diff --git a/packages/cli/src/commands/render.ts b/packages/cli/src/commands/render.ts
index 1916c0975..0c093d12e 100644
--- a/packages/cli/src/commands/render.ts
+++ b/packages/cli/src/commands/render.ts
@@ -49,6 +49,7 @@ import { bytesToMb } from "../telemetry/system.js";
 import { VERSION } from "../version.js";
 import { isDevMode } from "../utils/env.js";
 import { buildDockerRunArgs } from "../utils/dockerRunArgs.js";
+import { normalizeErrorMessage } from "../utils/errorMessage.js";
 import type { RenderJob } from "@hyperframes/producer";
 import {
   normalizeResolutionFlag,
@@ -863,7 +864,7 @@ function handleRenderError(
   docker: boolean,
   hint: string,
 ): never {
-  const message = error instanceof Error ? error.message : String(error);
+  const message = normalizeErrorMessage(error);
   trackRenderError({
     fps: fpsToNumber(options.fps),
     quality: options.quality,
diff --git a/packages/cli/src/utils/errorMessage.ts b/packages/cli/src/utils/errorMessage.ts
new file mode 100644
index 000000000..f2928f140
--- /dev/null
+++ b/packages/cli/src/utils/errorMessage.ts
@@ -0,0 +1,18 @@
+export function normalizeErrorMessage(error: unknown): string {
+  if (error instanceof Error) return error.message;
+  if (typeof error === "string") return error;
+  if (typeof error === "object" && error !== null) {
+    const msg = (error as Record<string, unknown>).message;
+    if (typeof msg === "string") return msg;
+    try {
+      return JSON.stringify(error);
+    } catch {
+      try {
+        return `{${Object.keys(error as object).join(", ")}}`;
+      } catch {
+        /* truly opaque object */
+      }
+    }
+  }
+  return String(error ?? "unknown error");
+}
diff --git a/packages/producer/src/index.ts b/packages/producer/src/index.ts
index 3d3de5117..44e2af832 100644
--- a/packages/producer/src/index.ts
+++ b/packages/producer/src/index.ts
@@ -68,6 +68,7 @@ export {
 } from "./server.js";
 
 // ── Utilities ───────────────────────────────────────────────────────────────
+export { normalizeErrorMessage } from "./utils/errorMessage.js";
 export { quantizeTimeToFrame } from "./utils/parityContract.js";
 export { resolveRenderPaths, type RenderPaths } from "./utils/paths.js";
 
diff --git a/packages/producer/src/services/render/captureCost.ts b/packages/producer/src/services/render/captureCost.ts
index 2ca552074..c4f3b2cb9 100644
--- a/packages/producer/src/services/render/captureCost.ts
+++ b/packages/producer/src/services/render/captureCost.ts
@@ -26,6 +26,7 @@ import type { CompiledComposition } from "../htmlCompiler.js";
 import type { FileServerHandle } from "../fileServer.js";
 import { defaultLogger, type ProducerLogger } from "../../logger.js";
 import type { RenderJob } from "../renderOrchestrator.js";
+import { normalizeErrorMessage } from "../../utils/errorMessage.js";
 
 export interface CaptureCostEstimate {
   multiplier: number;
@@ -417,7 +418,7 @@ export async function runCaptureCalibration(input: {
  * protocol errors that recover cleanly under screenshot mode.
  */
 export function shouldFallbackToScreenshotAfterCalibrationError(error: unknown): boolean {
-  const message = error instanceof Error ? error.message : String(error);
+  const message = normalizeErrorMessage(error);
   return /HeadlessExperimental\.beginFrame timed out|beginFrame probe timeout|Another frame is pending|Frame still pending|Protocol error.*HeadlessExperimental\.beginFrame|Runtime\.callFunctionOn timed out|Runtime\.evaluate timed out/i.test(
     message,
   );
diff --git a/packages/producer/src/services/render/cleanup.ts b/packages/producer/src/services/render/cleanup.ts
index 48b0c3ab8..d926840a0 100644
--- a/packages/producer/src/services/render/cleanup.ts
+++ b/packages/producer/src/services/render/cleanup.ts
@@ -9,6 +9,7 @@ import { type CaptureSession, closeCaptureSession } from "@hyperframes/engine";
 import type { FileServerHandle } from "../fileServer.js";
 import { defaultLogger, type ProducerLogger } from "../../logger.js";
 import type { HdrDiagnostics, RenderJob } from "../renderOrchestrator.js";
+import { normalizeErrorMessage } from "../../utils/errorMessage.js";
 
 /**
  * Wrap a cleanup operation so it never throws, but logs any failure.
@@ -80,7 +81,7 @@ export function buildRenderErrorDetails(input: {
   perfStages: Record<string, number>;
   hdrDiagnostics: HdrDiagnostics;
 }): NonNullable<RenderJob["errorDetails"]> {
-  const errorMessage = input.error instanceof Error ? input.error.message : String(input.error);
+  const errorMessage = normalizeErrorMessage(input.error);
   const errorStack = input.error instanceof Error ? input.error.stack : undefined;
   return {
     message: errorMessage,
diff --git a/packages/producer/src/services/renderOrchestrator.ts b/packages/producer/src/services/renderOrchestrator.ts
index 836a1a573..95700671e 100644
--- a/packages/producer/src/services/renderOrchestrator.ts
+++ b/packages/producer/src/services/renderOrchestrator.ts
@@ -93,6 +93,7 @@ import {
   updateJobStatus,
 } from "./render/shared.js";
 import { buildRenderErrorDetails, cleanupRenderResources, safeCleanup } from "./render/cleanup.js";
+import { normalizeErrorMessage } from "../utils/errorMessage.js";
 import { resolveEffectiveHdrMode } from "./render/hdrMode.js";
 import { buildRenderPerfSummary } from "./render/perfSummary.js";
 import {
@@ -566,7 +567,7 @@ export function getNextRetryWorkerCount(currentWorkers: number): number {
 }
 
 export function isRecoverableParallelCaptureError(error: unknown): boolean {
-  const message = error instanceof Error ? error.message : String(error);
+  const message = normalizeErrorMessage(error);
   return (
     message.includes("[Parallel] Capture failed") &&
     /Runtime\.callFunctionOn timed out|HeadlessExperimental\.beginFrame timed out|Waiting failed|timeout exceeded|timed out|Navigation timeout|Protocol error|Target closed/i.test(
@@ -2096,7 +2097,7 @@ export async function executeRenderJob(
         ? error
         : new RenderCancelledError("render_cancelled");
     }
-    const errorMessage = error instanceof Error ? error.message : String(error);
+    const errorMessage = normalizeErrorMessage(error);
 
     // Suggest single-worker retry on parallel capture timeout.
     // Video-heavy compositions often cause multi-worker timeouts because
diff --git a/packages/producer/src/utils/errorMessage.test.ts b/packages/producer/src/utils/errorMessage.test.ts
new file mode 100644
index 000000000..c645d7d67
--- /dev/null
+++ b/packages/producer/src/utils/errorMessage.test.ts
@@ -0,0 +1,43 @@
+import { describe, it, expect } from "vitest";
+import { normalizeErrorMessage } from "./errorMessage.js";
+
+describe("normalizeErrorMessage", () => {
+  it("extracts message from Error instances", () => {
+    expect(normalizeErrorMessage(new Error("boom"))).toBe("boom");
+  });
+
+  it("passes through strings", () => {
+    expect(normalizeErrorMessage("oops")).toBe("oops");
+  });
+
+  it("extracts .message from plain objects", () => {
+    expect(normalizeErrorMessage({ message: "hidden error" })).toBe("hidden error");
+  });
+
+  it("JSON-stringifies objects without .message", () => {
+    expect(normalizeErrorMessage({ code: 42 })).toBe('{"code":42}');
+  });
+
+  it("handles null", () => {
+    expect(normalizeErrorMessage(null)).toBe("unknown error");
+  });
+
+  it("handles undefined", () => {
+    expect(normalizeErrorMessage(undefined)).toBe("unknown error");
+  });
+
+  it("handles numbers", () => {
+    expect(normalizeErrorMessage(42)).toBe("42");
+  });
+
+  it("handles objects with non-string .message", () => {
+    expect(normalizeErrorMessage({ message: 123 })).toBe('{"message":123}');
+  });
+
+  it("handles circular references gracefully", () => {
+    const obj: Record<string, unknown> = {};
+    obj.self = obj;
+    // Falls through JSON.stringify failure to Object.keys()
+    expect(normalizeErrorMessage(obj)).toBe("{self}");
+  });
+});
diff --git a/packages/producer/src/utils/errorMessage.ts b/packages/producer/src/utils/errorMessage.ts
new file mode 100644
index 000000000..edc88225d
--- /dev/null
+++ b/packages/producer/src/utils/errorMessage.ts
@@ -0,0 +1,31 @@
+/**
+ * Normalize an unknown thrown value into a human-readable string.
+ *
+ * The default `String(error)` pattern produces `[object Object]` when the
+ * thrown value is a plain object — masking the real error in telemetry.
+ * This utility tries, in order:
+ *   1. `Error.message`
+ *   2. Raw string pass-through
+ *   3. `.message` property on a plain object
+ *   4. `JSON.stringify` for any other object
+ *   5. `String()` fallback for primitives (number, boolean, symbol, bigint)
+ *   6. `"unknown error"` for null / undefined
+ */
+export function normalizeErrorMessage(error: unknown): string {
+  if (error instanceof Error) return error.message;
+  if (typeof error === "string") return error;
+  if (typeof error === "object" && error !== null) {
+    const msg = (error as Record<string, unknown>).message;
+    if (typeof msg === "string") return msg;
+    try {
+      return JSON.stringify(error);
+    } catch {
+      try {
+        return `{${Object.keys(error as object).join(", ")}}`;
+      } catch {
+        /* truly opaque object */
+      }
+    }
+  }
+  return String(error ?? "unknown error");
+}