Document Windows-native command guidance

CONTRIBUTING.md

@@ -26,3 +26,10 @@ When changing a utility's behavior, prefer landing the change in the relevant
 upstream project first and then updating the submodule here. Windows-specific
 glue, packaging, and the multi-call binary wrapper live in this repo and are
 fair game for direct PRs.
+
+## Windows-native commands
+
+For Windows-native commands that are not directly provided by the upstream
+submodules, see [Windows-native command notes](docs/windows-native-commands.md)
+before opening an implementation PR. In general, please open an issue first so
+the command scope and option support can be agreed on.

docs/windows-native-commands.md

@@ -0,0 +1,22 @@
+# Windows-Native Command Notes
+
+Some commands may need a small Windows-native implementation when the upstream
+submodules do not provide a usable Windows backend.
+
+Before adding a new command, please open an issue first so maintainers can agree
+on the command scope and option support.
+
+Prefer small, script-friendly commands that are commonly available by default on
+Linux or macOS and can be implemented on Windows with clear, documented
+approximations. Interactive, non-default, or broad system-management tools should
+be discussed first because they can add significant maintenance cost.
+
+For GNU-compatible options:
+
+- Define options to match the GNU interface and upstream behavior where
+  practical.
+- Implement options that can reasonably work on Windows, even if approximated.
+- Return an error for options that cannot work on Windows but are important to
+  the command's behavior.
+- Document Windows-specific approximations or unsupported behavior near the
+  option definitions, or in user-facing docs when needed.