[M5+] add resolver::conan_probe

src/resolver/resolver.cppm

@@ -51,4 +51,24 @@ auto nix_cmake_scan(const std::filesystem::path& store_path,
                     const std::string& package_name)
     -> util::Result<NixCmakeCandidate>;
 
+// Output of a conan-center-index recipe scrape.
+struct ConanRecipe {
+    std::string find_package; // e.g. "fmt CONFIG REQUIRED"
+    std::vector<std::string> targets; // e.g. ["fmt::fmt"]
+};
+
+// Pure: scrapes a conanfile.py text for `cmake_target_name` and
+// `cmake_file_name`. Handles both the modern
+// `cpp_info.set_property("cmake_target_name", "...")` form and the
+// legacy `cpp_info.names["cmake_find_package"] = "..."` form. Returns
+// ResolutionUnknownPackage when no recognizable recipe is found.
+auto parse_conanfile(std::string_view conanfile_text, const std::string& fallback_name)
+    -> util::Result<ConanRecipe>;
+
+// Fetches https://raw.githubusercontent.com/conan-io/conan-center-index/
+// master/recipes/<name>/all/conanfile.py via `curl` and feeds it through
+// parse_conanfile. 404 → ResolutionUnknownPackage; transport errors →
+// ResolutionNetworkError.
+auto conan_probe(const std::string& name) -> util::Result<ConanRecipe>;
+
 } // namespace cargoxx::resolver