go-instrument is a CLI tool that automatically instruments Go source files with OpenTelemetry trace spans. It parses Go AST, identifies functions that accept a `context.Context` parameter, and inserts span creation, defer, and optional error recording statements. It handles various edge cases: anonymous functions, build constraints (ignore/exclude), generated files, custom context/error parameter names, already-instrumented functions, and preserves original line numbers for panic stack traces via compiler directives. The tool is implemented as a reusable library with a clear separation between the generic AST processing engine (`processor` package) and the specific instrumentation strategy (`instrument` package), allowing custom instrumenters. The CLI frontend is minimal; the core logic is in the `processor` and `instrument` packages and is cleanly abstracted via an `Instrumenter` interface. The codebase is well-tested, includes fuzz testing, and uses current Go tooling.