docs: add API client generation instructions to README and AGENTS.md (#273)

README.md

@@ -50,6 +50,17 @@ $ bun install
 $ bun run packages/opencode/src/index.ts
 ```
 
+#### Development Notes
+
+**API Client Generation**: After making changes to the TypeScript API endpoints in `packages/opencode/src/server/server.ts`, you need to regenerate the Go client and OpenAPI specification:
+
+```bash
+$ cd packages/tui
+$ go generate ./pkg/client/
+```
+
+This updates the generated Go client code that the TUI uses to communicate with the backend server.
+
 ### FAQ
 
 #### How is this different than Claude Code?