diff --git a/cli.py b/cli.py
index f89adec37803..1502521a213f 100644
--- a/cli.py
+++ b/cli.py
@@ -10183,7 +10183,14 @@ class HermesCLI(CLIAgentSetupMixin, CLICommandsMixin, CLIBillingMixin):
                 # "No changes from compression" no-op text. The wording
                 # distinguishes a confirmed holder from an unconfirmed
                 # acquisition failure (describe_compression_lock_skip).
-                if getattr(self.agent, "_compression_skipped_due_to_lock", None):
+                # Type-pinned check (is True / str): the flag's only real
+                # values are None/True/holder-string, and a bare getattr
+                # truthiness test is fooled by MagicMock auto-attributes on
+                # test-double agents (skill pitfall: MagicMock vs hasattr).
+                _lock_skip_signal = getattr(
+                    self.agent, "_compression_skipped_due_to_lock", None
+                )
+                if _lock_skip_signal is True or isinstance(_lock_skip_signal, str):
                     from agent.manual_compression_feedback import (
                         describe_compression_lock_skip,
                     )
diff --git a/gateway/slash_commands.py b/gateway/slash_commands.py
index d10baa56f8d7..9b6f989ff8b8 100644
--- a/gateway/slash_commands.py
+++ b/gateway/slash_commands.py
@@ -3573,7 +3573,7 @@ class GatewaySlashCommandsMixin:
                 # The deferred context-engine notification is discarded by
                 # the finally block below (finalize committed=False).
                 _lock_skipped = getattr(tmp_agent, "_compression_skipped_due_to_lock", None)
-                if _lock_skipped:
+                if _lock_skipped is True or isinstance(_lock_skipped, str):
                     from agent.manual_compression_feedback import (
                         describe_compression_lock_skip,
                     )
diff --git a/tui_gateway/server.py b/tui_gateway/server.py
index cc0d8a1e5dd0..176239b2ba52 100644
--- a/tui_gateway/server.py
+++ b/tui_gateway/server.py
@@ -3745,8 +3745,10 @@ def _compress_session_history(
     # If _compress_context returned unchanged because a concurrent
     # compression lock is held, raise so callers can surface a clear
     # message instead of the misleading "No changes from compression" text.
+    # Type-pinned (is True / str): real values are None/True/holder-string;
+    # bare truthiness is fooled by MagicMock auto-attrs on test doubles.
     _lock_skipped = getattr(agent, "_compression_skipped_due_to_lock", None)
-    if _lock_skipped:
+    if _lock_skipped is True or isinstance(_lock_skipped, str):
         agent._compression_skipped_due_to_lock = None
         # No boundary was committed on a lock-skip; discard any pending
         # deferred context-engine notification (exactly-once, no-op safe).