diff --git a/tests/gateway/test_session_api.py b/tests/gateway/test_session_api.py
index f9989e18e00..3f6f28bf7ee 100644
--- a/tests/gateway/test_session_api.py
+++ b/tests/gateway/test_session_api.py
@@ -176,9 +176,12 @@ async def test_session_crud_and_message_history(adapter, session_db):
 async def test_session_messages_follow_compression_tip(adapter, session_db):
     source_id = session_db.create_session("source-session", "api_server")
     session_db.append_message(source_id, "user", "before compression")
+    # Empty the parent BEFORE closing it: the closed-parent write guard
+    # (CompressionSessionClosedError) refuses durable writes to a session
+    # ended by compression, so the legacy-state simulation must run first.
+    session_db.replace_messages(source_id, [])
     session_db.end_session(source_id, "compression")
     session_db.create_session("tip-session", "api_server", parent_session_id=source_id)
-    session_db.replace_messages(source_id, [])
     session_db.append_message("tip-session", "user", "after compression")
 
     app = _create_session_app(adapter)
diff --git a/tests/hermes_cli/test_web_server.py b/tests/hermes_cli/test_web_server.py
index ad8cedab4de..7f0119ec2bc 100644
--- a/tests/hermes_cli/test_web_server.py
+++ b/tests/hermes_cli/test_web_server.py
@@ -2293,6 +2293,9 @@ class TestWebServerEndpoints:
         try:
             db.create_session(session_id="desktop-root", source="cli")
             db.append_message(session_id="desktop-root", role="user", content="before compression")
+            # Empty before closing: the closed-parent write guard refuses
+            # durable writes to compression-ended sessions.
+            db.replace_messages("desktop-root", [])
             db.end_session("desktop-root", "compression")
             now = _time.time()
             db._conn.execute(
@@ -2301,7 +2304,6 @@ class TestWebServerEndpoints:
             )
             db.create_session(session_id="desktop-tip", source="cli", parent_session_id="desktop-root")
             db._conn.execute("UPDATE sessions SET started_at = ? WHERE id = ?", (now - 4, "desktop-tip"))
-            db.replace_messages("desktop-root", [])
             db.append_message(session_id="desktop-tip", role="user", content="after compression")
             db._conn.commit()
         finally: