Document configuration comparison behavior

docs/consumers/guide.md

@@ -103,18 +103,21 @@ values.
 
 Use `ckconfig.Command(ckconfig.Suite[I, S]{...})` when the application needs
 multiple named scopes, selector flags, scope-aware input checks, or shared
-acquisition state. Input is initialized separately for each selected scope;
-state is shared by selected acquisitions. Factory results remain caller-owned,
-so separate initialization calls do not guarantee distinct objects. See
+acquisition state or a custom comparison provider. A declared `Diff` capability
+uses `Scope.Compare`; `ckconfig.FromConfigKit` and `AppCommand` provide the
+ConfigKit-backed implementation. Each comparison side gets its own initialized
+and checked input, while state is shared by the invocation. Factory results
+remain caller-owned, so separate initialization calls do not guarantee distinct
+objects. See
 [ckconfig.Suite's GoDoc](../../integrations/ckconfig/contracts.go) for factory
 timing, omitted-factory zero values (including nil pointers), and ownership.
 The application owns the state type and what it caches. `ckconfig.FromConfigKit`
 adapts a typed ConfigKit loader without calling it during construction.
 
 The `config` family provides scope discovery, validation, native effective YAML,
-source inventory, and path explanation for the capabilities declared by its
-scopes. The [CLI reference](../cli.md#configuration-scopes) owns operator
-syntax and report details.
+source inventory, path explanation, and ConfigKit-backed comparison for the
+capabilities declared by its scopes. The [CLI reference](../cli.md#configuration-scopes)
+owns operator syntax and report details.
 
 ## PromptKit configuration and definitions