docs: document configuration and diagnostics contracts

docs/src/sitl.md

@@ -32,6 +32,24 @@ never contributes a controller or truth observation.
 Open <https://app.gazebosim.org/visualization>, connect to
 `ws://localhost:9002`, and leave authorization blank to view the world.
 
+## Quad-X profile
+
+SITL starts through the same central `ConfigManager` composition used by the
+host protocol tests. Create and validate a private host profile file with:
+
+```sh
+kaptan-sitl config write-default kaptan-sitl.cbor
+kaptan-sitl config validate kaptan-sitl.cbor
+kaptan-sitl serve --config kaptan-sitl.cbor
+```
+
+The file selects the restart-only profile used to build the estimator,
+controller, allocator envelope, safety supervisor, and optional log filter at
+process start. It is not the raw GCS upload blob. `kaptan-sitl serve` retains
+the central manager for that boot but does not yet open a MAVLink config/log
+endpoint; see [Configuration](configuration.md) for the exact upload groundwork
+and safety boundary.
+
 ## Limits
 
 This model does not validate terrain, vision, flow/range sensing, wind,