perf(agent,gateway): back cancel-wait polls off from 1ms to 25ms (re-review #5)

The fence-cancel poll loops (sync host wait in conversation_compression,
async hygiene wait in gateway/run) spun at 1kHz while the worker held
the fence through its lock-setup window — which rides SessionDB write
patience and can last seconds. 25ms keeps sub-tick cancel latency
without the spin.

agent/conversation_compression.py

@@ -972,7 +972,12 @@ def run_compress_context_with_progress_timeout(
                 break
             cancelled = fence.try_cancel_before_commit()
             if cancelled is None:
-                time.sleep(0.001)
+                # Round-2 #5: the fence is only held transiently here (lock
+                # setup / cancel admission — an in-flight commit is caught by
+                # the commit_in_flight check above), but that window rides
+                # SessionDB write patience and can last seconds. 25ms keeps
+                # sub-tick latency without a 1kHz spin.
+                time.sleep(0.025)
         if not cancelled:
             # Pre-commit ceiling already elapsed, but begin_commit() won the
             # race. Waiting is intentional: SessionDB mutation cannot be

gateway/run.py

@@ -16747,7 +16747,12 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
                                                 _hyg_commit_fence.try_cancel_before_commit()
                                             )
                                             if _cancelled is None:
-                                                await asyncio.sleep(0.001)
+                                                # Round-2 #5: transient
+                                                # lock-setup windows ride
+                                                # write patience for seconds;
+                                                # 25ms keeps sub-tick latency
+                                                # without 1kHz spin.
+                                                await asyncio.sleep(0.025)
                                         if not _cancelled:
                                             # The worker crossed the commit boundary just
                                             # before the timeout. The fence poll waited for