diff --git a/packages/cli/src/auth/browser.ts b/packages/cli/src/auth/browser.ts
index fab036307..12bc79985 100644
--- a/packages/cli/src/auth/browser.ts
+++ b/packages/cli/src/auth/browser.ts
@@ -5,6 +5,7 @@
  */
 
 import { c } from "../ui/colors.js";
+import { normalizeErrorMessage } from "../utils/errorMessage.js";
 
 export interface OpenBrowserResult {
   /** True when we successfully invoked the platform "open" command. */
@@ -21,7 +22,7 @@ export async function openBrowser(url: string): Promise<OpenBrowserResult> {
     await open(url);
     return { opened: true };
   } catch (err) {
-    printManualInstructions(url, err instanceof Error ? err.message : String(err));
+    printManualInstructions(url, normalizeErrorMessage(err));
     return { opened: false };
   }
 }
diff --git a/packages/cli/src/browser/manager.ts b/packages/cli/src/browser/manager.ts
index 279bce673..d2615b53b 100644
--- a/packages/cli/src/browser/manager.ts
+++ b/packages/cli/src/browser/manager.ts
@@ -4,6 +4,7 @@ import { existsSync, readdirSync, rmSync } from "node:fs";
 import { basename } from "node:path";
 import { homedir } from "node:os";
 import { join } from "node:path";
+import { normalizeErrorMessage } from "../utils/errorMessage.js";
 
 type PuppeteerBrowsers = typeof import("@puppeteer/browsers");
 
@@ -11,7 +12,7 @@ async function loadPuppeteerBrowsers(): Promise<PuppeteerBrowsers> {
   try {
     return await import("@puppeteer/browsers");
   } catch (err) {
-    const cause = err instanceof Error ? err.message : String(err);
+    const cause = normalizeErrorMessage(err);
     throw new Error(
       `Failed to load @puppeteer/browsers: ${cause}\n` +
         `Fix: run \`npm install\` or \`bun install\` to restore missing packages, then retry.`,
@@ -268,7 +269,7 @@ export async function findBrowser(): Promise<BrowserResult | undefined> {
     try {
       return await downloadBrowser();
     } catch (err) {
-      const cause = err instanceof Error ? err.message : String(err);
+      const cause = normalizeErrorMessage(err);
       throw new Error(
         `Cached Chrome binary was missing at ${fromCache.staleHyperframesCachePath}, and re-download failed: ${cause}\n` +
           `Run \`hyperframes browser ensure --force\` to re-download.`,
diff --git a/packages/cli/src/capture/index.ts b/packages/cli/src/capture/index.ts
index c2124b8ab..a1c083d4e 100644
--- a/packages/cli/src/capture/index.ts
+++ b/packages/cli/src/capture/index.ts
@@ -18,6 +18,7 @@ import { extractTokens } from "./tokenExtractor.js";
 import { extractDesignStyles } from "./designStyleExtractor.js";
 import { downloadAssets, downloadAndRewriteFonts } from "./assetDownloader.js";
 import { extractFontMetadata } from "./fontMetadataExtractor.js";
+import { normalizeErrorMessage } from "../utils/errorMessage.js";
 // briefGenerator.ts, visual-style, capture-summary removed — DESIGN.md replaces them
 import {
   setupAnimationCapture,
@@ -353,7 +354,8 @@ export async function captureWebsite(
         `${designStyles.typography.length} typography roles, ${designStyles.buttons.length} button styles, ${designStyles.shadows.length} shadow values extracted`,
       );
     } catch (err) {
-      const errMsg = err instanceof Error ? `${err.message}\n${err.stack}` : String(err);
+      const errMsg =
+        err instanceof Error ? `${err.message}\n${err.stack}` : normalizeErrorMessage(err);
       console.error(`  ⚠ Design style extraction failed: ${errMsg}`);
       warnings.push(`Design style extraction failed: ${errMsg}`);
     }
@@ -480,10 +482,7 @@ export async function captureWebsite(
         }
       }
     } catch (err) {
-      console.warn(
-        "Font metadata extraction failed (non-fatal):",
-        err instanceof Error ? err.message : err,
-      );
+      console.warn("Font metadata extraction failed (non-fatal):", normalizeErrorMessage(err));
     }
 
     // Save animation catalog — lean version for the agent (not 745 raw CSS declarations)
diff --git a/packages/cli/src/cloud/detectAspectRatio.ts b/packages/cli/src/cloud/detectAspectRatio.ts
index 1de9fe445..5e60fa0bf 100644
--- a/packages/cli/src/cloud/detectAspectRatio.ts
+++ b/packages/cli/src/cloud/detectAspectRatio.ts
@@ -22,6 +22,7 @@
  */
 
 import { readFileSync } from "node:fs";
+import { normalizeErrorMessage } from "../utils/errorMessage.js";
 
 export type SupportedAspectRatio = "16:9" | "9:16" | "1:1";
 
@@ -87,7 +88,7 @@ export function detectAspectRatioFromHtml(entryHtmlPath: string): AspectRatioDet
   try {
     html = readFileSync(entryHtmlPath, "utf-8");
   } catch (err) {
-    return { kind: "read-error", error: err instanceof Error ? err.message : String(err) };
+    return { kind: "read-error", error: normalizeErrorMessage(err) };
   }
   return detectAspectRatioFromHtmlString(html);
 }
diff --git a/packages/cli/src/commands/batchRender.ts b/packages/cli/src/commands/batchRender.ts
index c62c11f9d..d1e9d1846 100644
--- a/packages/cli/src/commands/batchRender.ts
+++ b/packages/cli/src/commands/batchRender.ts
@@ -2,6 +2,7 @@ import { mkdirSync, readFileSync, writeFileSync } from "node:fs";
 import { dirname, join, resolve, sep } from "node:path";
 import { c } from "../ui/colors.js";
 import { errorBox } from "../ui/format.js";
+import { normalizeErrorMessage as errorMessage } from "../utils/errorMessage.js";
 import {
   loadProjectVariableSchema,
   reportVariableIssues,
@@ -90,10 +91,7 @@ function parseJson(raw: string, source: string): unknown {
   try {
     return JSON.parse(raw);
   } catch (error: unknown) {
-    throw new BatchRenderInputError(
-      "Invalid JSON in --batch",
-      `${source}: ${error instanceof Error ? error.message : String(error)}`,
-    );
+    throw new BatchRenderInputError("Invalid JSON in --batch", `${source}: ${errorMessage(error)}`);
   }
 }
 
@@ -239,7 +237,7 @@ export function prepareBatchRender(options: PrepareBatchRenderOptions): Prepared
   } catch (error: unknown) {
     throw new BatchRenderInputError(
       "Could not read --batch",
-      `${batchPath}: ${error instanceof Error ? error.message : String(error)}`,
+      `${batchPath}: ${errorMessage(error)}`,
     );
   }
 
@@ -310,10 +308,6 @@ function emitJsonEvent(event: Record<string, unknown>, json: boolean): void {
   if (json) console.log(JSON.stringify(event));
 }
 
-function errorMessage(error: unknown): string {
-  return error instanceof Error ? error.message : String(error);
-}
-
 async function renderBatchRow(
   row: PreparedBatchRow,
   manifest: BatchManifest,
diff --git a/packages/cli/src/commands/capture.ts b/packages/cli/src/commands/capture.ts
index b10d76f94..8a3c92627 100644
--- a/packages/cli/src/commands/capture.ts
+++ b/packages/cli/src/commands/capture.ts
@@ -1,6 +1,7 @@
 import { defineCommand } from "citty";
 import { resolve } from "node:path";
 import type { Example } from "./_examples.js";
+import { normalizeErrorMessage } from "../utils/errorMessage.js";
 
 export const examples: Example[] = [
   ["Capture a website into ./capture/", "hyperframes capture https://stripe.com"],
@@ -213,7 +214,7 @@ export default defineCommand({
         console.log();
       }
     } catch (err) {
-      const errMsg = err instanceof Error ? err.message : String(err);
+      const errMsg = normalizeErrorMessage(err);
       // Write BLOCKED.md so the user/agent knows the capture failed
       try {
         const { mkdirSync, writeFileSync } = await import("node:fs");
diff --git a/packages/cli/src/commands/cloud/render.ts b/packages/cli/src/commands/cloud/render.ts
index 85c52cd0b..c483eef9e 100644
--- a/packages/cli/src/commands/cloud/render.ts
+++ b/packages/cli/src/commands/cloud/render.ts
@@ -33,6 +33,7 @@ import {
 import { c } from "../../ui/colors.js";
 import { errorBox, formatBytes, formatDuration } from "../../ui/format.js";
 import { resolveProject } from "../../utils/project.js";
+import { normalizeErrorMessage } from "../../utils/errorMessage.js";
 import { createPublishArchive } from "../../utils/publishProject.js";
 import {
   reportVariableIssues,
@@ -541,7 +542,7 @@ async function maybeUploadProject(
   try {
     archive = createPublishArchive(project.dir);
   } catch (err) {
-    const msg = err instanceof Error ? err.message : String(err);
+    const msg = normalizeErrorMessage(err);
     errorBox("Zip failed", msg, "Check the project for missing files or unreadable permissions.");
     process.exit(1);
   }
@@ -733,7 +734,7 @@ async function streamVideo(
     }
     return { bytes: result.bytes };
   } catch (err) {
-    const message = err instanceof Error ? err.message : String(err);
+    const message = normalizeErrorMessage(err);
     errorBox(
       "Download failed",
       message,
diff --git a/packages/cli/src/commands/cloudrun.ts b/packages/cli/src/commands/cloudrun.ts
index 5953733f3..326806225 100644
--- a/packages/cli/src/commands/cloudrun.ts
+++ b/packages/cli/src/commands/cloudrun.ts
@@ -30,6 +30,7 @@ import {
   resolveVariablesArg,
   validateVariablesAgainstProject,
 } from "../utils/variables.js";
+import { normalizeErrorMessage } from "../utils/errorMessage.js";
 
 export const examples: Example[] = [
   ["Deploy the Cloud Run render stack", "hyperframes cloudrun deploy --project my-gcp-project"],
@@ -670,7 +671,7 @@ async function runRenderBatch(args: Record<string, unknown>): Promise<void> {
         } catch (err) {
           return {
             outputKey: entry.outputKey,
-            error: err instanceof Error ? err.message : String(err),
+            error: normalizeErrorMessage(err),
           };
         }
       }),
diff --git a/packages/cli/src/commands/lambda/policies.ts b/packages/cli/src/commands/lambda/policies.ts
index e22c44d4d..d2bbddb79 100644
--- a/packages/cli/src/commands/lambda/policies.ts
+++ b/packages/cli/src/commands/lambda/policies.ts
@@ -22,6 +22,7 @@
 
 import { readFileSync } from "node:fs";
 import { c } from "../../ui/colors.js";
+import { normalizeErrorMessage } from "../../utils/errorMessage.js";
 
 export type PoliciesVerb = "role" | "user" | "validate";
 
@@ -247,7 +248,7 @@ export async function runPolicies(args: PoliciesArgs): Promise<void> {
       try {
         result = validatePolicy(args.inputPath);
       } catch (err) {
-        const msg = err instanceof Error ? err.message : String(err);
+        const msg = normalizeErrorMessage(err);
         if (args.json) {
           console.log(JSON.stringify({ ok: false, error: msg }, null, 2));
           process.exitCode = 1;
diff --git a/packages/cli/src/commands/lambda/render-batch.ts b/packages/cli/src/commands/lambda/render-batch.ts
index 96c8322fe..2c5ad177c 100644
--- a/packages/cli/src/commands/lambda/render-batch.ts
+++ b/packages/cli/src/commands/lambda/render-batch.ts
@@ -36,6 +36,7 @@ import {
   reportVariableIssues,
   validateVariablesAgainstSchema,
 } from "../../utils/variables.js";
+import { normalizeErrorMessage } from "../../utils/errorMessage.js";
 import { warnOnDimensionMismatch } from "./_dimensions.js";
 import { requireStack } from "./state.js";
 
@@ -294,7 +295,7 @@ export async function runRenderBatch(args: RenderBatchArgs): Promise<void> {
         outputKey: entry.outputKey,
         executionArn: null,
         status: "failed-to-start",
-        error: err instanceof Error ? err.message : String(err),
+        error: normalizeErrorMessage(err),
       };
     }
   };
@@ -371,10 +372,7 @@ export function parseBatchFile(path: string): Array<{ entry: BatchEntry; lineNum
     try {
       parsed = JSON.parse(line);
     } catch (err) {
-      errorBox(
-        `Invalid JSON in batch file on line ${i + 1}`,
-        err instanceof Error ? err.message : String(err),
-      );
+      errorBox(`Invalid JSON in batch file on line ${i + 1}`, normalizeErrorMessage(err));
       process.exit(1);
     }
     if (parsed === null || typeof parsed !== "object" || Array.isArray(parsed)) {
diff --git a/packages/cli/src/commands/layout.ts b/packages/cli/src/commands/layout.ts
index 18d1fe811..34a70eb5f 100644
--- a/packages/cli/src/commands/layout.ts
+++ b/packages/cli/src/commands/layout.ts
@@ -5,6 +5,7 @@ import { fileURLToPath } from "node:url";
 import type { Example } from "./_examples.js";
 import { c } from "../ui/colors.js";
 import { resolveProject } from "../utils/project.js";
+import { normalizeErrorMessage } from "../utils/errorMessage.js";
 import { serveStaticProjectHtml } from "../utils/staticProjectServer.js";
 import { withMeta } from "../utils/updateCheck.js";
 import {
@@ -634,7 +635,7 @@ export function createInspectCommand(commandName: "inspect" | "layout") {
 
         process.exit(ok ? 0 : 1);
       } catch (err) {
-        const message = err instanceof Error ? err.message : String(err);
+        const message = normalizeErrorMessage(err);
         if (args.json) {
           console.log(
             JSON.stringify(
diff --git a/packages/cli/src/commands/preview.ts b/packages/cli/src/commands/preview.ts
index ce19734be..598d6e92e 100644
--- a/packages/cli/src/commands/preview.ts
+++ b/packages/cli/src/commands/preview.ts
@@ -26,6 +26,7 @@ import { createRequire } from "node:module";
 import * as clack from "@clack/prompts";
 import { c } from "../ui/colors.js";
 import { isDevMode } from "../utils/env.js";
+import { normalizeErrorMessage as errorMessage } from "../utils/errorMessage.js";
 import { buildNpxCommand } from "../utils/npxCommand.js";
 import type { StudioSelectionSnapshot } from "@hyperframes/studio-server";
 import {
@@ -307,10 +308,6 @@ function printSelectionFailure(code: string, message: string, json: boolean): vo
   process.exitCode = 1;
 }
 
-function errorMessage(error: unknown): string {
-  return error instanceof Error ? error.message : String(error);
-}
-
 function previewServerPayload(server: {
   port: number;
   host?: string;
@@ -471,11 +468,7 @@ async function printCurrentContext(
   try {
     fields = parseContextFields(options.fields);
   } catch (err) {
-    printSelectionFailure(
-      "invalid-context-fields",
-      err instanceof Error ? err.message : String(err),
-      options.json,
-    );
+    printSelectionFailure("invalid-context-fields", errorMessage(err), options.json);
     return;
   }
   const fullDetail = options.detail === "full";
diff --git a/packages/cli/src/commands/render.ts b/packages/cli/src/commands/render.ts
index 2c2ed2724..238d6fd3d 100644
--- a/packages/cli/src/commands/render.ts
+++ b/packages/cli/src/commands/render.ts
@@ -753,7 +753,7 @@ export default defineCommand({
         browserSpinner?.stop(c.error("Browser not available"));
         errorBox(
           "Chrome not found",
-          err instanceof Error ? err.message : String(err),
+          normalizeErrorMessage(err),
           "Run: npx hyperframes browser ensure",
         );
         process.exit(1);
@@ -1076,7 +1076,7 @@ function ensureDockerImage(version: string, platform: string, quiet: boolean): s
       { stdio: quiet ? "pipe" : "inherit", timeout: 600_000 },
     );
   } catch (error: unknown) {
-    const message = error instanceof Error ? error.message : String(error);
+    const message = normalizeErrorMessage(error);
     throw new Error(`Failed to build Docker image: ${message}`);
   } finally {
     rmSync(tmpDir, { recursive: true, force: true });
@@ -1149,7 +1149,7 @@ async function renderDocker(
   try {
     imageTag = ensureDockerImage(dockerVersion, platform, options.quiet);
   } catch (error: unknown) {
-    const message = error instanceof Error ? error.message : String(error);
+    const message = normalizeErrorMessage(error);
     const isDockerMissing = /connect|not found|ENOENT/i.test(message);
     errorBox(
       isDockerMissing ? "Docker not available" : "Docker image build failed",
diff --git a/packages/cli/src/commands/snapshot.ts b/packages/cli/src/commands/snapshot.ts
index 3b9606bdb..93e813924 100644
--- a/packages/cli/src/commands/snapshot.ts
+++ b/packages/cli/src/commands/snapshot.ts
@@ -5,6 +5,7 @@ import { existsSync, mkdtempSync, readFileSync, mkdirSync, rmSync, writeFileSync
 import { tmpdir } from "node:os";
 import { resolve, join, relative, isAbsolute, basename } from "node:path";
 import { resolveProject } from "../utils/project.js";
+import { normalizeErrorMessage } from "../utils/errorMessage.js";
 import { resolveCompositionViewportFromHtml } from "../utils/compositionViewport.js";
 import { serveStaticProjectHtml } from "../utils/staticProjectServer.js";
 import { c } from "../ui/colors.js";
@@ -594,8 +595,7 @@ export default defineCommand({
                 descriptions.push(`## ${result.value.filename}`, `${result.value.desc}`, ``);
               } else {
                 // Log first failure so Gemini issues are visible rather than silent
-                const errMsg =
-                  result.reason instanceof Error ? result.reason.message : String(result.reason);
+                const errMsg = normalizeErrorMessage(result.reason);
                 descriptions.push(`## (error)`, `Gemini call failed: ${errMsg.slice(0, 120)}`, ``);
               }
             }
@@ -605,12 +605,12 @@ export default defineCommand({
             console.log(`   ${c.dim("descriptions.md")} (Gemini frame analysis)`);
           }
         } catch (descErr) {
-          const msg = descErr instanceof Error ? descErr.message : String(descErr);
+          const msg = normalizeErrorMessage(descErr);
           console.log(`   ${c.dim(`--describe failed: ${msg.slice(0, 80)}`)}`);
         }
       }
     } catch (err) {
-      const msg = err instanceof Error ? err.message : String(err);
+      const msg = normalizeErrorMessage(err);
       console.error(`\n${c.error("✗")} Snapshot failed: ${msg}`);
       process.exit(1);
     }
diff --git a/packages/cli/src/commands/validate.ts b/packages/cli/src/commands/validate.ts
index 1aca7ada8..c08ba6e71 100644
--- a/packages/cli/src/commands/validate.ts
+++ b/packages/cli/src/commands/validate.ts
@@ -3,6 +3,7 @@ import { existsSync, readFileSync } from "node:fs";
 import { join, dirname } from "node:path";
 import { fileURLToPath } from "node:url";
 import { resolveProject } from "../utils/project.js";
+import { normalizeErrorMessage } from "../utils/errorMessage.js";
 import { resolveCompositionViewportFromHtml } from "../utils/compositionViewport.js";
 import { c } from "../ui/colors.js";
 import { withMeta } from "../utils/updateCheck.js";
@@ -226,7 +227,7 @@ async function validateInBrowser(
     });
 
     page.on("pageerror", (err) => {
-      const text = err instanceof Error ? err.message : String(err);
+      const text = normalizeErrorMessage(err);
       // CDN scripts (e.g. GSAP from jsdelivr) returning HTML error pages
       // instead of JS produce "Unexpected token '<'" SyntaxErrors. These
       // are network failures, not composition authoring errors.
@@ -394,7 +395,7 @@ Examples:
       const exitCode = printValidationResult(result, asJson);
       process.exit(exitCode);
     } catch (err: unknown) {
-      const message = err instanceof Error ? err.message : String(err);
+      const message = normalizeErrorMessage(err);
       emitFailureReport(message, asJson);
       process.exit(1);
     }
diff --git a/packages/cli/src/utils/errorMessage.test.ts b/packages/cli/src/utils/errorMessage.test.ts
index 19fb7fcc8..e8476d479 100644
--- a/packages/cli/src/utils/errorMessage.test.ts
+++ b/packages/cli/src/utils/errorMessage.test.ts
@@ -46,6 +46,26 @@ describe("normalizeErrorMessage", () => {
     expect(normalizeErrorMessage(hostile)).toBe("[object Object]");
   });
 
+  it("never yields '[object Object]' for a no-message object (the reported validate/inspect bug)", () => {
+    const out = normalizeErrorMessage({ code: 42 });
+    expect(out).not.toBe("[object Object]");
+    expect(out).toContain("42");
+  });
+
+  it("surfaces a Puppeteer-style protocol error object via its message", () => {
+    expect(normalizeErrorMessage({ name: "ProtocolError", message: "Target closed" })).toBe(
+      "Target closed",
+    );
+  });
+
+  it("surfaces a structured CDP error object (no message) instead of '[object Object]'", () => {
+    // The shape snapshot/render can receive when a CDP/protocol rejection is a
+    // plain object rather than an Error: no string `message`, only code + data.
+    const out = normalizeErrorMessage({ code: -32000, data: { reason: "navigation timeout" } });
+    expect(out).not.toBe("[object Object]");
+    expect(out).toContain("navigation timeout");
+  });
+
   it("returns 'unknown error' for null and undefined", () => {
     expect(normalizeErrorMessage(null)).toBe("unknown error");
     expect(normalizeErrorMessage(undefined)).toBe("unknown error");