Update AGENTS.md. Start fixing old weird errors

tools/eslint/base.ts

@@ -2,10 +2,15 @@ import * as path from 'node:path';
 import { includeIgnoreFile } from '@eslint/compat';
 import eslint from '@eslint/js';
 import importPlugin from 'eslint-plugin-import';
+// eslint-plugin-prefer-arrow-functions doesn't ship flat config types — cast needed
+import preferArrowFunctions from 'eslint-plugin-prefer-arrow-functions';
 import turboPlugin from 'eslint-plugin-turbo';
 import { defineConfig } from 'eslint/config';
 import tseslint from 'typescript-eslint';
 
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+const preferArrowPlugin = preferArrowFunctions as any;
+
 /**
  * All packages that leverage t3-env should use this rule
  */
@@ -45,6 +50,7 @@ export const baseConfig = defineConfig(
     plugins: {
       import: importPlugin,
       turbo: turboPlugin,
+      'prefer-arrow-functions': preferArrowPlugin,
     },
     extends: [
       eslint.configs.recommended,
@@ -58,10 +64,6 @@ export const baseConfig = defineConfig(
         'warn',
         { argsIgnorePattern: '^_', varsIgnorePattern: '^_' },
       ],
-      '@typescript-eslint/consistent-type-imports': [
-        'warn',
-        { prefer: 'type-imports', fixStyle: 'inline-type-imports' },
-      ],
       '@typescript-eslint/no-misused-promises': [
         2,
         { checksVoidReturn: { attributes: false } },
@@ -73,7 +75,17 @@ export const baseConfig = defineConfig(
         },
       ],
       '@typescript-eslint/no-non-null-assertion': 'error',
-      'import/consistent-type-specifier-style': ['error', 'prefer-top-level'],
+      '@typescript-eslint/consistent-type-definitions': 'off',
+      'prefer-arrow-functions/prefer-arrow-functions': [
+        'warn',
+        {
+          allowNamedFunctions: false,
+          classPropertiesAllowed: false,
+          disallowPrototype: false,
+          returnStyle: 'unchanged',
+          singleReturnOnly: false,
+        },
+      ],
     },
   },
   {