diff --git a/packages/engine/src/config.ts b/packages/engine/src/config.ts
index 969bbd611..b350f9e67 100644
--- a/packages/engine/src/config.ts
+++ b/packages/engine/src/config.ts
@@ -344,7 +344,6 @@ const BOOLEAN_ENGINE_CONFIG_FIELDS = [
 ] as const;
 
 const POSITIVE_NUMBER_ENGINE_CONFIG_FIELDS = [
-  "coresPerWorker",
   "browserTimeout",
   "protocolTimeout",
   "chunkSizeFrames",
@@ -394,6 +393,13 @@ function assertEngineConfigNumber(
   }
 }
 
+function assertPositiveEngineConfigNumber(config: Record<string, unknown>, field: string): void {
+  const value = config[field];
+  if (typeof value !== "number" || !Number.isFinite(value) || value <= 0) {
+    throw new Error(`Engine config ${field} must be a finite number > 0`);
+  }
+}
+
 function assertEngineConfigEnum(
   config: Record<string, unknown>,
   field: string,
@@ -435,7 +441,7 @@ function validateEngineConfigParallelism(config: Record<string, unknown>): void
   ) {
     throw new Error("Engine config concurrency must be a positive integer or auto");
   }
-  assertEngineConfigNumber(config, "coresPerWorker", 0);
+  assertPositiveEngineConfigNumber(config, "coresPerWorker");
   for (const field of ["minParallelFrames", "largeRenderThreshold"] as const) {
     assertEngineConfigNumber(config, field, 0, true);
   }
diff --git a/packages/producer/src/renderRequest.test.ts b/packages/producer/src/renderRequest.test.ts
index 728ccdf59..7fa68b6d2 100644
--- a/packages/producer/src/renderRequest.test.ts
+++ b/packages/producer/src/renderRequest.test.ts
@@ -1,5 +1,5 @@
 import { afterEach, describe, expect, it } from "vitest";
-import { DEFAULT_CONFIG } from "@hyperframes/engine";
+import { DEFAULT_CONFIG, resolveConfig } from "@hyperframes/engine";
 import {
   createRenderRequest,
   distributedConfigFromRequest,
@@ -8,6 +8,7 @@ import {
   renderRequestFromDistributedConfig,
   serializeRenderRequest,
 } from "./renderRequest.js";
+import { InvalidConfigError } from "./services/distributed/renderConfigValidation.js";
 
 const originalForceScreenshot = process.env.PRODUCER_FORCE_SCREENSHOT;
 
@@ -203,6 +204,52 @@ describe("RenderRequest", () => {
     }
   });
 
+  it("accepts fractional coresPerWorker snapshots from the canonical resolver", () => {
+    const engineConfig = resolveConfig({ coresPerWorker: 0.5 });
+    const value = createRenderRequest({
+      projectDir: "/project",
+      outputPath: "/output/video.mp4",
+      engineConfig,
+      options: {
+        fps: { num: 30, den: 1 },
+        quality: "standard",
+        format: "mp4",
+        distributed: { width: 1920, height: 1080, cfr: true },
+      },
+    });
+
+    expect(value.options.engineConfig.coresPerWorker).toBe(0.5);
+    expect(parseRenderRequest(serializeRenderRequest(value))).toEqual(value);
+
+    const distributed = distributedConfigFromRequest(value);
+    (distributed as { engineConfig: unknown }).engineConfig = engineConfig;
+    expect(
+      renderRequestFromDistributedConfig({
+        projectDir: value.projectDir,
+        outputPath: value.outputPath,
+        config: distributed,
+      }).options.engineConfig.coresPerWorker,
+    ).toBe(0.5);
+  });
+
+  it("preserves the distributed InvalidConfigError contract for engine snapshots", () => {
+    const value = request();
+    const distributed = distributedConfigFromRequest(value);
+    (distributed as { engineConfig: unknown }).engineConfig = {};
+
+    try {
+      renderRequestFromDistributedConfig({
+        projectDir: value.projectDir,
+        outputPath: value.outputPath,
+        config: distributed,
+      });
+      throw new Error("expected distributed validation to fail");
+    } catch (error) {
+      expect(error).toBeInstanceOf(InvalidConfigError);
+      expect((error as InvalidConfigError).field).toBe("config.engineConfig");
+    }
+  });
+
   it("validates the reverse distributed adapter at the wire boundary", () => {
     const distributed = distributedConfigFromRequest(request());
     distributed.width = 1921;
diff --git a/packages/producer/src/services/distributed/renderConfigValidation.ts b/packages/producer/src/services/distributed/renderConfigValidation.ts
index 812e725d1..261fc11d1 100644
--- a/packages/producer/src/services/distributed/renderConfigValidation.ts
+++ b/packages/producer/src/services/distributed/renderConfigValidation.ts
@@ -208,7 +208,14 @@ export function validateDistributedRenderConfig(
     validateVariablesPayload(config.variables);
   }
   if (config.engineConfig !== undefined) {
-    validateEngineConfigSnapshot(config.engineConfig);
+    try {
+      validateEngineConfigSnapshot(config.engineConfig);
+    } catch (error) {
+      throw new InvalidConfigError(
+        "config.engineConfig",
+        error instanceof Error ? error.message : "must be a valid engine config snapshot",
+      );
+    }
   }
 
   return config;