fix(mem): 5s force floor so delegate-batch closes don't stack trims

Efficiency-pass follow-up on the #66355 salvage: force=True bypassed the
cooldown entirely, and AIAgent.close() fires a forced trim for EVERY
in-process child subagent close (delegate_tool child.close(), parent
close step 5). A delegate batch of N children closing back-to-back in
the gateway process stacked N+1 uncooled full gc.collect()+malloc_trim
passes (50-500ms each with a large live heap). Forced trims now honor a
5s floor — bursts coalesce, the parent's final close-trim still fires.
Guard test mutation-checked (floor zeroed -> test fails).

hermes_cli/mem_trim.py

@@ -200,6 +200,18 @@ def trim_memory(
         )
         if not force and _last_trim_monotonic and now - _last_trim_monotonic < cooldown:
             return False
+        # Even forced trims honor a short floor: AIAgent.close() forces a trim,
+        # and delegate batches close N child subagents back-to-back in the SAME
+        # process — without a floor that stacks N+1 uncooled full gc.collect()
+        # passes (50-500ms each in a large gateway process). 5s coalesces the
+        # burst while keeping the parent's final close-trim effective.
+        _FORCE_FLOOR_SECONDS = 5.0
+        if (
+            force
+            and _last_trim_monotonic
+            and now - _last_trim_monotonic < _FORCE_FLOOR_SECONDS
+        ):
+            return False
         # Record the attempt before calling into libc so repeated failures do not
         # turn every turn boundary into an expensive full collection.
         _last_trim_monotonic = now

tests/hermes_cli/test_mem_trim.py

@@ -108,7 +108,10 @@ def test_force_logs_even_when_periodic_log_sampling_skips(monkeypatch, caplog):
     monkeypatch.setattr(mem_trim.gc, "collect", lambda: None)
     monkeypatch.setattr(mem_trim, "_malloc_trim", lambda _pad: 1)
     monkeypatch.setattr(mem_trim, "_config_settings", lambda: (True, 0.0, 99, 1.0))
-    monkeypatch.setattr(mem_trim.time, "monotonic", lambda: 100.0)
+    # Two ticks: the forced call comes after the 5s force floor so it runs
+    # (the floor exists to coalesce burst closes, not to mute logging).
+    _ticks = iter([100.0, 110.0])
+    monkeypatch.setattr(mem_trim.time, "monotonic", lambda: next(_ticks, 110.0))
     monkeypatch.setattr(
         mem_trim,
         "collect_memory_snapshot",
@@ -178,3 +181,36 @@ def test_libc_failure_is_fail_open_and_rate_limited(monkeypatch):
     assert mem_trim._last_trim_monotonic == 100.0
     assert mem_trim.trim_memory(cooldown_seconds=60) is False
     assert trim.call_count == 1
+
+
+def test_force_floor_coalesces_burst_closes(monkeypatch):
+    """A delegate batch closes N child agents back-to-back, each forcing a
+    trim — the short force floor must coalesce the burst instead of stacking
+    N uncooled full gc.collect() passes in the same process."""
+    collect = Mock()
+    trim = Mock(return_value=1)
+    monkeypatch.setattr(mem_trim.gc, "collect", collect)
+    monkeypatch.setattr(mem_trim, "_malloc_trim", trim)
+    monkeypatch.setattr(mem_trim, "_config_settings", lambda: (True, 0.0, 1, 0.0))
+    monkeypatch.setattr(
+        mem_trim,
+        "collect_memory_snapshot",
+        lambda: {"rss_kib": 4096, "rss_anon_kib": 3072, "thread_count": 3},
+    )
+    monkeypatch.setattr(mem_trim, "_last_trim_monotonic", 0.0)
+
+    # t=100: first forced close runs.
+    monkeypatch.setattr(mem_trim.time, "monotonic", lambda: 100.0)
+    assert mem_trim.trim_memory(force=True, reason="agent close") is True
+    assert trim.call_count == 1
+
+    # t=101..103: three more child closes inside the floor — all coalesced.
+    for t in (101.0, 102.0, 103.0):
+        monkeypatch.setattr(mem_trim.time, "monotonic", lambda t=t: t)
+        assert mem_trim.trim_memory(force=True, reason="agent close") is False
+    assert trim.call_count == 1, "burst closes must not stack forced trims"
+
+    # t=106: past the floor — the parent's final close-trim still fires.
+    monkeypatch.setattr(mem_trim.time, "monotonic", lambda: 106.0)
+    assert mem_trim.trim_memory(force=True, reason="agent close") is True
+    assert trim.call_count == 2