diff --git a/packages/core/src/agents/acknowledgedAgents.test.ts b/packages/core/src/agents/acknowledgedAgents.test.ts
index f6e45360db6..2fe59253d43 100644
--- a/packages/core/src/agents/acknowledgedAgents.test.ts
+++ b/packages/core/src/agents/acknowledgedAgents.test.ts
@@ -94,4 +94,34 @@ describe('AcknowledgedAgentsService', () => {
       false,
     );
   });
+
+  it.each([
+    'null',
+    '42',
+    '"str"',
+    '[]',
+    '{"/project": "str"}',
+    '{"/project": 42}',
+    '{"/project": null}',
+    '{"/project": []}',
+  ])(
+    'should fall back to empty for valid JSON with the wrong shape (%s, #29207)',
+    async (content) => {
+      const ackPath = Storage.getAcknowledgedAgentsPath();
+      await fs.mkdir(path.dirname(ackPath), { recursive: true });
+      await fs.writeFile(ackPath, content, 'utf-8');
+
+      const service = new AcknowledgedAgentsService();
+
+      await expect(
+        service.isAcknowledged('/project', 'Agent', 'hash'),
+      ).resolves.toBe(false);
+      await expect(
+        service.acknowledge('/project', 'Agent', 'hash'),
+      ).resolves.toBeUndefined();
+      await expect(
+        service.isAcknowledged('/project', 'Agent', 'hash'),
+      ).resolves.toBe(true);
+    },
+  );
 });
diff --git a/packages/core/src/agents/acknowledgedAgents.ts b/packages/core/src/agents/acknowledgedAgents.ts
index 98c90afb96c..6cb4af3e21d 100644
--- a/packages/core/src/agents/acknowledgedAgents.ts
+++ b/packages/core/src/agents/acknowledgedAgents.ts
@@ -17,6 +17,20 @@ export interface AcknowledgedAgentsMap {
   };
 }
 
+function isAcknowledgedAgentsMap(
+  value: unknown,
+): value is AcknowledgedAgentsMap {
+  if (!value || typeof value !== 'object' || Array.isArray(value)) {
+    return false;
+  }
+  // Each project entry must itself be a map object: a truthy primitive
+  // (e.g. {"/project": "str"}) would otherwise pass this guard and then
+  // crash acknowledge() with "Cannot create property on string".
+  return Object.values(value).every(
+    (entry) => !!entry && typeof entry === 'object' && !Array.isArray(entry),
+  );
+}
+
 export class AcknowledgedAgentsService {
   private acknowledgedAgents: AcknowledgedAgentsMap = {};
   private loaded = false;
@@ -27,8 +41,18 @@ export class AcknowledgedAgentsService {
     const filePath = Storage.getAcknowledgedAgentsPath();
     try {
       const content = await fs.readFile(filePath, 'utf-8');
-      // eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
-      this.acknowledgedAgents = JSON.parse(content);
+      const parsed: unknown = JSON.parse(content);
+      // A previous interrupted save (full disk, sync conflict, hand edit)
+      // can leave valid JSON with the wrong shape (null, array, scalar).
+      // Fall back to empty rather than crashing callers (#29207).
+      if (isAcknowledgedAgentsMap(parsed)) {
+        this.acknowledgedAgents = parsed;
+      } else {
+        debugLogger.error(
+          'Failed to load acknowledged agents: unexpected file shape, falling back to empty.',
+        );
+        this.acknowledgedAgents = {};
+      }
     } catch (error: unknown) {
       if (!isNodeError(error) || error.code !== 'ENOENT') {
         debugLogger.error(