fix(agents): prevent indefinite session model pinning from polluted fallback origin

wings1029 · claude · wings1029 · commit e4f9eb9e6539 · 2026-06-15T19:44:05.000+08:00
resolveAutoFallbackPrimaryProbe required the persisted modelOverrideFallbackOrigin to match the current configured primary before firing the snap-back probe. When the origin fields were polluted with the failing model instead of the configured primary (#92776), the guard returned undefined and the probe never fired — leaving the session permanently stuck on a degraded fallback model. Fix: use the current configured primary as the probe origin instead of requiring a matching persisted origin. This ensures the snap-back probe always fires, attempting to clear the auto-fallback override once the primary becomes available. Also relax entryMatchesAutoFallbackPrimaryProbe to match on the fallback override alone (provider/model) without requiring the persisted origin to match — polluted session entries must still be updatable after the probe fires. Test: updated 'skips primary probes for strict or stale fallback selections' — when origin differs from primary, the probe now returns a valid probe targeting the current primary instead of undefined. Fixes #92776. Co-Authored-By: Claude <noreply@anthropic.com>
diff --git a/src/agents/agent-scope.test.ts b/src/agents/agent-scope.test.ts
@@ -663,7 +663,12 @@ describe("resolveAgentConfig", () => {
         primaryModel: "gpt-5.4",
         probeState: new Map(),
       }),
-    ).toBeUndefined();
+    ).toEqual({
+      provider: "openai",
+      model: "gpt-5.4",
+      fallbackProvider: "google",
+      fallbackModel: "gemini-3-pro",
+    });
     expect(
       resolveAutoFallbackPrimaryProbe({
         entry: {
diff --git a/src/agents/agent-scope.ts b/src/agents/agent-scope.ts
@@ -151,25 +151,29 @@ export function resolveAutoFallbackPrimaryProbe(params: {
     return undefined;
   }
 
-  const originProvider = normalizeOptionalString(entry.modelOverrideFallbackOriginProvider);
-  const originModel = normalizeOptionalString(entry.modelOverrideFallbackOriginModel);
   const overrideProvider = normalizeOptionalString(entry.providerOverride);
   const overrideModel = normalizeOptionalString(entry.modelOverride);
   const primaryProvider = normalizeOptionalString(params.primaryProvider);
   const primaryModel = normalizeOptionalString(params.primaryModel);
-  if (!originProvider || !originModel || !overrideProvider || !overrideModel) {
+  if (!overrideProvider || !overrideModel) {
     return undefined;
   }
   if (!primaryProvider || !primaryModel) {
     return undefined;
   }
-  if (originProvider !== primaryProvider || originModel !== primaryModel) {
-    return undefined;
-  }
-  if (overrideProvider === originProvider && overrideModel === originModel) {
+  if (overrideProvider === primaryProvider && overrideModel === primaryModel) {
     return undefined;
   }
 
+  // Use the current configured primary as the probe origin rather than
+  // requiring a persisted origin that matches.  The persisted origin
+  // can be missing (first fallback), polluted with the failing model
+  // instead of the primary (#92776), or stale (primary changed).
+  // Using the current primary ensures the snap-back probe fires and
+  // clears the auto-fallback override once the primary is available.
+  const probeOriginProvider = primaryProvider;
+  const probeOriginModel = primaryModel;
+
   const now = params.now ?? Date.now();
   const minIntervalMs = params.minIntervalMs ?? AUTO_FALLBACK_PRIMARY_PROBE_INTERVAL_MS;
   const state = params.probeState ?? autoFallbackPrimaryProbeState;
@@ -181,8 +185,8 @@ export function resolveAutoFallbackPrimaryProbe(params: {
   });
   const key = autoFallbackPrimaryProbeStateKey({
     sessionKey: params.sessionKey,
-    primaryProvider: originProvider,
-    primaryModel: originModel,
+    primaryProvider: probeOriginProvider,
+    primaryModel: probeOriginModel,
   });
   const lastProbeAt = state.get(key);
   if (
@@ -197,8 +201,8 @@ export function resolveAutoFallbackPrimaryProbe(params: {
     entry.authProfileOverrideSource ??
     (entry.authProfileOverrideCompactionCount !== undefined ? "auto" : undefined);
   return {
-    provider: originProvider,
-    model: originModel,
+    provider: probeOriginProvider,
+    model: probeOriginModel,
     fallbackProvider: overrideProvider,
     fallbackModel: overrideModel,
     ...(fallbackAuthProfileId
@@ -263,11 +267,14 @@ export function entryMatchesAutoFallbackPrimaryProbe(
   if (entry.modelOverrideSource !== "auto" && !recoveredAutoFallbackOverride) {
     return false;
   }
+  // Match on the fallback override (the model the session was stuck on).
+  // We intentionally do NOT require the persisted origin to match the
+  // probe origin — the origin can be polluted (#92776) and the probe
+  // now always uses the current configured primary.  Matching only on
+  // the override ensures polluted session entries can still be updated.
   return (
     normalizeOptionalString(entry.providerOverride) === probe.fallbackProvider &&
-    normalizeOptionalString(entry.modelOverride) === probe.fallbackModel &&
-    normalizeOptionalString(entry.modelOverrideFallbackOriginProvider) === probe.provider &&
-    normalizeOptionalString(entry.modelOverrideFallbackOriginModel) === probe.model
+    normalizeOptionalString(entry.modelOverride) === probe.fallbackModel
   );
 }
 
