cgo-bindings

- Use `import "C"` with `// #cgo LDFLAGS:` and `// #cgo CFLAGS:` directives for linking. - Declare C header functions in comment block immediately above `import "C"` — no blank line between. - Type mapping: `C.int`, `C.long`, `C.char`. Use `C.CString()` and `C.GoString()` for string conversion. - Memory: `C.CString()` allocates — always `defer C.free(unsafe.Pointer(cStr))` immediately after creation. - Error handling: return error codes from C functions, convert to Go `error` values. Check all return values. - Link Rust static libraries: `// #cgo LDFLAGS: -L./target/release -lmylib`. Build Rust with `crate-type = ["staticlib"]`. - Thread safety: C functions called from Go may run on any OS thread. Use `runtime.LockOSThread()` when needed. - Go pointer passing: use `runtime.Pinner` (Go 1.21+) to pin Go memory passed to C. Never pass Go pointers without pinning. - Test with `go test` (requires `CGO_ENABLED=1`). Mock C layer for unit tests, use integration tests for real FFI. - Build: `CGO_ENABLED=1 go build`. Cross-compilation requires appropriate C toolchain. - Anti-patterns: leaking `C.CString` memory, passing unpinned Go pointers to C, ignoring C return codes.