Implement M1 authoring loop: library, editor, live preview, persistence

M1 MVP from docs/IMPLEMENTATION-PLAN.md, with the /alignment pass applied.

- core: Snippet model + factory; prepareSpecForRender (copy-not-mutate); per-theme Vega chart config
- state/orchestration: SnippetStore with debounced auto-save; IndexedDB adapter + read-time migration; startup hydration + write-through persistence
- ui: SnippetLibrary, SpecEditor (Monaco edcore.main — full editor features, JSON-only languages), LivePreview
- build: Monaco/Vega manual chunks; raised PWA precache ceiling
- alignment: flush a valid draft on snippet switch (+regression tests); TODO breadcrumbs for the preview render race and the window.confirm delete
- housekeeping: gitignore .claude/projects/

src/core/snippet.ts

@@ -0,0 +1,123 @@
+/**
+ * Snippet — the primary user-authored entity (spec §09A).
+ *
+ * Portable core: no browser APIs, no React. Defines the record shape, the
+ * current record schema version, and pure factories for creating new snippets
+ * (with the sample bar-chart template and an auto-generated date/time name).
+ *
+ * Specs are stored as **JSON text** (string). The data model permits a spec to
+ * be an object or a string; we standardize on the string form because it is what
+ * the Monaco editor edits and what survives round-tripping without reformatting.
+ * The preview parses the text into an object before rendering (see rendering.ts).
+ */
+
+/** Current schema version for a Snippet record (read-time migration target). */
+export const CURRENT_SNIPPET_VERSION = 1;
+
+export interface Snippet {
+  /** Unique, stable identifier. */
+  id: string;
+  /** Record schema version, for read-time migration. */
+  version: number;
+  /** Human-readable title shown in the library. */
+  name: string;
+  /** ISO timestamp — when first created. */
+  created: string;
+  /** ISO timestamp — when last saved. */
+  modified: string;
+  /** The published (stable) Vega-Lite spec, as JSON text. */
+  spec: string;
+  /** The working-draft Vega-Lite spec being edited, as JSON text. */
+  draftSpec: string;
+  /** Free-form user note. */
+  comment: string;
+  /** User-assigned labels. */
+  tags: string[];
+  /** Names of datasets referenced by this spec (maintained on publish). */
+  datasetRefs: string[];
+  /** Free-form, extensible metadata bag. */
+  meta: Record<string, unknown>;
+}
+
+/**
+ * The sample bar-chart template a fresh snippet starts from (spec §02 → Create
+ * New: "a small sample Vega-Lite bar-chart template with a few inline rows").
+ * Inline data only — datasets arrive in M3.
+ */
+export const SAMPLE_SPEC = {
+  $schema: 'https://vega.github.io/schema/vega-lite/v6.json',
+  description: 'A simple bar chart.',
+  data: {
+    values: [
+      { category: 'A', value: 28 },
+      { category: 'B', value: 55 },
+      { category: 'C', value: 43 },
+      { category: 'D', value: 91 },
+      { category: 'E', value: 81 },
+    ],
+  },
+  mark: 'bar',
+  encoding: {
+    x: { field: 'category', type: 'nominal', axis: { labelAngle: 0 } },
+    y: { field: 'value', type: 'quantitative' },
+  },
+} as const;
+
+/** The sample template rendered as pretty-printed JSON text. */
+export function sampleSpecText(): string {
+  return JSON.stringify(SAMPLE_SPEC, null, 2);
+}
+
+/** Two-digit zero-pad for the date/time name. */
+function pad(n: number): string {
+  return String(n).padStart(2, '0');
+}
+
+/**
+ * Auto-generated default name from a timestamp, e.g. "Snippet 2026-06-04 14:30:07".
+ * Including seconds keeps names unique for snippets created in quick succession.
+ */
+export function generateSnippetName(now: Date): string {
+  const date = `${now.getFullYear()}-${pad(now.getMonth() + 1)}-${pad(now.getDate())}`;
+  const time = `${pad(now.getHours())}:${pad(now.getMinutes())}:${pad(now.getSeconds())}`;
+  return `Snippet ${date} ${time}`;
+}
+
+export interface CreateSnippetOptions {
+  /** Override the auto-generated name. */
+  name?: string;
+  /** Override the starting spec text (defaults to the sample template). */
+  spec?: string;
+  /** Clock injection for deterministic tests; defaults to the current time. */
+  now?: Date;
+  /** Id injection for deterministic tests; defaults to a random UUID. */
+  id?: string;
+}
+
+/**
+ * Create a new snippet. `spec` and `draftSpec` start identical (nothing to
+ * publish yet); timestamps are equal at creation.
+ */
+export function createSnippet(options: CreateSnippetOptions = {}): Snippet {
+  const now = options.now ?? new Date();
+  const iso = now.toISOString();
+  const spec = options.spec ?? sampleSpecText();
+  return {
+    id: options.id ?? crypto.randomUUID(),
+    version: CURRENT_SNIPPET_VERSION,
+    name: options.name ?? generateSnippetName(now),
+    created: iso,
+    modified: iso,
+    spec,
+    draftSpec: spec,
+    comment: '',
+    tags: [],
+    datasetRefs: [],
+    meta: {},
+  };
+}
+
+/** True when the snippet's draft differs from its published spec (§03D). */
+export function hasUnpublishedChanges(snippet: Snippet): boolean {
+  return snippet.draftSpec !== snippet.spec;
+}