docs(agents): split ARCH.md into topic files under AGENTS/ARCH

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/AGENTS/ARCH/DEPENDENCIES.md b/AGENTS/ARCH/DEPENDENCIES.md
new file mode 100644
index 0000000..7a8b07f
--- /dev/null
+++ b/AGENTS/ARCH/DEPENDENCIES.md
@@ -0,0 +1,34 @@
+# Build dependencies and toolchain
+
+`doc/build.md` recommends which packages to install and which to download;
+CMake does not enforce that split. The modular `cmake/LocalDependencies.cmake`
+entry point extracts Debian, MSYS2 and Homebrew binary packages from the build
+directory's `deps/packages/` into `deps/root/`. Standard bin/lib/include layouts
+under the build directory are also searched. The shared
+`cmake/FindDependency.cmake` helper searches locally first, then the system, and
+reports missing required dependencies. Compilers, make, LLVM, support libraries,
+Pandoc, Git and installer/relocation tools use the same lookup policy. System-only
+and mixed installations are supported. Local dependencies override cached system
+paths except for supplied compilers. Cached or explicit CMake compiler paths and
+initial CC/CXX selections are preserved and validated; default discovery prefers
+clang-23/clang++-23, then unversioned clang/clang++. Build tools are resolved before
+`project()` enables compiler checks; compiler information is refreshed when the
+selected executable changes.
+Platform modules relocate package paths only inside the extraction directory;
+Homebrew bottles also receive local Cellar/opt links and Mach-O relocation/signing.
+Package hashes skip unchanged extractions; a changed package set rebuilds the
+managed root. Downloads belong to the explicit dependency commands and static LLD
+helper in `doc/build.md`, not to CMake. The Windows Pandoc ZIP is downloaded directly from its official
+release because MSYS2 has no Pandoc package.
+
+
+Windows build instructions retain MSYS2 MINGW64. Its LLVM/Clang package names
+and compiler executable names are unversioned; CMake still requires major 23.
+The build guide explicitly selects `/mingw64/bin/clang.exe` and `clang++.exe`
+through `cygpath -m`. MINGW64 retains the GNU C++ runtime; cpsc links with LLD. Switching to
+CLANG64 would change the C/C++ runtime and is a separate task.
+
+Build pin: **LLVM 23 and upstream Clang 23** (any 23.x release); 23.1.3 is verified
+on Linux. LLVM 23 uses `CreateGlobalString` for opaque string pointers,
+`hasTerminator()` for block termination checks (its `getTerminator()` requires an
+existing terminator), and an explicit `llvm::Triple` for the embedded target.