fix: format CliError/ArgumentError instead of leaking a raw stack trace in web fetch

src/fetch/command.test.ts

@@ -1,5 +1,6 @@
 import { describe, expect, it, vi } from 'vitest';
 import { formatWebFetchMarkdown, runClientOwnedWebFetch } from './command.js';
+import { CliError } from '../errors.js';
 
 describe('web fetch command', () => {
   it('renders fetch metadata before content', () => {
@@ -10,4 +11,25 @@ describe('web fetch command', () => {
     await runClientOwnedWebFetch(['web', 'fetch', '--url', 'https://a'], { webFetch, stdout: { write: vi.fn() } as never });
     expect(webFetch).toHaveBeenCalledOnce();
   });
+  it('formats a thrown CliError instead of letting it escape as a raw stack trace', async () => {
+    const webFetch = vi.fn().mockRejectedValue(new CliError('FETCH_BLOCKED', 'The site blocked non-browser fetches.', 'Use webcmd web fetch-browser for this URL.', 1));
+    const write = vi.fn();
+    const priorExitCode = process.exitCode;
+    await runClientOwnedWebFetch(['web', 'fetch', '--url', 'https://a'], { webFetch, stderr: { write } as never });
+    const output = write.mock.calls.map((call) => String(call[0])).join('');
+    expect(output).toContain('FETCH_BLOCKED');
+    expect(output).toContain('Use webcmd web fetch-browser for this URL.');
+    expect(process.exitCode).toBe(1);
+    process.exitCode = priorExitCode;
+  });
+  it('formats an ArgumentError from bad flags instead of letting it escape as a raw stack trace', async () => {
+    const write = vi.fn();
+    const priorExitCode = process.exitCode;
+    await runClientOwnedWebFetch(['web', 'fetch', '--url', 'not-a-url'], { stderr: { write } as never });
+    const output = write.mock.calls.map((call) => String(call[0])).join('');
+    expect(output).toContain('ARGUMENT');
+    expect(output).toContain('--url must be an http or https URL');
+    expect(process.exitCode).toBe(2);
+    process.exitCode = priorExitCode;
+  });
 });

src/fetch/command.ts

@@ -1,5 +1,5 @@
 import { cli, Strategy } from '../registry.js';
-import { ArgumentError } from '../errors.js';
+import { ArgumentError, CliError, EXIT_CODES, toEnvelope } from '../errors.js';
 import { webFetch, type WebFetchOptions, type WebFetchResult } from './client.js';
 
 export const webFetchCommand = cli({
@@ -31,7 +31,13 @@ function clientOptions(argv: readonly string[]): WebFetchOptions {
   return { url: values.url, timeoutSeconds: int('timeout', 30), maxChars: int('max-chars', 50000), allowPrivate: values['allow-private'] === true || values['allow-private'] === 'true' };
 }
 
-export async function runClientOwnedWebFetch(argv: readonly string[], dependencies: { webFetch?: typeof webFetch; stdout?: NodeJS.WritableStream } = {}): Promise<void> {
-  const result = await (dependencies.webFetch ?? webFetch)(clientOptions(argv));
-  (dependencies.stdout ?? process.stdout).write(`${formatWebFetchMarkdown(result)}\n`);
+export async function runClientOwnedWebFetch(argv: readonly string[], dependencies: { webFetch?: typeof webFetch; stdout?: NodeJS.WritableStream; stderr?: NodeJS.WritableStream } = {}): Promise<void> {
+  try {
+    const result = await (dependencies.webFetch ?? webFetch)(clientOptions(argv));
+    (dependencies.stdout ?? process.stdout).write(`${formatWebFetchMarkdown(result)}\n`);
+  } catch (err) {
+    const { formatErrorEnvelope } = await import('../output.js');
+    (dependencies.stderr ?? process.stderr).write(formatErrorEnvelope(toEnvelope(err), { cmdName: 'web/fetch' }));
+    process.exitCode = err instanceof CliError ? err.exitCode : EXIT_CODES.GENERIC_ERROR;
+  }
 }