diff --git a/packages/producer/src/services/render/stages/probeStage.ts b/packages/producer/src/services/render/stages/probeStage.ts
index e1655db55..f3ba06adc 100644
--- a/packages/producer/src/services/render/stages/probeStage.ts
+++ b/packages/producer/src/services/render/stages/probeStage.ts
@@ -13,8 +13,11 @@
  *     plan lists recompile as a sibling phase.
  *   - `composition` (videos/audios/duration) is mutated in place — callers
  *     downstream see the reconciled view through the same object reference.
- *   - `job.duration` and `job.totalFrames` are assigned at the same code
- *     points.
+ *   - The stage computes the final composition `duration` and `totalFrames`
+ *     and returns them. Assigning those values onto the `RenderJob` is the
+ *     sequencer's responsibility — a future chunk worker can't mutate the
+ *     orchestrator's `job` object, and keeping the assignment in one place
+ *     prevents the same value living in two writers.
  *   - The "Composition duration is 0" diagnostic builds the same hint
  *     string from the same console-buffer regex and `__timelines` probe.
  *   - The post-probe "failed network requests" warning fires with the same
@@ -288,10 +291,8 @@ export async function runProbeStage(input: ProbeStageInput): Promise<ProbeStageR
   }
   const browserProbeMs = Date.now() - probeStart;
 
-  job.duration = composition.duration;
-  job.totalFrames = Math.ceil(composition.duration * fpsToNumber(job.config.fps));
   const duration = composition.duration;
-  const totalFrames = job.totalFrames;
+  const totalFrames = Math.ceil(duration * fpsToNumber(job.config.fps));
 
   if (duration <= 0) {
     // Gather diagnostics to help users understand why the render would produce a black video.
diff --git a/packages/producer/src/services/renderOrchestrator.ts b/packages/producer/src/services/renderOrchestrator.ts
index 8e0192a50..fbed2b3f1 100644
--- a/packages/producer/src/services/renderOrchestrator.ts
+++ b/packages/producer/src/services/renderOrchestrator.ts
@@ -2153,10 +2153,8 @@ export async function executeRenderJob(
     fileServer = probeResult.fileServer;
     probeSession = probeResult.probeSession;
     lastBrowserConsole = probeResult.lastBrowserConsole;
-    // Re-assign through the typed result so the rest of the function sees
-    // `job.duration` and `job.totalFrames` narrowed to `number` — the
-    // assignments happened inside `runProbeStage`, but mirroring them here
-    // restores TypeScript's control-flow narrowing.
+    // The probe stage produces `duration` / `totalFrames` values; the
+    // sequencer owns the `RenderJob` and writes them onto it.
     job.duration = probeResult.duration;
     job.totalFrames = probeResult.totalFrames;
     const totalFrames = probeResult.totalFrames;