fix(cohere): support chat stream context managers (#418)

Delegate Cohere chat_stream enter/exit handling through the traced
stream wrapper so native with-statement usage keeps working while spans
still finish correctly.

Add VCR regression coverage for ClientV2.chat_stream used as a context
manager.

resolves
https://linear.app/braintrustdata/issue/BT-5179/braintrust-python-sdk-cohere-wrapper-chat-stream-doesnt-support-with

Author: AbhiPrasad

py/src/braintrust/integrations/cohere/cassettes/latest/test_wrap_cohere_chat_stream_v2_sync_context_manager.yaml

@@ -0,0 +1,106 @@
+interactions:
+- request:
+    body: '{"model":"command-a-03-2025","messages":[{"role":"user","content":"Say
+      hi in one word."}],"max_tokens":8,"stream":true}'
+    headers:
+      Accept:
+      - '*/*'
+      Accept-Encoding:
+      - gzip, deflate
+      Connection:
+      - keep-alive
+      Content-Length:
+      - '119'
+      Host:
+      - api.cohere.com
+      User-Agent:
+      - cohere/6.1.0
+      X-Fern-Language:
+      - Python
+      X-Fern-Platform:
+      - darwin/25.2.0
+      X-Fern-Runtime:
+      - python/3.14.3
+      X-Fern-SDK-Name:
+      - cohere
+      X-Fern-SDK-Version:
+      - 6.1.0
+      content-type:
+      - application/json
+    method: POST
+    uri: https://api.cohere.com/v2/chat
+  response:
+    body:
+      string: 'event: message-start
+
+        data: {"id":"b4256f33-1304-4943-b795-7f0d56d1fec9","type":"message-start","delta":{"message":{"role":"assistant","content":[],"tool_plan":"","tool_calls":[],"citations":[]}}}
+
+
+        event: content-start
+
+        data: {"type":"content-start","index":0,"delta":{"message":{"content":{"type":"text","text":""}}}}
+
+
+        event: content-delta
+
+        data: {"type":"content-delta","index":0,"delta":{"message":{"content":{"text":"Hi"}}}}
+
+
+        event: content-delta
+
+        data: {"type":"content-delta","index":0,"delta":{"message":{"content":{"text":"!"}}}}
+
+
+        event: content-end
+
+        data: {"type":"content-end","index":0}
+
+
+        event: message-end
+
+        data: {"type":"message-end","delta":{"finish_reason":"COMPLETE","usage":{"billed_units":{"input_tokens":6,"output_tokens":2},"tokens":{"input_tokens":501,"output_tokens":4},"cached_tokens":0}}}
+
+
+        data: [DONE]
+
+
+        '
+    headers:
+      Alt-Svc:
+      - h3=":443"; ma=2592000,h3-29=":443"; ma=2592000
+      Transfer-Encoding:
+      - chunked
+      Via:
+      - 1.1 google
+      access-control-expose-headers:
+      - X-Debug-Trace-ID
+      cache-control:
+      - no-cache, no-store, no-transform, must-revalidate, private, max-age=0
+      content-type:
+      - text/event-stream
+      date:
+      - Thu, 16 Apr 2026 22:25:13 GMT
+      expires:
+      - Thu, 01 Jan 1970 00:00:00 GMT
+      pragma:
+      - no-cache
+      server:
+      - envoy
+      vary:
+      - Origin
+      x-accel-expires:
+      - '0'
+      x-debug-trace-id:
+      - 6ad8e9afe35e1e8627c7779791b16cc4
+      x-endpoint-monthly-call-limit:
+      - '1000'
+      x-envoy-upstream-service-time:
+      - '303'
+      x-trial-endpoint-call-limit:
+      - '20'
+      x-trial-endpoint-call-remaining:
+      - '17'
+    status:
+      code: 200
+      message: OK
+version: 1

py/src/braintrust/integrations/cohere/test_cohere.py

@@ -567,6 +567,34 @@ def test_wrap_cohere_chat_stream_v2_sync(memory_logger):
     assert metrics.get("completion_tokens", 0) > 0
 
 
+@pytest.mark.vcr
+def test_wrap_cohere_chat_stream_v2_sync_context_manager(memory_logger):
+    assert not memory_logger.pop()
+    client = wrap_cohere(_v2_client(require_methods=("chat_stream",)))
+
+    start = time.time()
+    events = []
+    with client.chat_stream(
+        model=CHAT_MODEL,
+        messages=[{"role": "user", "content": "Say hi in one word."}],
+        max_tokens=8,
+    ) as stream:
+        for event in stream:
+            events.append(event)
+    end = time.time()
+
+    assert events
+
+    spans = memory_logger.pop()
+    assert len(spans) == 1
+    span = spans[0]
+    assert span["span_attributes"]["name"] == "cohere.chat_stream"
+    assert span["metadata"]["provider"] == "cohere"
+    assert span["metadata"]["model"] == CHAT_MODEL
+    assert span["metrics"]["start"] <= span["metrics"]["end"]
+    assert start <= span["metrics"]["start"] <= span["metrics"]["end"] <= end
+
+
 @pytest.mark.vcr
 def test_wrap_cohere_chat_stream_v2_rag_citations(memory_logger):
     if os.environ.get("BRAINTRUST_TEST_PACKAGE_VERSION") != "latest":

py/src/braintrust/integrations/cohere/tracing.py

@@ -840,6 +840,26 @@ def _finish(self, error: BaseException | None = None) -> None:
 class _TracedChatStream(_ChatStreamTracker):
     """Wrap a sync chat-stream iterator so exhaustion logs the aggregated span."""
 
+    def __enter__(self):
+        context_manager = self._iterator
+        enter = getattr(context_manager, "__enter__", None)
+        if enter is not None:
+            self._iterator = enter()
+            self._context_manager = context_manager
+        return self
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        suppress = False
+        context_manager = getattr(self, "_context_manager", self._iterator)
+        exit_method = getattr(context_manager, "__exit__", None)
+        if exit_method is not None:
+            suppress = bool(exit_method(exc_type, exc_value, traceback))
+        if exc_value is not None:
+            self._finish(error=exc_value)
+        else:
+            self._finish()
+        return suppress
+
     def __iter__(self):
         return self
 
@@ -859,6 +879,26 @@ def __next__(self):
 class _AsyncTracedChatStream(_ChatStreamTracker):
     """Async counterpart of :class:`_TracedChatStream`."""
 
+    async def __aenter__(self):
+        context_manager = self._iterator
+        aenter = getattr(context_manager, "__aenter__", None)
+        if aenter is not None:
+            self._iterator = await aenter()
+            self._context_manager = context_manager
+        return self
+
+    async def __aexit__(self, exc_type, exc_value, traceback):
+        suppress = False
+        context_manager = getattr(self, "_context_manager", self._iterator)
+        aexit = getattr(context_manager, "__aexit__", None)
+        if aexit is not None:
+            suppress = bool(await aexit(exc_type, exc_value, traceback))
+        if exc_value is not None:
+            self._finish(error=exc_value)
+        else:
+            self._finish()
+        return suppress
+
     def __aiter__(self):
         return self