test(agentex): correct late-connect test wording to connect-time check

The already-terminal-at-connect case is handled by the authoritative
connect-time check, not the removed keepalive fallback. Update the docstring,
comments, and assertion message accordingly; drop the now-unneeded ping-interval
override. Test logic unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: deepthi-rao-scale

agentex/tests/integration/test_task_stream.py

@@ -749,20 +749,18 @@ async def test_stream_ends_on_late_connect_to_terminal_task(
         self, test_agent_and_task, tasks_use_case, streams_use_case
     ):
         """
-        Fallback termination path: a viewer that connects *after* the task has
-        already reached a terminal state never receives a terminal task_updated
-        event (it is behind the snapshot cursor), so the event-driven exit can't
-        fire. The keepalive-cadence fallback must still end the stream instead of
-        blocking on the topic forever.
+        Connect-time termination path: a viewer that connects *after* the task
+        has already reached a terminal state never receives a terminal
+        task_updated event via the read loop — the event is behind the snapshot
+        cursor, so the in-loop check can't fire. The authoritative connect-time
+        check must end the stream (replay buffered events, then return) instead
+        of blocking on the topic forever.
         """
-        # Shrink the keepalive interval so the fallback check runs within ~1s
-        # instead of the production 15s.
-        streams_use_case.environment_variables.SSE_KEEPALIVE_PING_INTERVAL = 1
-
         _agent, task = test_agent_and_task
 
         # Finish the task BEFORE anyone subscribes. The terminal task_updated is
-        # XADDed to the stream now, so a later subscriber snapshots past it.
+        # XADDed to the stream now, so a later subscriber snapshots past it and
+        # the read loop never surfaces it.
         completed = await tasks_use_case.complete_task(id=task.id)
         assert completed.status == TaskStatus.COMPLETED
 
@@ -775,7 +773,7 @@ async def drain_until_end():
 
         reader_task = asyncio.create_task(drain_until_end())
 
-        # With no terminal event to react to, only the fallback can end it.
+        # The connect-time check should end it near-immediately.
         try:
             await asyncio.wait_for(reader_task, timeout=10)
         except TimeoutError as err:
@@ -786,7 +784,7 @@ async def drain_until_end():
                 pass
             raise AssertionError(
                 "SSE stream to an already-terminal task did not self-close — the "
-                "fallback termination check is not firing, so late-connect "
+                "connect-time terminal check is not firing, so late-connect "
                 "subscriptions leak as zombies."
             ) from err