diff --git a/internal/core/artifacts/artifacts.go b/internal/core/artifacts/artifacts.go
new file mode 100644
index 0000000..02e115a
--- /dev/null
+++ b/internal/core/artifacts/artifacts.go
@@ -0,0 +1,68 @@
+package artifacts
+
+import (
+	"encoding/json"
+	"time"
+
+	"gitea.maximumdirect.net/eric/notarius/internal/core/source"
+)
+
+type Candidate struct {
+	Index         int                `json:"index"`
+	ExtractorKey  string             `json:"extractor_key"`
+	ArtifactType  string             `json:"artifact_type"`
+	SchemaVersion string             `json:"schema_version"`
+	Payload       json.RawMessage    `json:"payload"`
+	SourceRefs    []source.SourceRef `json:"source_refs,omitempty"`
+	Metadata      map[string]any     `json:"metadata,omitempty"`
+}
+
+type Artifact struct {
+	ExtractorKey  string             `json:"extractor_key"`
+	ArtifactType  string             `json:"artifact_type"`
+	SchemaVersion string             `json:"schema_version"`
+	Payload       json.RawMessage    `json:"payload"`
+	SourceRefs    []source.SourceRef `json:"source_refs,omitempty"`
+	Metadata      map[string]any     `json:"metadata,omitempty"`
+}
+
+type RejectedArtifact struct {
+	Candidate     Candidate `json:"candidate"`
+	ValidatorName string    `json:"validator_name"`
+	ReasonCode    string    `json:"reason_code"`
+	Message       string    `json:"message"`
+}
+
+type RunManifest struct {
+	RunID            string     `json:"run_id,omitempty"`
+	InputAdapter     string     `json:"input_adapter,omitempty"`
+	SourceDigests    []string   `json:"source_digests,omitempty"`
+	Extractors       []string   `json:"extractors,omitempty"`
+	SchemaVersion    string     `json:"schema_version,omitempty"`
+	ValidationStatus string     `json:"validation_status,omitempty"`
+	StartedAt        *time.Time `json:"started_at,omitempty"`
+	CompletedAt      *time.Time `json:"completed_at,omitempty"`
+}
+
+func ArtifactFromCandidate(candidate Candidate) Artifact {
+	return Artifact{
+		ExtractorKey:  candidate.ExtractorKey,
+		ArtifactType:  candidate.ArtifactType,
+		SchemaVersion: candidate.SchemaVersion,
+		Payload:       append(json.RawMessage(nil), candidate.Payload...),
+		SourceRefs:    append([]source.SourceRef(nil), candidate.SourceRefs...),
+		Metadata:      copyMetadata(candidate.Metadata),
+	}
+}
+
+func copyMetadata(metadata map[string]any) map[string]any {
+	if len(metadata) == 0 {
+		return nil
+	}
+
+	copied := make(map[string]any, len(metadata))
+	for key, value := range metadata {
+		copied[key] = value
+	}
+	return copied
+}
diff --git a/internal/core/artifacts/artifacts_test.go b/internal/core/artifacts/artifacts_test.go
new file mode 100644
index 0000000..e3361c4
--- /dev/null
+++ b/internal/core/artifacts/artifacts_test.go
@@ -0,0 +1,134 @@
+package artifacts
+
+import (
+	"encoding/json"
+	"reflect"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/notarius/internal/core/source"
+)
+
+func TestArtifactFromCandidatePreservesCandidateFields(t *testing.T) {
+	candidate := Candidate{
+		Index:         7,
+		ExtractorKey:  "generic-extractor",
+		ArtifactType:  "generic-artifact",
+		SchemaVersion: "v1",
+		Payload:       json.RawMessage(`{"name":"example"}`),
+		SourceRefs: []source.SourceRef{
+			{SourceID: "source-1", StartUnitID: "u1", EndUnitID: "u2"},
+		},
+		Metadata: map[string]any{
+			"confidence": 0.75,
+		},
+	}
+
+	artifact := ArtifactFromCandidate(candidate)
+
+	if artifact.ExtractorKey != candidate.ExtractorKey {
+		t.Fatalf("ExtractorKey = %q, want %q", artifact.ExtractorKey, candidate.ExtractorKey)
+	}
+	if artifact.ArtifactType != candidate.ArtifactType {
+		t.Fatalf("ArtifactType = %q, want %q", artifact.ArtifactType, candidate.ArtifactType)
+	}
+	if artifact.SchemaVersion != candidate.SchemaVersion {
+		t.Fatalf("SchemaVersion = %q, want %q", artifact.SchemaVersion, candidate.SchemaVersion)
+	}
+	if string(artifact.Payload) != string(candidate.Payload) {
+		t.Fatalf("Payload = %s, want %s", artifact.Payload, candidate.Payload)
+	}
+	if !reflect.DeepEqual(artifact.SourceRefs, candidate.SourceRefs) {
+		t.Fatalf("SourceRefs = %#v, want %#v", artifact.SourceRefs, candidate.SourceRefs)
+	}
+	if !reflect.DeepEqual(artifact.Metadata, candidate.Metadata) {
+		t.Fatalf("Metadata = %#v, want %#v", artifact.Metadata, candidate.Metadata)
+	}
+
+	candidate.Payload[0] = '['
+	candidate.SourceRefs[0].StartUnitID = "changed"
+	candidate.Metadata["confidence"] = 0.5
+
+	if string(artifact.Payload) != `{"name":"example"}` {
+		t.Fatalf("Payload changed after candidate mutation: %s", artifact.Payload)
+	}
+	if artifact.SourceRefs[0].StartUnitID != "u1" {
+		t.Fatalf("SourceRefs changed after candidate mutation: %#v", artifact.SourceRefs)
+	}
+	if artifact.Metadata["confidence"] != 0.75 {
+		t.Fatalf("Metadata changed after candidate mutation: %#v", artifact.Metadata)
+	}
+}
+
+func TestJSONMarshalUsesExpectedFieldNames(t *testing.T) {
+	candidate := Candidate{
+		Index:         1,
+		ExtractorKey:  "generic-extractor",
+		ArtifactType:  "generic-artifact",
+		SchemaVersion: "v1",
+		Payload:       json.RawMessage(`{"value":true}`),
+		SourceRefs: []source.SourceRef{
+			{SourceID: "source-1", StartUnitID: "u1", EndUnitID: "u1"},
+		},
+		Metadata: map[string]any{
+			"reviewed": true,
+		},
+	}
+	rejected := RejectedArtifact{
+		Candidate:     candidate,
+		ValidatorName: "generic-validator",
+		ReasonCode:    "invalid",
+		Message:       "candidate was not accepted",
+	}
+
+	gotJSON, err := json.Marshal(rejected)
+	if err != nil {
+		t.Fatalf("json.Marshal() error = %v", err)
+	}
+
+	var got map[string]any
+	if err := json.Unmarshal(gotJSON, &got); err != nil {
+		t.Fatalf("json.Unmarshal() error = %v", err)
+	}
+
+	assertHasKeys(t, got, "candidate", "validator_name", "reason_code", "message")
+
+	gotCandidate, ok := got["candidate"].(map[string]any)
+	if !ok {
+		t.Fatalf("candidate = %#v, want object", got["candidate"])
+	}
+	assertHasKeys(t, gotCandidate, "index", "extractor_key", "artifact_type", "schema_version", "payload", "source_refs", "metadata")
+
+	gotRefs, ok := gotCandidate["source_refs"].([]any)
+	if !ok {
+		t.Fatalf("source_refs = %#v, want array", gotCandidate["source_refs"])
+	}
+	if len(gotRefs) != 1 {
+		t.Fatalf("len(source_refs) = %d, want 1", len(gotRefs))
+	}
+	gotRef, ok := gotRefs[0].(map[string]any)
+	if !ok {
+		t.Fatalf("source_refs[0] = %#v, want object", gotRefs[0])
+	}
+	assertHasKeys(t, gotRef, "source_id", "start_unit_id", "end_unit_id")
+}
+
+func TestRunManifestOmitsEmptyOptionalFields(t *testing.T) {
+	gotJSON, err := json.Marshal(RunManifest{})
+	if err != nil {
+		t.Fatalf("json.Marshal() error = %v", err)
+	}
+
+	if string(gotJSON) != "{}" {
+		t.Fatalf("json.Marshal(RunManifest{}) = %s, want {}", gotJSON)
+	}
+}
+
+func assertHasKeys(t *testing.T, values map[string]any, keys ...string) {
+	t.Helper()
+
+	for _, key := range keys {
+		if _, ok := values[key]; !ok {
+			t.Fatalf("missing key %q in %#v", key, values)
+		}
+	}
+}