fix: align local WebGPU capture behavior (#2907)

* fix: align local WebGPU capture behavior

* fix: address WebGPU capture review feedback

* fix: retain overlapping GPU seek work

* fix: satisfy runtime seek completion types

* fix: drain concurrent GPU seek work

* fix: prevent WebGPU capture barrier starvation

* fix: keep WebGPU presentation active during render seeks

packages/cli/src/browser/gpuPolicy.test.ts

@@ -0,0 +1,34 @@
+import { describe, expect, it } from "vitest";
+import {
+  assertWebGpuRequirement,
+  compositionRequiresWebGpu,
+  resolveLocalBrowserGpuMode,
+} from "./gpuPolicy.js";
+
+describe("local browser GPU policy", () => {
+  it("defaults to auto and preserves explicit CLI/env overrides", () => {
+    expect(resolveLocalBrowserGpuMode(undefined, undefined)).toBe("auto");
+    expect(resolveLocalBrowserGpuMode(undefined, "hardware")).toBe("hardware");
+    expect(resolveLocalBrowserGpuMode(undefined, "software")).toBe("software");
+    expect(resolveLocalBrowserGpuMode(true, "software")).toBe("hardware");
+    expect(resolveLocalBrowserGpuMode(false, "hardware")).toBe("software");
+  });
+
+  it("detects the explicit WebGPU capability marker on the composition root", () => {
+    expect(
+      compositionRequiresWebGpu(
+        '<div data-requires-webgpu data-composition-id="gpu" data-duration="2"></div>',
+      ),
+    ).toBe(true);
+    expect(compositionRequiresWebGpu('<div data-composition-id="dom"></div>')).toBe(false);
+  });
+
+  it("rejects an auto software fallback for required WebGPU compositions", () => {
+    const html = '<div data-composition-id="gpu" data-requires-webgpu></div>';
+    expect(() => assertWebGpuRequirement(html, "auto", "software")).toThrow(
+      "PRODUCER_BROWSER_GPU_MODE=hardware",
+    );
+    expect(() => assertWebGpuRequirement(html, "hardware", "hardware")).not.toThrow();
+    expect(() => assertWebGpuRequirement(html, "software", "software")).not.toThrow();
+  });
+});