fix(engine): self-verify parallel disk drawElement samples (PRINFRA-352)

packages/engine/src/utils/psnr.ts

@@ -0,0 +1,42 @@
+import { execFile } from "node:child_process";
+import { mkdtemp, rm, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+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> {
+  const dir = await mkdtemp(join(tmpdir(), "hf-de-verify-"));
+  try {
+    const pa = join(dir, "a.jpg");
+    const pb = join(dir, "b.jpg");
+    await Promise.all([writeFile(pa, a), writeFile(pb, b)]);
+    const { stderr } = await execFileP(
+      getFfmpegBinary(),
+      ["-hide_banner", "-i", pa, "-i", pb, "-lavfi", "psnr", "-f", "null", "-"],
+      { maxBuffer: 4 * 1024 * 1024 },
+    );
+    const m = /average:(inf|[\d.]+)/.exec(stderr);
+    if (!m) throw new Error(`psnr parse failed: ${stderr.slice(-300)}`);
+    return m[1] === "inf" ? Infinity : Number(m[1]);
+  } finally {
+    await rm(dir, { recursive: true, force: true }).catch(() => {});
+  }
+}
+
+/**
+ * The drawElement self-verify PSNR floor (dB). HF_DE_VERIFY_MIN_DB overrides,
+ * clamped to [10, 60]; out-of-range or unset falls back to 32 — the threshold
+ * every prior eval used to separate real compositor damage from encoder noise.
+ */
+export function resolveDeVerifyMinDb(): number {
+  const raw = Number(process.env.HF_DE_VERIFY_MIN_DB ?? "32");
+  return Number.isFinite(raw) && raw >= 10 && raw <= 60 ? raw : 32;
+}