fix: move cause-chain traversal before timeout heuristic (review feedback)

src/agents/failover-error.ts

@@ -238,10 +238,9 @@ export function resolveFailoverReasonFromError(err: unknown): FailoverReason | n
   ) {
     return "timeout";
   }
-  if (isTimeoutError(err)) {
+  // Walk into error cause chain *before* timeout heuristics so that a specific
-    return "timeout";
+  // cause (e.g. RESOURCE_EXHAUSTED wrapped in AbortError) overrides a parent
-  }
+  // message-based "timeout" guess from isTimeoutError.
-  // Walk into error cause chain (e.g. AbortError wrapping a rate-limit cause)
   const cause = getErrorCause(err);
   if (cause && cause !== err) {
     const causeReason = resolveFailoverReasonFromError(cause);
@@ -249,6 +248,9 @@ export function resolveFailoverReasonFromError(err: unknown): FailoverReason | n
       return causeReason;
     }
   }
+  if (isTimeoutError(err)) {
+    return "timeout";
+  }
   if (!message) {
     return null;
   }

src/agents/model-fallback.probe.test.ts

@@ -394,6 +394,15 @@ describe("runWithModelFallback – probe logic", () => {
 
     // All three candidates must be attempted — the abort must not short-circuit
     expect(run).toHaveBeenCalledTimes(3);
+
+    // Verify the primary error is classified as rate_limit, not timeout — the
+    // cause chain (RESOURCE_EXHAUSTED) must override the parent AbortError message.
+    try {
+      await runWithModelFallback({ cfg, provider: "google", model: "gemini-3-flash-preview", run });
+    } catch (err) {
+      expect(String(err)).toContain("(rate_limit)");
+      expect(String(err)).not.toMatch(/gemini.*\(timeout\)/);
+    }
     expect(run).toHaveBeenNthCalledWith(1, "google", "gemini-3-flash-preview", {
       allowTransientCooldownProbe: true,
     });