diff --git a/.github/workflows/windows-render.yml b/.github/workflows/windows-render.yml
index db3100e127..aba92da2a3 100644
--- a/.github/workflows/windows-render.yml
+++ b/.github/workflows/windows-render.yml
@@ -484,10 +484,10 @@ jobs:
         shell: pwsh
         run: bunx vitest run packages/producer/src/services/hyperframeLint.file-race.test.ts --maxWorkers=2
 
-      - name: Verify catalog source reads on Windows
+      - name: Verify catalog file operations on Windows
         if: matrix.lane == 'studio-engine-cli'
         shell: pwsh
-        run: bunx vitest run scripts/catalog/catalog-payload-assets.file-race.test.ts --maxWorkers=2
+        run: bunx vitest run scripts/catalog/catalog-payload-assets.file-race.test.ts scripts/catalog/catalog-payload-assets.cache-race.test.ts --maxWorkers=2
 
       - name: Run runtime contract test
         if: matrix.runtime_contract
diff --git a/scripts/catalog-payload-assets.ts b/scripts/catalog-payload-assets.ts
index de6462b376..04c019959f 100644
--- a/scripts/catalog-payload-assets.ts
+++ b/scripts/catalog-payload-assets.ts
@@ -9,8 +9,11 @@
 
 import { createHash } from "node:crypto";
 import {
-  existsSync,
   mkdirSync,
+  lstatSync,
+  linkSync,
+  mkdtempSync,
+  rmSync,
   readdirSync,
   readFileSync,
   readSync,
@@ -206,6 +209,33 @@ export interface AssetTarget {
   urlBase: string;
 }
 
+/** Publish a complete cache entry without replacing a competing file or link. */
+function cacheAsset(bytes: Buffer<ArrayBuffer>, ext: string, target: AssetTarget): string {
+  const name = `${createHash("sha256").update(bytes).digest("hex").slice(0, 16)}${ext}`;
+  const dest = join(target.dir, name);
+  // Cache hits need no writable directory. A miss still has to win linkSync.
+  if (lstatSync(dest, { throwIfNoEntry: false })) return name;
+  mkdirSync(target.dir, { recursive: true });
+  if (!lstatSync(target.dir).isDirectory())
+    throw new Error("Catalog cache must be a real directory");
+  const staging = mkdtempSync(join(target.dir, ".hf-asset-"));
+  try {
+    const staged = join(staging, "content");
+    writeFileSync(staged, bytes, { flag: "wx" });
+    try {
+      linkSync(staged, dest);
+    } catch (error) {
+      if (!(error instanceof Error && "code" in error && error.code === "EEXIST")) throw error;
+    }
+  } finally {
+    // Cleanup must not mask a publication error or fail an already published asset.
+    try {
+      rmSync(staging, { recursive: true, force: true });
+    } catch {}
+  }
+  return name;
+}
+
 /**
  * Point every local reference at something the browser can fetch.
  *
@@ -252,12 +282,7 @@ export function processAssets(html: string, projectDir: string, target: AssetTar
     }
 
     if (HOSTED_EXTENSIONS.has(ext)) {
-      const name = `${createHash("sha256").update(bytes).digest("hex").slice(0, 16)}${ext}`;
-      const dest = join(target.dir, name);
-      if (!existsSync(dest)) {
-        mkdirSync(target.dir, { recursive: true });
-        writeFileSync(dest, bytes);
-      }
+      const name = cacheAsset(bytes, ext, target);
       out = out.split(ref).join(`${target.urlBase}/${name}`);
       hosted += 1;
       continue;
@@ -305,12 +330,7 @@ export function externalizeDataUris(
       const bytes = Buffer.from(blob, "base64");
       if (bytes.length < EXTERNALIZE_MIN_BYTES) return whole;
 
-      const name = `${createHash("sha256").update(bytes).digest("hex").slice(0, 16)}${ext}`;
-      const dest = join(target.dir, name);
-      if (!existsSync(dest)) {
-        mkdirSync(target.dir, { recursive: true });
-        writeFileSync(dest, bytes);
-      }
+      const name = cacheAsset(bytes, ext, target);
       externalized += 1;
       return `${target.urlBase}/${name}`;
     },
diff --git a/scripts/catalog/catalog-payload-assets.cache-race.test.ts b/scripts/catalog/catalog-payload-assets.cache-race.test.ts
new file mode 100644
index 0000000000..c461721db8
--- /dev/null
+++ b/scripts/catalog/catalog-payload-assets.cache-race.test.ts
@@ -0,0 +1,163 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { createHash } from "node:crypto";
+import { join, dirname } from "node:path";
+import { tmpdir } from "node:os";
+import { processAssets, externalizeDataUris } from "../catalog-payload-assets.ts";
+
+const hooks = vi.hoisted(() => {
+  const state: {
+    dest: string;
+    beforePublish?: () => void;
+    failWrite: boolean;
+    failLink: boolean;
+    failCleanup: boolean;
+    stagedBytes?: Buffer;
+    stages: string[];
+  } = { dest: "", failWrite: false, failLink: false, failCleanup: false, stages: [] };
+  return state;
+});
+vi.mock("node:fs", async (importOriginal) => {
+  const fs = await importOriginal<typeof import("node:fs")>();
+  function beforePublish(): void {
+    const hook = hooks.beforePublish;
+    hooks.beforePublish = undefined;
+    hook?.();
+  }
+  return {
+    ...fs,
+    mkdtempSync: (...args: Parameters<typeof fs.mkdtempSync>) => {
+      const dir = fs.mkdtempSync(...args);
+      hooks.stages.push(String(dir));
+      return dir;
+    },
+    writeFileSync: (...args: Parameters<typeof fs.writeFileSync>) => {
+      if (String(args[0]) === hooks.dest) beforePublish();
+      if (hooks.failWrite) {
+        fs.writeFileSync(args[0], "partial");
+        throw new Error("write failure");
+      }
+      return fs.writeFileSync(...args);
+    },
+    linkSync: (...args: Parameters<typeof fs.linkSync>) => {
+      hooks.stagedBytes = fs.readFileSync(args[0]);
+      beforePublish();
+      if (hooks.failLink) throw new Error("link failure");
+      return fs.linkSync(...args);
+    },
+    rmSync: (...args: Parameters<typeof fs.rmSync>) => {
+      if (hooks.failCleanup) throw new Error("cleanup failure");
+      return fs.rmSync(...args);
+    },
+  };
+});
+const fs = await vi.importActual<typeof import("node:fs")>("node:fs");
+let root: string;
+let project: string;
+let target: { dir: string; urlBase: string };
+const bytes = Buffer.alloc(4096, 42);
+const name = `${createHash("sha256").update(bytes).digest("hex").slice(0, 16)}.png`;
+beforeEach(() => {
+  root = fs.mkdtempSync(join(tmpdir(), "hf-catalog-cache-"));
+  project = join(root, "project");
+  fs.mkdirSync(project);
+  fs.writeFileSync(join(project, "asset.png"), bytes);
+  target = { dir: join(root, "cache"), urlBase: "/assets" };
+  Object.assign(hooks, {
+    dest: join(target.dir, name),
+    beforePublish: undefined,
+    failWrite: false,
+    failLink: false,
+    failCleanup: false,
+    stagedBytes: undefined,
+    stages: [],
+  });
+});
+afterEach(() => fs.rmSync(root, { recursive: true, force: true }));
+function publish(kind: string): string {
+  if (kind === "reference") {
+    const result = processAssets('<img src="asset.png">', project, target);
+    expect(result.hosted).toBe(1);
+    expect(result.inlined).toBe(0);
+    expect(result.unresolved).toEqual([]);
+    return result.html;
+  }
+  const result = externalizeDataUris(
+    `<img src="data:image/png;base64,${bytes.toString("base64")}">`,
+    target,
+  );
+  expect(result.externalized).toBe(1);
+  return result.html;
+}
+function assertNoStages(): void {
+  for (const stage of hooks.stages) expect(fs.existsSync(stage)).toBe(false);
+}
+
+describe.each(["reference", "data URI"])("catalog %s cache publication", (kind) => {
+  it("publishes complete bytes with the existing hash and reuses cache hits without staging", () => {
+    expect(publish(kind)).toBe(`<img src="/assets/${name}">`);
+    expect(hooks.stagedBytes).toEqual(bytes);
+    expect(fs.readFileSync(hooks.dest)).toEqual(bytes);
+    assertNoStages();
+    hooks.failWrite = true;
+    const count = hooks.stages.length;
+    expect(publish(kind)).toBe(`<img src="/assets/${name}">`);
+    expect(hooks.stages.length).toBe(count);
+  });
+  it.each(["file", "symlink", "dangling symlink"])("does not overwrite a competing %s", (entry) => {
+    const outside = join(root, "outside.png");
+    if (entry === "symlink") fs.writeFileSync(outside, "outside");
+    hooks.beforePublish = () => {
+      if (entry === "file") fs.writeFileSync(hooks.dest, "winner");
+      else fs.symlinkSync(outside, hooks.dest, "file");
+    };
+    expect(publish(kind)).toBe(`<img src="/assets/${name}">`);
+    expect(hooks.beforePublish).toBeUndefined();
+    if (entry === "file") expect(fs.readFileSync(hooks.dest, "utf8")).toBe("winner");
+    else {
+      expect(fs.lstatSync(hooks.dest).isSymbolicLink()).toBe(true);
+      if (entry === "symlink") expect(fs.readFileSync(outside, "utf8")).toBe("outside");
+      else expect(fs.existsSync(outside)).toBe(false);
+    }
+    assertNoStages();
+  });
+  it("leaves a pre-existing dangling destination link untouched", () => {
+    fs.mkdirSync(target.dir);
+    const outside = join(root, "outside.png");
+    fs.symlinkSync(outside, hooks.dest, "file");
+    publish(kind);
+    expect(fs.existsSync(outside)).toBe(false);
+    expect(fs.lstatSync(hooks.dest).isSymbolicLink()).toBe(true);
+    expect(hooks.stages).toEqual([]);
+  });
+  it("rejects a cache directory linked outside without writing there", () => {
+    const outside = join(root, "outside");
+    fs.mkdirSync(outside);
+    fs.symlinkSync(outside, target.dir, process.platform === "win32" ? "junction" : "dir");
+    expect(() => publish(kind)).toThrow("Catalog cache must be a real directory");
+    expect(fs.readdirSync(outside)).toEqual([]);
+  });
+  it("removes a partial staging file after write failure without publishing it", () => {
+    hooks.failWrite = true;
+    expect(() => publish(kind)).toThrow("write failure");
+    expect(fs.existsSync(hooks.dest)).toBe(false);
+    assertNoStages();
+  });
+  it("preserves publication errors and cleans staging", () => {
+    hooks.failLink = true;
+    expect(() => publish(kind)).toThrow("link failure");
+    expect(fs.existsSync(hooks.dest)).toBe(false);
+    assertNoStages();
+  });
+  it("does not replace a publication error with a cleanup error", () => {
+    hooks.failLink = true;
+    hooks.failCleanup = true;
+    expect(() => publish(kind)).toThrow("link failure");
+    expect(fs.existsSync(hooks.dest)).toBe(false);
+  });
+  it("keeps a successful publication successful if cleanup fails", () => {
+    hooks.failCleanup = true;
+    expect(publish(kind)).toBe(`<img src="/assets/${name}">`);
+    expect(fs.readFileSync(hooks.dest)).toEqual(bytes);
+    expect(hooks.stages.map((stage) => dirname(stage))).toEqual([target.dir]);
+  });
+});