docs: Add AGENTS.md files for OpenAI Codex compatibility

AGENTS.md

@@ -0,0 +1,5 @@
+# AGENTS.md
+
+**MANDATORY: Read `CLAUDE.md` before starting any task.**
+
+All project instructions are in `CLAUDE.md`.

CLAUDE.md

@@ -62,7 +62,8 @@ Each package README has the detailed API. Don't duplicate here.
 
 ## Learnings
 
-<!-- Add specific lessons learned during development. Format: what happened → what to do instead -->
+<!-- MANDATORY: Document failures here to prevent repeated mistakes -->
+<!-- Format: what went wrong → what to do instead -->
 
 <!-- Example:
 - Forgot to rebuild ui package before testing ui-react → Always `pnpm build` from root, not package

packages/core/AGENTS.md

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+# @mcp-apps-kit/core
+
+Server-side framework for MCP applications. Handles tool definitions, UI resources, adapters, middleware, and Express server setup.
+
+## Quick Commands
+
+```bash
+pnpm -C packages/core test        # Run tests
+pnpm -C packages/core typecheck   # Type check only
+pnpm -C packages/core lint        # Lint only
+```
+
+## Key Exports
+
+- `createApp` - Main entry point for creating an MCP app
+- `defineTool` - Type-safe tool definition helper
+- `defineUI` - UI resource definition helper
+- `createPlugin` - Plugin system for extending apps
+
+## Patterns
+
+Use `defineTool` and `defineUI` for type inference instead of inline objects.
+
+Middleware is Koa-style: always `await next()` or the chain breaks.
+
+Exports are centralized through `src/index.ts`, which re-exports from barrel files (`index.ts`) in subdirectories: `adapters/`, `debug/`, `events/`, `middleware/`, `plugins/`, `server/`, and `server/oauth/`. Subdirectory barrel files are local re-exports only - all public API goes through the root `src/index.ts`.
+
+## Dependencies
+
+- Express 5 (async error handling differs from v4)
+- Zod 4 (breaking changes from v3)
+- @modelcontextprotocol/sdk
+
+## Common Mistakes
+
+- Forgetting to `await next()` in middleware
+- Using Zod 3 APIs that changed in v4 (check migration guide)
+- Adding exports outside `index.ts`
+
+---
+
+## Learnings
+
+<!-- MANDATORY: Document failures here to prevent repeated mistakes -->
+<!-- Format: what went wrong → what to do instead -->
+
+<!-- Example:
+- Type error in handler because input wasn't validated → Always use Zod schema, never trust raw input
+- Middleware chain broke silently → Add logging middleware first to debug chain issues
+-->

packages/create-app/AGENTS.md

@@ -0,0 +1,52 @@
+# @mcp-apps-kit/create-app
+
+CLI tool for scaffolding MCP applications. Creates new projects with React or vanilla JS templates.
+
+## Quick Commands
+
+```bash
+pnpm -C packages/create-app test        # Run tests
+pnpm -C packages/create-app typecheck   # Type check only
+pnpm -C packages/create-app lint        # Lint only
+```
+
+## Key Exports
+
+- `scaffoldProject` - Programmatic project creation
+- CLI binary: `create-mcp-apps-kit`
+
+## Templates
+
+- `react` - React + Vite + @mcp-apps-kit/ui-react
+- `vanilla` - Vanilla JS + Vite + @mcp-apps-kit/ui
+
+Both include:
+
+- Server with example tool
+- UI with theming
+- Integration tests
+- Optional Vercel deployment config
+
+## Dependencies
+
+- commander (CLI framework)
+- @inquirer/prompts (interactive prompts)
+- figlet, chalk (CLI styling)
+
+## Common Mistakes
+
+- Running in non-empty directory (fails)
+- Fetches latest package versions from npm at runtime
+- Generated projects use npm (not pnpm) to avoid workspace conflicts
+
+---
+
+## Learnings
+
+<!-- MANDATORY: Document failures here to prevent repeated mistakes -->
+<!-- Format: what went wrong → what to do instead -->
+
+<!-- Example:
+- Template file had wrong path → Use path.join() not string concatenation for cross-platform
+- npm install failed in generated project → Check if package versions are valid on npm registry
+-->

packages/testing/AGENTS.md

@@ -0,0 +1,52 @@
+# @mcp-apps-kit/testing
+
+Comprehensive testing library for MCP applications. Supports unit, integration, behavior, property, and LLM evaluation testing.
+
+## Quick Commands
+
+```bash
+pnpm -C packages/testing test        # Run tests
+pnpm -C packages/testing typecheck   # Type check only
+pnpm -C packages/testing lint        # Lint only
+```
+
+## Key Exports
+
+- `createTestEnvironment` - Full test setup with server and client
+- `startTestServer` / `createTestClient` - Individual components
+- `expectToolResult` - Fluent assertions for tool results
+- `createMCPEval` / `describeEval` - LLM-based evaluation
+- Framework adapters: `@mcp-apps-kit/testing/vitest`, `@mcp-apps-kit/testing/jest`
+
+## Patterns
+
+```typescript
+const env = await createTestEnvironment({ app });
+const result = await env.client.callTool("greet", { name: "Alice" });
+expectToolResult(result).toMatchObject({ message: "Hello, Alice!" });
+await env.cleanup();
+```
+
+## Dependencies
+
+- @modelcontextprotocol/sdk
+- Zod 4
+- Optional: vitest, jest, fast-check, openai, @anthropic-ai/sdk
+
+## Common Mistakes
+
+- Forgetting `await env.cleanup()` (leaves server running)
+- Not setting up vitest/jest matchers in setup file
+- Missing optional peer deps for LLM eval features
+
+---
+
+## Learnings
+
+<!-- MANDATORY: Document failures here to prevent repeated mistakes -->
+<!-- Format: what went wrong → what to do instead -->
+
+<!-- Example:
+- Tests hung indefinitely → Server wasn't cleaned up from previous run, use port: 0 for random port
+- Matcher not found error → Import setupVitestMatchers in setup file before tests run
+-->

packages/testing/tests/unit/eval/generators.test.ts

@@ -262,7 +262,9 @@ describe.skipIf(!isFastCheckAvailable)("generated value validation", () => {
     const gen = generators.float(0, 1);
     const resolved = await resolveArbitrary(gen);
     const samples = fc.sample(resolved, 50);
-    expect(samples.every((n) => n >= 0 && n <= 1)).toBe(true);
+    // Use small epsilon for floating point comparison tolerance
+    const epsilon = 1e-10;
+    expect(samples.every((n) => n >= 0 - epsilon && n <= 1 + epsilon)).toBe(true);
   });
 
   it("should generate booleans", async () => {

packages/ui-react-builder/AGENTS.md

@@ -0,0 +1,54 @@
+# @mcp-apps-kit/ui-react-builder
+
+Build tool for React-based MCP application UIs. Bundles React components into self-contained HTML.
+
+## Quick Commands
+
+```bash
+pnpm -C packages/ui-react-builder test        # Run tests
+pnpm -C packages/ui-react-builder typecheck   # Type check only
+pnpm -C packages/ui-react-builder lint        # Lint only
+```
+
+## Key Exports
+
+- `defineReactUI` - Define UI with React component
+- `buildReactUIs` / `buildReactUI` - Build to HTML
+- `buildAndTransform` - Build and convert to core UIDefs in one step
+- Vite plugin available via `@mcp-apps-kit/ui-react-builder/vite`
+
+## Patterns
+
+```typescript
+const widgetUI = defineReactUI({
+  component: MyWidget,
+  name: "My Widget",
+  prefersBorder: true,
+});
+
+const uis = await buildAndTransform({ "my-widget": widgetUI });
+```
+
+## Dependencies
+
+- esbuild (bundling)
+- @typescript-eslint/typescript-estree (AST parsing)
+- Peer deps: @mcp-apps-kit/core, @mcp-apps-kit/ui-react, react, react-dom, vite (optional)
+
+## Common Mistakes
+
+- Forgetting to rebuild after component changes
+- Not including component dependencies in build
+- Missing vite peer dep when using vite plugin
+
+---
+
+## Learnings
+
+<!-- MANDATORY: Document failures here to prevent repeated mistakes -->
+<!-- Format: what went wrong → what to do instead -->
+
+<!-- Example:
+- Build succeeded but component didn't render → Check if all imports are included in bundle
+- esbuild error about JSX → Ensure .tsx extension and jsx: 'automatic' in config
+-->

packages/ui-react/AGENTS.md

@@ -0,0 +1,56 @@
+# @mcp-apps-kit/ui-react
+
+React bindings for MCP applications. Provides hooks and context for building UIs.
+
+## Quick Commands
+
+```bash
+pnpm -C packages/ui-react test        # Run tests
+pnpm -C packages/ui-react typecheck   # Type check only
+pnpm -C packages/ui-react lint        # Lint only
+```
+
+## Key Exports
+
+- `AppsProvider` - Context provider (wrap your app)
+- `useAppsClient` - Get client instance
+- `useToolResult` - Get current tool result
+- `useHostContext` - Get host context (theme, locale, etc.)
+- `useDocumentTheme` / `useHostStyleVariables` - Auto-apply theming
+
+## Patterns
+
+```tsx
+<AppsProvider>
+  <App />
+</AppsProvider>;
+
+function App() {
+  const result = useToolResult<ToolOutputs>();
+  useDocumentTheme("light", "dark");
+  // ...
+}
+```
+
+## Dependencies
+
+- @mcp-apps-kit/ui (re-exports many types)
+- React 18 or 19
+
+## Common Mistakes
+
+- Forgetting `AppsProvider` wrapper
+- Not typing `useToolResult<T>()` generic
+- Using hooks outside provider context
+
+---
+
+## Learnings
+
+<!-- MANDATORY: Document failures here to prevent repeated mistakes -->
+<!-- Format: what went wrong → what to do instead -->
+
+<!-- Example:
+- Hook returned undefined unexpectedly → Ensure component is wrapped in AppsProvider
+- Re-renders caused infinite loop → Check useEffect dependencies, avoid object literals in deps
+-->

packages/ui/AGENTS.md

@@ -0,0 +1,49 @@
+# @mcp-apps-kit/ui
+
+Client-side SDK for MCP applications (vanilla JavaScript). Auto-detects host platform (MCP Apps vs ChatGPT) and provides unified API.
+
+## Quick Commands
+
+```bash
+pnpm -C packages/ui test        # Run tests
+pnpm -C packages/ui typecheck   # Type check only
+pnpm -C packages/ui lint        # Lint only
+```
+
+## Key Exports
+
+- `createClient` - Main entry point, auto-detects platform
+- `detectProtocol` - Manual platform detection
+- `McpAdapter` / `OpenAIAdapter` / `MockAdapter` - Protocol adapters
+- Theme/style utilities: `applyDocumentTheme`, `applyHostStyleVariables`
+
+## Patterns
+
+```typescript
+const client = await createClient<typeof app.tools>();
+const result = await client.callTool("greet", { name: "Alice" });
+```
+
+Subscribe to events with `onHostContextChange`, `onToolResult`.
+
+## Dependencies
+
+- @modelcontextprotocol/ext-apps
+
+## Common Mistakes
+
+- Forgetting to await `createClient()` (it's async)
+- Not handling both MCP and OpenAI response formats
+- Missing type parameter for typed tool calls
+
+---
+
+## Learnings
+
+<!-- MANDATORY: Document failures here to prevent repeated mistakes -->
+<!-- Format: what went wrong → what to do instead -->
+
+<!-- Example:
+- Client connected but no events fired → Check if adapter.connect() was awaited
+- Theme not applying → Verify onHostContextChange subscription is set up before first render
+-->