Demonstrate config diff in simple consumer

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Implement ConfigKit adoption and configuration comparison
 
-Status: implementation in progress; Stages 1–8 are complete.
+Status: implementation in progress; Stages 1–9 are complete.
 
 ## Scope and authority
 
@@ -445,9 +445,15 @@ without custom comparison wiring.
    go run . config diff --config fixtures/before.yml --against-config fixtures/after.yml
    ```
 
-**Completion evidence:** the complete consumer compiles in ckconfig's suite;
-fixture comparison and unchanged default commands run without external services.
-Composed state/cache and PromptKit changes belong only to Stage 10.
+**Completion evidence — complete:** the simple consumer now uses ConfigKit file
+sources when `--config` is supplied, preserves the in-memory default when it is
+omitted, and forwards supplied overlays through ConfigKit options. The required
+before/after fixtures and README invocation are present. Its assembled-app test
+checks `changes.greeting: Goodbye`, equal fixture selections with empty
+categories, default `config show`, default `greet`, and explicit empty config
+selection failing instead of falling back. The documented diff, show, and greet
+commands also run locally without external services; the ckconfig suite passes.
+Composed state/cache and PromptKit changes remain for the following stage.
 
 ## Stage 10: Demonstrate composed selection and typed-input cache identity
 

integrations/ckconfig/examples/simple/README.md

@@ -4,6 +4,7 @@ Run the maintained example with:
 
 ```sh
 go run . config show
+go run . config diff --config fixtures/before.yml --against-config fixtures/after.yml
 go run . greet
 go run . greet --count=0 --tag=first --tag second
 ```
@@ -11,4 +12,6 @@ go run . greet --count=0 --tag=first --tag second
 The `config` family comes from one typed ConfigKit scope. The custom `greet`
 command uses CommandKit's typed bindings and shows the difference between an
 omitted `--count` and an explicitly supplied zero, plus ordered repeated tags.
-The configuration is synthetic and stays in memory.
+With no `--config`, application settings use the in-memory default. A supplied
+configuration and overlay are passed to ConfigKit unchanged. The comparison
+command loads the two local fixtures and reports `changes.greeting: Goodbye`.

integrations/ckconfig/examples/simple/fixtures/after.yml

@@ -0,0 +1 @@
+greeting: Goodbye

integrations/ckconfig/examples/simple/fixtures/before.yml

@@ -0,0 +1 @@
+greeting: Hello

integrations/ckconfig/examples/simple/main.go

@@ -20,10 +20,19 @@ type greetInput struct {
 	Tags  commandkit.Supplied[[]string]
 }
 
-func loadAppConfiguration(_ context.Context, _ ckconfig.Selection) (*configkit.Result[appConfiguration], error) {
-	return configkit.Load[appConfiguration](configkit.Mapping("simple application settings", map[string]any{
+func loadAppConfiguration(_ context.Context, selection ckconfig.Selection) (*configkit.Result[appConfiguration], error) {
+	source := configkit.Mapping("simple application settings", map[string]any{
 		"greeting": "Hello",
-	}))
+	})
+	if selection.Config.Set {
+		source = configkit.File(selection.Config.Value)
+	}
+	options := configkit.Options[appConfiguration]{}
+	if selection.Overlay.Set {
+		options.Overlay = selection.Overlay.Value
+		options.Filesystem = &configkit.FilesystemContext{Root: ".", BaseDir: "."}
+	}
+	return configkit.Load(source, options)
 }
 
 func newApp() (*commandkit.App, error) {

integrations/ckconfig/examples/simple/main_test.go

@@ -0,0 +1,81 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"testing"
+
+	commandkit "gitea.maximumdirect.net/eric/CommandKit"
+	"gitea.maximumdirect.net/eric/CommandKit/integrations/ckconfig"
+	"go.yaml.in/yaml/v4"
+)
+
+func TestSimpleAppComparesFixturesAndKeepsDefaultCommands(t *testing.T) {
+	app, err := newApp()
+	if err != nil {
+		t.Fatal(err)
+	}
+	var output bytes.Buffer
+	outcome := app.Execute(context.Background(), []string{"config", "diff", "--config", "fixtures/before.yml", "--against-config", "fixtures/after.yml"}, commandkit.Streams{Out: &output, Err: io.Discard})
+	if outcome.Kind != commandkit.OutcomeSuccess {
+		t.Fatalf("fixture comparison outcome = %#v", outcome)
+	}
+	var report yaml.Node
+	if err := yaml.Unmarshal(output.Bytes(), &report); err != nil {
+		t.Fatalf("comparison report is not YAML: %q: %v", output.String(), err)
+	}
+	changes := field(report.Content[0], "changes")
+	greeting := field(changes, "greeting")
+	if greeting == nil || greeting.Value != "Goodbye" {
+		t.Fatalf("fixture comparison report = %q", output.String())
+	}
+
+	output.Reset()
+	outcome = app.Execute(context.Background(), []string{"config", "diff", "--config", "fixtures/before.yml", "--against-config", "fixtures/before.yml"}, commandkit.Streams{Out: &output, Err: io.Discard})
+	if outcome.Kind != commandkit.OutcomeSuccess {
+		t.Fatalf("equal fixture comparison outcome = %#v", outcome)
+	}
+	if reportNode, err := decodeReport(output.Bytes()); err != nil || len(field(reportNode, "additions").Content) != 0 || len(field(reportNode, "changes").Content) != 0 || len(field(reportNode, "deletions").Content) != 0 {
+		t.Fatalf("equal fixture report = %q, decode error %v", output.String(), err)
+	}
+
+	output.Reset()
+	outcome = app.Execute(context.Background(), []string{"config", "show"}, commandkit.Streams{Out: &output, Err: io.Discard})
+	if outcome.Kind != commandkit.OutcomeSuccess || output.String() != "greeting: Hello\n" {
+		t.Fatalf("default show outcome/output = %#v / %q", outcome, output.String())
+	}
+
+	output.Reset()
+	outcome = app.Execute(context.Background(), []string{"greet"}, commandkit.Streams{Out: &output, Err: io.Discard})
+	if outcome.Kind != commandkit.OutcomeSuccess || len(output.String()) == 0 || output.String()[:5] != "Hello" {
+		t.Fatalf("default greeting outcome/output = %#v / %q", outcome, output.String())
+	}
+}
+
+func TestSimpleLoaderDoesNotReplaceExplicitEmptyConfiguration(t *testing.T) {
+	_, err := loadAppConfiguration(context.Background(), ckconfig.Selection{Config: commandkit.Supplied[string]{Set: true}})
+	if err == nil {
+		t.Fatal("explicit empty configuration fell back to the default source")
+	}
+}
+
+func field(mapping *yaml.Node, name string) *yaml.Node {
+	if mapping == nil || mapping.Kind != yaml.MappingNode {
+		return nil
+	}
+	for index := 0; index+1 < len(mapping.Content); index += 2 {
+		if mapping.Content[index].Value == name {
+			return mapping.Content[index+1]
+		}
+	}
+	return nil
+}
+
+func decodeReport(data []byte) (*yaml.Node, error) {
+	var document yaml.Node
+	if err := yaml.Unmarshal(data, &document); err != nil {
+		return nil, err
+	}
+	return document.Content[0], nil
+}