feat(image-pipeline): add wasm simd fallback backend scaffold

tests/image-pipeline/wasm-backend.test.ts

@@ -0,0 +1,154 @@
+// @vitest-environment jsdom
+
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+import type { ImagePipelineBackend } from "@/lib/image-pipeline/backend/backend-types";
+import { createBackendRouter } from "@/lib/image-pipeline/backend/backend-router";
+import type { WasmKernelModule } from "@/lib/image-pipeline/backend/wasm/wasm-loader";
+import { createWasmSimdBackend } from "@/lib/image-pipeline/backend/wasm/wasm-backend";
+
+function createStep() {
+  return {
+    nodeId: "n1",
+    type: "color-adjust",
+    params: {
+      hsl: {
+        hue: 0,
+        saturation: 0,
+        luminance: 0,
+      },
+      temperature: 0,
+      tint: 0,
+      vibrance: 0,
+    },
+  } as const;
+}
+
+function createCpuBackend(overrides?: {
+  preview?: ImagePipelineBackend["runPreviewStep"];
+  full?: ImagePipelineBackend["runFullPipeline"];
+}): ImagePipelineBackend {
+  return {
+    id: "cpu",
+    runPreviewStep: overrides?.preview ?? vi.fn(),
+    runFullPipeline: overrides?.full ?? vi.fn(),
+  };
+}
+
+describe("wasm backend rollout selection", () => {
+  beforeEach(() => {
+    vi.resetModules();
+    vi.unstubAllGlobals();
+  });
+
+  it("selects wasm when webgl is unavailable and wasm simd is enabled + available", async () => {
+    vi.doMock("@/lib/image-pipeline/backend/feature-flags", async () => {
+      const actual = await vi.importActual("@/lib/image-pipeline/backend/feature-flags");
+      return {
+        ...actual,
+        getBackendFeatureFlags: () => ({
+          forceCpu: false,
+          webglEnabled: true,
+          wasmEnabled: true,
+        }),
+      };
+    });
+
+    vi.doMock("@/lib/image-pipeline/backend/capabilities", async () => {
+      const actual = await vi.importActual("@/lib/image-pipeline/backend/capabilities");
+      return {
+        ...actual,
+        detectBackendCapabilities: () => ({
+          webgl: false,
+          wasmSimd: true,
+          offscreenCanvas: false,
+        }),
+      };
+    });
+
+    const backendRouter = await import("@/lib/image-pipeline/backend/backend-router");
+
+    expect(backendRouter.getPreviewBackendHintForSteps([createStep()])).toBe("wasm");
+  });
+});
+
+describe("wasm backend fallback behavior", () => {
+  it("downgrades to cpu with runtime_error when wasm initialization fails", () => {
+    const fallbackEvents: Array<{
+      reason: string;
+      requestedBackend: string;
+      fallbackBackend: string;
+    }> = [];
+    const cpuPreview = vi.fn();
+    const cpuBackend = createCpuBackend({
+      preview: cpuPreview,
+    });
+    const wasmBackend = createWasmSimdBackend({
+      loadModule: () => {
+        throw new Error("wasm init failed");
+      },
+    });
+    const router = createBackendRouter({
+      backends: [cpuBackend, wasmBackend],
+      backendAvailability: {
+        wasm: {
+          supported: true,
+          enabled: true,
+        },
+      },
+      featureFlags: {
+        forceCpu: false,
+        webglEnabled: false,
+        wasmEnabled: true,
+      },
+      onFallback: (event) => {
+        fallbackEvents.push({
+          reason: event.reason,
+          requestedBackend: event.requestedBackend,
+          fallbackBackend: event.fallbackBackend,
+        });
+      },
+    });
+
+    router.runPreviewStep({
+      pixels: new Uint8ClampedArray(4),
+      step: createStep(),
+      width: 1,
+      height: 1,
+      backendHint: "wasm",
+    });
+
+    expect(cpuPreview).toHaveBeenCalledTimes(1);
+    expect(fallbackEvents).toEqual([
+      {
+        reason: "runtime_error",
+        requestedBackend: "wasm",
+        fallbackBackend: "cpu",
+      },
+    ]);
+  });
+
+  it("does not require SharedArrayBuffer or threads", () => {
+    vi.stubGlobal("SharedArrayBuffer", undefined);
+    vi.stubGlobal("Worker", undefined);
+
+    const module: WasmKernelModule = {
+      applyPreviewStep: vi.fn(),
+      applyFullPipeline: vi.fn(),
+    };
+
+    const backend = createWasmSimdBackend({
+      loadModule: () => module,
+    });
+
+    expect(() => {
+      backend.runPreviewStep({
+        pixels: new Uint8ClampedArray(4),
+        step: createStep(),
+        width: 1,
+        height: 1,
+      });
+    }).not.toThrow();
+    expect(module.applyPreviewStep).toHaveBeenCalledTimes(1);
+  });
+});