feat(sdk): ws-b variables/brand — object-valued font/image + B1 JSON model (#1569)

## WS-B — variables / brand, object-valued (end-to-end)

Part of the AI Studio (Pacific) SDK integration. **Base of the SDK-hotspot stack** (`main → ws-b → ws-c → ws-d → ws-3c → ws-3f`).

### Problem
The variable system was split-brained: SDK `setVariableValue` wrote a `--{id}` CSS custom prop, while the runtime `getVariables()` read a separate JSON model (`data-composition-variables` / `__hfVariables`). The two never connected, and there was no `--brand-*` convention. Variables were scalar-only.

### What this does
- **B1 — one source of truth.** `setVariableValue` now drives the runtime variable model (`data-composition-variables` / `__hfVariables`), with CSS compatibility emitted as explicit `stylePath`-based patches alongside the model patch. A brand kit is a variables JSON; a batch of `setVariableValue` re-skins in one frame.
- **B2 — object-valued variables.** The `CompositionVariable` union extends from scalar-only to typed objects: `font` (`{name, source}`) and `image` (`{url, …}`), end-to-end (core union → SDK op → runtime merge). Colors stay scalar (per §7 LOCKED decision).

### Implementation notes
CSS compatibility was moved out of `apply-patches.ts` (where it was incorrectly writing CSS props as a side-effect of model patches, breaking inverse/undo) and into explicit patches emitted in `mutate.ts`. Forward emits `[modelPatch, cssPatch]` for scalars; inverse correctly generates `patchRemove` for the CSS prop when there was no prior CSS prop. Font/image variables never become CSS props.

### Files (12 changed, +441 −32)
- `packages/core`: `core.types.ts`, `lint/rules/composition.ts`, `parsers/htmlParser.ts` (+test), `runtime/validateVariables.ts`
- `packages/sdk`: `engine/mutate.ts` (+test), `engine/apply-patches.ts`, `engine/patches.ts`, `index.ts`, `types.ts`

### Gates
- `bun run build` ✅
- `bun test` SDK 304/0 ✅ · `validateVariables.test.ts` 13/0 ✅
- `bunx oxlint` 0/0 ✅ · `bunx oxfmt --check` ✅
- `fallow audit --gate new-only` ✅ (complexity inherited only)

> The +8 new `htmlParser.test.ts` font/image tests fail under the pre-existing `DOMParser is not defined` happy-dom limitation (main already carries 425 such failures) — not a logic bug; the pure runtime logic is covered by `validateVariables.test.ts`.

### Deferred
Brand-kit picker UI and `batch(setVariableValue × N)` wiring are Pacific-side; per-composition variable scoping beyond `__hfVariablesByComp`.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

packages/core/src/parsers/htmlParser.test.ts

@@ -666,13 +666,9 @@ describe("extractCompositionMetadata", () => {
     expect(meta.variables[1].type).toBe("number");
   });
 
-  // T9 — CompositionVariable font/image parse (spec for R1).
-  // These tests are intentionally red until R1 adds "font" and "image" to
-  // CompositionVariableType and updates parseCompositionVariables accordingly.
-  // Currently failing (spec): tests 1, 2, 3 — filter rejects unknown types.
-  // Currently passing (baseline): test 4 — unknown type graceful rejection already works.
+  // T9 — CompositionVariable font/image parse (WS-B R1 implemented).
 
-  it.fails("[spec] parses a font variable (type: font) with name and source", () => {
+  it("parses a font variable (type: font) with name and source", () => {
     const variables = JSON.stringify([
       {
         id: "brand-font-primary",
@@ -699,7 +695,7 @@ describe("extractCompositionMetadata", () => {
     expect((v as Record<string, unknown>)?.default_source).toBe("");
   });
 
-  it.fails("[spec] parses an image variable with brandRole logo:primary", () => {
+  it("parses an image variable with brandRole logo:primary", () => {
     const variables = JSON.stringify([
       { id: "brand-logo", type: "image", label: "Logo", default: "", brandRole: "logo:primary" },
     ]);
@@ -710,7 +706,6 @@ describe("extractCompositionMetadata", () => {
     const v = meta.variables.find((x) => x.id === "brand-logo");
     expect(v).toBeDefined();
     expect(v?.type).toBe("image");
-    // TODO(R1): remove cast once ImageVariable.brandRole is typed
     expect((v as Record<string, unknown>)?.brandRole).toBe("logo:primary");
   });
 

packages/core/src/parsers/htmlParser.ts

@@ -760,7 +760,8 @@ function parseCompositionVariables(htmlEl: Element): CompositionVariable[] {
     return parsed.filter((v): v is CompositionVariable => {
       if (typeof v !== "object" || v === null) return false;
       if (typeof v.id !== "string" || typeof v.label !== "string") return false;
-      if (!["string", "number", "color", "boolean", "enum"].includes(v.type)) return false;
+      if (!["string", "number", "color", "boolean", "enum", "font", "image"].includes(v.type))
+        return false;
 
       switch (v.type) {
         case "string":
@@ -773,6 +774,12 @@ function parseCompositionVariables(htmlEl: Element): CompositionVariable[] {
           return typeof v.default === "boolean";
         case "enum":
           return typeof v.default === "string" && Array.isArray(v.options);
+        case "font":
+          // default is the font-family name string; extra metadata fields are optional
+          return typeof v.default === "string";
+        case "image":
+          // default is the fallback image URL string; extra metadata fields are optional
+          return typeof v.default === "string";
         default:
           return false;
       }