refact: add cargo cxx feature

store/Cargo.toml

@@ -15,11 +15,13 @@ crate-type = ["cdylib", "rlib", "staticlib"]
 [features]
 # Enable Python bindings (required for maturin / AI training). Not available on wasm32.
 python = ["pyo3"]
+# Enable C++ bridge for OpenSpiel integration. Not available on wasm32.
+cpp = ["dep:cxx"]
 
 [dependencies]
 anyhow = "1.0"
 base64 = "0.21.7"
-cxx = "1.0"
+cxx = { version = "1.0", optional = true }
 # provides macros for creating log messages to be used by a logger (for example env_logger)
 log = "0.4.20"
 merge = "0.1.0"

store/build.rs

@@ -1,7 +1,9 @@
 fn main() {
-    cxx_build::bridge("src/cxxengine.rs")
-        .std("c++17")
-        .compile("trictrac-cxx");
+    if std::env::var("CARGO_FEATURE_CPP").is_ok() {
+        cxx_build::bridge("src/cxxengine.rs")
+            .std("c++17")
+            .compile("trictrac-cxx");
 
-    println!("cargo:rerun-if-changed=src/cxxengine.rs");
+        println!("cargo:rerun-if-changed=src/cxxengine.rs");
+    }
 }

store/src/lib.rs

@@ -24,4 +24,5 @@ pub mod training_common;
 mod pyengine;
 
 // C++ interface via cxx.rs (for OpenSpiel C++ integration)
+#[cfg(feature = "cpp")]
 pub mod cxxengine;