Keep exception text out of stored and exported span errors

Span.fail stored the exception message in span.error, which is stored and
exported whatever the content settings; a provider's content-filter error
can quote the prompt. span.error now holds the exception type, and the
message is a capture-gated preview, like tool errors already were. A
yielded stream error on the agent span is treated the same way.

docsgpt/logging.py

@@ -234,7 +234,9 @@ def _end_agent_span(span: Any, context: "LogContext", *, error: BaseException |
         span.end(error=error, attributes=attributes)
     elif context.stream_error:
         span.set(**attributes, **{"error.type": "StreamError"})
-        span.error = context.stream_error
+        # The error event's text is gated like any other content.
+        span.preview("error", context.stream_error)
+        span.error = "StreamError"
         span.end(tracing.STATUS_ERROR)
     else:
         span.end(None if completed else tracing.STATUS_CANCELLED, attributes=attributes)

docsgpt/tracing/core.py

@@ -146,10 +146,21 @@ class Span:
         return self
 
     def fail(self, exc: BaseException) -> "Span":
-        """Record ``exc`` on the span without ending it."""
+        """Record ``exc`` on the span without ending it.
+
+        ``error`` and ``error.type`` hold only the exception type: they are
+        stored and exported whatever the content settings, and exception text
+        can quote the prompt (a provider's content-filter error) or a tool
+        result. The message itself becomes the capture-gated ``error``
+        preview, dropped with every other preview when capture is off or a
+        guardrail fired.
+        """
         self.status = STATUS_ERROR
-        self.error = str(exc)[:500] or type(exc).__name__
+        self.error = type(exc).__name__
         self.attributes["error.type"] = type(exc).__name__
+        message = str(exc)
+        if message:
+            self.preview("error", message)
         return self
 
     def end(

tests/test_logging.py

@@ -398,8 +398,6 @@ class TestAccumulateResponseSummary:
         assert ctx.tool_call_count == 2
 
 
-
-
 class TestLogActivityTraceSpan:
     """``@log_activity`` opens the ``invoke_agent`` span for every agent run."""
 
@@ -475,7 +473,8 @@ class TestLogActivityTraceSpan:
         with patch("docsgpt.logging._log_activity_to_db"), tracing.activate(trace):
             list(gen(self._Agent()))
         assert trace.spans[0].status == "error"
-        assert trace.spans[0].error == "node failed"
+        assert trace.spans[0].error == "StreamError"
+        assert trace.spans[0].previews["error"] == "node failed"
 
     def test_raised_error_marks_span_error(self):
         from docsgpt import tracing

tests/tracing/test_trace.py

@@ -133,7 +133,20 @@ class TestNesting:
         span = trace.spans[0]
         assert span.status == "error"
         assert span.attributes["error.type"] == "ValueError"
-        assert span.error == "boom"
+        # Exception text can quote a prompt: it is a capture-gated preview,
+        # never the always-stored/exported ``error``.
+        assert span.error == "ValueError"
+        assert span.previews["error"] == "boom"
+
+    def test_exception_text_is_dropped_when_capture_is_off(self, monkeypatch):
+        monkeypatch.setattr(settings, "TRACES_CAPTURE_CONTENT", False)
+        trace = tracing.start_trace(source="stream")
+        with tracing.activate(trace):
+            with pytest.raises(ValueError):
+                with tracing.span(tracing.KIND_LLM, "chat"):
+                    raise ValueError("content filter: <the user's prompt>")
+        trace.finish()
+        assert "the user's prompt" not in str(trace.to_record())
 
     def test_generator_exit_marks_span_cancelled(self):
         trace = tracing.start_trace(source="stream")