feat(web): expose EnableIndexDualWrite toggle in admin Global Settings

Closes the operator-facing gap left by M5.d.2: the feature flag was
plumbed server-side (AdminConfiguration model + TableConfigRepository
Store/Map) but the UI had no way to flip it. Without this change the
entire M5.d pipeline was unreachable in production.

Wire-up mirrors the existing allowAgentDowngrade toggle (closest analog
— also a developer/ops-level bool with caveat copy):

- types/adminConfig.ts: add optional enableIndexDualWrite field with a
  doc comment pointing at Plan §M5.d so future maintainers understand
  what toggling it does.
- AdminConfigContext.tsx: add state + setter, hydrate from GET response
  (default false), include in save-spread, include in reset fallback,
  expose via context value + save-useCallback deps.
- AdminConfigSettingsSection.tsx: add prop pair and a checkbox-style
  toggle below the ModernDeployment harmless-IDs input. Copy explains
  the 5 index tables + the 2h safety-net timer + warns that it should
  only be flipped after release-gate verification.
- SectionGlobalSettings.tsx: destructure + forward the new prop pair.

Round-trip is safe: GET (System.Text.Json, camelCase) emits
enableIndexDualWrite, UI spreads it back into PUT body, Newtonsoft
case-insensitive deserialization binds to EnableIndexDualWrite on the
model — so an operator save no longer silently resets the flag.

Verification: npx tsc --noEmit clean, vitest suite 168/168 green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Web/autopilot-monitor-web/app/admin/AdminConfigContext.tsx

@@ -34,6 +34,8 @@ interface AdminConfigContextValue {
   setAllowAgentDowngrade: (value: boolean) => void;
   modernDeploymentHarmlessEventIds: string;
   setModernDeploymentHarmlessEventIds: (value: string) => void;
+  enableIndexDualWrite: boolean;
+  setEnableIndexDualWrite: (value: boolean) => void;
 
   // Diagnostics log paths
   globalDiagPaths: DiagnosticsLogPath[];
@@ -110,6 +112,7 @@ export function AdminConfigProvider({ children }: { children: React.ReactNode })
   const [opsEventRetentionDays, setOpsEventRetentionDays] = useState(90);
   const [allowAgentDowngrade, setAllowAgentDowngrade] = useState(false);
   const [modernDeploymentHarmlessEventIds, setModernDeploymentHarmlessEventIds] = useState("100, 1005");
+  const [enableIndexDualWrite, setEnableIndexDualWrite] = useState(false);
 
   // Diagnostics Log Paths state
   const [globalDiagPaths, setGlobalDiagPaths] = useState<DiagnosticsLogPath[]>([]);
@@ -162,6 +165,7 @@ export function AdminConfigProvider({ children }: { children: React.ReactNode })
         setOpsEventRetentionDays(data.opsEventRetentionDays ?? 90);
         setAllowAgentDowngrade(data.allowAgentDowngrade ?? false);
         setModernDeploymentHarmlessEventIds(parseHarmlessEventIdsJson(data.modernDeploymentHarmlessEventIdsJson));
+        setEnableIndexDualWrite(data.enableIndexDualWrite ?? false);
         try {
           setGlobalDiagPaths(data.diagnosticsGlobalLogPathsJson ? JSON.parse(data.diagnosticsGlobalLogPathsJson) : []);
         } catch {
@@ -255,6 +259,7 @@ export function AdminConfigProvider({ children }: { children: React.ReactNode })
         opsEventRetentionDays,
         allowAgentDowngrade,
         modernDeploymentHarmlessEventIdsJson: serializeHarmlessEventIds(modernDeploymentHarmlessEventIds),
+        enableIndexDualWrite,
       };
 
       const response = await authenticatedFetch(api.globalConfig.get(), getAccessToken, {
@@ -281,7 +286,7 @@ export function AdminConfigProvider({ children }: { children: React.ReactNode })
     } finally {
       setSavingConfig(false);
     }
-  }, [adminConfig, globalRateLimit, platformStatsBlobSasUrl, collectorIdleTimeoutMinutes, maxSessionWindowHours, maintenanceBlockDurationHours, opsEventRetentionDays, allowAgentDowngrade, modernDeploymentHarmlessEventIds, getAccessToken]);
+  }, [adminConfig, globalRateLimit, platformStatsBlobSasUrl, collectorIdleTimeoutMinutes, maxSessionWindowHours, maintenanceBlockDurationHours, opsEventRetentionDays, allowAgentDowngrade, modernDeploymentHarmlessEventIds, enableIndexDualWrite, getAccessToken]);
 
   // Reset admin config
   const handleResetAdminConfig = useCallback(() => {
@@ -294,6 +299,7 @@ export function AdminConfigProvider({ children }: { children: React.ReactNode })
     setOpsEventRetentionDays(adminConfig.opsEventRetentionDays ?? 90);
     setAllowAgentDowngrade(adminConfig.allowAgentDowngrade ?? false);
     setModernDeploymentHarmlessEventIds(parseHarmlessEventIdsJson(adminConfig.modernDeploymentHarmlessEventIdsJson));
+    setEnableIndexDualWrite(adminConfig.enableIndexDualWrite ?? false);
     try {
       setGlobalDiagPaths(adminConfig.diagnosticsGlobalLogPathsJson ? JSON.parse(adminConfig.diagnosticsGlobalLogPathsJson) : []);
     } catch {
@@ -418,6 +424,7 @@ export function AdminConfigProvider({ children }: { children: React.ReactNode })
       opsEventRetentionDays, setOpsEventRetentionDays,
       allowAgentDowngrade, setAllowAgentDowngrade,
       modernDeploymentHarmlessEventIds, setModernDeploymentHarmlessEventIds,
+      enableIndexDualWrite, setEnableIndexDualWrite,
       globalDiagPaths, setGlobalDiagPaths, savingDiagPaths,
       opsAlertRules, setOpsAlertRules,
       opsAlertTelegramEnabled, setOpsAlertTelegramEnabled,

src/Web/autopilot-monitor-web/app/admin/components/AdminConfigSettingsSection.tsx

@@ -16,6 +16,8 @@ interface AdminConfigSettingsSectionProps {
   setAllowAgentDowngrade: (value: boolean) => void;
   modernDeploymentHarmlessEventIds: string;
   setModernDeploymentHarmlessEventIds: (value: string) => void;
+  enableIndexDualWrite: boolean;
+  setEnableIndexDualWrite: (value: boolean) => void;
   onSave: () => Promise<void>;
   onReset: () => void;
 }
@@ -34,6 +36,8 @@ export function AdminConfigSettingsSection({
   setAllowAgentDowngrade,
   modernDeploymentHarmlessEventIds,
   setModernDeploymentHarmlessEventIds,
+  enableIndexDualWrite,
+  setEnableIndexDualWrite,
   onSave,
   onReset,
 }: AdminConfigSettingsSectionProps) {
@@ -152,6 +156,34 @@ export function AdminConfigSettingsSection({
               </label>
             </div>
 
+            <div>
+              <label className="flex items-start space-x-3 cursor-pointer">
+                <input
+                  type="checkbox"
+                  checked={enableIndexDualWrite}
+                  onChange={(e) => setEnableIndexDualWrite(e.target.checked)}
+                  className="mt-1 h-5 w-5 rounded border-indigo-300 dark:border-indigo-600 text-indigo-600 focus:ring-indigo-500"
+                />
+                <span>
+                  <span className="text-indigo-900 dark:text-indigo-100 font-medium">V2 Decision Engine: Enable index-table dual-write</span>
+                  <p className="text-sm text-indigo-800 dark:text-gray-300 mt-1">
+                    Feature flag for the M5.d secondary-index fan-out. When <strong>off</strong> (default), the V2 telemetry
+                    ingest path writes only the primary <code className="text-xs bg-indigo-100 dark:bg-indigo-900 dark:text-indigo-200 px-1 rounded">Signals</code> and
+                    <code className="ml-1 text-xs bg-indigo-100 dark:bg-indigo-900 dark:text-indigo-200 px-1 rounded">DecisionTransitions</code> tables. When
+                    <strong> on</strong>, each committed primary row is also enqueued onto the <code className="text-xs bg-indigo-100 dark:bg-indigo-900 dark:text-indigo-200 px-1 rounded">telemetry-index-reconcile</code> queue
+                    and fanned out into the 5 cross-session index tables
+                    (<code className="text-xs bg-indigo-100 dark:bg-indigo-900 dark:text-indigo-200 px-1 rounded">SessionsByTerminal</code>,
+                    <code className="ml-1 text-xs bg-indigo-100 dark:bg-indigo-900 dark:text-indigo-200 px-1 rounded">SessionsByStage</code>,
+                    <code className="ml-1 text-xs bg-indigo-100 dark:bg-indigo-900 dark:text-indigo-200 px-1 rounded">DeadEndsByReason</code>,
+                    <code className="ml-1 text-xs bg-indigo-100 dark:bg-indigo-900 dark:text-indigo-200 px-1 rounded">ClassifierVerdictsByIdLevel</code>,
+                    <code className="ml-1 text-xs bg-indigo-100 dark:bg-indigo-900 dark:text-indigo-200 px-1 rounded">SignalsByKind</code>).
+                    A 2h timer re-scans the last 4h as a safety net against queue failures. Flip this on only after the
+                    M5.d release-gate tests have been verified in the target environment.
+                  </p>
+                </span>
+              </label>
+            </div>
+
             {adminConfig && (
               <div className="bg-blue-50 dark:bg-gray-700 border border-blue-200 dark:border-indigo-600 rounded-lg p-3">
                 <div className="flex items-start space-x-2">

src/Web/autopilot-monitor-web/app/admin/settings/sections/SectionGlobalSettings.tsx

@@ -12,6 +12,7 @@ export function SectionGlobalSettings() {
     collectorIdleTimeoutMinutes, setCollectorIdleTimeoutMinutes,
     allowAgentDowngrade, setAllowAgentDowngrade,
     modernDeploymentHarmlessEventIds, setModernDeploymentHarmlessEventIds,
+    enableIndexDualWrite, setEnableIndexDualWrite,
     handleSaveAdminConfig, handleResetAdminConfig,
   } = useAdminConfig();
 
@@ -32,6 +33,8 @@ export function SectionGlobalSettings() {
         setAllowAgentDowngrade={setAllowAgentDowngrade}
         modernDeploymentHarmlessEventIds={modernDeploymentHarmlessEventIds}
         setModernDeploymentHarmlessEventIds={setModernDeploymentHarmlessEventIds}
+        enableIndexDualWrite={enableIndexDualWrite}
+        setEnableIndexDualWrite={setEnableIndexDualWrite}
         onSave={handleSaveAdminConfig}
         onReset={handleResetAdminConfig}
       />

src/Web/autopilot-monitor-web/types/adminConfig.ts

@@ -24,6 +24,13 @@ export interface AdminConfiguration {
   opsAlertSlackWebhookUrl?: string;
   allowAgentDowngrade?: boolean;
   modernDeploymentHarmlessEventIdsJson?: string;
+  /**
+   * Feature flag for the V2 Decision Engine index-table dual-write (Plan §M5.d).
+   * When true, IngestTelemetryFunction enqueues telemetry-index-reconcile envelopes after
+   * committing each primary row, and the 2h IndexReconcileTimer re-scans the last 4h as
+   * a safety net. Default false — keeps pre-M5.d behaviour bit-exact until explicitly flipped.
+   */
+  enableIndexDualWrite?: boolean;
 }
 
 export interface OpsAlertRule {