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/

docs/architecture/08-vega-editor-techniques.md

@@ -73,6 +73,29 @@ self-hosting.
 **Accepted cost:** the explicit worker wiring (§1) is inherent to self-hosting — it is the
 price of offline, paid in any non-CDN setup, and the wrapper would not remove it.
 
+### Entry point: `edcore.main`, never `editor.api` (trim languages, not features)
+
+Self-hosting raw Monaco forces a choice of ESM entry point, and the granularity matters:
+
+| Import | What you get | Use? |
+|---|---|---|
+| `monaco-editor` (barrel) | All features **+ every basic language** (sql, abap, solidity, …) | ❌ language bloat (~20 dead chunks) |
+| `esm/vs/editor/editor.api` | The API surface only — **zero feature contributions** | ❌ a text box: no folding, suggest widget, `Cmd+Backspace`, find, bracket colorization |
+| `esm/vs/editor/edcore.main` | `editor.all` (all 59 feature contributions) + API, **no languages** | ✅ full editor UX, JSON-only weight |
+
+Import **`edcore.main`** and add only the JSON language service
+(`esm/vs/language/json/monaco.contribution`). `edcore.main` ships no `.d.ts` of its own —
+add an ambient `declare module … { export * from '…/editor.api'; }` so types (and Monaco's
+global `MonacoEnvironment` augmentation) resolve. Two editor options worth setting because
+they bite Vega-Lite specs specifically: `showFoldingControls: 'always'` (fold arrows always
+visible), and `quickSuggestions: { strings: true }` (VL enum values like `"bar"` live inside
+JSON strings, where Monaco disables auto-suggest by default).
+
+> Reaching for `editor.api` to "drop unused languages" silently strips every editor feature —
+> the languages live elsewhere. This is the concrete case behind AGENTS.md's **"trim content,
+> not capability"** rule: cut the unwanted _content_, keep the _behavior_, and verify the
+> behavior survived by exercising the editor, not by a green build.
+
 ---
 
 > **The single biggest surprise:** vega/editor does **not** use `vega-embed` for its live