More config debug.

TODO/_current.md

@@ -36,6 +36,8 @@
 * Config test sometimes reads empty.
     - Empty is written on init, then quickly filled with defaults for the write test.
     - Maybe the empty write is happening after the filled somehow?
+        - Nope, tracing shows a full write request and commit.
+        - But the file is empty on error.. (empty as in `#` for TOML, not zero-sized) 
 
 * Review save debounce.
 * Test concurrent access to same config.

zero-ui-core/src/config.rs

@@ -62,6 +62,8 @@ impl AppExtension for ConfigManager {}
 ///
 /// Config sources must be loaded using [`CONFIG.load`], otherwise the config only leaves for the
 /// duration of the app instance.
+///
+/// [`CONFIG.load`]: CONFIG::load
 pub struct CONFIG;
 impl CONFIG {
     /// Replace the config source.