Add Chart Builder: no-JSON Vega-Lite composer from a dataset (M4)

src/core/snippet.ts

@@ -14,6 +14,13 @@
 /** Current schema version for a Snippet record (read-time migration target). */
 export const CURRENT_SNIPPET_VERSION = 1;
 
+/**
+ * The Vega-Lite schema URL stamped into generated specs (`$schema`). Shared so the
+ * sample template and the Chart Builder agree on one version; the Monaco schema
+ * service pins the same URI independently (infrastructure/monaco-schema.ts).
+ */
+export const VEGA_LITE_SCHEMA_URL = 'https://vega.github.io/schema/vega-lite/v6.json';
+
 export interface Snippet {
   /** Unique, stable identifier. */
   id: string;
@@ -45,7 +52,7 @@ export interface Snippet {
  * Inline data only — datasets arrive in M3.
  */
 export const SAMPLE_SPEC = {
-  $schema: 'https://vega.github.io/schema/vega-lite/v6.json',
+  $schema: VEGA_LITE_SCHEMA_URL,
   description: 'A simple bar chart.',
   data: {
     values: [
@@ -92,6 +99,8 @@ export interface CreateSnippetOptions {
   now?: Date;
   /** Id injection for deterministic tests; defaults to a random UUID. */
   id?: string;
+  /** Seed the extensible metadata bag (e.g. Chart Builder provenance). */
+  meta?: Record<string, unknown>;
 }
 
 /**
@@ -113,7 +122,7 @@ export function createSnippet(options: CreateSnippetOptions = {}): Snippet {
     comment: '',
     tags: [],
     datasetRefs: [],
-    meta: {},
+    meta: options.meta ?? {},
   };
 }