diff --git a/src/server/proxy-core/runtime/codexSessionResponseStore.test.ts b/src/server/proxy-core/runtime/codexSessionResponseStore.test.ts
index 6543758..ba25742 100644
--- a/src/server/proxy-core/runtime/codexSessionResponseStore.test.ts
+++ b/src/server/proxy-core/runtime/codexSessionResponseStore.test.ts
@@ -126,4 +126,32 @@ describe('codexSessionResponseStore', () => {
 
     resetCodexSessionResponseStore();
   });
+
+  it('keeps the latest continuation id when the same downstream session drifts back to an earlier scope', () => {
+    resetCodexSessionResponseStore();
+
+    const originalScopedKey = buildCodexSessionResponseStoreKey({
+      sessionId: 'session-roundtrip',
+      siteId: 10,
+      accountId: 20,
+      channelId: 30,
+    });
+    const driftedScopedKey = buildCodexSessionResponseStoreKey({
+      sessionId: 'session-roundtrip',
+      siteId: 10,
+      accountId: 21,
+      channelId: 31,
+    });
+
+    setCodexSessionResponseId(originalScopedKey, 'resp-roundtrip-1');
+
+    expect(getCodexSessionResponseId(driftedScopedKey)).toBe('resp-roundtrip-1');
+
+    setCodexSessionResponseId(driftedScopedKey, 'resp-roundtrip-2');
+
+    expect(getCodexSessionResponseId(driftedScopedKey)).toBe('resp-roundtrip-2');
+    expect(getCodexSessionResponseId(originalScopedKey)).toBe('resp-roundtrip-2');
+
+    resetCodexSessionResponseStore();
+  });
 });
diff --git a/src/server/proxy-core/runtime/codexSessionResponseStore.ts b/src/server/proxy-core/runtime/codexSessionResponseStore.ts
index 7baff1b..487b6f8 100644
--- a/src/server/proxy-core/runtime/codexSessionResponseStore.ts
+++ b/src/server/proxy-core/runtime/codexSessionResponseStore.ts
@@ -57,6 +57,16 @@ function getSessionStoreKeys(sessionId: string): string[] {
   ];
 }
 
+function reconcileScopedSessionFallback(bareSessionKey: string): void {
+  if (!bareSessionKey) return;
+
+  for (const key of codexSessionResponseIds.keys()) {
+    if (key === bareSessionKey) continue;
+    if (getBareSessionStoreKey(key) !== bareSessionKey) continue;
+    codexSessionResponseIds.delete(key);
+  }
+}
+
 function normalizeSessionId(sessionId: string): string {
   return sessionId.trim();
 }
@@ -87,7 +97,10 @@ export function getCodexSessionResponseId(sessionId: string): string | null {
 
   for (const fallbackKey of getFallbackSessionStoreKeys(normalized)) {
     const fallback = codexSessionResponseIds.get(fallbackKey);
-    if (fallback) return fallback;
+    if (fallback) {
+      reconcileScopedSessionFallback(fallbackKey);
+      return fallback;
+    }
   }
 
   return null;