diff --git a/src/lib/server/osoh-state.json b/src/lib/server/osoh-state.json
new file mode 100644
index 0000000..6395c2b
--- /dev/null
+++ b/src/lib/server/osoh-state.json
@@ -0,0 +1,26 @@
+{
+  "monitoredSites": [
+    {
+      "siteId": "sentinel-demo",
+      "siteSlug": "sentinel-demo",
+      "displayName": "Sentinel Demo",
+      "classification": "external_monitored_surface",
+      "status": "active_monitored_surface",
+      "createdAt": "2026-01-01T00:00:00.000Z",
+      "updatedAt": "2026-01-01T00:00:00.000Z"
+    }
+  ],
+  "monitoredSurfaceTokens": [
+    {
+      "tokenId": "token-sentinel-demo",
+      "siteId": "sentinel-demo",
+      "tokenHash": "f17bed16f9e3d3f1d9f4f81b19bf5f7f62e8c31c6f6b2c1e6d9d2a1a5f6b4c3d",
+      "scope": "ingest",
+      "revoked": false,
+      "createdAt": "2026-01-01T00:00:00.000Z",
+      "updatedAt": "2026-01-01T00:00:00.000Z"
+    }
+  ],
+  "monitoringEvents": [],
+  "auditTrail": []
+}
diff --git a/src/lib/server/osoh-store.ts b/src/lib/server/osoh-store.ts
index 58b87e0..a3f68e3 100644
--- a/src/lib/server/osoh-store.ts
+++ b/src/lib/server/osoh-store.ts
@@ -1,3 +1,6 @@
+import { readFile, writeFile } from 'node:fs/promises';
+import { resolve } from 'node:path';
+
 export type IsoUtcTimestamp = string;
 
 export type OsohMonitoredSurfaceClass = 'external_monitored_surface';
@@ -18,7 +21,9 @@ export type OsohAuditAction =
   | 'site_updated'
   | 'site_disabled'
   | 'token_created'
-  | 'token_revoked';
+  | 'token_revoked'
+  | 'ingest_auth_failed'
+  | 'ingest_event_accepted';
 
 export interface OsohMonitoredSiteRecord {
   siteId: string;
@@ -69,9 +74,21 @@ export interface OsohStoreState {
   auditTrail: OsohAuditTrailRecord[];
 }
 
+const statePath = resolve(process.cwd(), 'src/lib/server/osoh-state.json');
+
 export const createEmptyOsohStoreState = (): OsohStoreState => ({
   monitoredSites: [],
   monitoredSurfaceTokens: [],
   monitoringEvents: [],
   auditTrail: [],
 });
+
+export const loadOsohStoreState = async (): Promise<OsohStoreState> => {
+  const raw = await readFile(statePath, 'utf8');
+  const parsed = JSON.parse(raw) as OsohStoreState;
+  return parsed;
+};
+
+export const saveOsohStoreState = async (state: OsohStoreState): Promise<void> => {
+  await writeFile(statePath, JSON.stringify(state, null, 2) + "`n", 'utf8');
+};
diff --git a/src/pages/api/v1/monitoring/ingest.ts b/src/pages/api/v1/monitoring/ingest.ts
index 2d707db..b2711bc 100644
--- a/src/pages/api/v1/monitoring/ingest.ts
+++ b/src/pages/api/v1/monitoring/ingest.ts
@@ -8,7 +8,8 @@ import type {
   OsohStoreState,
 } from '../../../../../lib/server/osoh-store';
 import {
-  createEmptyOsohStoreState,
+  loadOsohStoreState,
+  saveOsohStoreState,
 } from '../../../../../lib/server/osoh-store';
 import {
   resolveIngestAuth,
@@ -17,7 +18,7 @@ import {
 
 export const prerender = false;
 
-type RouteStage = 'auth' | 'validation' | 'accepted';
+type RouteStage = 'auth' | 'validation' | 'storage' | 'accepted';
 
 type RouteErrorReason =
   | 'missing_token'
@@ -32,7 +33,8 @@ type RouteErrorReason =
   | 'missing_occurred_at'
   | 'invalid_occurred_at'
   | 'missing_payload_body'
-  | 'invalid_payload_body';
+  | 'invalid_payload_body'
+  | 'state_write_failed';
 
 const json = (body: unknown, status: number): Response =>
   new Response(JSON.stringify(body), {
@@ -45,43 +47,20 @@ const json = (body: unknown, status: number): Response =>
 
 const nowIso = (): IsoUtcTimestamp => new Date().toISOString();
 
-const loadOsohStoreState = async (): Promise<OsohStoreState> => {
-  return createEmptyOsohStoreState();
-};
-
-const appendMonitoringEvent = async (
+const appendMonitoringEvent = (
   state: OsohStoreState,
   event: OsohMonitoringEventRecord,
-): Promise<void> => {
+): void => {
   state.monitoringEvents.push(event);
 };
 
-const appendAuditTrailRecord = async (
+const appendAuditTrailRecord = (
   state: OsohStoreState,
   record: OsohAuditTrailRecord,
-): Promise<void> => {
+): void => {
   state.auditTrail.push(record);
 };
 
-const auditAuthFailure = async (
-  state: OsohStoreState,
-  reason: Extract<
-    RouteErrorReason,
-    'missing_token' | 'unknown_token' | 'revoked_token' | 'inactive_site' | 'invalid_scope'
-  >,
-): Promise<void> => {
-  await appendAuditTrailRecord(state, {
-    auditId: randomUUID(),
-    siteId: 'unknown',
-    action: 'site_updated',
-    occurredAt: nowIso(),
-    details: {
-      category: 'ingest_auth_failure',
-      reason,
-    },
-  });
-};
-
 export const POST: APIRoute = async ({ request }) => {
   const state = await loadOsohStoreState();
 
@@ -91,13 +70,35 @@ export const POST: APIRoute = async ({ request }) => {
   );
 
   if (!authResult.ok) {
-    await auditAuthFailure(state, authResult.reason);
+    appendAuditTrailRecord(state, {
+      auditId: randomUUID(),
+      siteId: 'unknown',
+      action: 'ingest_auth_failed',
+      occurredAt: nowIso(),
+      details: {
+        category: 'ingest_auth_failure',
+        reason: authResult.reason,
+      },
+    });
+
+    try {
+      await saveOsohStoreState(state);
+    } catch {
+      return json(
+        {
+          ok: false,
+          stage: 'storage',
+          reason: 'state_write_failed',
+        },
+        500,
+      );
+    }
 
     return json(
       {
         ok: false,
-        stage: 'auth' satisfies RouteStage,
-        reason: authResult.reason satisfies RouteErrorReason,
+        stage: 'auth',
+        reason: authResult.reason,
       },
       401,
     );
@@ -111,8 +112,8 @@ export const POST: APIRoute = async ({ request }) => {
     return json(
       {
         ok: false,
-        stage: 'validation' satisfies RouteStage,
-        reason: 'invalid_json' satisfies RouteErrorReason,
+        stage: 'validation',
+        reason: 'invalid_json',
       },
       400,
     );
@@ -124,8 +125,8 @@ export const POST: APIRoute = async ({ request }) => {
     return json(
       {
         ok: false,
-        stage: 'validation' satisfies RouteStage,
-        reason: validationResult.reason satisfies RouteErrorReason,
+        stage: 'validation',
+        reason: validationResult.reason,
       },
       400,
     );
@@ -134,7 +135,7 @@ export const POST: APIRoute = async ({ request }) => {
   const receivedAt = nowIso();
   const eventId = randomUUID();
 
-  await appendMonitoringEvent(state, {
+  appendMonitoringEvent(state, {
     eventId,
     siteId: authResult.siteId,
     eventType: validationResult.normalized.eventType,
@@ -143,10 +144,10 @@ export const POST: APIRoute = async ({ request }) => {
     payload: validationResult.normalized.payload,
   });
 
-  await appendAuditTrailRecord(state, {
+  appendAuditTrailRecord(state, {
     auditId: randomUUID(),
     siteId: authResult.siteId,
-    action: 'site_updated',
+    action: 'ingest_event_accepted',
     occurredAt: receivedAt,
     details: {
       category: 'ingest_event_accepted',
@@ -155,10 +156,23 @@ export const POST: APIRoute = async ({ request }) => {
     },
   });
 
+  try {
+    await saveOsohStoreState(state);
+  } catch {
+    return json(
+      {
+        ok: false,
+        stage: 'storage',
+        reason: 'state_write_failed',
+      },
+      500,
+    );
+  }
+
   return json(
     {
       ok: true,
-      stage: 'accepted' satisfies RouteStage,
+      stage: 'accepted',
       eventId,
       siteId: authResult.siteId,
       receivedAt,