fix(mcp): keep conversation_id across later user messages

.sampo/changesets/persistent-conversation-id.md

@@ -0,0 +1,5 @@
+---
+pypi/posthog: patch
+---
+
+Keep MCP conversation sessions consistent across user messages.

posthog/mcp/constants.py

@@ -28,8 +28,11 @@
 )
 
 DEFAULT_CONVERSATION_ID_DESCRIPTION = (
-    "Echo the conversation_id from the server's previous response. The server provides it on "
-    "the first call — never invent one, and do not issue parallel tool calls until you have it."
+    "Pass the exact conversation_id from the server's previous response, unchanged. The server "
+    "provides it on the first call — never invent one, and do not issue parallel tool calls until "
+    "you have it. Keep passing the same conversation_id for the rest of the conversation, including "
+    "after later user messages or on a different task; do not reset it when the user starts a new "
+    "request."
 )
 
 DEFAULT_MODEL_PARAMETER_DESCRIPTION = (

posthog/test/mcp/test_units.py

@@ -230,6 +230,11 @@ def test_add_conversation_id_adds_property():
         {"type": "object", "properties": {"x": {"type": "string"}}}, "t"
     )
     assert out["properties"]["conversation_id"]["type"] == "string"
+    # Without this clause, ChatGPT drops the handle on each new user message and every message becomes its own session.
+    assert (
+        "rest of the conversation, including after later user messages"
+        in out["properties"]["conversation_id"]["description"]
+    )
 
 
 def test_add_conversation_id_skips_when_already_present():