diff --git a/tui_gateway/methods_prompt.py b/tui_gateway/methods_prompt.py
index d0efe89f9f057..07d4a43f0733d 100644
--- a/tui_gateway/methods_prompt.py
+++ b/tui_gateway/methods_prompt.py
@@ -118,6 +118,13 @@ def _(rid, params: dict) -> dict:
     # in turn: a stale "hud" would tell the model the user is still floating
     # over another app when they are back in Hermes.
     session["client_surface"] = "hud" if params.get("surface") == "hud" else ""
+    # Per-turn group-chat note (desktop rooms): context the model needs about
+    # the room THIS turn — who was invited, who the members are. Same channel
+    # as reaction notes: model input only, never persisted, so the transcript
+    # stays clean and the cached prefix survives. Rewritten (not setdefault)
+    # every submit so a stale note can't outlive the room state it described.
+    _group_note = params.get("group_note")
+    session["group_note"] = _group_note.strip() if isinstance(_group_note, str) else ""
     if truncate_user_ordinal is not None and isinstance(text, str):
         # A rewind/regenerate replays a turn from what the transcript shows. A
         # skill turn shows its invocation, so re-expand it here — otherwise
diff --git a/tui_gateway/server.py b/tui_gateway/server.py
index 14d6dbc2f2fad..807ac220eb1d4 100644
--- a/tui_gateway/server.py
+++ b/tui_gateway/server.py
@@ -9961,6 +9961,11 @@ def _run_prompt_submit(
             # Reactions the user added since the last turn.
             run_message = _prepend_note(run_message, _pending_reaction_notes(session))
 
+            # Desktop group-chat room note (who's in the room / who was just
+            # invited) — per-turn state, so it cannot live in the (byte-stable)
+            # system prompt. Consumed on read: one submit, one note.
+            run_message = _prepend_note(run_message, str(session.pop("group_note", "") or ""))
+
             # Which window the message was typed into. HUD mode is per-turn
             # state, so it cannot live in the (byte-stable) system prompt.
             run_message = _prepend_note(run_message, _hud_surface_note(session))