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+DR-005-infra: Directory Structure for S-CORE Bazel C++ Toolchain Configuration Repository
+====================================================================================
+
+Overview
+--------
+
+This repository acts as a **pure configuration layer** for C++ toolchains used in Bazel builds.
+It contains **only configuration files** (``BUILD.bazel``, ``.bzl``), while all **toolchain
+binaries** are downloaded from external repositories via ``http_archive``.
+
+Platform definitions are **not** part of this repository—they are provided separately by the
+S-CORE Bazel Platforms module.
+
+This structure supports:
+
+- Multiple compiler versions
+- Multiple OS/CPU combinations
+- Clean layering following Bazel best practices
+- Bzlmod-compatible module extensions
+- Reusability and long-term maintainability
+
+----
+
+High-Level Goals
+----------------
+
+- Provide a **central place** for all C++ toolchain configuration logic.
+- Separate toolchain **binaries** from **configurations**.
+- Provide scalable support for:
+
+  - Linux (x86_64, arm64)
+  - QNX (x86_64, arm64)
+  - Multiple compiler variants (GCC, Clang, QCC)
+  - Multiple versions per compiler
+
+- Allow all consuming repositories to pull toolchains via **Bzlmod** with simple configuration.
+
+----
+
+Proposed Directory Structure
+----------------------------
+
+.. code-block:: text
+
+    <repo_root>/
+    ├── MODULE.bazel
+    ├── BUILD.bazel
+    │
+    ├── toolchains/
+    │   ├── linux/
+    │   │   ├── x86_64/
+    │   │   │   ├── gcc/
+    │   │   │   │   ├── 12.2.0/
+    │   │   │   │   │   ├── BUILD.bazel
+    │   │   │   │   │   ├── cc_toolchain_config.bzl
+    │   │   │   │   │   └── third_party/
+    │   │   │   │   │       └── gcc.BUILD
+    │   │   │   │   └── ...
+    │   │   │   └── llvm/
+    │   │   │       ├── 16/
+    │   │   │       └── ...
+    │   │   │
+    │   │   └── arm64/
+    │   │       ├── gcc/
+    │   │       │   ├── 12.2.0/
+    │   │       │   └── ...
+    │   │       └── llvm/
+    │   │           ├── 16/
+    │   │           └── ...
+    │   │
+    │   ├── qnx/
+    │   │   ├── x86_64/
+    │   │   └── arm64/
+    │   │       └── qcc/
+    │   │           ├── 7.1/
+    │   │           ├── 8.0/
+    │   │           └── ...
+    │   │
+    │   ├── rules/
+    │   │   ├── BUILD.bazel
+    │   │   ├── gcc.bzl
+    │   │   ├── llvm.bzl
+    │   │   └── qcc.bzl
+    │   │
+    │   ├── extentions/
+    │   │   ├── BUILD.bazel
+    │   │   ├── gcc.bzl
+    │   │   ├── llvm.bzl
+    │   │   └── qcc.bzl
+    │   │
+    │   └── common/
+    │       ├── cc_config_common.bzl
+    │       ├── toolchain_features.bzl
+    │       └── version_matrix.bzl
+    │
+    ├── tests/
+    │   └── ...
+    │
+    └── docs/
+        ├── repo_overview.md
+        ├── naming_convention.md
+        ├── how_to_add_toolchain.md
+        └── version_policy.md
+
+----
+
+Structure Rationale
+-------------------
+
+1. OS → Architecture → Compiler → Version Hierarchy
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This structure provides:
+
+- Clear separation of toolchains
+- Easy extension when adding:
+
+  - New compilers
+  - New versions
+  - New platforms
+
+Example:
+
+.. code-block:: text
+
+    toolchains/linux/x86_64/gcc/13.1.0/
+
+----
+
+2. Clean Separation from Binaries
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+All binaries remain outside:
+
+- Toolchain binaries provided by vendor archives  
+- Retrieved via ``http_archive``
+- Only configuration logic lives here
+
+Each versioned toolchain directory pulls paths from package repository
+``toolchain_cpp_packages`` (full name: ``S-CORE Bazel CPP Toolchain packages``) such as:
+
+::
+
+    @score_toolchain_linux_x86_64_gcc12_2_0
+
+or:
+
+::
+
+    @score_toolchain_linux_arm64_gcc13_1_0
+
+This ensures the configuration repo remains lightweight and portable.
+
+----
+
+3. Shared Common Logic
+~~~~~~~~~~~~~~~~~~~~~~
+
+All shared logic lives under:
+
+::
+
+    toolchains/common/
+
+Contained files:
+
++------------------------------+-----------------------------------------------+
+| File                         | Purpose                                       |
++==============================+===============================================+
+| ``cc_config_common.bzl``     | Common flags and default configurations       |
++------------------------------+-----------------------------------------------+
+| ``toolchain_features.bzl``   | Helper functions for constructing features    |
++------------------------------+-----------------------------------------------+
+| ``version_matrix.bzl``       | Single source of truth for supported versions |
++------------------------------+-----------------------------------------------+
+
+This avoids duplication across the full matrix of platform/compiler/version combinations.
+
+----
+
+4. Bzlmod Extension
+~~~~~~~~~~~~~~~~~~~
+
+The repository exposes module extensions defined in the ``extentions`` directory.
+
+Example:
+
+::
+
+    module_extension(
+        name = "gcc",
+        extension_file = "//toolchains/extentions:gcc.bzl",
+    )
+
+or:
+
+::
+
+    module_extension(
+        name = "llvm",
+        extension_file = "//toolchains/extentions:llvm.bzl",
+    )
+
+The extension:
+
+- Loads toolchain definitions
+- Provides interface for root module to set desired version and options
+- Maps toolchains to the Bazel Platforms module
+
+----
+
+5. Documentation
+~~~~~~~~~~~~~~~~
+
+A dedicated ``docs/`` directory ensures maintainability:
+
+- **repo_overview.md** — high-level purpose
+- **naming_convention.md** — toolchain naming scheme
+- **how_to_add_toolchain.md** — step-by-step contributor guide
+- **toolchain_testing_and_validation** — integration-gate validation specification
+- **version_policy.md** — rules for adding/deprecating versions
+
+----
+
+Benefits Summary
+----------------
+
++-------------------+--------------------------------------------------------------+
+| **Benefit**       | **Explanation**                                              |
++===================+==============================================================+
+| Scalable          | Clean hierarchy allows adding platforms and compilers        |
+|                   | easily.                                                      |
++-------------------+--------------------------------------------------------------+
+| Modular           | Fully compatible with Bzlmod.                                |
++-------------------+--------------------------------------------------------------+
+| Lightweight       | No binaries stored in the repository.                        |
++-------------------+--------------------------------------------------------------+
+| Consistent        | Shared logic centralized under ``toolchains/common``.        |
++-------------------+--------------------------------------------------------------+
+| Traceable         | Version matrix gives a clear overview of supported versions. |
++-------------------+--------------------------------------------------------------+
+