Add prototype testing overlay configuration

docs/roadmap/implementation.md

@@ -74,7 +74,9 @@ historical v0.3.1 evidence. Do not claim overlay integration yet.
 
 ## Stage 2: Add Overlay Loading and Configuration Fixtures
 
-**Status:** Pending. **Depends on:** Stage 1.
+**Status:** Complete (2026-09-24). **Depends on:** Stage 1. On-disk overlay and
+profile fixtures, precedence, inheritance, rejection, and runtime assembly tests
+pass in the nested module (`go test ./...`).
 
 Start with `config.go`, `config_test.go`, `config.yaml`, and `profiles/`. Extend
 `loadConfig` with an explicit overlay-selection argument or a small invocation

examples/library-adoption/config.go

@@ -31,8 +31,9 @@ type LLMConfig struct {
 	OperationTimeout  time.Duration `yaml:"operation_timeout"`
 }
 
-func loadConfig(source ck.Source, overrides ...ck.Override) (*ck.Result[Config], error) {
+func loadConfig(source ck.Source, overlay string, overrides ...ck.Override) (*ck.Result[Config], error) {
 	return ck.Load(source, ck.Options[Config]{
+		Overlay:   overlay,
 		Overrides: overrides,
 		Definition: ck.Definition[Config]{
 			Defaults: func() Config {

examples/library-adoption/config_test.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"encoding/json"
 	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
@@ -46,7 +47,7 @@ func TestConfigurationContract(t *testing.T) {
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Setenv("AUDITA_PROTOTYPE_KEY", tc.key)
-			loaded, err := loadConfig(ck.Bytes("example", []byte(tc.edit(string(original)))))
+			loaded, err := loadConfig(ck.Bytes("example", []byte(tc.edit(string(original)))), "")
 			if tc.bad {
 				if err == nil {
 					t.Fatal("expected rejection")
@@ -90,11 +91,11 @@ func TestConfigurationContract(t *testing.T) {
 	if err := os.Unsetenv("AUDITA_PROTOTYPE_KEY"); err != nil {
 		t.Fatal(err)
 	}
-	if _, err := loadConfig(ck.Bytes("example", original)); err == nil {
+	if _, err := loadConfig(ck.Bytes("example", original), ""); err == nil {
 		t.Fatal("missing secret accepted")
 	}
 	t.Setenv("AUDITA_PROTOTYPE_KEY", "key")
-	loaded, err := loadConfig(ck.Bytes("example", original), intOverride("transient_retries", 0), ck.Override{Path: ck.Keys("llm", "validation_profile"), Value: "proposal", Flag: "--validation-profile"})
+	loaded, err := loadConfig(ck.Bytes("example", original), "", intOverride("transient_retries", 0), ck.Override{Path: ck.Keys("llm", "validation_profile"), Value: "proposal", Flag: "--validation-profile"})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -103,9 +104,90 @@ func TestConfigurationContract(t *testing.T) {
 	}
 }
 
+func TestSelectedOverlayConfiguration(t *testing.T) {
+	t.Setenv("AUDITA_PROTOTYPE_KEY", "synthetic-test-secret")
+	base, err := os.ReadFile("config.yaml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	overlay, err := os.ReadFile("overlays/testing.yml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, tc := range []struct {
+		name, base, overlay, selection, proposal, validation string
+		overrides                                            []ck.Override
+		invalid                                              bool
+	}{
+		{name: "omitted", base: string(base), overlay: string(overlay), proposal: "proposal", validation: "assessment"},
+		{name: "empty", base: string(base), overlay: string(overlay), selection: "", proposal: "proposal", validation: "assessment"},
+		{name: "default", base: string(base), overlay: string(overlay), selection: "default", proposal: "proposal", validation: "assessment"},
+		{name: "testing", base: string(base), overlay: string(overlay), selection: "testing", proposal: "proposal-testing", validation: "assessment-testing"},
+		{name: "proposal override", base: string(base), overlay: string(overlay), selection: "testing", proposal: "proposal", validation: "assessment-testing", overrides: []ck.Override{{Path: ck.Keys("llm", "proposal_profile"), Value: "proposal", Flag: "--proposal-profile"}}},
+		{name: "validation override", base: string(base), overlay: string(overlay), selection: "testing", proposal: "proposal-testing", validation: "assessment", overrides: []ck.Override{{Path: ck.Keys("llm", "validation_profile"), Value: "assessment", Flag: "--validation-profile"}}},
+		{name: "inherited overlay proposal", base: strings.Replace(string(base), "  validation_profile: assessment\n", "", 1), overlay: "llm:\n  proposal_profile: proposal-testing\n", selection: "testing", proposal: "proposal-testing", validation: "proposal-testing"},
+		{name: "inherited override", base: strings.Replace(string(base), "  validation_profile: assessment\n", "", 1), overlay: "llm:\n  proposal_profile: proposal-testing\n", selection: "testing", proposal: "proposal", validation: "proposal", overrides: []ck.Override{{Path: ck.Keys("llm", "proposal_profile"), Value: "proposal", Flag: "--proposal-profile"}}},
+		{name: "explicit base assessment", base: string(base), overlay: "llm:\n  proposal_profile: proposal-testing\n", selection: "testing", proposal: "proposal-testing", validation: "assessment"},
+		{name: "empty overlay assessment", base: string(base), overlay: "llm:\n  validation_profile: ''\n", selection: "testing", invalid: true},
+		{name: "null overlay assessment", base: string(base), overlay: "llm:\n  validation_profile: null\n", selection: "testing", invalid: true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			dir := t.TempDir()
+			if err := os.MkdirAll(filepath.Join(dir, "overlays"), 0700); err != nil {
+				t.Fatal(err)
+			}
+			if err := os.WriteFile(filepath.Join(dir, "config.yaml"), []byte(tc.base), 0600); err != nil {
+				t.Fatal(err)
+			}
+			if err := os.WriteFile(filepath.Join(dir, "overlays", "testing.yml"), []byte(tc.overlay), 0600); err != nil {
+				t.Fatal(err)
+			}
+			loaded, err := loadConfig(ck.File(filepath.Join(dir, "config.yaml")), tc.selection, tc.overrides...)
+			if tc.invalid {
+				if err == nil {
+					t.Fatal("expected invalid validation selection")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got := loaded.Config.LLM; got.ProposalProfile != tc.proposal || got.ValidationProfile != tc.validation {
+				t.Fatalf("roles = %q, %q; want %q, %q", got.ProposalProfile, got.ValidationProfile, tc.proposal, tc.validation)
+			}
+			for _, name := range []string{"proposal.yaml", "assessment.yaml", "proposal-testing.yaml", "assessment-testing.yaml"} {
+				data, err := os.ReadFile(filepath.Join("profiles", name))
+				if err != nil {
+					t.Fatal(err)
+				}
+				if err := os.MkdirAll(filepath.Join(dir, "profiles"), 0700); err != nil {
+					t.Fatal(err)
+				}
+				if err := os.WriteFile(filepath.Join(dir, "profiles", name), data, 0600); err != nil {
+					t.Fatal(err)
+				}
+			}
+			r, err := newRuntime(loaded.Config, dir, demonstrationClient())
+			if err != nil {
+				t.Fatal(err)
+			}
+			for role, selected := range map[string]string{"proposal": tc.proposal, "assessment": tc.validation} {
+				profile := r.Profiles[role]
+				if profile.ProfileID != selected || profile.EffectiveModelParams.BackendID != "offline" {
+					t.Fatalf("%s resolved to %+v", role, profile)
+				}
+				models := map[string]string{"proposal": "synthetic-grammar", "assessment": "synthetic-review", "proposal-testing": "synthetic-grammar-testing", "assessment-testing": "synthetic-review-testing"}
+				if profile.EffectiveModelParams.Model != models[selected] {
+					t.Fatalf("%s model = %q", role, profile.EffectiveModelParams.Model)
+				}
+			}
+		})
+	}
+}
+
 func TestProfilesRespectSharedBackendBoundary(t *testing.T) {
 	t.Setenv("AUDITA_PROTOTYPE_KEY", "synthetic-test-secret")
-	loaded, err := loadConfig(ck.File("config.yaml"))
+	loaded, err := loadConfig(ck.File("config.yaml"), "")
 	if err != nil {
 		t.Fatal(err)
 	}

examples/library-adoption/main.go

@@ -16,7 +16,7 @@ func main() {
 		fmt.Fprintln(os.Stderr, err)
 		os.Exit(1)
 	}
-	loaded, err := loadConfig(ck.File("config.yaml"))
+	loaded, err := loadConfig(ck.File("config.yaml"), "")
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)
 		os.Exit(1)

examples/library-adoption/overlays/testing.yml

@@ -0,0 +1,3 @@
+llm:
+  proposal_profile: proposal-testing
+  validation_profile: assessment-testing

examples/library-adoption/profiles/assessment-testing.yaml

@@ -0,0 +1,4 @@
+id: assessment-testing
+backend: offline
+model: synthetic-review-testing
+timeout_seconds: 600

examples/library-adoption/profiles/proposal-testing.yaml

@@ -0,0 +1,4 @@
+id: proposal-testing
+backend: offline
+model: synthetic-grammar-testing
+timeout_seconds: 600

examples/library-adoption/workflow_test.go

@@ -22,7 +22,7 @@ type step struct {
 func testRuntime(t *testing.T, transport http.RoundTripper, overrides ...ck.Override) *Runtime {
 	t.Helper()
 	t.Setenv("AUDITA_PROTOTYPE_KEY", "synthetic-test-secret")
-	loaded, err := loadConfig(ck.File("config.yaml"), overrides...)
+	loaded, err := loadConfig(ck.File("config.yaml"), "", overrides...)
 	if err != nil {
 		t.Fatal(err)
 	}