diff --git a/agent/api_error_summary.py b/agent/api_error_summary.py
index 3e907dbaf3..5a1e884c27 100644
--- a/agent/api_error_summary.py
+++ b/agent/api_error_summary.py
@@ -142,7 +142,9 @@ class ApiErrorSummaryMixin:
                 )
             current = current.__cause__ or current.__context__
 
-        if isinstance(error, ValueError) and "expected ident at line" in raw.lower():
+        if isinstance(error, ValueError) and any(
+            marker in raw.lower() for marker in ("expected ident at line", "expected value at line")
+        ):
             return f"Malformed provider streaming response: {raw[:300]}"
 
         prefix = _http_prefix(error)
diff --git a/agent/chat_completion_helpers.py b/agent/chat_completion_helpers.py
index e44353d0e0..e573e7068b 100644
--- a/agent/chat_completion_helpers.py
+++ b/agent/chat_completion_helpers.py
@@ -3019,6 +3019,7 @@ class _StreamingCall(StreamingWaitMonitor):
         self._writer_token = None
         _stream_context = {"manager": None, "stream": None}
         base_final_message = None
+        stream_parse_error = None
 
         from agent import relay_llm
         from agent.anthropic_adapter import sanitize_anthropic_kwargs
@@ -3074,6 +3075,17 @@ class _StreamingCall(StreamingWaitMonitor):
                         raise EmptyStreamError(
                             "Provider returned an empty stream with no events (possible upstream error or malformed event stream).") from None
                     raise
+        except ValueError as exc:
+            # Fine-grained tool streaming exposes raw partial JSON. The Anthropic SDK
+            # may fail while incrementally decoding it before get_final_message() can
+            # return its buffered/repaired representation. Only recover after a tool
+            # block started; unrelated ValueErrors retain their normal handling.
+            _error_text = str(exc).strip().lower()
+            if not has_tool_use or not any(
+                marker in _error_text for marker in ("expected value at line", "expected ident at line")
+            ):
+                raise
+            stream_parse_error = exc
         finally:
             try:
                 self._close_managed_stream()
@@ -3084,6 +3096,19 @@ class _StreamingCall(StreamingWaitMonitor):
 
         if self.agent._interrupt_requested:
             return None
+        if stream_parse_error is not None:
+            fallback_kwargs = dict(self.api_kwargs)
+            fallback_kwargs.pop("stream", None)
+            sanitize_anthropic_kwargs(
+                fallback_kwargs, log_prefix=getattr(self.agent, "log_prefix", "")
+            )
+            logger.warning(
+                "%sAnthropic tool stream JSON parsing failed (%s); retrying once with buffered messages.create()",
+                getattr(self.agent, "log_prefix", ""),
+                stream_parse_error,
+            )
+            base_final_message = request_client.messages.create(**fallback_kwargs)
+            return self._check_anthropic_message(base_final_message)
         if base_final_message is not None:
             self._check_anthropic_message(base_final_message, tool_drop=False)
             if not stream.output_modified:
diff --git a/run_agent.py b/run_agent.py
index e6601e440c..3174c413ed 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -485,7 +485,8 @@ class AIAgent(
         that is wire trouble, not local validation, so it follows the truncated-JSON retry path."""
         return (getattr(self, "api_mode", None) == "anthropic_messages" and isinstance(error, ValueError)
                 and not isinstance(error, (UnicodeEncodeError, json.JSONDecodeError))
-                and "expected ident at line" in str(error).strip().lower())
+                and any(marker in str(error).strip().lower() for marker in (
+                    "expected ident at line", "expected value at line")))
 
     _log_stream_retry = _forward("agent.stream_diag", "log_stream_retry")
     _emit_stream_drop = _forward("agent.stream_diag", "emit_stream_drop")
diff --git a/tests/agent/test_streaming.py b/tests/agent/test_streaming.py
index 52426a6a2b..c5e15fd548 100644
--- a/tests/agent/test_streaming.py
+++ b/tests/agent/test_streaming.py
@@ -1136,6 +1136,52 @@ class TestAnthropicStreamCallbacks:
         assert mock_rebuild.call_count == 0
         assert agent._anthropic_client.close.call_count >= 1
 
+    def test_anthropic_malformed_tool_json_falls_back_to_buffered_message(self):
+        """Malformed fine-grained tool JSON uses Anthropic's buffered response."""
+        from run_agent import AIAgent
+
+        agent = AIAgent(
+            api_key="test-key",
+            base_url="https://api.anthropic.com",
+            model="claude-sonnet-4-5",
+            quiet_mode=True,
+            skip_context_files=True,
+            skip_memory=True,
+        )
+        agent.api_mode = "anthropic_messages"
+        agent._interrupt_requested = False
+
+        class _MalformedToolStream:
+            response = None
+
+            def __enter__(self):
+                return self
+
+            def __exit__(self, *_args):
+                return False
+
+            def __iter__(self):
+                yield SimpleNamespace(
+                    type="content_block_start",
+                    content_block=SimpleNamespace(type="tool_use", name="cronjob_manage"),
+                )
+                raise ValueError("expected value at line 1 column 11")
+
+        repaired_message = SimpleNamespace(
+            content=[SimpleNamespace(type="tool_use", name="cronjob_manage", input={"names": "cronjob_manage"})],
+            stop_reason="tool_use",
+        )
+        agent._anthropic_client = MagicMock()
+        agent._anthropic_client.messages.stream.return_value = _MalformedToolStream()
+        agent._anthropic_client.messages.create.return_value = repaired_message
+        agent._create_request_anthropic_client = lambda *a, **k: agent._anthropic_client
+
+        response = agent._interruptible_streaming_api_call({"model": agent.model})
+
+        assert response is repaired_message
+        assert agent._anthropic_client.messages.stream.call_count == 1
+        assert agent._anthropic_client.messages.create.call_count == 1
+
     @patch("run_agent.AIAgent._replace_primary_openai_client")
     def test_generic_anthropic_valueerror_still_propagates_without_stream_retry(
         self, mock_replace, monkeypatch,