": 3,
+  "app/admin/customs-archive/page.tsx": 2,
+  "app/admin/metrics/sections/SectionAgentMetrics.tsx": 1,
+  "app/admin/metrics/sections/SectionImePatternHealth.tsx": 1,
+  "app/admin/metrics/sections/SectionMcpUsage.tsx": 2,
+  "app/admin/metrics/sections/SectionPlatformUsage.tsx": 1,
+  "app/admin/metrics/sections/SectionVerdictCalibration.tsx": 1,
+  "app/admin/ops/session-cleanup/components/DeletionManifestSummaryView.tsx": 2,
+  "app/admin/ops/session-cleanup/components/MaintenanceStatusBanner.tsx": 2,
+  "app/admin/ops/session-cleanup/components/RestoreBrowserTab.tsx": 2,
+  "app/admin/ops/session-cleanup/components/RestoreConfirmDialog.tsx": 1,
+  "app/admin/ops/session-cleanup/page.tsx": 3,
+  "app/admin/presence/page.tsx": 1,
+  "app/admin/settings/sections/SectionDelegatedAdmins.tsx": 4,
+  "app/admin/settings/sections/SectionEmailTemplates.tsx": 4,
+  "app/admin/settings/sections/SectionTenantGroups.tsx": 2,
+  "app/admin/settings/sections/SectionUsagePlans.tsx": 2,
+  "app/admin/tenants/sections/SectionTenantConfigReport.tsx": 2,
+  "app/analyze-rules/page.tsx": 2,
+  "app/annotations/page.tsx": 1,
+  "app/apps/components/InventoryTab.tsx": 1,
+  "app/apps/components/VulnerabilitiesTab.tsx": 1,
+  "app/apps/detail/page.tsx": 2,
+  "app/audit/page.tsx": 1,
+  "app/dashboard/hooks/useBlockDevice.ts": 1,
+  "app/dashboard/hooks/useDashboardSessions.ts": 3,
+  "app/dashboard/hooks/useDashboardStats.ts": 1,
+  "app/dashboard/hooks/useDeleteSession.ts": 3,
+  "app/dashboard/hooks/useTenantList.ts": 1,
+  "app/dashboard/page.tsx": 1,
+  "app/delegations/accept/page.tsx": 2,
+  "app/diagnosis/page.tsx": 3,
+  "app/fleet-health/hooks/useFleetHealth.ts": 1,
+  "app/fleet-health/page.tsx": 1,
+  "app/fleet/hooks/useFleetSummaries.ts": 1,
+  "app/gather-rules/page.tsx": 1,
+  "app/geographic-performance/page.tsx": 1,
+  "app/geographic-performance/sessions/page.tsx": 1,
+  "app/health-check/page.tsx": 2,
+  "app/progress/hooks/useProgressEvents.ts": 3,
+  "app/progress/hooks/useProgressSearch.ts": 1,
+  "app/sessions/components/AnalysisResultsSection.tsx": 1,
+  "app/sessions/components/CollectLogsButton.tsx": 3,
+  "app/sessions/components/DeviceHistoryBanner.tsx": 1,
+  "app/sessions/components/SessionAnnotationsCard.tsx": 2,
+  "app/sessions/hooks/useSessionAnalysis.ts": 2,
+  "app/sessions/hooks/useSessionDetail.ts": 1,
+  "app/sessions/hooks/useSessionEvents.ts": 2,
+  "app/sessions/network-timeline/page.tsx": 2,
+  "app/sessions/page.tsx": 5,
+  "app/settings/TenantConfigContext.tsx": 20,
+  "app/settings/components/HardwareRejectionInsights.tsx": 1,
+  "app/settings/components/McpUsersSection.tsx": 8,
+  "app/settings/components/NotRegisteredDevicesInsights.tsx": 1,
+  "app/settings/components/OffboardingSection.tsx": 1,
+  "app/settings/components/TpmIncompatibleDevicesInsights.tsx": 1,
+  "app/settings/reporting/sections/SectionMcpUsage.tsx": 2,
+  "app/settings/tenant/sections/SectionDelegatedAccess.tsx": 6,
+  "app/settings/tenant/sections/SectionOptionalGraphCapabilities.tsx": 2,
+  "app/settings/tenant/sections/SectionSubmitLogs.tsx": 1,
+  "app/sla/page.tsx": 1,
+  "app/usage-metrics/page.tsx": 1,
+  "components/DelegatedSlotPrompt.tsx": 1,
+  "components/FeedbackBubble.tsx": 3,
+  "components/GlobalSearch.tsx": 1,
+  "contexts/GlobalNotificationContext.tsx": 3,
+  "contexts/SignalRContext.tsx": 3,
+  "contexts/TenantNotificationContext.tsx": 3,
+  "hooks/useDiagnosticsPathsCatalog.ts": 1,
+  "hooks/useTenantList.ts": 1,
+};
+
+export const DEDUPEDAUTHFETCH_BASELINE: Record<string, number> = {
+};
+
+export const JSONPARSE_BASELINE: Record<string, number> = {
+  "app/activation/page.tsx": 1,
+  "app/admin/AdminConfigContext.tsx": 8,
+  "app/admin/backups/components/RestoreRowDiffModal.tsx": 1,
+  "app/admin/backups/detail/page.tsx": 2,
+  "app/admin/backups/page.tsx": 3,
+  "app/admin/components/ConfigReseedSection.tsx": 8,
+  "app/admin/components/DeviceBlockSection.tsx": 6,
+  "app/admin/components/DistressReportsSection.tsx": 1,
+  "app/admin/components/FeedbackSection.tsx": 1,
+  "app/admin/components/IdentityBindingsSection.tsx": 3,
+  "app/admin/components/IgnoredSoftwareTab.tsx": 2,
+  "app/admin/components/MaintenanceTriggerSection.tsx": 1,
+  "app/admin/components/MappedSoftwareTab.tsx": 3,
+  "app/admin/components/OpsEventsSection.tsx": 1,
+  "app/admin/components/SessionExportSection.tsx": 1,
+  "app/admin/components/SessionReportsSection.tsx": 2,
+  "app/admin/components/TenantAdminSection.tsx": 5,
+  "app/admin/components/TenantManagementSection.tsx": 12,
+  "app/admin/components/UnmappedSoftwareTab.tsx": 3,
+  "app/admin/components/VersionBlockSection.tsx": 3,
+  "app/admin/components/VulnerabilityDataSection.tsx": 11,
+  "app/admin/customs-archive/detail/page.tsx": 2,
+  "app/admin/customs-archive/page.tsx": 2,
+  "app/admin/metrics/sections/SectionAgentMetrics.tsx": 1,
+  "app/admin/metrics/sections/SectionImePatternHealth.tsx": 1,
+  "app/admin/metrics/sections/SectionMcpUsage.tsx": 2,
+  "app/admin/metrics/sections/SectionPlatformUsage.tsx": 1,
+  "app/admin/metrics/sections/SectionVerdictCalibration.tsx": 1,
+  "app/admin/ops/session-cleanup/components/DeletionManifestSummaryView.tsx": 1,
+  "app/admin/ops/session-cleanup/components/MaintenanceStatusBanner.tsx": 1,
+  "app/admin/ops/session-cleanup/components/RestoreBrowserTab.tsx": 2,
+  "app/admin/ops/session-cleanup/components/RestoreConfirmDialog.tsx": 1,
+  "app/admin/ops/session-cleanup/page.tsx": 3,
+  "app/admin/presence/page.tsx": 1,
+  "app/admin/settings/sections/SectionDelegatedAdmins.tsx": 4,
+  "app/admin/settings/sections/SectionEmailTemplates.tsx": 3,
+  "app/admin/settings/sections/SectionTenantGroups.tsx": 2,
+  "app/admin/settings/sections/SectionUsagePlans.tsx": 3,
+  "app/admin/tenants/sections/SectionTenantConfigReport.tsx": 2,
+  "app/analyze-rules/page.tsx": 2,
+  "app/annotations/page.tsx": 1,
+  "app/apps/components/InventoryTab.tsx": 1,
+  "app/apps/components/VulnerabilitiesTab.tsx": 1,
+  "app/apps/detail/page.tsx": 2,
+  "app/audit/page.tsx": 1,
+  "app/dashboard/hooks/deleteSessionResponse.ts": 1,
+  "app/dashboard/hooks/useBlockDevice.ts": 1,
+  "app/dashboard/hooks/useDashboardSessions.ts": 4,
+  "app/dashboard/hooks/useDashboardStats.ts": 2,
+  "app/dashboard/hooks/useTenantList.ts": 1,
+  "app/dashboard/page.tsx": 1,
+  "app/delegations/accept/page.tsx": 3,
+  "app/diagnosis/page.tsx": 3,
+  "app/fleet-health/hooks/useFleetHealth.ts": 2,
+  "app/fleet-health/page.tsx": 1,
+  "app/fleet/hooks/useFleetSummaries.ts": 1,
+  "app/gather-rules/page.tsx": 1,
+  "app/geographic-performance/page.tsx": 1,
+  "app/geographic-performance/sessions/page.tsx": 1,
+  "app/health-check/page.tsx": 3,
+  "app/progress/hooks/useProgressEvents.ts": 3,
+  "app/progress/hooks/useProgressSearch.ts": 1,
+  "app/sessions/components/AnalysisResultsSection.tsx": 1,
+  "app/sessions/components/CollectLogsButton.tsx": 1,
+  "app/sessions/components/DeviceHistoryBanner.tsx": 1,
+  "app/sessions/components/SessionAnnotationsCard.tsx": 2,
+  "app/sessions/hooks/useSessionAnalysis.ts": 2,
+  "app/sessions/hooks/useSessionDetail.ts": 1,
+  "app/sessions/hooks/useSessionEvents.ts": 2,
+  "app/sessions/network-timeline/page.tsx": 2,
+  "app/sessions/page.tsx": 2,
+  "app/settings/TenantConfigContext.tsx": 23,
+  "app/settings/components/HardwareRejectionInsights.tsx": 1,
+  "app/settings/components/McpUsersSection.tsx": 8,
+  "app/settings/components/NotRegisteredDevicesInsights.tsx": 1,
+  "app/settings/components/TpmIncompatibleDevicesInsights.tsx": 1,
+  "app/settings/reporting/sections/SectionMcpUsage.tsx": 2,
+  "app/settings/tenant/sections/SectionDelegatedAccess.tsx": 6,
+  "app/settings/tenant/sections/SectionOptionalGraphCapabilities.tsx": 1,
+  "app/settings/tenant/sections/SectionSubmitLogs.tsx": 1,
+  "app/sla/page.tsx": 1,
+  "app/usage-metrics/page.tsx": 1,
+  "components/DelegatedSlotPrompt.tsx": 1,
+  "components/FeedbackBubble.tsx": 1,
+  "components/GlobalSearch.tsx": 1,
+  "components/landing/StatsBand.tsx": 2,
+  "contexts/AuthContext.tsx": 3,
+  "contexts/GlobalNotificationContext.tsx": 1,
+  "contexts/TenantNotificationContext.tsx": 1,
+  "hooks/useDiagnosticsPathsCatalog.ts": 1,
+  "hooks/useTenantList.ts": 1,
+};
+
+export const TOKENEXPIRED_BASELINE: Record<string, number> = {
+  "app/admin/AdminConfigContext.tsx": 6,
+  "app/admin/backups/components/RestoreRowDiffModal.tsx": 1,
+  "app/admin/backups/detail/page.tsx": 2,
+  "app/admin/backups/page.tsx": 3,
+  "app/admin/components/ConfigReseedSection.tsx": 4,
+  "app/admin/components/DeviceBlockSection.tsx": 6,
+  "app/admin/components/DistressReportsSection.tsx": 1,
+  "app/admin/components/FeedbackSection.tsx": 1,
+  "app/admin/components/IdentityBindingsSection.tsx": 1,
+  "app/admin/components/MaintenanceTriggerSection.tsx": 2,
+  "app/admin/components/MappedSoftwareTab.tsx": 3,
+  "app/admin/components/OpsEventsSection.tsx": 1,
+  "app/admin/components/SessionExportSection.tsx": 1,
+  "app/admin/components/SessionReportsSection.tsx": 3,
+  "app/admin/components/TenantAdminSection.tsx": 5,
+  "app/admin/components/TenantManagementSection.tsx": 6,
+  "app/admin/components/UnmappedSoftwareTab.tsx": 2,
+  "app/admin/components/VersionBlockSection.tsx": 3,
+  "app/admin/components/VulnerabilityDataSection.tsx": 5,
+  "app/admin/customs-archive/detail/page.tsx": 1,
+  "app/admin/customs-archive/page.tsx": 2,
+  "app/admin/metrics/sections/SectionAgentMetrics.tsx": 1,
+  "app/admin/metrics/sections/SectionImePatternHealth.tsx": 1,
+  "app/admin/metrics/sections/SectionMcpUsage.tsx": 1,
+  "app/admin/metrics/sections/SectionPlatformUsage.tsx": 1,
+  "app/admin/metrics/sections/SectionVerdictCalibration.tsx": 1,
+  "app/admin/ops/session-cleanup/components/DeletionManifestSummaryView.tsx": 2,
+  "app/admin/ops/session-cleanup/components/MaintenanceStatusBanner.tsx": 2,
+  "app/admin/ops/session-cleanup/components/RestoreBrowserTab.tsx": 2,
+  "app/admin/ops/session-cleanup/components/RestoreConfirmDialog.tsx": 1,
+  "app/admin/ops/session-cleanup/page.tsx": 3,
+  "app/admin/presence/page.tsx": 1,
+  "app/admin/settings/sections/SectionDelegatedAdmins.tsx": 1,
+  "app/admin/settings/sections/SectionEmailTemplates.tsx": 1,
+  "app/admin/settings/sections/SectionTenantGroups.tsx": 1,
+  "app/admin/settings/sections/SectionUsagePlans.tsx": 2,
+  "app/admin/tenants/sections/SectionTenantConfigReport.tsx": 2,
+  "app/apps/components/InventoryTab.tsx": 1,
+  "app/apps/components/VulnerabilitiesTab.tsx": 1,
+  "app/apps/detail/page.tsx": 2,
+  "app/audit/page.tsx": 1,
+  "app/dashboard/hooks/useBlockDevice.ts": 2,
+  "app/dashboard/hooks/useDashboardSessions.ts": 3,
+  "app/dashboard/hooks/useDashboardStats.ts": 1,
+  "app/dashboard/hooks/useDeleteSession.ts": 2,
+  "app/dashboard/hooks/useTenantSecurityConfig.ts": 1,
+  "app/delegations/accept/page.tsx": 1,
+  "app/diagnosis/page.tsx": 3,
+  "app/fleet-health/hooks/useFleetHealth.ts": 1,
+  "app/fleet-health/page.tsx": 1,
+  "app/geographic-performance/page.tsx": 1,
+  "app/geographic-performance/sessions/page.tsx": 1,
+  "app/health-check/page.tsx": 1,
+  "app/progress/hooks/useProgressEvents.ts": 1,
+  "app/progress/hooks/useProgressSearch.ts": 1,
+  "app/sessions/components/CollectLogsButton.tsx": 1,
+  "app/sessions/components/SessionAnnotationsCard.tsx": 1,
+  "app/sessions/hooks/useSessionDetail.ts": 1,
+  "app/sessions/hooks/useSessionEvents.ts": 1,
+  "app/sessions/page.tsx": 1,
+  "app/settings/TenantConfigContext.tsx": 16,
+  "app/settings/components/McpUsersSection.tsx": 6,
+  "app/settings/components/OffboardingSection.tsx": 1,
+  "app/settings/reporting/sections/SectionMcpUsage.tsx": 1,
+  "app/settings/tenant/sections/SectionDelegatedAccess.tsx": 1,
+  "app/settings/tenant/sections/SectionSubmitLogs.tsx": 1,
+  "app/sla/page.tsx": 1,
+  "app/usage-metrics/page.tsx": 1,
+};
diff --git a/src/Web/autopilot-monitor-web/lib/__tests__/apiClient.guard.test.ts b/src/Web/autopilot-monitor-web/lib/__tests__/apiClient.guard.test.ts
new file mode 100644
index 00000000..dd070417
--- /dev/null
+++ b/src/Web/autopilot-monitor-web/lib/__tests__/apiClient.guard.test.ts
@@ -0,0 +1,160 @@
+import { describe, it, expect } from "vitest";
+import { readdirSync, readFileSync, statSync } from "node:fs";
+import { join, relative } from "node:path";
+import {
+  AUTHENTICATEDFETCH_BASELINE,
+  DEDUPEDAUTHFETCH_BASELINE,
+  JSONPARSE_BASELINE,
+  PERMANENT,
+  TOKENEXPIRED_BASELINE,
+} from "./apiClient.guard.baseline";
+
+/**
+ * Ratchet for the one API call layer (lib/apiClient.ts, D-203): pages, components, hooks and
+ * contexts call the backend through fetchJson<T>/fetchOk/fetchBlob and render failures through
+ * describeApiError/apiErrorText/notifyError. Raw `authenticatedFetch(`, `.json()` parses and
+ * `instanceof TokenExpiredError` branches are legacy; their per-file counts live in the baseline
+ * module and may only go down. A count above its baseline (or a file not in the baseline) is a new
+ * raw site; a count below it is a stale baseline entry that must be lowered — so the baseline
+ * always states the true remaining debt.
+ *
+ * Comment lines are ignored; test files are excluded (they stub fetch deliberately).
+ */
+
+const WEB_ROOT = join(__dirname, "..", "..");
+const SCAN_DIRS = ["app", "components", "hooks", "contexts"];
+/** The lib-level hook is itself a fetchJson consumer and the one place allowed to spell TokenExpiredError. */
+const EXEMPT_FILES = new Set(["hooks/useAuthenticatedFetch.ts"]);
+
+interface Pattern {
+  name: string;
+  regex: RegExp;
+  baseline: Record<string, number>;
+  remedy: string;
+}
+
+const PATTERNS: Pattern[] = [
+  {
+    name: "authenticatedFetch(",
+    regex: /\bauthenticatedFetch\(/g,
+    baseline: AUTHENTICATEDFETCH_BASELINE,
+    remedy: "call fetchJson<T>/fetchOk/fetchBlob from @/lib/apiClient instead",
+  },
+  {
+    name: "dedupedAuthFetch(",
+    regex: /\bdedupedAuthFetch\(/g,
+    baseline: DEDUPEDAUTHFETCH_BASELINE,
+    remedy: "call dedupedFetchJson<T> from @/lib/dedupedAuthFetch instead",
+  },
+  {
+    name: ".json()",
+    regex: /\.json\(\)/g,
+    baseline: JSONPARSE_BASELINE,
+    remedy: "fetchJson<T> parses the body; a hand parse hides the error envelope",
+  },
+  {
+    name: "instanceof TokenExpiredError",
+    regex: /instanceof TokenExpiredError/g,
+    baseline: TOKENEXPIRED_BASELINE,
+    remedy: "notifyError/apiErrorText render a token expiry centrally; keep a branch only where the UI must act (route, reset)",
+  },
+];
+
+function collectFiles(dir: string, acc: string[]): void {
+  for (const entry of readdirSync(dir)) {
+    if (entry === "node_modules" || entry === "__tests__" || entry.startsWith(".")) continue;
+    const full = join(dir, entry);
+    if (statSync(full).isDirectory()) {
+      collectFiles(full, acc);
+    } else if (/\.(ts|tsx)$/.test(entry) && !/\.test\.(ts|tsx)$/.test(entry)) {
+      acc.push(full);
+    }
+  }
+}
+
+function isCommentLine(line: string): boolean {
+  const trimmed = line.trimStart();
+  return trimmed.startsWith("//") || trimmed.startsWith("*") || trimmed.startsWith("/*");
+}
+
+/** file (repo-relative, forward slashes) → code lines. */
+function scannedSources(): Map<string, string[]> {
+  const files: string[] = [];
+  for (const dir of SCAN_DIRS) collectFiles(join(WEB_ROOT, dir), files);
+  const out = new Map<string, string[]>();
+  for (const file of files) {
+    const rel = relative(WEB_ROOT, file).replace(/\\/g, "/");
+    if (EXEMPT_FILES.has(rel)) continue;
+    out.set(
+      rel,
+      readFileSync(file, "utf-8")
+        .split("\n")
+        .filter((l) => !isCommentLine(l)),
+    );
+  }
+  return out;
+}
+
+function countPerFile(sources: Map<string, string[]>, regex: RegExp): Map<string, number> {
+  const counts = new Map<string, number>();
+  for (const [rel, lines] of sources) {
+    let n = 0;
+    for (const line of lines) n += line.match(regex)?.length ?? 0;
+    if (n > 0) counts.set(rel, n);
+  }
+  return counts;
+}
+
+const sources = scannedSources();
+
+describe("apiClient ratchet", () => {
+  it("scans the app (plausibility floor)", () => {
+    expect(sources.size).toBeGreaterThan(50);
+  });
+
+  for (const pattern of PATTERNS) {
+    describe(pattern.name, () => {
+      const counts = countPerFile(sources, pattern.regex);
+
+      it("has no raw site above its baseline", () => {
+        const violations: string[] = [];
+        for (const [rel, n] of counts) {
+          const allowed = pattern.baseline[rel] ?? 0;
+          if (n > allowed) violations.push(`${rel}: ${n} (baseline ${allowed})`);
+        }
+        expect(
+          violations,
+          `New raw \`${pattern.name}\` site(s) — ${pattern.remedy}:\n  ${violations.join("\n  ")}`,
+        ).toEqual([]);
+      });
+
+      it("has no stale baseline entry (the baseline states the true remaining debt)", () => {
+        const stale: string[] = [];
+        for (const [rel, allowed] of Object.entries(pattern.baseline)) {
+          const n = counts.get(rel) ?? 0;
+          if (n < allowed) stale.push(`${rel}: now ${n} (baseline ${allowed})`);
+        }
+        expect(
+          stale,
+          `Lower these entries in lib/__tests__/apiClient.guard.baseline.ts (${pattern.name}):\n  ${stale.join("\n  ")}`,
+        ).toEqual([]);
+      });
+    });
+  }
+
+  it("never calls fetchJson without an explicit type argument", () => {
+    const violations: string[] = [];
+    for (const [rel, lines] of sources) {
+      lines.forEach((line, i) => {
+        if (/\b(?:fetchJson|dedupedFetchJson)\(/.test(line)) violations.push(`${rel}:${i + 1}`);
+      });
+    }
+    expect(violations, "fetchJson<T>(…) — name the wire type (utils/wire-types.generated):\n  " + violations.join("\n  ")).toEqual([]);
+  });
+
+  it("documents every permanent exception against a file that is still in a baseline", () => {
+    const inSomeBaseline = new Set(PATTERNS.flatMap((p) => Object.keys(p.baseline)));
+    const rotten = Object.keys(PERMANENT).filter((rel) => !inSomeBaseline.has(rel));
+    expect(rotten, "PERMANENT names a file with no baseline entry left — drop the reason").toEqual([]);
+  });
+});
diff --git a/src/Web/autopilot-monitor-web/lib/__tests__/apiClient.test.ts b/src/Web/autopilot-monitor-web/lib/__tests__/apiClient.test.ts
new file mode 100644
index 00000000..8510f87d
--- /dev/null
+++ b/src/Web/autopilot-monitor-web/lib/__tests__/apiClient.test.ts
@@ -0,0 +1,169 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import {
+  ApiError,
+  apiErrorFromResponse,
+  apiErrorNotification,
+  apiErrorText,
+  describeApiError,
+  fetchBlob,
+  fetchJson,
+  fetchOk,
+} from "../apiClient";
+import { TokenExpiredError } from "../authenticatedFetch";
+
+vi.mock("../appInsights", () => ({ trackEvent: vi.fn() }));
+
+function jsonResponse(status: number, body: unknown, statusText = "Error", headers: Record<string, string> = {}): Response {
+  return new Response(JSON.stringify(body), { status, statusText, headers: { "Content-Type": "application/json", ...headers } });
+}
+
+describe("apiErrorFromResponse", () => {
+  it("reads the error envelope: error, code, correlationId, hint, retryAfterSeconds", async () => {
+    const err = await apiErrorFromResponse(
+      jsonResponse(429, {
+        error: "Rate limit exceeded.",
+        code: "RateLimitExceeded",
+        correlationId: "3f2a9c1e-7b4d-4e0a-9d2c-1a2b3c4d5e6f",
+        hint: "Slow down.",
+        retryAfterSeconds: 12,
+      }),
+    );
+
+    expect(err).toBeInstanceOf(ApiError);
+    expect(err.status).toBe(429);
+    expect(err.message).toBe("Rate limit exceeded.");
+    expect(err.code).toBe("RateLimitExceeded");
+    expect(err.correlationId).toBe("3f2a9c1e-7b4d-4e0a-9d2c-1a2b3c4d5e6f");
+    expect(err.hint).toBe("Slow down.");
+    expect(err.retryAfterSeconds).toBe(12);
+  });
+
+  it("takes Retry-After from the header when the body has no retryAfterSeconds", async () => {
+    const err = await apiErrorFromResponse(jsonResponse(503, { error: "Busy.", code: "ServiceUnavailable", correlationId: "c" }, "x", { "Retry-After": "5" }));
+    expect(err.retryAfterSeconds).toBe(5);
+
+    const none = await apiErrorFromResponse(jsonResponse(503, { error: "Busy.", code: "ServiceUnavailable", correlationId: "c" }));
+    expect(none.retryAfterSeconds).toBeNull();
+  });
+
+  it("falls back to the pre-envelope message, then to statusText; an empty body is not an exception", async () => {
+    const legacy = await apiErrorFromResponse(jsonResponse(400, { success: false, message: "tenantId is required" }, "Bad Request"));
+    expect(legacy.message).toBe("tenantId is required");
+    expect(legacy.code).toBe("");
+    expect(legacy.correlationId).toBe("");
+
+    const bare = await apiErrorFromResponse(new Response("not json", { status: 502, statusText: "Bad Gateway" }));
+    expect(bare.message).toBe("Bad Gateway");
+    expect(bare.hint).toBeNull();
+
+    const empty = await apiErrorFromResponse(new Response("", { status: 500, statusText: "Internal Server Error" }));
+    expect(empty.message).toBe("Internal Server Error");
+  });
+});
+
+describe("fetchJson / fetchOk / fetchBlob", () => {
+  beforeEach(() => vi.stubGlobal("fetch", vi.fn()));
+  afterEach(() => {
+    vi.unstubAllGlobals();
+    vi.restoreAllMocks();
+  });
+  const fetchMock = () => globalThis.fetch as ReturnType<typeof vi.fn>;
+  const getToken = () => vi.fn().mockResolvedValue("tok");
+
+  it("returns the parsed body on success and throws the envelope ApiError otherwise", async () => {
+    fetchMock().mockResolvedValueOnce(jsonResponse(200, { items: [1] }));
+    await expect(fetchJson<{ items: number[] }>("https://api/x", getToken())).resolves.toEqual({ items: [1] });
+
+    fetchMock().mockResolvedValueOnce(jsonResponse(403, { error: "Access denied.", code: "Forbidden", correlationId: "cid-1" }));
+    const err = await fetchJson<unknown>("https://api/x", getToken()).catch((e) => e);
+    expect(err).toBeInstanceOf(ApiError);
+    expect((err as ApiError).code).toBe("Forbidden");
+    expect((err as ApiError).correlationId).toBe("cid-1");
+  });
+
+  it("refuses an empty or malformed 2xx body instead of handing back undefined", async () => {
+    fetchMock().mockResolvedValueOnce(new Response("", { status: 200 }));
+    const empty = await fetchJson<unknown>("https://api/x", getToken()).catch((e) => e);
+    expect(empty).toBeInstanceOf(ApiError);
+    expect((empty as ApiError).message).toBe("Empty response body");
+
+    fetchMock().mockResolvedValueOnce(new Response("<html>", { status: 200 }));
+    const html = await fetchJson<unknown>("https://api/x", getToken()).catch((e) => e);
+    expect((html as ApiError).message).toBe("Malformed response body");
+  });
+
+  it("sets Content-Type: application/json for a string body unless the caller set one", async () => {
+    fetchMock().mockResolvedValue(jsonResponse(200, {}));
+    await fetchJson<unknown>("https://api/x", getToken(), { method: "POST", body: JSON.stringify({ a: 1 }) });
+    const headers1 = fetchMock().mock.calls[0][1].headers as Headers;
+    expect(headers1.get("Content-Type")).toBe("application/json");
+
+    await fetchOk("https://api/x", getToken(), { method: "PUT", body: "raw", headers: { "Content-Type": "text/plain" } });
+    const headers2 = fetchMock().mock.calls[1][1].headers as Headers;
+    expect(headers2.get("Content-Type")).toBe("text/plain");
+
+    await fetchOk("https://api/x", getToken(), { method: "DELETE" });
+    const headers3 = fetchMock().mock.calls[2][1].headers as Headers;
+    expect(headers3.has("Content-Type")).toBe(false);
+  });
+
+  it("fetchOk returns the response for status checks and throws on non-ok; fetchBlob returns the blob", async () => {
+    fetchMock().mockResolvedValueOnce(new Response("", { status: 202 }));
+    const res = await fetchOk("https://api/x", getToken(), { method: "POST" });
+    expect(res.status).toBe(202);
+
+    fetchMock().mockResolvedValueOnce(jsonResponse(409, { error: "Locked.", code: "Conflict", correlationId: "c" }));
+    await expect(fetchOk("https://api/x", getToken())).rejects.toBeInstanceOf(ApiError);
+
+    fetchMock().mockResolvedValueOnce(new Response(new Blob(["zip"]), { status: 200 }));
+    const blob = await fetchBlob("https://api/x", getToken());
+    expect(await blob.text()).toBe("zip");
+  });
+
+  it("lets TokenExpiredError pass through untouched", async () => {
+    const noToken = vi.fn().mockResolvedValue(null);
+    await expect(fetchJson<unknown>("https://api/x", noToken)).rejects.toBeInstanceOf(TokenExpiredError);
+  });
+});
+
+describe("describeApiError / apiErrorText / apiErrorNotification", () => {
+  it("renders an ApiError with the short correlation id as reference", () => {
+    const err = new ApiError(500, "GetSessions failed.", "InternalError", "3f2a9c1e-7b4d-4e0a-9d2c-1a2b3c4d5e6f");
+    expect(describeApiError(err)).toEqual({ message: "GetSessions failed.", reference: "3f2a9c1e" });
+    expect(apiErrorText(err)).toBe("GetSessions failed. (Ref 3f2a9c1e)");
+  });
+
+  it("adds the retry advice on 429 and 503", () => {
+    const limited = new ApiError(429, "Rate limit exceeded.", "RateLimitExceeded", "cid", null, 12);
+    expect(describeApiError(limited).message).toBe("Rate limit exceeded. Try again in 12 s.");
+    const busy = new ApiError(503, "", "ServiceUnavailable", "cid");
+    expect(describeApiError(busy).message).toBe("Service temporarily unavailable. Try again shortly.");
+  });
+
+  it("has no reference for a token expiry or a plain Error, and uses the fallback for unknown values", () => {
+    expect(describeApiError(new TokenExpiredError()).reference).toBeNull();
+    expect(describeApiError(new Error("boom"))).toEqual({ message: "boom", reference: null });
+    expect(describeApiError(undefined, "Could not load.")).toEqual({ message: "Could not load.", reference: null });
+    expect(describeApiError(new ApiError(502, "", "", ""), "Upstream failed.").message).toBe("Upstream failed.");
+    expect(apiErrorText(new Error("boom"))).toBe("boom");
+  });
+
+  it("builds the notification: caller title and key, reference from the envelope; token expiry overrides both", () => {
+    const err = new ApiError(404, "Session not found.", "NotFound", "3f2a9c1e-7b4d-4e0a-9d2c-1a2b3c4d5e6f");
+    expect(apiErrorNotification("Backend Error", err, "apps-list-error")).toEqual({
+      type: "error",
+      title: "Backend Error",
+      message: "Session not found.",
+      key: "apps-list-error",
+      reference: "3f2a9c1e",
+    });
+    expect(apiErrorNotification("Backend Error", new TokenExpiredError(), "apps-list-error")).toEqual({
+      type: "error",
+      title: "Session Expired",
+      message: new TokenExpiredError().message,
+      key: "session-expired",
+      reference: undefined,
+    });
+    expect(apiErrorNotification("Backend Error", "?", undefined, "Unable to load.").message).toBe("Unable to load.");
+  });
+});
diff --git a/src/Web/autopilot-monitor-web/lib/__tests__/scopedFetch.test.ts b/src/Web/autopilot-monitor-web/lib/__tests__/scopedFetch.test.ts
deleted file mode 100644
index de60aeb3..00000000
--- a/src/Web/autopilot-monitor-web/lib/__tests__/scopedFetch.test.ts
+++ /dev/null
@@ -1,71 +0,0 @@
-import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
-import { ApiError, apiErrorFromResponse, describeApiError, fetchJson } from "../scopedFetch";
-import { TokenExpiredError } from "../authenticatedFetch";
-
-vi.mock("../appInsights", () => ({ trackEvent: vi.fn() }));
-
-function jsonResponse(status: number, body: unknown, statusText = "Error"): Response {
-  return new Response(JSON.stringify(body), { status, statusText, headers: { "Content-Type": "application/json" } });
-}
-
-describe("apiErrorFromResponse", () => {
-  it("reads the error envelope: error, code, correlationId, hint", async () => {
-    const err = await apiErrorFromResponse(
-      jsonResponse(404, { error: "Session not found", code: "NotFound", correlationId: "3f2a9c1e-7b4d-4e0a-9d2c-1a2b3c4d5e6f", hint: "Check the id." }),
-    );
-
-    expect(err).toBeInstanceOf(ApiError);
-    expect(err.status).toBe(404);
-    expect(err.message).toBe("Session not found");
-    expect(err.code).toBe("NotFound");
-    expect(err.correlationId).toBe("3f2a9c1e-7b4d-4e0a-9d2c-1a2b3c4d5e6f");
-    expect(err.hint).toBe("Check the id.");
-  });
-
-  it("falls back to the pre-envelope message and then to statusText", async () => {
-    const legacy = await apiErrorFromResponse(jsonResponse(400, { success: false, message: "tenantId is required" }, "Bad Request"));
-    expect(legacy.message).toBe("tenantId is required");
-    expect(legacy.code).toBe("");
-    expect(legacy.correlationId).toBe("");
-
-    const bare = await apiErrorFromResponse(new Response("not json", { status: 502, statusText: "Bad Gateway" }));
-    expect(bare.message).toBe("Bad Gateway");
-    expect(bare.hint).toBeNull();
-  });
-});
-
-describe("fetchJson", () => {
-  beforeEach(() => vi.stubGlobal("fetch", vi.fn()));
-  afterEach(() => {
-    vi.unstubAllGlobals();
-    vi.restoreAllMocks();
-  });
-
-  it("returns the parsed body on success and throws the envelope ApiError otherwise", async () => {
-    const fetchMock = globalThis.fetch as ReturnType<typeof vi.fn>;
-    fetchMock.mockResolvedValueOnce(jsonResponse(200, { items: [1] }));
-    const getToken = vi.fn().mockResolvedValue("tok");
-
-    await expect(fetchJson<{ items: number[] }>("https://api/x", getToken)).resolves.toEqual({ items: [1] });
-
-    fetchMock.mockResolvedValueOnce(jsonResponse(403, { error: "Access denied.", code: "Forbidden", correlationId: "cid-1" }));
-    const err = await fetchJson("https://api/x", getToken).catch((e) => e);
-    expect(err).toBeInstanceOf(ApiError);
-    expect((err as ApiError).code).toBe("Forbidden");
-    expect((err as ApiError).correlationId).toBe("cid-1");
-  });
-});
-
-describe("describeApiError", () => {
-  it("renders an ApiError with the short correlation id as reference", () => {
-    const err = new ApiError(500, "GetSessions failed.", "InternalError", "3f2a9c1e-7b4d-4e0a-9d2c-1a2b3c4d5e6f");
-    expect(describeApiError(err)).toEqual({ message: "GetSessions failed.", reference: "3f2a9c1e" });
-  });
-
-  it("has no reference for a token expiry or a plain Error, and uses the fallback for unknown values", () => {
-    expect(describeApiError(new TokenExpiredError()).reference).toBeNull();
-    expect(describeApiError(new Error("boom"))).toEqual({ message: "boom", reference: null });
-    expect(describeApiError(undefined, "Could not load.")).toEqual({ message: "Could not load.", reference: null });
-    expect(describeApiError(new ApiError(502, "", "", ""), "Upstream failed.").message).toBe("Upstream failed.");
-  });
-});
diff --git a/src/Web/autopilot-monitor-web/lib/apiClient.ts b/src/Web/autopilot-monitor-web/lib/apiClient.ts
new file mode 100644
index 00000000..c9ba8e36
--- /dev/null
+++ b/src/Web/autopilot-monitor-web/lib/apiClient.ts
@@ -0,0 +1,164 @@
+import { authenticatedFetch, TokenExpiredError } from "./authenticatedFetch";
+import { shortCorrelationId } from "./correlationId";
+import type { ApiErrorResponse } from "@/utils/wire-types.generated";
+
+/**
+ * The one API call layer above authenticatedFetch: ok-check, body parse and the backend's
+ * error envelope in one place, so no call site hand-rolls `if (!res.ok)`, `.json()` or an
+ * `instanceof TokenExpiredError` branch (guarded by lib/__tests__/apiClient.guard.test.ts).
+ *
+ *   fetchJson<T>  — JSON body expected; throws ApiError on non-2xx, empty or malformed body
+ *   fetchOk       — action calls whose body nobody reads; returns the ok Response (status only)
+ *   fetchBlob     — downloads
+ *
+ * Every non-2xx body is the typed envelope `{ error, code, correlationId, hint?,
+ * retryAfterSeconds? }` (D-192); TokenExpiredError from authenticatedFetch passes through
+ * untouched and is rendered by describeApiError like any other failure.
+ */
+
+export type GetAccessToken = (forceRefresh?: boolean) => Promise<string | null>;
+
+export class ApiError extends Error {
+  constructor(
+    public readonly status: number,
+    message: string,
+    /** Machine-readable code (Constants.ApiErrorCodes or a domain code class); "" when the body had none. */
+    public readonly code: string = "",
+    /** The request's correlation id — the handle for the backend log; "" when the body had none. */
+    public readonly correlationId: string = "",
+    public readonly hint: string | null = null,
+    /** Seconds the server asked us to wait (429/503); null when it sent none. */
+    public readonly retryAfterSeconds: number | null = null,
+  ) {
+    super(message);
+    this.name = "ApiError";
+  }
+}
+
+/**
+ * What a non-2xx body may carry: the generated envelope plus `message`, which pre-envelope
+ * backends wrote. The `message` fallback is a deploy-window remnant (backend 1.5.1171 shipped the
+ * envelope on 2026-09-05); drop it once no older backend can answer this web build.
+ */
+type ErrorEnvelope = Partial<ApiErrorResponse> & { message?: unknown };
+
+const str = (v: unknown): string | null => (typeof v === "string" && v.length > 0 ? v : null);
+const num = (v: unknown): number | null => (typeof v === "number" && Number.isFinite(v) ? v : null);
+
+function retryAfterFromHeader(response: Response): number | null {
+  // Platform CORS may not expose the header to browser script; the body's retryAfterSeconds
+  // is the primary source, this is the best-effort second one.
+  const raw = response.headers?.get?.("Retry-After");
+  if (!raw) return null;
+  const seconds = Number.parseInt(raw, 10);
+  return Number.isFinite(seconds) && seconds >= 0 ? seconds : null;
+}
+
+/** Build an ApiError from a non-ok response: envelope fields when present, statusText otherwise. */
+export async function apiErrorFromResponse(response: Response): Promise<ApiError> {
+  let body: ErrorEnvelope | null = null;
+  try {
+    const text = await response.text();
+    if (text.length > 0) body = JSON.parse(text) as ErrorEnvelope;
+  } catch {
+    /* not JSON */
+  }
+  const message = str(body?.error) ?? str(body?.message) ?? response.statusText;
+  return new ApiError(
+    response.status,
+    message,
+    str(body?.code) ?? "",
+    str(body?.correlationId) ?? "",
+    str(body?.hint),
+    num(body?.retryAfterSeconds) ?? retryAfterFromHeader(response),
+  );
+}
+
+/** A string body without an explicit Content-Type is JSON — every backend route deserialises JSON. */
+function withJsonContentType(init: RequestInit | undefined): RequestInit | undefined {
+  if (typeof init?.body !== "string") return init;
+  const headers = new Headers(init.headers);
+  if (headers.has("Content-Type")) return init;
+  headers.set("Content-Type", "application/json");
+  return { ...init, headers };
+}
+
+/** Parse the JSON body of an ok response; an empty or malformed body is an ApiError, never `undefined`. */
+export async function parseJsonBody<T>(response: Response): Promise<T> {
+  const text = await response.text();
+  if (text.length === 0) throw new ApiError(response.status, "Empty response body");
+  try {
+    return JSON.parse(text) as T;
+  } catch {
+    throw new ApiError(response.status, "Malformed response body");
+  }
+}
+
+export async function fetchJson<T>(url: string, getAccessToken: GetAccessToken, init?: RequestInit): Promise<T> {
+  const response = await authenticatedFetch(url, getAccessToken, withJsonContentType(init));
+  if (!response.ok) throw await apiErrorFromResponse(response);
+  return parseJsonBody<T>(response);
+}
+
+/** For calls whose body nobody reads: resolves with the ok Response (for status checks), throws ApiError otherwise. */
+export async function fetchOk(url: string, getAccessToken: GetAccessToken, init?: RequestInit): Promise<Response> {
+  const response = await authenticatedFetch(url, getAccessToken, withJsonContentType(init));
+  if (!response.ok) throw await apiErrorFromResponse(response);
+  return response;
+}
+
+export async function fetchBlob(url: string, getAccessToken: GetAccessToken, init?: RequestInit): Promise<Blob> {
+  const response = await authenticatedFetch(url, getAccessToken, init);
+  if (!response.ok) throw await apiErrorFromResponse(response);
+  return response.blob();
+}
+
+function retryAdvice(err: ApiError): string {
+  return err.retryAfterSeconds !== null && err.retryAfterSeconds > 0
+    ? `Try again in ${err.retryAfterSeconds} s.`
+    : "Try again shortly.";
+}
+
+/**
+ * One rendering for any thrown error: the user-facing message plus, for backend failures,
+ * the short correlation id as a reference the user can quote to support. 429 and 503 add the
+ * server's retry advice. Pass `reference` to addNotification so the bell shows it.
+ */
+export function describeApiError(err: unknown, fallback = "Request failed."): { message: string; reference: string | null } {
+  if (err instanceof TokenExpiredError) return { message: err.message, reference: null };
+  if (err instanceof ApiError) {
+    let message = err.message || fallback;
+    if (err.status === 429) message = `${err.message || "Too many requests."} ${retryAdvice(err)}`;
+    else if (err.status === 503) message = `${err.message || "Service temporarily unavailable."} ${retryAdvice(err)}`;
+    return { message, reference: err.correlationId ? shortCorrelationId(err.correlationId) : null };
+  }
+  if (err instanceof Error && err.message) return { message: err.message, reference: null };
+  return { message: fallback, reference: null };
+}
+
+/** describeApiError as one string for inline error slots (`setError`): "message (Ref abcd1234)". */
+export function apiErrorText(err: unknown, fallback = "Request failed."): string {
+  const { message, reference } = describeApiError(err, fallback);
+  return reference ? `${message} (Ref ${reference})` : message;
+}
+
+export interface ApiErrorNotification {
+  type: "error";
+  title: string;
+  message: string;
+  key: string | undefined;
+  reference: string | undefined;
+}
+
+/**
+ * The notification for a failed call. A token expiry always renders as "Session Expired" under
+ * one dedup key, whatever the caller's title — that is the one dialect every catch block used to
+ * hand-write.
+ */
+export function apiErrorNotification(title: string, err: unknown, key?: string, fallback?: string): ApiErrorNotification {
+  const { message, reference } = describeApiError(err, fallback);
+  if (err instanceof TokenExpiredError) {
+    return { type: "error", title: "Session Expired", message, key: "session-expired", reference: undefined };
+  }
+  return { type: "error", title, message, key, reference: reference ?? undefined };
+}
diff --git a/src/Web/autopilot-monitor-web/lib/dedupedAuthFetch.ts b/src/Web/autopilot-monitor-web/lib/dedupedAuthFetch.ts
index 91ff91f9..d847a808 100644
--- a/src/Web/autopilot-monitor-web/lib/dedupedAuthFetch.ts
+++ b/src/Web/autopilot-monitor-web/lib/dedupedAuthFetch.ts
@@ -16,8 +16,7 @@
  * body stream is independently readable.
  */
 import { authenticatedFetch } from './authenticatedFetch';
-
-type GetAccessToken = (forceRefresh?: boolean) => Promise<string | null>;
+import { apiErrorFromResponse, parseJsonBody, type GetAccessToken } from './apiClient';
 
 const inFlight = new Map<string, Promise<Response>>();
 
@@ -47,6 +46,13 @@ export async function dedupedAuthFetch(
   return (await pending).clone();
 }
 
+/** dedupedAuthFetch with the apiClient contract: ApiError on non-ok, parsed JSON body otherwise. */
+export async function dedupedFetchJson<T>(url: string, getAccessToken: GetAccessToken, init?: RequestInit): Promise<T> {
+  const response = await dedupedAuthFetch(url, getAccessToken, init);
+  if (!response.ok) throw await apiErrorFromResponse(response);
+  return parseJsonBody<T>(response);
+}
+
 /**
  * Test-only helper to clear the in-flight Map between tests so they don't
  * leak state into one another.
diff --git a/src/Web/autopilot-monitor-web/lib/scopedFetch.ts b/src/Web/autopilot-monitor-web/lib/scopedFetch.ts
deleted file mode 100644
index 6f001aaa..00000000
--- a/src/Web/autopilot-monitor-web/lib/scopedFetch.ts
+++ /dev/null
@@ -1,74 +0,0 @@
-import { authenticatedFetch, TokenExpiredError } from "./authenticatedFetch";
-import { shortCorrelationId } from "./correlationId";
-
-/**
- * JSON fetch layer for the scope-migrated pages: authenticatedFetch + ok-check + body
- * parse in one call, so call sites stop hand-rolling the response boilerplate. Throws
- * ApiError on a non-ok response carrying the backend's error envelope
- * (`{ error, code, correlationId, hint? }` — every non-2xx body since the 2026-09 envelope
- * pass; TokenExpiredError from authenticatedFetch passes through untouched).
- */
-export class ApiError extends Error {
-  constructor(
-    public readonly status: number,
-    message: string,
-    /** Machine-readable code (Constants.ApiErrorCodes or a domain code class); "" when the body had none. */
-    public readonly code: string = "",
-    /** The request's correlation id — the handle for the backend log; "" when the body had none. */
-    public readonly correlationId: string = "",
-    public readonly hint: string | null = null,
-  ) {
-    super(message);
-    this.name = "ApiError";
-  }
-}
-
-/** Shape of the backend error envelope (ApiErrorResponse and its specialised siblings). */
-interface ErrorEnvelope {
-  error?: unknown;
-  code?: unknown;
-  correlationId?: unknown;
-  hint?: unknown;
-  /** Pre-envelope bodies used `message`; still read for the deploy window between backend and web. */
-  message?: unknown;
-}
-
-const str = (v: unknown): string | null => (typeof v === "string" && v.length > 0 ? v : null);
-
-/** Build an ApiError from a non-ok response: envelope fields when present, statusText otherwise. */
-export async function apiErrorFromResponse(response: Response): Promise<ApiError> {
-  let body: ErrorEnvelope | null = null;
-  try {
-    body = (await response.json()) as ErrorEnvelope;
-  } catch {
-    /* not JSON */
-  }
-  const message = str(body?.error) ?? str(body?.message) ?? response.statusText;
-  return new ApiError(response.status, message, str(body?.code) ?? "", str(body?.correlationId) ?? "", str(body?.hint));
-}
-
-export async function fetchJson<T>(
-  url: string,
-  getAccessToken: (forceRefresh?: boolean) => Promise<string | null>,
-  init?: RequestInit,
-): Promise<T> {
-  const response = await authenticatedFetch(url, getAccessToken, init);
-  if (!response.ok) {
-    throw await apiErrorFromResponse(response);
-  }
-  return (await response.json()) as T;
-}
-
-/**
- * One rendering for any thrown error: the user-facing message plus, for backend failures,
- * the short correlation id as a reference the user can quote to support. Pass `reference`
- * to addNotification so the bell shows it.
- */
-export function describeApiError(err: unknown, fallback = "Request failed."): { message: string; reference: string | null } {
-  if (err instanceof TokenExpiredError) return { message: err.message, reference: null };
-  if (err instanceof ApiError) {
-    return { message: err.message || fallback, reference: err.correlationId ? shortCorrelationId(err.correlationId) : null };
-  }
-  if (err instanceof Error && err.message) return { message: err.message, reference: null };
-  return { message: fallback, reference: null };
-}