fix(config): preserve raw values for config coercion (#2747)

Fixes #2746. Returning the inner yargs parser result applies option
coercers twice, so JSON-configured viewport and wsHeaders fail.
Returning the original JSON values after strict validation lets the
outer parser coerce them once and preserves CLI overrides. Tests: npm
run test -- tests/cli.test.ts and npm run check-format pass. The full
npm run test reaches five unrelated PWA failures because the test server
cannot bind 0.0.0.0:10236 with EACCES on this Windows host.

src/config/mcp-options.ts

@@ -456,7 +456,7 @@ export function parser(
           throw new Error('Config must be a JSON object');
         }
 
-        return yargs()
+        yargs()
           .parserConfiguration({
             'strip-aliased': true,
             'camel-case-expansion': false,
@@ -467,6 +467,7 @@ export function parser(
           .fail(false)
           .exitProcess(false)
           .parseSync([]);
+        return parsed;
       } catch (err) {
         throw new Error(`Invalid JSON config file: ${(err as Error).message}`);
       }

tests/cli.test.ts

@@ -487,6 +487,34 @@ describe('cli args parsing', () => {
     assert.strictEqual(args.categoryMemory, true);
   });
 
+  it('applies config coercion for viewport and wsHeaders', async () => {
+    using testConfig = createTempFile(
+      JSON.stringify({
+        wsEndpoint: 'ws://127.0.0.1:9222/devtools/browser/abc123',
+        wsHeaders: '{"Authorization":"Bearer token"}',
+        viewport: '1280x720',
+      }),
+      'cd4a.test.config.coercion.json',
+    );
+    const args = parseArguments(['--config', testConfig.path]);
+    assert.deepStrictEqual(args.viewport, {width: 1280, height: 720});
+    assert.deepStrictEqual(args.wsHeaders, {Authorization: 'Bearer token'});
+  });
+
+  it('lets cli options override coerced config values', async () => {
+    using testConfig = createTempFile(
+      JSON.stringify({viewport: '1280x720'}),
+      'cd4a.test.config.coercion-override.json',
+    );
+    const args = parseArguments([
+      '--config',
+      testConfig.path,
+      '--viewport',
+      '800x600',
+    ]);
+    assert.deepStrictEqual(args.viewport, {width: 800, height: 600});
+  });
+
   it('parses config should not allow no prefix', async () => {
     using testConfig = createTempFile(
       JSON.stringify({