diff --git a/scripts/mirror-vgi-bench-media.test.ts b/scripts/mirror-vgi-bench-media.test.ts
index e9dc7038..0d278f5e 100644
--- a/scripts/mirror-vgi-bench-media.test.ts
+++ b/scripts/mirror-vgi-bench-media.test.ts
@@ -1,9 +1,11 @@
 import { describe, expect, test } from "bun:test";
 
 import { VGI_BENCH_DEFAULT_REVISION } from "../src/benchmarks/vgi-bench/benchmark";
+import { assertFailure, assertSuccess } from "../src/internal/testing";
 import type { ManifestEntry } from "./mirror-vgi-bench-media";
 import {
   candidateSources,
+  describeReadOptionsError,
   extensionOf,
   hashManifest,
   readOptions,
@@ -42,7 +44,9 @@ describe("extensionOf", () => {
 
 describe("readOptions", () => {
   test("applies defaults", () => {
-    const options = readOptions([]);
+    const result = readOptions([]);
+    assertSuccess(result);
+    const options = result.success;
     expect(options.concurrency).toBe(8);
     expect(options.revision).toBe(VGI_BENCH_DEFAULT_REVISION);
     expect(options.limit).toBeUndefined();
@@ -51,7 +55,7 @@ describe("readOptions", () => {
   });
 
   test("parses provided flags", () => {
-    const options = readOptions([
+    const result = readOptions([
       "--concurrency=3",
       "--limit=5",
       "--out=manifest.json",
@@ -59,7 +63,8 @@ describe("readOptions", () => {
       "--force",
       "--dry-run",
     ]);
-    expect(options).toEqual({
+    assertSuccess(result);
+    expect(result.success).toEqual({
       concurrency: 3,
       limit: 5,
       out: "manifest.json",
@@ -69,9 +74,41 @@ describe("readOptions", () => {
     });
   });
 
-  test("rejects invalid numeric flags", () => {
-    expect(() => readOptions(["--concurrency=0"])).toThrow();
-    expect(() => readOptions(["--limit=abc"])).toThrow();
+  test("fails with concurrency_not_positive_integer for --concurrency=0", () => {
+    const result = readOptions(["--concurrency=0"]);
+    assertFailure(result);
+    expect(result.failure).toEqual({
+      kind: "concurrency_not_positive_integer",
+    });
+  });
+
+  test("fails with limit_not_positive_integer for --limit=abc", () => {
+    const result = readOptions(["--limit=abc"]);
+    assertFailure(result);
+    expect(result.failure).toEqual({ kind: "limit_not_positive_integer" });
+  });
+
+  test("reports the first failing flag when both are invalid", () => {
+    const result = readOptions(["--concurrency=1.5", "--limit=0"]);
+    assertFailure(result);
+    expect(result.failure).toEqual({
+      kind: "concurrency_not_positive_integer",
+    });
+  });
+});
+
+describe("describeReadOptionsError", () => {
+  test.each([
+    [
+      { kind: "concurrency_not_positive_integer" },
+      "--concurrency must be a positive integer",
+    ],
+    [
+      { kind: "limit_not_positive_integer" },
+      "--limit must be a positive integer",
+    ],
+  ] as const)("renders %p as the CLI message", (error, message) => {
+    expect(describeReadOptionsError(error)).toBe(message);
   });
 });
 
diff --git a/scripts/mirror-vgi-bench-media.ts b/scripts/mirror-vgi-bench-media.ts
index 31a7d4ec..db23b20a 100644
--- a/scripts/mirror-vgi-bench-media.ts
+++ b/scripts/mirror-vgi-bench-media.ts
@@ -1,4 +1,5 @@
 import { S3Client } from "bun";
+import * as Result from "effect/Result";
 
 import {
   VGI_BENCH_CONFIG,
@@ -88,7 +89,13 @@ type MirrorOutcome =
   | { readonly kind: "mirrored"; readonly entry: ManifestEntry }
   | { readonly kind: "unresolved"; readonly reason: string };
 
-export function readOptions(argv: readonly string[]): MirrorOptions {
+export type ReadOptionsError =
+  | { readonly kind: "concurrency_not_positive_integer" }
+  | { readonly kind: "limit_not_positive_integer" };
+
+export function readOptions(
+  argv: readonly string[]
+): Result.Result<MirrorOptions, ReadOptionsError> {
   const flag = (name: string): string | undefined => {
     const prefixed = `--${name}=`;
     const match = argv.find((arg) => arg.startsWith(prefixed));
@@ -96,21 +103,35 @@ export function readOptions(argv: readonly string[]): MirrorOptions {
   };
   const concurrency = Number(flag("concurrency") ?? "8");
   if (!Number.isInteger(concurrency) || concurrency < 1) {
-    throw new Error("--concurrency must be a positive integer");
+    return Result.fail({ kind: "concurrency_not_positive_integer" });
   }
   const rawLimit = flag("limit");
   const limit = rawLimit === undefined ? undefined : Number(rawLimit);
   if (limit !== undefined && (!Number.isInteger(limit) || limit < 1)) {
-    throw new Error("--limit must be a positive integer");
+    return Result.fail({ kind: "limit_not_positive_integer" });
   }
-  return {
+  return Result.succeed({
     concurrency,
     out: flag("out") ?? "vgi-bench-media-manifest.json",
     force: argv.includes("--force"),
     dryRun: argv.includes("--dry-run"),
     revision: flag("revision") ?? VGI_BENCH_DEFAULT_REVISION,
     limit,
-  };
+  });
+}
+
+export function describeReadOptionsError(error: ReadOptionsError): string {
+  switch (error.kind) {
+    case "concurrency_not_positive_integer": {
+      return "--concurrency must be a positive integer";
+    }
+    case "limit_not_positive_integer": {
+      return "--limit must be a positive integer";
+    }
+    default: {
+      return error satisfies never;
+    }
+  }
 }
 
 export type { ManifestEntry };
@@ -238,7 +259,12 @@ export function hashManifest(entries: readonly ManifestEntry[]): string {
 
 async function main(): Promise<void> {
   const env = readMediaMirrorEnv();
-  const options = readOptions(process.argv.slice(2));
+  const parsed = readOptions(process.argv.slice(2));
+  if (Result.isFailure(parsed)) {
+    process.stderr.write(`${describeReadOptionsError(parsed.failure)}\n`);
+    process.exit(1);
+  }
+  const options = parsed.success;
   const s3 = new S3Client(env);
   const allVideos = await fetchSourceVideos(
     options.revision,