Add run manifest and logical output file contracts

internal/framework/contracts/contracts.go

@@ -182,8 +182,17 @@ type OutputRequest struct {
 	Metadata   map[string]any               `json:"metadata,omitempty"`
 }
 
+type OutputFile struct {
+	Name        string `json:"name"`
+	ContentType string `json:"content_type,omitempty"`
+	Bytes       []byte `json:"-"`
+}
+
 type OutputResult struct {
-	Bytes       []byte    `json:"-"`
+	Files []OutputFile `json:"files,omitempty"`
+	// Bytes is the legacy single-output payload. New encoders should return Files.
+	Bytes []byte `json:"-"`
+	// ContentType is the legacy single-output content type. New encoders should return Files.
 	ContentType string    `json:"content_type,omitempty"`
 	Warnings    []Warning `json:"warnings,omitempty"`
 }
@@ -192,3 +201,7 @@ type OutputEncoder interface {
 	Key() string
 	Encode(ctx context.Context, req OutputRequest) (OutputResult, error)
 }
+
+type ManifestMetadataProvider interface {
+	ManifestMetadata() map[string]any
+}