fix: follow-up for salvaged PR #10854

- Extract duplicated activity-callback polling into shared
  touch_activity_if_due() helper in tools/environments/base.py
- Use helper from both base.py _wait_for_process and
  code_execution_tool.py local polling loop (DRY)
- Add test assertion that timeout output field contains the
  timeout message and emoji (#10807)
- Add stream_consumer test for tool-boundary fallback scenario
  where continuation is empty but final_text differs from
  visible prefix (#10807)

tools/environments/modal_utils.py

@@ -105,9 +105,11 @@ class BaseModalExecutionEnvironment(BaseEnvironment):
         if self._client_timeout_grace_seconds is not None:
             deadline = time.monotonic() + prepared.timeout + self._client_timeout_grace_seconds
 
-        _last_activity_touch = time.monotonic()
-        _modal_exec_start = time.monotonic()
-        _ACTIVITY_INTERVAL = 10.0  # match _wait_for_process cadence
+        _now = time.monotonic()
+        _activity_state = {
+            "last_touch": _now,
+            "start": _now,
+        }
 
         while True:
             if is_interrupted():
@@ -133,20 +135,11 @@ class BaseModalExecutionEnvironment(BaseEnvironment):
                 return self._timeout_result_for_modal(prepared.timeout)
 
             # Periodic activity touch so the gateway knows we're alive
-            _now = time.monotonic()
-            if _now - _last_activity_touch >= _ACTIVITY_INTERVAL:
-                _last_activity_touch = _now
-                try:
-                    from tools.environments.base import _get_activity_callback
-                    _cb = _get_activity_callback()
-                except Exception:
-                    _cb = None
-                if _cb:
-                    try:
-                        _elapsed = int(_now - _modal_exec_start)
-                        _cb(f"modal command running ({_elapsed}s elapsed)")
-                    except Exception:
-                        pass
+            try:
+                from tools.environments.base import touch_activity_if_due
+                touch_activity_if_due(_activity_state, "modal command running")
+            except Exception:
+                pass
 
             time.sleep(self._poll_interval_seconds)