diff --git a/docs/03-data-model.md b/docs/03-data-model.md
index 4380e74..5a1f966 100644
--- a/docs/03-data-model.md
+++ b/docs/03-data-model.md
@@ -386,6 +386,9 @@ segment (the M1 grounding invariant, asserted by the golden-transcript test).
   // via `set_auto_start` also writes a per-user `HKCU\...\Run` entry (no admin);
   // startup reconciles the OS entry to this flag (e.g. after a reinstall).
   "auto_start": false,
+  // Closing the window hides WhispAssist to the system tray (keep running in background) instead of
+  // quitting; ON by default. Tray "Quit" is the real exit. Enforced in the Rust on_window_event handler.
+  "close_to_tray": true,
   // Optional MS Graph calendar source (M4.4, T8.9, FR-CAL-6). Opt-in, explicit consent via OAuth
   // PKCE — OFF by default. `credential_ref` points into the OS credential store; the token itself
   // is never written here (same invariant as sync credentials, FR-SYNC-6).