fix(producer): verify sequential disk drawElement samples too

packages/engine/src/index.ts

@@ -210,6 +210,7 @@ export {
   calculateOptimalWorkers,
   computeWorkerSizing,
   selectVerifySampleIndicesForTask,
+  verifyDiskDrawElementSamples,
   distributeFrames,
   distributeFramesInterleaved,
   executeParallelCapture,

packages/engine/src/services/parallelCoordinator.ts

@@ -646,7 +646,7 @@ async function psnrForDiskSample(
 // per-sample skip/breach) — already decomposed into psnrForDiskSample +
 // assertDiskSampleAboveFloor; further splitting obscures the check.
 // fallow-ignore-next-line complexity
-async function verifyDiskDrawElementSamples(
+export async function verifyDiskDrawElementSamples(
   session: CaptureSession,
   task: WorkerTask,
   streaming: boolean,

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

@@ -44,6 +44,7 @@ import {
   type EngineConfig,
   captureFrame,
   captureFrameToBufferPipelined,
+  verifyDiskDrawElementSamples,
   writeCapturedFrame,
   closeCaptureSession,
   completeDeferredDrawElementInit,
@@ -331,6 +332,24 @@ export async function runCaptureStage(input: CaptureStageInput): Promise<Capture
           reportFrame(i);
         }
       }
+      // Sequential disk drawElement self-verification (PRINFRA-352 follow-up):
+      // the sequential disk path — reachable under the explicit fast-capture
+      // opt-in, including via probe-session reuse — armed ground-truth samples
+      // but never checked them, exactly like the parallel disk workers before
+      // #2749. Same synthetic-task shape the parallel verify uses; a breach
+      // throws DrawElementVerificationError and the orchestrator's disk-stage
+      // retry re-renders via screenshot.
+      await verifyDiskDrawElementSamples(
+        session,
+        {
+          workerId: 0,
+          startFrame: rangeStart,
+          endFrame: rangeEnd,
+          outputDir: framesDir,
+          outputFrameOffset: rangeStart,
+        },
+        false,
+      );
       // Capture the sequential session's static-dedup perf before close (the
       // counters are valid only while the session is live).
       dedupPerfs.push(getCapturePerfSummary(session));