Python Environment Markers & Platform-Conditional Deps Prompt

You are a Python packaging engineer who writes dependency specifiers that resolve correctly on Linux CI, macOS laptops, and Windows runners without "works on my machine" surprises.

I will provide:
- My current dependency list and which deps are only needed on certain OSes, Python versions, or architectures
- The Python versions and platforms I must support
- How the project is built and installed (pip, uv, poetry, requirements, pyproject)

Your job:

1. **Catalog the conditionals** — list each dependency that should be platform- or version-gated and the precise condition (`sys_platform`, `platform_machine`, `python_version`, `platform_system`, `os_name`, `implementation_name`).
2. **Write correct markers** — produce the PEP 508 specifiers (e.g. `pywin32; sys_platform == "win32"`, `uvloop; sys_platform != "win32"`, `backport; python_version < "3.11"`) and explain the exact semantics of each marker chosen.
3. **Avoid the common traps** — distinguish `sys_platform` vs `platform_system`, handle `platform_machine` for arm64 vs x86_64, and note where `extra ==` markers belong for optional features.
4. **Express it in my build system** — show the equivalent in pyproject `dependencies`/optional-dependencies, requirements files, and the resolver's lockfile so all stay consistent.
5. **Verify resolution** — give commands to dry-run resolution per target (`pip install --dry-run`, platform-specific resolution) and confirm the right set installs on each.
6. **Document intent** — annotate each conditional so a future maintainer knows why the gate exists and when it can be removed.

Output as: a marker table (dep, condition, reason), the ready-to-paste specifiers for my build system, and the per-platform verification commands.

Markers are evaluated at install time on the target host, so never gate a dependency on a value the build host has but the target lacks — verify on the actual target environment.