chore: align ESLint rules with the monorepo's portable ruleset

Port the portable, non-custom, non-React rules from factory-mono-alpha's
shared @factory/eslint-config into our ESLint 9 flat config, so the public
SDK enforces the same standards as the internal source of truth.

Added rules: no-empty-object-type (error), no-require-imports, no-barrel-files,
import/no-default-export, import/named, import/no-extraneous-dependencies,
import/extensions, eslint-comments/no-unused-disable, no-void, default-case,
no-constant-condition, no-param-reassign, no-promise-executor-return,
prefer-promise-reject-errors, prefer-arrow-callback, no-restricted-syntax
(incl. ExportAllDeclaration ban), and vitest/expect-expect + valid-expect
for tests.

Excluded the monorepo's factory/* custom-plugin rules (not installable from
npm) and React/Next rules (no React here). Refactored to comply: deleted the
unused src/protocol/index.ts export* barrel and converted src/index.ts to
explicit named re-exports. Public-API barrels are exempted from no-barrel-files
(matching the monorepo's index.ts exemption). Fixed all resulting violations.

New devDeps: eslint-plugin-no-barrel-files, eslint-plugin-eslint-comments,
@vitest/eslint-plugin.

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

Author: varin-nair-factory

eslint.config.js

@@ -1,5 +1,8 @@
 import eslint from '@eslint/js';
+import vitest from '@vitest/eslint-plugin';
+import eslintComments from 'eslint-plugin-eslint-comments';
 import importPlugin from 'eslint-plugin-import';
+import noBarrelFiles from 'eslint-plugin-no-barrel-files';
 import unusedImports from 'eslint-plugin-unused-imports';
 import tseslint from 'typescript-eslint';
 
@@ -11,6 +14,8 @@ export default tseslint.config(
     plugins: {
       'unused-imports': unusedImports,
       import: importPlugin,
+      'no-barrel-files': noBarrelFiles,
+      'eslint-comments': eslintComments,
     },
     languageOptions: {
       parserOptions: {
@@ -36,7 +41,43 @@ export default tseslint.config(
       ],
       '@typescript-eslint/no-floating-promises': 'error',
       '@typescript-eslint/explicit-function-return-type': 'off',
-      '@typescript-eslint/no-empty-object-type': 'off',
+      '@typescript-eslint/no-empty-object-type': 'error',
+      '@typescript-eslint/no-require-imports': 'error',
+      'no-barrel-files/no-barrel-files': 'error',
+      'import/no-default-export': 'error',
+      'import/named': 'error',
+      'import/no-extraneous-dependencies': ['error', { devDependencies: true }],
+      'eslint-comments/no-unused-disable': 'error',
+      'no-void': ['error', { allowAsStatement: true }],
+      'default-case': 'error',
+      'no-constant-condition': ['error', { checkLoops: false }],
+      'no-param-reassign': ['error', { props: false }],
+      'no-promise-executor-return': 'error',
+      'prefer-promise-reject-errors': 'error',
+      'prefer-arrow-callback': ['error', { allowNamedFunctions: true }],
+      'no-restricted-syntax': [
+        'error',
+        {
+          selector: 'ForInStatement',
+          message:
+            'for..in loops iterate over the entire prototype chain, which is virtually never what you want. Use Object.{keys,values,entries}, and iterate over the resulting array.',
+        },
+        {
+          selector: 'LabeledStatement',
+          message:
+            'Labels are a form of GOTO; using them makes code confusing and hard to maintain and understand.',
+        },
+        {
+          selector: 'WithStatement',
+          message:
+            '`with` is disallowed in strict mode because it makes code impossible to predict and optimize.',
+        },
+        {
+          selector: 'ExportAllDeclaration',
+          message:
+            "Export all doesn't work well if imported in ESM due to how they are transpiled, and they can also lead to unexpected exposure of internal methods.",
+        },
+      ],
       'unused-imports/no-unused-imports': 'error',
       'import/order': [
         'error',
@@ -61,15 +102,24 @@ export default tseslint.config(
         },
       ],
       'import/no-cycle': 'error',
+      'import/extensions': ['error', 'ignorePackages', { js: 'always', ts: 'never' }],
       'no-console': 'error',
     },
   },
   {
     files: ['tests/**/*.ts'],
+    plugins: {
+      vitest,
+    },
     rules: {
       '@typescript-eslint/no-explicit-any': 'off',
       '@typescript-eslint/consistent-type-assertions': 'off',
       'no-console': 'off',
+      'vitest/expect-expect': [
+        'error',
+        { assertFunctionNames: ['expect', 'expect*', 'assert*'] },
+      ],
+      'vitest/valid-expect': ['error', { maxArgs: 2 }],
     },
   },
   {
@@ -79,6 +129,40 @@ export default tseslint.config(
       'no-console': 'off',
     },
   },
+  {
+    // Dedicated public-API barrels: their sole purpose is re-exporting the
+    // package surface, so the no-barrel-files rule does not apply. The
+    // protocol barrels mirror the upstream source-of-truth layout and rely on
+    // `export *`, so the ExportAllDeclaration ban is lifted for them too.
+    files: [
+      'src/index.ts',
+      'src/schemas/index.ts',
+      'src/daemon/index.ts',
+      'src/protocol/index.ts',
+      'src/protocol/daemon/index.ts',
+    ],
+    rules: {
+      'no-barrel-files/no-barrel-files': 'off',
+      'no-restricted-syntax': [
+        'error',
+        {
+          selector: 'ForInStatement',
+          message:
+            'for..in loops iterate over the entire prototype chain, which is virtually never what you want. Use Object.{keys,values,entries}, and iterate over the resulting array.',
+        },
+        {
+          selector: 'LabeledStatement',
+          message:
+            'Labels are a form of GOTO; using them makes code confusing and hard to maintain and understand.',
+        },
+        {
+          selector: 'WithStatement',
+          message:
+            '`with` is disallowed in strict mode because it makes code impossible to predict and optimize.',
+        },
+      ],
+    },
+  },
   {
     ignores: ['dist/', 'node_modules/', '*.config.*'],
   }

examples/hook-execution.ts

@@ -55,6 +55,9 @@ async function main(): Promise<void> {
         case DroidMessageType.Result:
           console.log('\n\n--- Turn complete ---');
           break;
+
+        default:
+          break;
       }
     }
   } finally {

examples/session-stream.ts

@@ -44,6 +44,9 @@ async function main(): Promise<void> {
             );
           }
           break;
+
+        default:
+          break;
       }
     }
   } finally {