build(ts): TypeScript foundation — tsconfig + typecheck in CI (T1)

Adopting TypeScript incrementally (the move off plain JS). Upgraded jsconfig ->
tsconfig with strict + noUncheckedIndexedAccess, but allowJs + checkJs:false so
every existing .js/.jsx keeps resolving and running untouched — only .ts/.tsx
get type-checked. Added 'npm run typecheck' (tsc --noEmit) and wired it into
'npm run ci'. Installed typescript 6 + @types/react/react-dom 19. Client-scoped
(Vite resolves the '@/' paths); the CommonJS server is a separate TS story.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

jsconfig.json

@@ -1,15 +0,0 @@
-{
-  "compilerOptions": {
-    "baseUrl": ".",
-    "ignoreDeprecations": "6.0",
-    "paths": {
-      "@/*": ["./client/*"]
-    },
-    "jsx": "react-jsx",
-    "module": "ESNext",
-    "moduleResolution": "bundler",
-    "resolveJsonModule": true
-  },
-  "include": ["client/**/*"],
-  "exclude": ["node_modules", "dist"]
-}

package-lock.json

@@ -54,6 +54,8 @@
         "@eslint/js": "^9.39.4",
         "@playwright/test": "^1.50.1",
         "@testing-library/react": "^16.3.2",
+        "@types/react": "^19.2.17",
+        "@types/react-dom": "^19.2.3",
         "@vitejs/plugin-react": "^4.3.3",
         "autoprefixer": "^10.4.20",
         "babel-plugin-react-compiler": "^1.0.0",
@@ -65,6 +67,7 @@
         "jsdom": "^29.1.1",
         "postcss": "^8.4.47",
         "tailwindcss": "^3.4.14",
+        "typescript": "^6.0.3",
         "vite": "^5.4.10",
         "vite-plugin-pwa": "^1.3.0",
         "vitest": "^4.1.8"
@@ -6026,6 +6029,26 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@types/react": {
+      "version": "19.2.17",
+      "resolved": "https://registry.npmjs.org/@types/react/-/react-19.2.17.tgz",
+      "integrity": "sha512-MXfmqaVPEVgkBT/aY0aGCkRWWtByiYQXo3xdQ8r5RzuFrPiRn8Gar2tQdXSUQ2GKV3bkXckek89V8wQBY2Q/Aw==",
+      "devOptional": true,
+      "license": "MIT",
+      "dependencies": {
+        "csstype": "^3.2.2"
+      }
+    },
+    "node_modules/@types/react-dom": {
+      "version": "19.2.3",
+      "resolved": "https://registry.npmjs.org/@types/react-dom/-/react-dom-19.2.3.tgz",
+      "integrity": "sha512-jp2L/eY6fn+KgVVQAOqYItbF0VY/YApe5Mz2F0aykSO8gx31bYCZyvSeYxCHKvzHG5eZjc+zyaS5BrBWya2+kQ==",
+      "devOptional": true,
+      "license": "MIT",
+      "peerDependencies": {
+        "@types/react": "^19.2.0"
+      }
+    },
     "node_modules/@types/resolve": {
       "version": "1.20.2",
       "resolved": "https://registry.npmjs.org/@types/resolve/-/resolve-1.20.2.tgz",
@@ -7198,6 +7221,13 @@
         "node": ">=4"
       }
     },
+    "node_modules/csstype": {
+      "version": "3.2.3",
+      "resolved": "https://registry.npmjs.org/csstype/-/csstype-3.2.3.tgz",
+      "integrity": "sha512-z1HGKcYy2xA8AGQfwrn0PAy+PB7X/GSj3UVJW9qKyn43xWa+gl5nXmU4qqLMRzWVLFC8KusUX8T/0kCiOYpAIQ==",
+      "devOptional": true,
+      "license": "MIT"
+    },
     "node_modules/data-urls": {
       "version": "7.0.0",
       "resolved": "https://registry.npmjs.org/data-urls/-/data-urls-7.0.0.tgz",
@@ -12969,6 +12999,20 @@
         "url": "https://github.com/sponsors/ljharb"
       }
     },
+    "node_modules/typescript": {
+      "version": "6.0.3",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-6.0.3.tgz",
+      "integrity": "sha512-y2TvuxSZPDyQakkFRPZHKFm+KKVqIisdg9/CZwm9ftvKXLP8NRWj38/ODjNbr43SsoXqNuAisEf1GdCxqWcdBw==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "bin": {
+        "tsc": "bin/tsc",
+        "tsserver": "bin/tsserver"
+      },
+      "engines": {
+        "node": ">=14.17"
+      }
+    },
     "node_modules/unbox-primitive": {
       "version": "1.1.0",
       "resolved": "https://registry.npmjs.org/unbox-primitive/-/unbox-primitive-1.1.0.tgz",

package.json

@@ -10,6 +10,7 @@
     "build": "vite build",
     "check:server": "find server.js db middleware routes services utils -name '*.js' -print0 | xargs -0 -n1 node --check",
     "lint": "eslint client",
+    "typecheck": "tsc --noEmit -p tsconfig.json",
     "check": "npm run check:server && npm run build",
     "test": "node --test tests/*.test.js",
     "test:client": "vitest run",
@@ -19,7 +20,7 @@
     "test:e2e:update": "node e2e/setup/prepare-db.js && playwright test --project=chromium-desktop --project=chromium-mobile --update-snapshots",
     "test:e2e:probe": "node e2e/setup/prepare-db.js && playwright test --project=probe",
     "smoke:prod": "bash scripts/prod-smoke.sh",
-    "ci": "npm run lint && npm run check:server && npm run test:all && npm run build",
+    "ci": "npm run lint && npm run typecheck && npm run check:server && npm run test:all && npm run build",
     "start": "node server.js"
   },
   "dependencies": {
@@ -68,6 +69,8 @@
     "@eslint/js": "^9.39.4",
     "@playwright/test": "^1.50.1",
     "@testing-library/react": "^16.3.2",
+    "@types/react": "^19.2.17",
+    "@types/react-dom": "^19.2.3",
     "@vitejs/plugin-react": "^4.3.3",
     "autoprefixer": "^10.4.20",
     "babel-plugin-react-compiler": "^1.0.0",
@@ -79,6 +82,7 @@
     "jsdom": "^29.1.1",
     "postcss": "^8.4.47",
     "tailwindcss": "^3.4.14",
+    "typescript": "^6.0.3",
     "vite": "^5.4.10",
     "vite-plugin-pwa": "^1.3.0",
     "vitest": "^4.1.8"

tsconfig.json

@@ -0,0 +1,27 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "lib": ["ES2023", "DOM", "DOM.Iterable"],
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "jsx": "react-jsx",
+    "paths": { "@/*": ["./client/*"] },
+    "resolveJsonModule": true,
+    "esModuleInterop": true,
+    "isolatedModules": true,
+    "skipLibCheck": true,
+    "noEmit": true,
+
+    // Gradual adoption: existing .js/.jsx still resolve and run untouched
+    // (checkJs off = not type-checked), while new/converted .ts/.tsx are checked
+    // under full strict mode. Convert file-by-file; nothing breaks in between.
+    "allowJs": true,
+    "checkJs": false,
+    "strict": true,
+    "noUncheckedIndexedAccess": true,
+
+    "types": ["vite/client"]
+  },
+  "include": ["client/**/*"],
+  "exclude": ["node_modules", "dist", "client/**/*.test.*"]
+}