diff --git a/src/relay/cursor-sidecar-scan.test.ts b/src/relay/cursor-sidecar-scan.test.ts
index 16ac0e5d0a2..491109aa179 100644
--- a/src/relay/cursor-sidecar-scan.test.ts
+++ b/src/relay/cursor-sidecar-scan.test.ts
@@ -313,6 +313,30 @@ describe('scanCursorSidecars', () => {
     )
   })
 
+  it('isolates response-invalid file timestamps without rejecting other sidecars', async () => {
+    const root = await createRoot()
+    const chatsRoot = join(root, 'chats')
+    const bucket = 'acacacacacacacacacacacacacacacac'
+    await Promise.all([
+      addSession(chatsRoot, bucket, 'invalid-time'),
+      addSession(chatsRoot, bucket, 'valid')
+    ])
+    await setSessionMtime(chatsRoot, bucket, 'invalid-time', -1_000)
+
+    const result = await scanCursorSidecars(
+      defaultCursorSidecarScanRequest(chatsRoot, [], process.platform),
+      context
+    )
+
+    expect(result.sidecars.map((sidecar) => sidecar.sessionId)).toEqual(['valid'])
+    expect(result.issues).toContainEqual(
+      expect.objectContaining({
+        path: join(chatsRoot, bucket, 'invalid-time', 'meta.json'),
+        message: 'Cursor session metadata has invalid file timestamps.'
+      })
+    )
+  })
+
   it('normalizes scope truncation deterministically inside the owning-host scan', async () => {
     const root = await createRoot()
     const chatsRoot = join(root, 'chats')
diff --git a/src/shared/cursor-sidecar-scan-discovery.ts b/src/shared/cursor-sidecar-scan-discovery.ts
index 73bec4e896a..3a1e50ae669 100644
--- a/src/shared/cursor-sidecar-scan-discovery.ts
+++ b/src/shared/cursor-sidecar-scan-discovery.ts
@@ -192,6 +192,18 @@ async function inspectSession(
     if (!meta.isFile() || meta.isSymbolicLink() || !store.isFile() || store.isSymbolicLink()) {
       return null
     }
+    if (!isFiniteNonnegative(meta.mtimeMs) || !isFiniteNonnegative(store.mtimeMs)) {
+      addIssue(
+        args.response,
+        metaPath,
+        new Error('Cursor session metadata has invalid file timestamps.')
+      )
+      return null
+    }
+    if (!isFiniteNonnegative(meta.size)) {
+      addIssue(args.response, metaPath, new Error('Cursor session metadata has an invalid size.'))
+      return null
+    }
     if (meta.size > args.caps.sidecarBytes) {
       addIssue(
         args.response,
@@ -277,3 +289,7 @@ function isMissing(error: unknown): boolean {
   const code = (error as NodeJS.ErrnoException | null)?.code
   return code === 'ENOENT' || code === 'ENOTDIR'
 }
+
+function isFiniteNonnegative(value: number): boolean {
+  return Number.isFinite(value) && value >= 0
+}