fix(summary): log LLM error response body

agent_core/providers/summary.py

@@ -32,6 +32,22 @@ class SummaryCandidate(TypedDict):
 })
 
 
+_ERROR_BODY_LOG_LIMIT = 2000
+
+
+def _error_body_excerpt(response: httpx.Response) -> str:
+    try:
+        body = response.text
+    except Exception:  # body may be unread or undecodable
+        return "(unreadable)"
+    body = body.strip()
+    if not body:
+        return "(empty)"
+    if len(body) > _ERROR_BODY_LOG_LIMIT:
+        return body[:_ERROR_BODY_LOG_LIMIT] + f"...[truncated {len(body) - _ERROR_BODY_LOG_LIMIT} chars]"
+    return body
+
+
 def default_summary_retryable(error: Exception) -> bool:
     """Retry transport faults and 5xx, but not permanent request errors."""
     status = getattr(getattr(error, "response", None), "status_code", None)
@@ -222,6 +238,16 @@ async def _summarize_one(
                 return ""
             except Exception as error:
                 logger.warning("Summary LLM attempt %d failed: %s", attempt + 1, error)
+                if isinstance(error, httpx.HTTPStatusError):
+                    # The status line alone ("400 Bad Request") hides why the
+                    # provider rejected the request; log the response body.
+                    logger.warning(
+                        "Summary LLM HTTP %d response body (candidate %d, model %s): %s",
+                        error.response.status_code,
+                        candidate_index + 1,
+                        model,
+                        _error_body_excerpt(error.response),
+                    )
                 if not self.retryable(error):
                     logger.warning(
                         "Summary candidate %d failed permanently; not retrying",

changes/summary-log-error-body.fix.md

@@ -0,0 +1 @@
+Summary LLM failures now log the provider HTTP response body, making rejected requests easier to diagnose.

tests/test_summary_engine.py

@@ -211,3 +211,35 @@ def err(status: int) -> httpx.HTTPStatusError:
     assert default_summary_retryable(err(429))
     assert default_summary_retryable(err(503))
     assert default_summary_retryable(TimeoutError("timeout"))
+
+
+def test_error_response_body_is_logged(
+    monkeypatch: pytest.MonkeyPatch, caplog: pytest.LogCaptureFixture
+) -> None:
+    """A bare "400 Bad Request" hides why the provider rejected the call."""
+    reason = '{"error":{"message":"invalid image_url in content"}}'
+    _install(monkeypatch, [_Response(400, reason)])
+
+    async def sleep(_delay: float) -> None:
+        return None
+
+    engine = SummaryLLMEngine(sleep=sleep, fallback_limit=10)
+    with caplog.at_level("WARNING", logger=summary_mod.__name__):
+        asyncio.run(
+            engine.summarize(
+                "content",
+                "focus",
+                [{"endpoint": "https://a/v1/chat/completions", "model": "m1"}],
+            ),
+        )
+    assert any(
+        "HTTP 400 response body" in r.getMessage() and reason in r.getMessage()
+        for r in caplog.records
+    )
+
+
+def test_error_body_excerpt_truncates() -> None:
+    long = "x" * (summary_mod._ERROR_BODY_LOG_LIMIT + 50)
+    out = summary_mod._error_body_excerpt(httpx.Response(400, text=long))
+    assert out.endswith("[truncated 50 chars]")
+    assert summary_mod._error_body_excerpt(httpx.Response(400, text="")) == "(empty)"