diff --git a/src/main/daemon/daemon-pty-adapter-protocol-compatibility.test.ts b/src/main/daemon/daemon-pty-adapter-protocol-compatibility.test.ts
index 8132f2de4e2..3fc255b60ec 100644
--- a/src/main/daemon/daemon-pty-adapter-protocol-compatibility.test.ts
+++ b/src/main/daemon/daemon-pty-adapter-protocol-compatibility.test.ts
@@ -243,16 +243,29 @@ describe('DaemonPtyAdapter (IPtyProvider)', () => {
   })
 
   describe('background stream thinning compatibility', () => {
-    it('reports authoritative snapshot support only for the corrected serializer protocol', () => {
+    it('reports authoritative snapshot support only for the corrected serializer protocol', async () => {
+      const { id } = await adapter.spawn({ cols: 80, rows: 24 })
       const legacy = new DaemonPtyAdapter({ socketPath, tokenPath, protocolVersion: 31 })
       try {
-        expect(legacy.canProvideAuthoritativeBufferSnapshot('legacy-session')).toBe(false)
-        expect(adapter.canProvideAuthoritativeBufferSnapshot('current-session')).toBe(true)
+        expect(legacy.canProvideAuthoritativeBufferSnapshot(id)).toBe(false)
+        expect(adapter.canProvideAuthoritativeBufferSnapshot(id)).toBe(true)
       } finally {
         legacy.dispose()
       }
     })
 
+    // Why this matters beyond tidiness: getProviderForPty falls back to the local provider for
+    // any id it cannot place, so these ids reach this adapter for real. Answered from the
+    // protocol flag alone they came back `true`, which the renderer caches as a definitive
+    // per-pty licence to unmount a pane whose bytes this daemon never held.
+    it('refuses an authoritative snapshot claim for a session it does not own', async () => {
+      const { id } = await adapter.spawn({ cols: 80, rows: 24 })
+
+      expect(adapter.canProvideAuthoritativeBufferSnapshot(id)).toBe(true)
+      expect(adapter.canProvideAuthoritativeBufferSnapshot('remote:env-1:pty-1')).toBe(false)
+      expect(adapter.canProvideAuthoritativeBufferSnapshot('never-spawned-session')).toBe(false)
+    })
+
     it('reports background state on the authoritative-snapshot protocol', () => {
       const notifySpy = vi.spyOn(DaemonClient.prototype, 'notify')
       try {
diff --git a/src/main/daemon/daemon-pty-runtime-state.ts b/src/main/daemon/daemon-pty-runtime-state.ts
index e471f698748..38480af1489 100644
--- a/src/main/daemon/daemon-pty-runtime-state.ts
+++ b/src/main/daemon/daemon-pty-runtime-state.ts
@@ -237,8 +237,12 @@ export abstract class DaemonPtyRuntimeState {
     return this.protocolVersion >= GIT_CREDENTIAL_GUARD_HOST_PROTOCOL_VERSION
   }
 
-  canProvideAuthoritativeBufferSnapshot(_id: string): boolean {
-    return this.supportsAuthoritativeBufferSnapshots
+  // Why the id is read rather than ignored: the contract promises a fact about THIS pty, and
+  // getProviderForPty falls back to the local provider for any id it cannot place. A
+  // remote-runtime id therefore reaches this adapter, and answering from the protocol flag
+  // alone returned `true` for a session this daemon has never owned.
+  canProvideAuthoritativeBufferSnapshot(id: string): boolean {
+    return this.supportsAuthoritativeBufferSnapshots && this.activeSessionIds.has(id)
   }
 
   protected get canDelegateBackgroundToDaemon(): boolean {