fix(agent): preserve nested API error bodies

agent/error_classifier.py

@@ -1317,19 +1317,25 @@ def _extract_status_code(error: Exception) -> Optional[int]:
 
 
 def _extract_error_body(error: Exception) -> dict:
-    """Extract the structured error body from an SDK exception."""
-    body = getattr(error, "body", None)
-    if isinstance(body, dict):
-        return body
-    # Some errors have .response.json()
-    response = getattr(error, "response", None)
-    if response is not None:
-        try:
-            json_body = response.json()
-            if isinstance(json_body, dict):
-                return json_body
-        except Exception:
-            pass
+    """Extract the structured error body from an SDK exception or its cause chain."""
+    current = error
+    for _ in range(5):  # Match _extract_status_code() traversal depth.
+        body = getattr(current, "body", None)
+        if isinstance(body, dict):
+            return body
+        # Some errors have .response.json()
+        response = getattr(current, "response", None)
+        if response is not None:
+            try:
+                json_body = response.json()
+                if isinstance(json_body, dict):
+                    return json_body
+            except Exception:
+                pass
+        cause = getattr(current, "__cause__", None) or getattr(current, "__context__", None)
+        if cause is None or cause is current:
+            break
+        current = cause
     return {}
 
 

tests/agent/test_error_classifier.py

@@ -127,6 +127,18 @@ class TestExtractErrorBody:
         e = MockAPIError("fail", body={"error": {"message": "bad"}})
         assert _extract_error_body(e) == {"error": {"message": "bad"}}
 
+    def test_from_cause_chain_body_attr(self):
+        inner = MockAPIError(
+            "inner",
+            status_code=402,
+            body={"error": {"message": "Usage limit reached, try again in 5 minutes"}},
+        )
+        outer = Exception("outer")
+        outer.__cause__ = inner
+        assert _extract_error_body(outer) == {
+            "error": {"message": "Usage limit reached, try again in 5 minutes"},
+        }
+
     def test_empty_when_no_body(self):
         assert _extract_error_body(Exception("generic")) == {}
 
@@ -300,6 +312,21 @@ class TestClassifyApiError:
         assert result.retryable is False
         assert result.should_fallback is True
 
+    def test_wrapped_402_uses_nested_body_message(self):
+        inner = MockAPIError(
+            "inner",
+            status_code=402,
+            body={"error": {"message": "Usage limit reached, try again in 5 minutes"}},
+        )
+        outer = Exception("outer")
+        outer.__cause__ = inner
+
+        result = classify_api_error(outer)
+
+        assert result.reason == FailoverReason.rate_limit
+        assert result.retryable is True
+        assert result.message == "Usage limit reached, try again in 5 minutes"
+
     # ── Rate limit ──
 
     def test_429_rate_limit(self):