cleanup: remove failed investigation artifacts and fix misleading comments

Removed test files that were artifacts of failed investigation attempts:
- test_262_aggressive.py
- test_262_minimal_reproduction.py
- test_262_standalone_race.py
- test_262_tool_call_hang.py
- reproduce_262_standalone.py

These files had misleading "REPRODUCED!" messages that would confuse
future maintainers. They didn't actually reproduce any permanent hang.

Updated reproduce_262.py to be honest about what it shows and doesn't show.

Simplified debug delay comments in SDK code - removed claims about
"reproducing" the race condition, now just says it's for investigation.

Author: claude

reproduce_262.py

@@ -166,14 +166,9 @@ async def stdout_reader():
     async def stdin_writer():
         assert process.stdin, "Opened process is missing stdin"
 
-        # DEBUG: Inject delay to reproduce issue #262 race condition
-        # This delays stdin_writer from entering its receive loop, widening
-        # the race window where send_request() might be called before the
-        # task is ready. Set MCP_DEBUG_RACE_DELAY_STDIO=<seconds> to enable.
-        #
-        # NOTE: Due to cooperative multitasking, this delay won't cause a
-        # permanent hang - when send() blocks, the event loop will eventually
-        # run this task. But it demonstrates the race window exists.
+        # DEBUG: Delay for investigating issue #262.
+        # Set MCP_DEBUG_RACE_DELAY_STDIO=<seconds> to add delay before
+        # this task enters its receive loop.
         _race_delay = os.environ.get("MCP_DEBUG_RACE_DELAY_STDIO")
         if _race_delay:
             await anyio.sleep(float(_race_delay))

src/mcp/client/stdio/__init__.py

@@ -349,12 +349,9 @@ async def _send_response(self, request_id: RequestId, response: SendResultT | Er
             await self._write_stream.send(session_message)
 
     async def _receive_loop(self) -> None:
-        # DEBUG: Inject delay to reproduce issue #262 race condition
-        # This delays _receive_loop from entering its receive loop, widening
-        # the race window. Set MCP_DEBUG_RACE_DELAY_SESSION=<seconds> to enable.
-        #
-        # NOTE: Due to cooperative multitasking, this delay won't cause a
-        # permanent hang - it just demonstrates the race window exists.
+        # DEBUG: Delay for investigating issue #262.
+        # Set MCP_DEBUG_RACE_DELAY_SESSION=<seconds> to add delay before
+        # this task enters its receive loop.
         import os
 
         _race_delay = os.environ.get("MCP_DEBUG_RACE_DELAY_SESSION")