TanStack
diff --git a/‎.changeset/tighten-typescript-safety.md‎
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diff --git a/‎eslint.config.js‎
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diff --git a/‎examples/ts-code-mode-web/package.json‎
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diff --git a/‎examples/ts-code-mode-web/src/lib/reports/create-handler-bindings.ts‎
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diff --git a/‎examples/ts-code-mode-web/src/routes/_home/api.product-codemode.ts‎
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diff --git a/‎examples/ts-group-chat/chat-server/capnweb-rpc.ts‎
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diff --git a/‎examples/ts-group-chat/chat-server/claude-service.ts‎
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diff --git a/‎examples/ts-group-chat/package.json‎
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diff --git a/‎examples/ts-group-chat/src/routes/index.tsx‎
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diff --git a/‎examples/ts-react-chat/package.json‎
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@@ -0,0 +1,46 @@
+---
+'@tanstack/ai': patch
+'@tanstack/ai-anthropic': patch
+'@tanstack/ai-code-mode': patch
+'@tanstack/ai-code-mode-skills': patch
+'@tanstack/ai-devtools-core': patch
+'@tanstack/ai-elevenlabs': patch
+'@tanstack/ai-fal': patch
+'@tanstack/ai-gemini': patch
+'@tanstack/ai-grok': patch
+'@tanstack/ai-groq': patch
+'@tanstack/ai-isolate-node': patch
+'@tanstack/ai-isolate-quickjs': patch
+'@tanstack/ai-ollama': patch
+'@tanstack/ai-openai': patch
+'@tanstack/ai-openrouter': patch
+'@tanstack/ai-react-ui': patch
+'@tanstack/ai-solid-ui': patch
+'@tanstack/ai-vue-ui': patch
+'@tanstack/openai-base': patch
+'@tanstack/preact-ai-devtools': patch
+'@tanstack/react-ai-devtools': patch
+'@tanstack/solid-ai-devtools': patch
+---
+
+Tighten TypeScript safety: enable `noImplicitOverride`,
+`noFallthroughCasesInSwitch`, and `useDefineForClassFields` in the
+root `tsconfig.json`; add a typed-ESLint block scoped to
+`packages/typescript/*/src/**` that turns on `no-floating-promises`,
+`no-misused-promises`, `await-thenable`,
+`switch-exhaustiveness-check`, `consistent-type-exports`,
+`prefer-readonly`, and `no-non-null-assertion` (errors), plus
+`no-explicit-any` (warning). `@ts-ignore` and `@ts-nocheck` are
+disallowed in library source via `@typescript-eslint/ban-ts-comment`,
+and `as unknown as <T>` double-casts are blocked by a
+`no-restricted-syntax` rule (escape hatches available with an inline
+reason). Two flags from the original five-flag set —
+`noPropertyAccessFromIndexSignature` and `exactOptionalPropertyTypes`
+— were tried and rolled back: they produced ~500 lines of bracket-
+access and conditional-spread churn without catching any real bugs,
+and `exactOptionalPropertyTypes` would have forced consumers using
+it themselves to deal with our internals' style preferences.
+
+User-visible API surface is unchanged; this is a hardening pass to
+keep streaming/agent-loop correctness and discriminated-union
+exhaustiveness honest going forward. See issue #564.
@@ -19,6 +19,74 @@ const config = [
       'pnpm/json-enforce-catalog': 'off',
     },
   },
+  {
+    // Typed-linting rules scoped to library source — issue #564.
+    //
+    // Restricted to `packages/typescript/*/src/**` so streaming + agent-loop
+    // bugs that violate `no-floating-promises`, exhaustive-switch checks, or
+    // async-misuse guarantees fail in CI without dragging tests, examples,
+    // or build artefacts under the typed-linting cost.
+    name: 'tanstack/ai/typed',
+    files: ['packages/typescript/*/src/**/*.{ts,tsx}'],
+    rules: {
+      '@typescript-eslint/no-floating-promises': 'error',
+      '@typescript-eslint/no-misused-promises': 'error',
+      '@typescript-eslint/await-thenable': 'error',
+      '@typescript-eslint/switch-exhaustiveness-check': 'error',
+      '@typescript-eslint/consistent-type-exports': 'error',
+      '@typescript-eslint/prefer-readonly': 'error',
+      '@typescript-eslint/no-non-null-assertion': 'error',
+      // `no-explicit-any` stays as a warning — much of the existing `any`
+      // is structurally load-bearing (`Tool<any, any>` / `Adapter<any>`
+      // variance wildcards, `Record<string, any>` provider option
+      // carriers), but new `any` introductions should still get a second
+      // look. Tracked as warnings to surface in editors without blocking CI.
+      '@typescript-eslint/no-explicit-any': 'warn',
+      // Override the base config which currently allows `@ts-ignore` with a
+      // description and forbids `@ts-expect-error`. Invert that: require
+      // descriptions on `@ts-expect-error` (which self-heals when the
+      // underlying error disappears) and disallow `@ts-ignore` outright.
+      '@typescript-eslint/ban-ts-comment': [
+        'error',
+        {
+          'ts-expect-error': 'allow-with-description',
+          'ts-ignore': false,
+          'ts-nocheck': true,
+          'ts-check': false,
+        },
+      ],
+    },
+  },
+  {
+    // `no-restricted-syntax` banning `as unknown as <Type>` double-casts.
+    //
+    // Why separate from the typed-linting block: a few packages still ship a
+    // local `eslint.config.js` that re-exports root. Flat-config evaluates
+    // `files` globs relative to the *config-file's* directory, so the typed
+    // block's `packages/typescript/*/src/**` glob fails to match anything
+    // when re-exported from inside `packages/typescript/<pkg>/`. The dual
+    // glob below works in both contexts.
+    //
+    // Why ban `as unknown as T`: it bypasses TS's structural-overlap check
+    // (the safety net that errors when two types don't sufficiently
+    // overlap), like `@ts-ignore` for type assertions. Plain `as T` keeps
+    // the check. Genuine boundaries (vendor SDK shape drift, DOM lib
+    // limitations, conditional-return narrowing failures) can opt out via
+    // `// eslint-disable-next-line no-restricted-syntax -- <reason>`.
+    name: 'tanstack/ai/no-double-as',
+    files: ['packages/typescript/*/src/**/*.{ts,tsx}', 'src/**/*.{ts,tsx}'],
+    rules: {
+      'no-restricted-syntax': [
+        'error',
+        {
+          selector:
+            "TSAsExpression > TSAsExpression[typeAnnotation.type='TSUnknownKeyword']",
+          message:
+            "Avoid `as unknown as <Type>` — it bypasses TS's structural overlap check. Prefer plain `as <Type>`, fix the root cause, or opt out with `// eslint-disable-next-line no-restricted-syntax -- <reason>`.",
+        },
+      ],
+    },
+  },
 ]
 
 export default config
@@ -6,7 +6,8 @@
     "dev": "vite dev --port 3001",
     "build": "vite build",
     "serve": "vite preview",
-    "test": "exit 0"
+    "test": "exit 0",
+    "test:types": "tsc --noEmit"
   },
   "dependencies": {
     "@radix-ui/react-collapsible": "^1.1.2",
 
@@ -74,8 +74,8 @@ function createBinding(
 
 export function createHandlerBindings(
   context?: HandlerBindingContext,
-  reportId?: string,
-  canvasId: string = 'diagram',
+  _reportId?: string,
+  _canvasId: string = 'diagram',
 ): Record<string, ToolBinding> {
   // Helper to track binding calls
   const track = (name: string) => context?.onBindingCall?.(name)
 
@@ -188,7 +188,7 @@ function instrumentAdapter(adapter: AnyTextAdapter): {
 }
 
 function wrapWithTimingEvents(
-  stream: AsyncGenerator<StreamChunk>,
+  stream: AsyncIterable<StreamChunk>,
   adapter: AnyTextAdapter,
 ): AsyncGenerator<StreamChunk> {
   const requestStartTimeMs = Date.now()
 
@@ -63,7 +63,6 @@ export const clients = new Map<string, (...args: Array<any>) => void>()
 // Chat Server Implementation (one per connection)
 export class ChatServer extends RpcTarget {
   public currentUsername: string | null = null
-  private webSocket: WebSocket | null = null
 
   constructor() {
     super()
@@ -74,8 +73,6 @@ export class ChatServer extends RpcTarget {
 
   // Set the WebSocket connection for this server instance
   setWebSocket(ws: WebSocket) {
-    this.webSocket = ws
-
     // Handle WebSocket disconnection
     ws.on('close', () => {
       if (this.currentUsername) {
 
@@ -40,7 +40,9 @@ const getWeatherTool = toolDefinition({
     'Get the current weather for a location. Returns temperature, conditions, and humidity.',
   inputSchema: getWeatherInputSchema,
   outputSchema: getWeatherOutputSchema,
-}).server((args) => {
+}).server((rawArgs) => {
+  // JSONSchema doesn't carry compile-time types, so `rawArgs` is `unknown`.
+  const args = rawArgs as { location: string; unit?: string }
   // Mock weather data - in a real app this would call a weather API
   const mockWeatherData: Record<
     string,
@@ -53,8 +55,8 @@ const getWeatherTool = toolDefinition({
     sydney: { temp: 78, conditions: 'Clear skies', humidity: 45 },
   }
 
-  const location = (args.location as string).toLowerCase()
-  const unit = (args.unit as string | undefined) ?? 'celsius'
+  const location = args.location.toLowerCase()
+  const unit = args.unit ?? 'celsius'
   const weather = mockWeatherData[location] ?? {
     temp: 65,
     conditions: 'Unknown',
@@ -157,7 +159,7 @@ export class ClaudeService {
       })) {
         chunkCount++
 
-        if (chunk.type === 'content' && chunk.delta) {
+        if (chunk.type === 'TEXT_MESSAGE_CONTENT' && chunk.delta) {
           accumulatedContent += chunk.delta
           console.log(
             `🤖 Claude: Chunk #${chunkCount} [content] delta: "${chunk.delta}" (total: ${accumulatedContent.length} chars)`,
 
@@ -5,7 +5,8 @@
   "scripts": {
     "dev": "vite dev --port 4000",
     "build": "exit 0",
-    "test": "exit 0"
+    "test": "exit 0",
+    "test:types": "tsc --noEmit"
   },
   "dependencies": {
     "@tailwindcss/vite": "^4.1.18",
 
@@ -1,4 +1,4 @@
-import { createFileRoute, Link } from '@tanstack/react-router'
+import { createFileRoute } from '@tanstack/react-router'
 import { useState, useEffect } from 'react'
 
 import { useChatConnection } from '@/hooks/useChatConnection'
 
@@ -6,7 +6,8 @@
     "dev": "vite dev --port 3000",
     "build": "vite build",
     "serve": "vite preview",
-    "test": "exit 0"
+    "test": "exit 0",
+    "test:types": "tsc --noEmit"
   },
   "dependencies": {
     "@tailwindcss/vite": "^4.1.18",
Original file line number	Diff line number	Diff line change
`@@ -188,7 +188,7 @@ function instrumentAdapter(adapter: AnyTextAdapter): {`
`188`	`188`	`}`
`189`	`189`
`190`	`190`	`function wrapWithTimingEvents(`
`191`		`- stream: AsyncGenerator<StreamChunk>,`
	`191`	`+ stream: AsyncIterable<StreamChunk>,`
`192`	`192`	`adapter: AnyTextAdapter,`
`193`	`193`	`): AsyncGenerator<StreamChunk> {`
`194`	`194`	`const requestStartTimeMs = Date.now()`
Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,4 @@`
`1`		`-import { createFileRoute, Link } from '@tanstack/react-router'`
	`1`	`+import { createFileRoute } from '@tanstack/react-router'`
`2`	`2`	`import { useState, useEffect } from 'react'`
`3`	`3`
`4`	`4`	`import { useChatConnection } from '@/hooks/useChatConnection'`