feat(build): add flat-bin kind and FAT [archive] packing for OS-dev

docs/reference/dcr-toml.mdx

@@ -33,6 +33,9 @@ Main project configuration file. Located at the project root.
 
 [run]
 # run settings
+
+[archive]
+# optional: pack FAT disk image after build
 ```
 
 ## [package]
@@ -62,18 +65,18 @@ author = "John Doe"
 
 | Field | Default | Description |
 |-------|---------|-------------|
-| `language` | `"c"` | `"c"`, `"c++"`, `"cpp"`, `"cxx"`, `"asm"` (optional, defaults to `"c"`) |
+| `language` | `"c"` | `"c"`, `"c++"`, `"cpp"`, `"cxx"`, `"asm"`, `"llvm_ir"`, `"llvm-ir"`, `"ll"` (optional, defaults to `"c"`) |
 | `standard` | `"c11"` | C standard (`c11`, `c17`, `c23`) |
 | `cxx_standard` | — | C++ standard (`c++17`, `c++20`, `c++23`) |
 | `compiler` | `"clang"` | Preferred compiler (optional, defaults to `"clang"`) |
-| `kind` | `"bin"` | `bin`, `staticlib`, `sharedlib`, `efi`, `elf`, `none`, `custom` |
+| `kind` | `"bin"` | `bin`, `staticlib`, `sharedlib`, `efi`, `elf`, `none`, `custom`, `flat-bin` |
 | `target` | host | Target triple for cross-compilation |
 | `platform` | `"native"` | `native`, `efi` |
 | `cflags` | `[]` | Additional C/C++/ASM flags |
 | `ldflags` | `[]` | Additional linker flags |
 | `filename` | `""` | Custom output file name |
-| `extension` | `""` | Custom file extension |
-| `roots` | `["src"]` | Source root directories |
+| `extension` | `""` | Custom file extension (for `flat-bin`, default is `bin`) |
+| `roots` | `["src"]` | Source roots: directories and/or individual source/header files |
 | `exclude` | `[]` | Exclude patterns |
 | `include` | `[]` | Additional include directories |
 | `src_disable` | `false` | Disable auto source discovery |
@@ -96,7 +99,7 @@ Settings from raw config (not in typed struct):
 - `ldscript` — linker script path
 - `build.steps` / `build.post_steps` — codegen steps
 
-## Per-language overrides: `[build.c]`, `[build.cxx]`, `[build.asm]`
+## Per-language overrides: `[build.c]`, `[build.cxx]`, `[build.asm]`, `[build.llvm_ir]`
 
 Each language can have its own table that overrides the flat `[build]` settings:
 
@@ -116,6 +119,9 @@ compiler = "g++"
 [build.asm]
 compiler = "nasm"
 flags = ["-felf64"]
+
+[build.llvm_ir]
+compiler = "llc"
 ```
 
 The flat `[build]` acts as fallback; per-language tables take precedence for their language.
@@ -172,3 +178,82 @@ Default `cmd` = `./target/{profile}/{name}` (macOS/Windows) or `./target/<triple
 ## [workspace]
 
 See [workspaces](/docs/reference/workspaces).
+
+## [archive]
+
+Optional post-build step: format a FAT volume and copy built artifacts into a disk image. Runs after a successful package build (and after workspace member builds that define `[archive]`).
+
+| Field | Required | Description |
+|-------|----------|-------------|
+| `output` | yes | Image path relative to project root (`{profile}` allowed) |
+| `format` | yes | `fat12`, `fat16`, or `fat32` |
+| `size` | no | Image size: bytes or `K`/`KB`/`M`/`MB`/`G`/`GB` (default `1474560` ≈ 1.44 MiB) |
+| `offset` | no | Byte offset of the FAT volume inside the image (default `0`) |
+| `label` | no | Volume label (max 11 chars, default `VOLUME`) |
+| `bootsector` | no | Path to a 512-byte boot sector written at offset 0 when `offset` is 0 (`{profile}` allowed) |
+| `layout` | no | List of `{ from, to }` entries (files or globs → path inside the volume) |
+
+```toml
+[archive]
+output = "target/{profile}/disk.img"
+format = "fat12"
+size = "1440K"
+label = "MYOS"
+bootsector = "target/{profile}/boot.bin"
+
+[[archive.layout]]
+from = "target/{profile}/kernel.bin"
+to = "KERNEL.BIN"
+
+[[archive.layout]]
+from = "assets/*"
+to = "/"
+```
+
+Typical pairing with `kind = "flat-bin"` (NASM `-f bin`) for bootloaders and pure-ASM OS images.
+
+## `flat-bin` (kind)
+
+Produces a raw binary (default extension `bin`) for boot sectors, kernels, and freestanding payloads.
+
+### Assemblers
+
+| Tool | Language / compiler | How flat-bin is produced |
+|------|---------------------|--------------------------|
+| NASM | `language = "asm"`, `compiler = "nasm"` | `-f bin` → `<stem>.bin` |
+| FASM | `compiler = "fasm"` | direct write (use `format binary` in source) |
+| GAS | `compiler = "as"` / `"gas"` | assemble → `objcopy -O binary` |
+| MASM | `compiler = "ml"` / `"ml64"` | assemble → `objcopy -O binary` |
+| LLC | `language = "llvm_ir"`, `compiler = "llc"` | `-filetype=obj` → `objcopy -O binary` |
+
+```toml
+[build]
+language = "asm"
+compiler = "nasm"
+kind = "flat-bin"
+extension = "bin"
+roots = ["src/boot.asm"]
+```
+
+### C / C++
+
+Compile all sources, link with `-nostdlib -static` (plus your `ldflags` / `ldscript`), then convert the intermediate ELF/PE with `objcopy -O binary` to `<filename|name>.bin`.
+
+```toml
+[build]
+language = "c"
+compiler = "clang"
+kind = "flat-bin"
+freestanding = true
+filename = "kernel"
+extension = "bin"
+ldscript = "linker.ld"
+ldflags = ["-T", "linker.ld"]
+```
+
+Notes:
+
+- Multi-file **ASM** packages emit one `<stem>.bin` per source; **C/C++** emit a single project binary.
+- `objcopy` tools tried in order: `llvm-objcopy`, `objcopy`, `gobjcopy`.
+- Incompatible with `build.qt = true`.
+- `dcr run` rejects `flat-bin` (not a host executable).