fix(producer): copy extracted frames on Windows to avoid symlink EPERM

The local render path (renderOrchestrator → runExtractVideosStage) materialized
each video's extracted frames into the compiled dir via symlinkSync, with no
materializeSymlinks flag. On Windows without Developer Mode/Administrator,
symlinkSync throws EPERM, so local video renders failed at the video_extract
stage (users worked around it with materializeSymlinks patches / snapshot-frame
hacks). The distributed plan() path already copies (materializeSymlinks: true).

Pass materializeSymlinks: shouldCopyExtractedFrames(process.platform) at the
local caller — copy on win32 (symlinks unavailable), symlink elsewhere (cheap).
New pure shouldCopyExtractedFrames() helper + unit tests.

packages/producer/src/services/render/stages/extractVideosStage.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { appendAutoDetectedVideoAudio } from "./extractVideosStage.js";
+import { appendAutoDetectedVideoAudio, shouldCopyExtractedFrames } from "./extractVideosStage.js";
 import type { ExtractedFrames, VideoElement } from "@hyperframes/engine";
 
 function makeVideo(overrides: Partial<VideoElement> = {}): VideoElement {
@@ -81,3 +81,14 @@ describe("appendAutoDetectedVideoAudio", () => {
     expect(composition.audios).toHaveLength(1);
   });
 });
+
+describe("shouldCopyExtractedFrames", () => {
+  it("copies frames on Windows (symlinkSync throws EPERM without Developer Mode)", () => {
+    expect(shouldCopyExtractedFrames("win32")).toBe(true);
+  });
+
+  it("symlinks on macOS and Linux (cheaper, symlinks allowed)", () => {
+    expect(shouldCopyExtractedFrames("darwin")).toBe(false);
+    expect(shouldCopyExtractedFrames("linux")).toBe(false);
+  });
+});

packages/producer/src/services/render/stages/extractVideosStage.ts

@@ -96,6 +96,18 @@ export interface ExtractVideosStageResult {
   videoExtractMs: number;
 }
 
+/**
+ * Whether the extract stage should COPY frames into the compiled dir instead of
+ * symlinking them. Windows without Developer Mode / Administrator can't create
+ * symlinks (`symlinkSync` throws EPERM), which failed local video renders; copy
+ * there instead. Elsewhere symlinking is cheaper, so keep it. (The distributed
+ * `plan()` path already forces copying for a different reason — a self-contained
+ * planDir — by passing `materializeSymlinks: true` explicitly.)
+ */
+export function shouldCopyExtractedFrames(platform: NodeJS.Platform): boolean {
+  return platform === "win32";
+}
+
 export async function runExtractVideosStage(
   input: ExtractVideosStageInput,
 ): Promise<ExtractVideosStageResult> {

packages/producer/src/services/renderOrchestrator.ts

@@ -110,7 +110,10 @@ import {
 import { type HdrPerfCollector, type HdrPerfSummary } from "./render/hdrPerf.js";
 import { runCompileStage } from "./render/stages/compileStage.js";
 import { runProbeStage } from "./render/stages/probeStage.js";
-import { runExtractVideosStage } from "./render/stages/extractVideosStage.js";
+import {
+  runExtractVideosStage,
+  shouldCopyExtractedFrames,
+} from "./render/stages/extractVideosStage.js";
 import { runAudioStage } from "./render/stages/audioStage.js";
 import { runCaptureStage } from "./render/stages/captureStage.js";
 import { runCaptureStreamingStage } from "./render/stages/captureStreamingStage.js";
@@ -1350,6 +1353,9 @@ export async function executeRenderJob(
           composition,
           abortSignal,
           assertNotAborted,
+          // Copy (don't symlink) extracted frames on Windows — symlinkSync throws
+          // EPERM there without Developer Mode/admin, which failed local renders.
+          materializeSymlinks: shouldCopyExtractedFrames(process.platform),
         }),
     );
     const {