[M5+] add resolver::vcpkg_probe

src/resolver/resolver.cppm

@@ -71,4 +71,22 @@ auto parse_conanfile(std::string_view conanfile_text, const std::string& fallbac
 // ResolutionNetworkError.
 auto conan_probe(const std::string& name) -> util::Result<ConanRecipe>;
 
+// Output of a microsoft/vcpkg port usage-file scrape.
+struct VcpkgRecipe {
+    std::string find_package; // e.g. "fmt CONFIG REQUIRED"
+    std::vector<std::string> targets; // e.g. ["fmt::fmt"]
+};
+
+// Pure: scrape a vcpkg port `usage` file (plain CMake) for the first
+// find_package(...) arguments and the targets named in the corresponding
+// target_link_libraries(...) call. Returns ResolutionUnknownPackage when
+// no find_package directive appears.
+auto parse_vcpkg_usage(std::string_view usage_text)
+    -> util::Result<VcpkgRecipe>;
+
+// Fetches https://raw.githubusercontent.com/microsoft/vcpkg/master/ports/<name>/usage
+// via `curl` and feeds it through parse_vcpkg_usage. 404 →
+// ResolutionUnknownPackage; transport errors → ResolutionNetworkError.
+auto vcpkg_probe(const std::string& name) -> util::Result<VcpkgRecipe>;
+
 } // namespace cargoxx::resolver