diff --git a/packages/cli/src/commands/render.test.ts b/packages/cli/src/commands/render.test.ts
index 48f0ce7c2..e3a1fdabe 100644
--- a/packages/cli/src/commands/render.test.ts
+++ b/packages/cli/src/commands/render.test.ts
@@ -123,6 +123,20 @@ vi.mock("../telemetry/config.js", () => ({
     configState.cache = { ...configState.disk };
     return { ...configState.disk };
   }),
+  recordRecentRender: vi.fn((id: string, ok: boolean) => {
+    // Mirrors the real ring update (readConfigFresh → append, cap 5 → write)
+    // against the mock's disk state, so a render's recent-renders write is
+    // modeled like every other config mutation here. Fixed timestamp keeps it
+    // deterministic (tests never assert on `at`).
+    const disk = configState.disk as Record<string, unknown>;
+    const ring = [
+      ...((disk.recentRenders as unknown[]) ?? []),
+      { id, at: "2026-01-01T00:00:00Z", ok },
+    ];
+    const next = { ...disk, recentRenders: ring.slice(-5) };
+    configState.disk = next;
+    configState.cache = { ...next };
+  }),
   writeConfig: vi.fn((config: Record<string, unknown>) => {
     configState.writeConfigCalls.push({ ...config });
     if (configState.failWrites > 0) {
diff --git a/packages/engine/src/utils/psnr.ts b/packages/engine/src/utils/psnr.ts
index 4d92ac110..675594ec4 100644
--- a/packages/engine/src/utils/psnr.ts
+++ b/packages/engine/src/utils/psnr.ts
@@ -5,14 +5,17 @@ import { join } from "node:path";
 import { promisify } from "node:util";
 import { getFfmpegBinary } from "./ffmpegBinaries.js";
 
-const execFileP = promisify(execFile);
-
 /**
  * PSNR (average, dB) between two same-dimension encoded images via ffmpeg.
  * Infinity means bit-identical pixels. Single source of truth for every
  * drawElement self-verify comparison (streaming drain + parallel disk path).
  */
 export async function psnrDb(a: Buffer, b: Buffer): Promise<number> {
+  // promisify(execFile) lazily, not at module load: this module is in the
+  // engine's parallel-capture import chain, and a top-level call to a builtin
+  // crashes any downstream test that partially mocks node:child_process
+  // without an execFile export (vitest surfaces it as a load-time error).
+  const execFileP = promisify(execFile);
   const dir = await mkdtemp(join(tmpdir(), "hf-de-verify-"));
   try {
     const pa = join(dir, "a.jpg");