diff --git a/AGENTS.md b/AGENTS.md
index 33f5018..b33dad4 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -21,6 +21,7 @@ crafter-build is a C++26 modules build system. A project is described by a `proj
 
 Partitions and what they own:
 
+- `:Toolchain` resolves the compiler once per process (`GetToolchain`): clang++, clang, llvm-ar, libclang, libc++'s std module source and the default sysroots, from `CRAFTER_BUILD_LLVM_DIR`, else a toolchain installed beside crafter-build, else PATH. It also holds the version baked in at build time.
 - `:Clang` holds `Configuration`, `Build()`, `VariantId()`, `ApplyStandardArgs`, `HostTarget`, the CLI entry point `Crafter::Run`, and the lint and test data types.
 - `:Platform` runs commands, implements `LoadProject` (compile and load `project.cpp`), the host PCM cache, `#pragma crafter dependency`, and all OS-specific code.
 - `:Interface` and `:Implementation` model module units, their staleness checks and their compiles.
@@ -31,7 +32,7 @@ Partitions and what they own:
 
 ## Dev environment
 
-Prerequisites on Linux: `clang` (with `libclang`, which the AST lint rules load at runtime), `lld`, `libc++` with `/usr/share/libc++/v1/std.cppm`, `cmake`, `git`. Network access to `forgejo.catcrafts.net` and `github.com` is needed: loading `project.cpp` fetches Crafter.Math, Crafter.Asset and Crafter.LintRules into `~/.cache/crafter.build/external/`, and the bootstrap clones glslang. Those sources are unpinned, so every invocation runs `git pull` on them.
+Prerequisites on Linux: `clang` (with `libclang`, which the AST lint rules load at runtime), `lld`, `libc++` with its std module source (`share/libc++/v1/std.cppm`), `cmake`, `git`. `crafter-build --version` prints which compiler was resolved; `CRAFTER_BUILD_LLVM_DIR` points it at another LLVM prefix, and `build.sh` honours the same variable. Network access to `forgejo.catcrafts.net` and `github.com` is needed: loading `project.cpp` fetches Crafter.Math, Crafter.Asset and Crafter.LintRules into `~/.cache/crafter.build/external/`, and the bootstrap clones glslang. Those sources are unpinned, so every invocation runs `git pull` on them.
 
 ```bash
 ./build.sh              # bootstrap: bin/crafter-build, lib/libcrafter-build.a, share/crafter-build/
diff --git a/README.md b/README.md
index a5ebf0a..6af758c 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,8 @@ Bootstrap requires `clang`, `cmake`, `git`, `lld`, and `libc++`.
 ./bin/crafter-build                       # rebuild via project.cpp
 ```
 
+The compiler is resolved once per run: `CRAFTER_BUILD_LLVM_DIR` if set, else a `clang++` installed beside crafter-build (`<prefix>/bin`), else PATH. `crafter-build --version` prints the version and the compiler in use; `crafter-build --help` lists the other overrides (`CRAFTER_BUILD_LIBCXX_DIR`, `CRAFTER_BUILD_LIBCLANG`, `CRAFTER_BUILD_WASI_SYSROOT`, `CRAFTER_MINGW_DIR`). A `Configuration` targets the host triple unless `cfg.target` says otherwise.
+
 The bootstrap targets the host toolchain's own triple (`clang++ -print-target-triple`): `x86_64-pc-linux-gnu` on glibc distros, `x86_64-alpine-linux-musl` on Alpine/postmarketOS (`apk add clang clang-dev lld libc++-dev llvm-libunwind-dev llvm-runtimes llvm llvm-dev cmake build-base python3 git`). Override with `CRAFTER_BUILD_TARGET=`. CI ships both: `crafter-build-linux-x86_64-v{2,3,4}.tar.gz` (glibc) and `crafter-build-linux-x86_64-musl-v2.tar.gz` (musl, needs `libc++` at runtime — the launcher dlopens `project.so`, so it cannot be static).
 
 To build the system as a distro package on Arch:
@@ -34,7 +36,6 @@ extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> a
     cfg.path = "./";
     cfg.name = "myapp";
     cfg.outputName = "myapp";
-    cfg.target = "x86_64-pc-linux-gnu";
     cfg.type = ConfigurationType::Executable;
 
     std::array<fs::path, 1> ifaces = { "interfaces/Hello" };
@@ -204,7 +205,6 @@ extern "C" Configuration CrafterBuildProject(std::span<const std::string_view>)
     cfg.path = "tests/UnitFoo/";
     cfg.name = "UnitFoo";
     cfg.outputName = "UnitFoo";
-    cfg.target = "x86_64-pc-linux-gnu";
     cfg.type = ConfigurationType::Executable;
     cfg.dependencies = { ParentLib("MyLib") };       // <-- the magic line