fix(otel): filter spans before adding origin attributes

py/src/braintrust/otel/__init__.py

@@ -92,6 +92,29 @@ def _with_span_origin_attributes(span, environment):
     return _SpanWithAttributes(span, attributes)
 
 
+class _SpanOriginProcessor:
+    """Add Braintrust span origin attributes after any upstream filtering."""
+
+    def __init__(self, processor, environment):
+        self._processor = processor
+        self._environment = environment
+
+    def on_start(self, span, parent_context=None):
+        self._processor.on_start(span, parent_context)
+
+    def on_end(self, span):
+        self._processor.on_end(_with_span_origin_attributes(span, self._environment))
+
+    def _on_ending(self, span):
+        _forward_on_ending(self._processor, span)
+
+    def shutdown(self):
+        self._processor.shutdown()
+
+    def force_flush(self, timeout_millis=30000):
+        return self._processor.force_flush(timeout_millis)
+
+
 class AISpanProcessor:
     """
     A span processor that filters spans to only export filtered telemetry.
@@ -355,14 +378,13 @@ def __init__(
         if SpanProcessor is None:
             SpanProcessor = BatchSpanProcessor
 
-        # Always create a BatchSpanProcessor first
-        processor = SpanProcessor(self._exporter)
+        # Add provenance downstream so filtering decisions use the span's original attributes.
+        processor = _SpanOriginProcessor(SpanProcessor(self._exporter), self._environment)
 
         if filter_ai_spans:
-            # Wrap the BatchSpanProcessor with filtering
+            # Wrap the origin-injecting processor so filtering runs first.
             self._processor = AISpanProcessor(processor, custom_filter=custom_filter)
         else:
-            # Use BatchSpanProcessor directly
             self._processor = processor
 
     def on_start(self, span, parent_context=None):
@@ -418,7 +440,7 @@ def _get_parent_otel_braintrust_parent(self, parent_context):
     def on_end(self, span):
         """Forward span end events to the inner processor."""
         self._exporter.initialize()
-        self._processor.on_end(_with_span_origin_attributes(span, self._environment))
+        self._processor.on_end(span)
 
     def _on_ending(self, span):
         """Forward pre-end hook when the wrapped processor supports it."""

py/src/braintrust/test_otel.py

@@ -124,8 +124,11 @@ def test_braintrust_span_processor_merges_span_origin_with_context_json_set_afte
 
     memory_exporter = InMemorySpanExporter()
     provider = TracerProvider()
-    processor = BraintrustSpanProcessor(api_key="test-api-key", parent="project_name:test")
-    processor._processor = SimpleSpanProcessor(memory_exporter)
+    processor = BraintrustSpanProcessor(
+        api_key="test-api-key",
+        parent="project_name:test",
+        SpanProcessor=lambda _exporter: SimpleSpanProcessor(memory_exporter),
+    )
     provider.add_span_processor(processor)
     tracer = provider.get_tracer("test_tracer")
 
@@ -146,6 +149,43 @@ def test_braintrust_span_processor_merges_span_origin_with_context_json_set_afte
         provider.shutdown()
 
 
+def test_braintrust_span_processor_filters_before_adding_span_origin():
+    if not _check_otel_installed():
+        pytest.skip("OpenTelemetry SDK not fully installed, skipping test")
+
+    from braintrust.otel import BraintrustSpanProcessor
+    from opentelemetry.sdk.trace import TracerProvider
+    from opentelemetry.sdk.trace.export import SimpleSpanProcessor
+    from opentelemetry.sdk.trace.export.in_memory_span_exporter import InMemorySpanExporter
+
+    memory_exporter = InMemorySpanExporter()
+    provider = TracerProvider()
+    processor = BraintrustSpanProcessor(
+        api_key="test-api-key",
+        parent="project_name:test",
+        filter_ai_spans=True,
+        SpanProcessor=lambda _exporter: SimpleSpanProcessor(memory_exporter),
+    )
+    provider.add_span_processor(processor)
+    tracer = provider.get_tracer("test_tracer")
+
+    try:
+        with tracer.start_as_current_span("GET /health") as span:
+            span.set_attribute("http.route", "/health")
+        with tracer.start_as_current_span("SELECT users") as span:
+            span.set_attribute("db.system", "postgresql")
+        with tracer.start_as_current_span("chat") as span:
+            span.set_attribute("gen_ai.operation.name", "chat")
+
+        provider.force_flush()
+        spans = memory_exporter.get_finished_spans()
+        assert [span.name for span in spans] == ["chat"]
+        context = json.loads(spans[0].attributes["braintrust.context_json"])
+        assert context["span_origin"]["instrumentation"]["name"] == "braintrust-python-otel"
+    finally:
+        provider.shutdown()
+
+
 def test_merge_span_origin_context_uses_passed_instrumentation_name():
     from braintrust.span_origin import merge_span_origin_context