Add invocation coordination and diagnostics

command.go

@@ -99,6 +99,7 @@ type commandPayload interface {
 	hasRun() bool
 	bridgeFlags() []internalcobra.Flag
 	prepare([][]string, []string, bool) (func() any, error)
+	checkInput(any) error
 	run(Invocation, any) Outcome
 }
 
@@ -146,6 +147,13 @@ func (c typedCommand[I]) run(invocation Invocation, input any) Outcome {
 	return c.spec.Run(invocation, *input.(*I))
 }
 
+func (c typedCommand[I]) checkInput(input any) error {
+	if c.spec.CheckInput == nil {
+		return nil
+	}
+	return c.spec.CheckInput(*input.(*I))
+}
+
 // NewCommand validates and creates a typed command declaration. It retains
 // callbacks without invoking them and copies the declarative flag and argument
 // slices.