diff --git a/hermes_cli/web_server.py b/hermes_cli/web_server.py
index 8232ab77c0a5c..8f5b7eca974da 100644
--- a/hermes_cli/web_server.py
+++ b/hermes_cli/web_server.py
@@ -3601,6 +3601,23 @@ async def get_action_status(name: str, lines: int = 200):
     }
 
 
+_SESSION_LIST_OMITTED_FIELDS = ("system_prompt", "model_config")
+
+
+def _trim_session_list_payload(session: Dict[str, Any]) -> Dict[str, Any]:
+    """Drop heavy/internal fields from session-list rows before JSON encoding.
+
+    ``SessionDB.list_sessions_rich()`` returns the full ``sessions`` row for
+    CLI/internal consumers, including the cached system prompt.  Desktop only
+    needs list metadata; serializing 40-50 full prompts turns every sidebar
+    refresh into multi-megabyte JSON and can starve the single uvicorn event
+    loop while the renderer retries timed-out requests.
+    """
+    for key in _SESSION_LIST_OMITTED_FIELDS:
+        session.pop(key, None)
+    return session
+
+
 @app.get("/api/sessions")
 async def get_sessions(
     limit: int = 20,
@@ -3671,6 +3688,7 @@ async def get_sessions(
             )
             now = time.time()
             for s in sessions:
+                _trim_session_list_payload(s)
                 s["is_active"] = (
                     s.get("ended_at") is None
                     and (now - s.get("last_active", s.get("started_at", 0))) < 300
@@ -3783,6 +3801,7 @@ def get_profiles_sessions(
             total += profile_total
             profile_totals[name] = profile_total
             for s in rows:
+                _trim_session_list_payload(s)
                 s["profile"] = name
                 s["is_default_profile"] = name == "default"
                 s["is_active"] = (
diff --git a/tests/hermes_cli/test_web_server.py b/tests/hermes_cli/test_web_server.py
index 18f5facbb6b64..34cacdb5fa663 100644
--- a/tests/hermes_cli/test_web_server.py
+++ b/tests/hermes_cli/test_web_server.py
@@ -677,6 +677,32 @@ def close(self):
         assert captured["list"] == 3
         assert captured["count"] == 3
 
+    def test_get_sessions_omits_heavy_internal_prompt_fields(self):
+        """The Desktop sidebar list must not serialize full cached prompts.
+
+        Real profiles can have 40-50 visible rows with ~40KB cached system
+        prompts each; returning those made every refresh multi-megabyte JSON.
+        """
+        from hermes_state import SessionDB
+
+        db = SessionDB()
+        try:
+            db.create_session(
+                session_id="heavy-list-row",
+                source="cli",
+                system_prompt="prompt" * 10_000,
+                model_config={"large": "config" * 10_000},
+            )
+            db.append_message(session_id="heavy-list-row", role="user", content="hi")
+        finally:
+            db.close()
+
+        resp = self.client.get("/api/sessions?limit=20&min_messages=0")
+        assert resp.status_code == 200
+        row = next(s for s in resp.json()["sessions"] if s["id"] == "heavy-list-row")
+        assert "system_prompt" not in row
+        assert "model_config" not in row
+
     def test_rename_session_updates_title(self):
         """PATCH /api/sessions/{id} renames a session (regression: the route
         was missing entirely, so the desktop rename dialog got a 405)."""
@@ -768,7 +794,12 @@ def test_profiles_sessions_tags_default_profile(self):
 
         db = SessionDB()
         try:
-            db.create_session(session_id="agg-me", source="cli")
+            db.create_session(
+                session_id="agg-me",
+                source="cli",
+                system_prompt="prompt" * 10_000,
+                model_config={"large": "config" * 10_000},
+            )
             db.append_message(session_id="agg-me", role="user", content="hi")
         finally:
             db.close()
@@ -779,6 +810,8 @@ def test_profiles_sessions_tags_default_profile(self):
         row = next(s for s in data["sessions"] if s["id"] == "agg-me")
         assert row["profile"] == "default"
         assert row["is_default_profile"] is True
+        assert "system_prompt" not in row
+        assert "model_config" not in row
         assert isinstance(data.get("errors"), list)
 
     def test_profiles_sessions_rejects_unknown_archived_value(self):