Migrate ESLint 8→10: flat config, upgrade eslint-plugin-vue to v10

- Upgrade eslint-plugin-vue from ^9.33.0 to ^10.8.0 (required for ESLint 10 compat)
- Add @eslint/js and globals as devDependencies
- Replace .eslintrc.cjs with eslint.config.js (flat config format)
- Update lint script to drop legacy --ext flag
- Remove stale eslint-disable-next-line in demo-seed.mjs (no-constant-condition no longer flagged)

Resolves ERESOLVE peer conflict: eslint-plugin-vue@9 requires eslint<10

Author: Chris0Jeky

frontend/taskdeck-web/.eslintrc.cjs

@@ -0,0 +1,98 @@
+import pluginVue from 'eslint-plugin-vue'
+import tsParser from '@typescript-eslint/parser'
+import tsPlugin from '@typescript-eslint/eslint-plugin'
+import eslint from '@eslint/js'
+import vueParser from 'vue-eslint-parser'
+import globals from 'globals'
+
+export default [
+  // Base recommended config
+  eslint.configs.recommended,
+
+  // TypeScript and Vue source files
+  {
+    files: ['**/*.ts', '**/*.vue'],
+    plugins: { '@typescript-eslint': tsPlugin },
+    languageOptions: {
+      parser: vueParser,
+      parserOptions: {
+        parser: tsParser,
+        sourceType: 'module',
+        ecmaVersion: 'latest',
+        extraFileExtensions: ['.vue'],
+      },
+      globals: {
+        ...globals.browser,
+        ...globals.node,
+        ...globals.es2022,
+      },
+    },
+    rules: {
+      ...tsPlugin.configs.recommended.rules,
+      // TypeScript handles undefined checking, no-undef causes false positives with TS namespaces
+      'no-undef': 'off',
+      'no-console': 'off',
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        { argsIgnorePattern: '^_', varsIgnorePattern: '^_' },
+      ],
+    },
+  },
+
+  // JavaScript / MJS scripts
+  {
+    files: ['**/*.mjs', '**/*.js'],
+    languageOptions: {
+      globals: {
+        ...globals.browser,
+        ...globals.node,
+        ...globals.es2022,
+      },
+    },
+    rules: {
+      'no-control-regex': 'off',
+    },
+  },
+
+  // Vue-specific rules
+  ...pluginVue.configs['flat/essential'],
+  {
+    files: ['**/*.vue'],
+    rules: {
+      'vue/multi-word-component-names': 'off',
+      'vue/attributes-order': 'off',
+      'vue/html-quotes': 'off',
+      'vue/html-self-closing': 'off',
+      'vue/max-attributes-per-line': 'off',
+      'vue/singleline-html-element-content-newline': 'off',
+    },
+  },
+
+  // Test files (vitest)
+  {
+    files: ['**/*.spec.ts', '**/*.test.ts', 'src/tests/**/*.ts', 'tests/**/*.ts'],
+    languageOptions: {
+      globals: {
+        ...globals.browser,
+        ...globals.node,
+        ...globals.es2022,
+        ...globals.vitest,
+      },
+    },
+    rules: {
+      '@typescript-eslint/no-unused-expressions': 'off',
+    },
+  },
+
+  // Ignores
+  {
+    ignores: [
+      'dist/**',
+      'coverage/**',
+      'test-results/**',
+      'playwright-report/**',
+      'node_modules/**',
+    ],
+  },
+]

frontend/taskdeck-web/eslint.config.js

@@ -15,7 +15,7 @@
     "demo:snapshot": "node ./scripts/demo-snapshot.mjs --out ./demo-artifacts/snapshot.json",
     "demo:director": "node ./scripts/demo-director.mjs",
     "demo:director:smoke": "node ./scripts/demo-director.mjs --output-dir ./demo-artifacts/ci-smoke --e2e-db ./taskdeck.demo.ci.db --reset-e2e-db --scenario engineering-sprint --skip-llm --turns 0 --rng-seed ci-smoke",
-    "lint": "eslint . --ext .ts,.vue --max-warnings=0",
+    "lint": "eslint . --max-warnings=0",
     "typecheck": "vue-tsc -b",
     "build": "npm run typecheck && vite build",
     "preview": "vite preview",
@@ -40,6 +40,7 @@
     "ws": "file:vendor/ws-7.5.10.tgz"
   },
   "devDependencies": {
+    "@eslint/js": "^9.0.0",
     "@playwright/test": "^1.56.1",
     "@types/dompurify": "^3.0.5",
     "@types/node": "^24.10.0",
@@ -53,7 +54,8 @@
     "autoprefixer": "^10.4.22",
     "baseline-browser-mapping": "^2.9.19",
     "eslint": "^10.1.0",
-    "eslint-plugin-vue": "^9.33.0",
+    "eslint-plugin-vue": "^10.8.0",
+    "globals": "^17.4.0",
     "happy-dom": "^20.8.9",
     "postcss": "^8.5.6",
     "tailwindcss": "^3.4.18",

frontend/taskdeck-web/package-lock.json

@@ -508,7 +508,6 @@ async function ensureUser({ username, email, password }) {
 
 async function waitFor(fn, { timeoutMs = 45000, intervalMs = 750, label = 'condition' } = {}) {
   const start = Date.now()
-  // eslint-disable-next-line no-constant-condition
   while (true) {
     const val = await fn()
     if (val) return val