Added:

- `build.kind = "efi"` — UEFI PE32+ executable support. Links with `-shared -nostdlib -Wl,-dll -Wl,--subsystem,10`, output via `efi_path()` with `.efi` extension, rejected by `dcr run`.
- `build.kind = "elf"` — bare-metal ELF executable support. Uses `elf_path()` output path, rejected by `dcr run`, no extra linker flags.

Fixed:

- `dcr run` with `--target` or `build.target` now correctly finds the binary in the arch-specific target directory.
- `dcr run` checks profile-specific `build.{profile}.kind` before rejecting library builds (previously only checked `build.kind`).
- `dcr clean` now reads `build.target` from `dcr.toml` when no `--target` flag is given.
- Linux: target directory is now consistent — `target/<arch>-unknown-linux-gnu/<profile>/` (no stale `target/<profile>/`).
- `dcr.lock` is now populated with all resolved dependencies (registry, path, git) instead of being always empty.
- Git dependencies are now properly recognized and recorded in `dcr.lock`.
- `is_registry_dep` correctly identifies version-based registry dependency tables (`{ version = "..." }`) and rejects tables with unknown keys.
- `dcr test` accepts `--debug`/`--release` flags (defaults to `debug` profile instead of always `release`).
- Build fingerprint cache (`build_cache_path`) now includes `target_dir` — different targets no longer share a single cache entry.
- `object_path` no longer hardcodes the `src/` prefix — works correctly with custom `build.roots` (e.g. `roots = ["lib"]`).
- `dcr update` now generates `.exe` candidates for all Windows targets, not just `x86_64-pc-windows-msvc`.
- Compiler existence is verified before starting the build (clear error if compiler is not found in PATH).
- Consolidated duplicate `OUTPUT_MUTEX` definitions — MSVC backend now uses the shared mutex from `common.rs`.
- Registry cache root directory is created if missing (prevents cryptic errors when `~/.dcr/` does not exist).

src/core/builder/mod.rs

@@ -33,6 +33,12 @@ pub struct BuildContext<'a> {
 
 pub fn build(ctx: &BuildContext) -> Result<f64, String> {
     let compiler = ctx.compiler.to_lowercase();
+    if !check_compiler_exists(ctx.compiler) {
+        return Err(format!(
+            "Compiler not found: {}. Make sure it is installed and available in PATH.",
+            ctx.compiler
+        ));
+    }
     if compiler.contains("clang-cl") {
         return msvc::build(ctx);
     }
@@ -48,6 +54,14 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
     unix_cc::build(ctx)
 }
 
+fn check_compiler_exists(compiler: &str) -> bool {
+    let name = if compiler.is_empty() { "cc" } else { compiler };
+    std::process::Command::new(name)
+        .arg("--version")
+        .output()
+        .is_ok()
+}
+
 pub fn collect_sources(ctx: &BuildContext) -> Result<Vec<String>, String> {
     let compiler = ctx.compiler.to_lowercase();
     if compiler.contains("clang-cl") || compiler == "cl" || compiler.contains("msvc") {