feat(manifest): auto-discovery loader with signature verification

Load() reads .core/view.yml from any directory via io.Medium,
LoadVerified() adds ed25519 signature check. Uses MockMedium for tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/manifest/loader.go

@@ -0,0 +1,43 @@
+package manifest
+
+import (
+	"crypto/ed25519"
+	"fmt"
+	"path/filepath"
+
+	"forge.lthn.ai/core/go/pkg/io"
+	"gopkg.in/yaml.v3"
+)
+
+const manifestPath = ".core/view.yml"
+
+// marshalYAML serializes a manifest to YAML bytes.
+func marshalYAML(m *Manifest) ([]byte, error) {
+	return yaml.Marshal(m)
+}
+
+// Load reads and parses a .core/view.yml from the given root directory.
+func Load(medium io.Medium, root string) (*Manifest, error) {
+	path := filepath.Join(root, manifestPath)
+	data, err := medium.Read(path)
+	if err != nil {
+		return nil, fmt.Errorf("manifest.Load: %w", err)
+	}
+	return Parse([]byte(data))
+}
+
+// LoadVerified reads, parses, and verifies the ed25519 signature.
+func LoadVerified(medium io.Medium, root string, pub ed25519.PublicKey) (*Manifest, error) {
+	m, err := Load(medium, root)
+	if err != nil {
+		return nil, err
+	}
+	ok, err := Verify(m, pub)
+	if err != nil {
+		return nil, fmt.Errorf("manifest.LoadVerified: %w", err)
+	}
+	if !ok {
+		return nil, fmt.Errorf("manifest.LoadVerified: signature verification failed for %q", m.Code)
+	}
+	return m, nil
+}

pkg/manifest/loader_test.go

@@ -0,0 +1,63 @@
+package manifest
+
+import (
+	"crypto/ed25519"
+	"testing"
+
+	"forge.lthn.ai/core/go/pkg/io"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestLoad_Good(t *testing.T) {
+	fs := io.NewMockMedium()
+	fs.Files[".core/view.yml"] = `
+code: test-app
+name: Test App
+version: 1.0.0
+layout: HLCRF
+slots:
+  C: main-content
+`
+	m, err := Load(fs, ".")
+	require.NoError(t, err)
+	assert.Equal(t, "test-app", m.Code)
+	assert.Equal(t, "main-content", m.Slots["C"])
+}
+
+func TestLoad_Bad_NoManifest(t *testing.T) {
+	fs := io.NewMockMedium()
+	_, err := Load(fs, ".")
+	assert.Error(t, err)
+}
+
+func TestLoadVerified_Good(t *testing.T) {
+	pub, priv, _ := ed25519.GenerateKey(nil)
+	m := &Manifest{
+		Code: "signed-app", Name: "Signed", Version: "1.0.0",
+		Layout: "HLCRF", Slots: map[string]string{"C": "main"},
+	}
+	_ = Sign(m, priv)
+
+	raw, _ := marshalYAML(m)
+	fs := io.NewMockMedium()
+	fs.Files[".core/view.yml"] = string(raw)
+
+	loaded, err := LoadVerified(fs, ".", pub)
+	require.NoError(t, err)
+	assert.Equal(t, "signed-app", loaded.Code)
+}
+
+func TestLoadVerified_Bad_Tampered(t *testing.T) {
+	pub, priv, _ := ed25519.GenerateKey(nil)
+	m := &Manifest{Code: "app", Version: "1.0.0"}
+	_ = Sign(m, priv)
+
+	raw, _ := marshalYAML(m)
+	tampered := "code: evil\n" + string(raw)[6:]
+	fs := io.NewMockMedium()
+	fs.Files[".core/view.yml"] = tampered
+
+	_, err := LoadVerified(fs, ".", pub)
+	assert.Error(t, err)
+}