Tests markers changing with required-environments

Test case for astral-sh/uv#16824 (comment). Introduces `required-environments` to packse.

Author: konstin

scenarios/wheels/markers-change-after-selection.toml

@@ -0,0 +1,24 @@
+name = "markers-change-after-selection"
+description = '''A package is first used under a marker that is a subset of the required environments that it fulfills, and then under a marker that is a subset it doesn't fulfill.
+
+See <https://github.com/astral-sh/uv/pull/16824#discussion_r2556176057>
+'''
+
+[resolver_options]
+universal = true
+required_environments = ['sys_platform == "linux"', 'sys_platform == "win32"']
+
+[root]
+requires = ["a; sys_platform == 'win32'", "b"]
+
+[expected]
+satisfiable = false
+
+[packages.a.versions."1.0.0"]
+sdist = false
+wheel_tags = [
+  "cp312-abi3-win_amd64",
+]
+
+[packages.b.versions."1.0.0"]
+requires = ["a; sys_platform == 'linux'"]

src/packse/scenario.py

@@ -143,6 +143,11 @@ class ResolverOptions(msgspec.Struct, forbid_unknown_fields=True):
     The Python platform to use for resolution.
     """
 
+    required_environments: list[str] | None = None
+    """
+    A list of required platforms, for packages that lack source distributions.
+    """
+
     def hash(self) -> str:
         """
         Return a hash of the contents
@@ -160,6 +165,9 @@ def hash(self) -> str:
             hasher.update(self.universal.to_bytes())
         if self.python_platform is not None:
             hasher.update(self.python_platform.encode())
+        if self.required_environments is not None:
+            for required_environment in self.required_environments:
+                hasher.update(required_environment.encode())
 
         return hasher.hexdigest()