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/unix_cc.rs

@@ -20,7 +20,10 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
         ctx.exclude_dirs,
         ctx.include_paths,
     )?;
-    let obj_dir = Path::new("./target").join(ctx.profile).join("obj");
+    let obj_dir = match ctx.target_dir {
+        Some(dir) => Path::new(dir).join("obj"),
+        None => Path::new("./target").join(ctx.profile).join("obj"),
+    };
     let objects = build_objects(compiler, &sources, &obj_dir, ctx, "o")?;
 
     if ctx.kind == "staticlib" {
@@ -51,6 +54,12 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
             cmd.arg("-shared");
         }
     }
+    if ctx.kind == "efi" {
+        cmd.arg("-shared");
+        cmd.arg("-nostdlib");
+        cmd.arg("-Wl,-dll");
+        cmd.arg("-Wl,--subsystem,10");
+    }
     for obj in &objects {
         cmd.arg(obj);
     }
@@ -73,6 +82,10 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
 
     let out_path = if ctx.kind == "sharedlib" {
         platform::shared_lib_path(ctx.profile, &final_name, ctx.target_dir)
+    } else if ctx.kind == "efi" {
+        platform::efi_path(ctx.profile, &final_name, ctx.target_dir)
+    } else if ctx.kind == "elf" {
+        platform::elf_path(ctx.profile, &final_name, ctx.target_dir)
     } else {
         platform::bin_path(ctx.profile, &final_name, ctx.target_dir)
     };