diff --git a/Cargo.lock b/Cargo.lock
index 320dcb8..a43261e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1222,6 +1222,32 @@ dependencies = [
  "libloading",
 ]
 
+[[package]]
+name = "clap"
+version = "4.5.60"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2797f34da339ce31042b27d23607e051786132987f595b02ba4f6a6dffb7030a"
+dependencies = [
+ "clap_builder",
+]
+
+[[package]]
+name = "clap_builder"
+version = "4.5.60"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "24a241312cea5059b13574bb9b3861cabf758b879c15190b37b6d6fd63ab6876"
+dependencies = [
+ "anstyle",
+ "clap_lex",
+ "strsim",
+]
+
+[[package]]
+name = "clap_lex"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3a822ea5bc7590f9d40f1ba12c0dc3c2760f3482c6984db1573ad11031420831"
+
 [[package]]
 name = "cmake"
 version = "0.1.57"
@@ -1242,6 +1268,17 @@ dependencies = [
  "unicode-width 0.2.0",
 ]
 
+[[package]]
+name = "codespan-reporting"
+version = "0.13.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "af491d569909a7e4dee0ad7db7f5341fef5c614d5b8ec8cf765732aba3cff681"
+dependencies = [
+ "serde",
+ "termcolor",
+ "unicode-width 0.2.0",
+]
+
 [[package]]
 name = "color_quant"
 version = "1.1.0"
@@ -1943,6 +1980,68 @@ dependencies = [
  "libloading",
 ]
 
+[[package]]
+name = "cxx"
+version = "1.0.194"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "747d8437319e3a2f43d93b341c137927ca70c0f5dabeea7a005a73665e247c7e"
+dependencies = [
+ "cc",
+ "cxx-build",
+ "cxxbridge-cmd",
+ "cxxbridge-flags",
+ "cxxbridge-macro",
+ "foldhash 0.2.0",
+ "link-cplusplus",
+]
+
+[[package]]
+name = "cxx-build"
+version = "1.0.194"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b0f4697d190a142477b16aef7da8a99bfdc41e7e8b1687583c0d23a79c7afc1e"
+dependencies = [
+ "cc",
+ "codespan-reporting 0.13.1",
+ "indexmap",
+ "proc-macro2",
+ "quote",
+ "scratch",
+ "syn 2.0.114",
+]
+
+[[package]]
+name = "cxxbridge-cmd"
+version = "1.0.194"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d0956799fa8678d4c50eed028f2de1c0552ae183c76e976cf7ca8c4e36a7c328"
+dependencies = [
+ "clap",
+ "codespan-reporting 0.13.1",
+ "indexmap",
+ "proc-macro2",
+ "quote",
+ "syn 2.0.114",
+]
+
+[[package]]
+name = "cxxbridge-flags"
+version = "1.0.194"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "23384a836ab4f0ad98ace7e3955ad2de39de42378ab487dc28d3990392cb283a"
+
+[[package]]
+name = "cxxbridge-macro"
+version = "1.0.194"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6acc6b5822b9526adfb4fc377b67128fdd60aac757cc4a741a6278603f763cf"
+dependencies = [
+ "indexmap",
+ "proc-macro2",
+ "quote",
+ "syn 2.0.114",
+]
+
 [[package]]
 name = "darling"
 version = "0.20.11"
@@ -3733,6 +3832,15 @@ dependencies = [
  "vcpkg",
 ]
 
+[[package]]
+name = "link-cplusplus"
+version = "1.0.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f78c730aaa7d0b9336a299029ea49f9ee53b0ed06e9202e8cb7db9bae7b8c82"
+dependencies = [
+ "cc",
+]
+
 [[package]]
 name = "linux-raw-sys"
 version = "0.4.15"
@@ -4000,7 +4108,7 @@ dependencies = [
  "bitflags 2.10.0",
  "cfg-if",
  "cfg_aliases",
- "codespan-reporting",
+ "codespan-reporting 0.12.0",
  "half",
  "hashbrown 0.15.5",
  "hexf-parse",
@@ -5489,6 +5597,12 @@ version = "1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "94143f37725109f92c262ed2cf5e59bce7498c01bcc1502d7b9afe439a4e9f49"
 
+[[package]]
+name = "scratch"
+version = "1.0.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d68f2ec51b097e4c1a75b681a8bec621909b5e91f15bb7b840c4f2f7b01148b2"
+
 [[package]]
 name = "sdl2"
 version = "0.37.0"
@@ -6617,7 +6731,10 @@ dependencies = [
 name = "trictrac-store"
 version = "0.1.0"
 dependencies = [
+ "anyhow",
  "base64 0.21.7",
+ "cxx",
+ "cxx-build",
  "log",
  "merge",
  "pyo3",
diff --git a/justfile b/justfile
index 33c0654..2bfc052 100644
--- a/justfile
+++ b/justfile
@@ -23,6 +23,10 @@ pythonlib:
   rm -rf target/wheels
   maturin build -m store/Cargo.toml --release
   pip install --no-deps --force-reinstall --prefix .devenv/state/venv target/wheels/*.whl
+cxxlib:
+  cargo build --release -p trictrac-store
+  @echo "Static lib: $(ls target/release/libtrictrac_store.a)"
+  @echo "CXX header: $(find target -name 'cxxengine.rs.h' | head -1)"
 trainbot algo:
   #python ./store/python/trainModel.py
   # cargo run --bin=train_dqn # ok
diff --git a/store/Cargo.toml b/store/Cargo.toml
index 846e5fb..a9234ff 100644
--- a/store/Cargo.toml
+++ b/store/Cargo.toml
@@ -7,12 +7,15 @@ edition = "2021"
 
 [lib]
 name = "trictrac_store"
-# "cdylib" is necessary to produce a shared library for Python to import from.
-# Only "rlib" is needed for other Rust crates to use this library
-crate-type = ["cdylib", "rlib"]
+# "cdylib"   → Python .so built by maturin (pyengine)
+# "rlib"     → used by other workspace crates (bot, client_cli)
+# "staticlib" → used by the C++ OpenSpiel game (cxxengine)
+crate-type = ["cdylib", "rlib", "staticlib"]
 
 [dependencies]
+anyhow = "1.0"
 base64 = "0.21.7"
+cxx = "1.0"
 # provides macros for creating log messages to be used by a logger (for example env_logger)
 log = "0.4.20"
 merge = "0.1.0"
@@ -21,3 +24,6 @@ pyo3 = { version = "0.23", features = ["extension-module", "abi3-py38"] }
 rand = "0.9"
 serde = { version = "1.0", features = ["derive"] }
 transpose = "0.2.2"
+
+[build-dependencies]
+cxx-build = "1.0"
diff --git a/store/build.rs b/store/build.rs
new file mode 100644
index 0000000..852bcf6
--- /dev/null
+++ b/store/build.rs
@@ -0,0 +1,7 @@
+fn main() {
+    cxx_build::bridge("src/cxxengine.rs")
+        .std("c++17")
+        .compile("trictrac-cxx");
+
+    println!("cargo:rerun-if-changed=src/cxxengine.rs");
+}
diff --git a/store/src/cxxengine.rs b/store/src/cxxengine.rs
new file mode 100644
index 0000000..86aa382
--- /dev/null
+++ b/store/src/cxxengine.rs
@@ -0,0 +1,223 @@
+//! C++ bindings for the TricTrac game engine via cxx.rs.
+//!
+//! Exposes an opaque `TricTracEngine` type to C++. The C++ side
+//! (open_spiel/games/trictrac/trictrac.cc) holds it via
+//! `rust::Box<trictrac_engine::TricTracEngine>`.
+//!
+//! The Rust engine always reasons from White's (player 1's) perspective.
+//! For Black (player 2), the board is mirrored before computing actions
+//! and events are mirrored back before being applied — exactly as in
+//! pyengine.rs.
+
+use crate::dice::Dice;
+use crate::game::{GameEvent, GameState, Stage, TurnStage};
+use crate::training_common::{get_valid_action_indices, TrictracAction};
+
+// ── cxx bridge declaration ────────────────────────────────────────────────────
+
+#[cxx::bridge(namespace = "trictrac_engine")]
+pub mod ffi {
+    // ── Shared types (transparent to both Rust and C++) ───────────────────────
+
+    /// Two dice values passed from C++ when applying a chance outcome.
+    struct DicePair {
+        die1: u8,
+        die2: u8,
+    }
+
+    /// Both players' cumulative scores: holes * 12 + points.
+    struct PlayerScores {
+        score_p1: i32,
+        score_p2: i32,
+    }
+
+    // ── Opaque Rust type and its free-function constructor ────────────────────
+
+    extern "Rust" {
+        /// Opaque handle to a running TricTrac game.
+        /// C++ accesses this only through `rust::Box<TricTracEngine>`.
+        type TricTracEngine;
+
+        /// Construct a fresh engine with two players; player 1 (White) goes first.
+        fn new_trictrac_engine() -> Box<TricTracEngine>;
+
+        /// Deep-copy the engine — required by OpenSpiel's State::Clone().
+        fn clone_engine(self: &TricTracEngine) -> Box<TricTracEngine>;
+
+        // ── Queries ───────────────────────────────────────────────────────────
+
+        /// True when the game is in TurnStage::RollWaiting (OpenSpiel chance node).
+        fn needs_roll(self: &TricTracEngine) -> bool;
+
+        /// True when Stage::Ended.
+        fn is_game_ended(self: &TricTracEngine) -> bool;
+
+        /// Active player index: 0 = player 1 (White), 1 = player 2 (Black).
+        fn current_player_idx(self: &TricTracEngine) -> u64;
+
+        /// Legal action indices for `player_idx` in [0, 513].
+        /// Returns an empty vector when it is not that player's turn.
+        fn get_legal_actions(self: &TricTracEngine, player_idx: u64) -> Vec<u64>;
+
+        /// Human-readable description of an action index.
+        fn action_to_string(self: &TricTracEngine, player_idx: u64, action_idx: u64) -> String;
+
+        /// Both players' scores.
+        fn get_players_scores(self: &TricTracEngine) -> PlayerScores;
+
+        /// 36-element state vector (i8).  Mirrored for player_idx == 1.
+        fn get_tensor(self: &TricTracEngine, player_idx: u64) -> Vec<i8>;
+
+        /// Human-readable state description for `player_idx`.
+        fn get_observation_string(self: &TricTracEngine, player_idx: u64) -> String;
+
+        /// Full debug representation of the current state.
+        fn to_debug_string(self: &TricTracEngine) -> String;
+
+        // ── Mutations ─────────────────────────────────────────────────────────
+
+        /// Apply a dice-roll result.  Returns Err (C++ exception) if not in
+        /// the RollWaiting stage.
+        fn apply_dice_roll(self: &mut TricTracEngine, dice: DicePair) -> Result<()>;
+
+        /// Apply a player action.  Returns Err (C++ exception) if the action
+        /// is not legal in the current state.
+        fn apply_action(self: &mut TricTracEngine, action_idx: u64) -> Result<()>;
+    }
+}
+
+// ── Opaque type ───────────────────────────────────────────────────────────────
+
+pub struct TricTracEngine {
+    game_state: GameState,
+}
+
+// ── Free-function constructor (declared in the bridge as a plain function) ────
+
+pub fn new_trictrac_engine() -> Box<TricTracEngine> {
+    let mut game_state = GameState::new(false); // schools_enabled = false
+    game_state.init_player("player1");
+    game_state.init_player("player2");
+    game_state.consume(&GameEvent::BeginGame { goes_first: 1 });
+    Box::new(TricTracEngine { game_state })
+}
+
+// ── Method implementations ────────────────────────────────────────────────────
+
+impl TricTracEngine {
+    fn clone_engine(&self) -> Box<TricTracEngine> {
+        Box::new(TricTracEngine {
+            game_state: self.game_state.clone(),
+        })
+    }
+
+    fn needs_roll(&self) -> bool {
+        self.game_state.turn_stage == TurnStage::RollWaiting
+    }
+
+    fn is_game_ended(&self) -> bool {
+        self.game_state.stage == Stage::Ended
+    }
+
+    fn current_player_idx(&self) -> u64 {
+        self.game_state.active_player_id - 1
+    }
+
+    fn get_legal_actions(&self, player_idx: u64) -> Vec<u64> {
+        if player_idx != self.current_player_idx() {
+            return vec![];
+        }
+        if player_idx == 0 {
+            get_valid_action_indices(&self.game_state)
+                .into_iter()
+                .map(|i| i as u64)
+                .collect()
+        } else {
+            let mirror = self.game_state.mirror();
+            get_valid_action_indices(&mirror)
+                .into_iter()
+                .map(|i| i as u64)
+                .collect()
+        }
+    }
+
+    fn action_to_string(&self, player_idx: u64, action_idx: u64) -> String {
+        TrictracAction::from_action_index(action_idx as usize)
+            .map(|a| format!("{}:{}", player_idx, a))
+            .unwrap_or_else(|| "unknown action".into())
+    }
+
+    fn get_players_scores(&self) -> ffi::PlayerScores {
+        ffi::PlayerScores {
+            score_p1: self.score_for(1),
+            score_p2: self.score_for(2),
+        }
+    }
+
+    fn score_for(&self, player_id: u64) -> i32 {
+        self.game_state
+            .players
+            .get(&player_id)
+            .map(|p| p.holes as i32 * 12 + p.points as i32)
+            .unwrap_or(-1)
+    }
+
+    fn get_tensor(&self, player_idx: u64) -> Vec<i8> {
+        if player_idx == 0 {
+            self.game_state.to_vec()
+        } else {
+            self.game_state.mirror().to_vec()
+        }
+    }
+
+    fn get_observation_string(&self, player_idx: u64) -> String {
+        if player_idx == 0 {
+            format!("{}", self.game_state)
+        } else {
+            format!("{}", self.game_state.mirror())
+        }
+    }
+
+    fn to_debug_string(&self) -> String {
+        format!("{}", self.game_state)
+    }
+
+    fn apply_dice_roll(&mut self, dice: ffi::DicePair) -> anyhow::Result<()> {
+        if self.game_state.turn_stage != TurnStage::RollWaiting {
+            anyhow::bail!("apply_dice_roll: not in RollWaiting stage (currently {:?})",
+                self.game_state.turn_stage);
+        }
+        let player_id = self.game_state.active_player_id;
+        let dice = Dice {
+            values: (dice.die1, dice.die2),
+        };
+        self.game_state
+            .consume(&GameEvent::RollResult { player_id, dice });
+        Ok(())
+    }
+
+    fn apply_action(&mut self, action_idx: u64) -> anyhow::Result<()> {
+        let needs_mirror = self.game_state.active_player_id == 2;
+
+        let event = TrictracAction::from_action_index(action_idx as usize).and_then(|a| {
+            let state = if needs_mirror {
+                &self.game_state.mirror()
+            } else {
+                &self.game_state
+            };
+            a.to_event(state)
+                .map(|e| if needs_mirror { e.get_mirror(false) } else { e })
+        });
+
+        match event {
+            Some(evt) if self.game_state.validate(&evt) => {
+                self.game_state.consume(&evt);
+                Ok(())
+            }
+            Some(_) => anyhow::bail!("apply_action: action {} is not valid in current state",
+                action_idx),
+            None => anyhow::bail!("apply_action: could not build event from action index {}",
+                action_idx),
+        }
+    }
+}
diff --git a/store/src/lib.rs b/store/src/lib.rs
index 1bb8d1d..4fc8dff 100644
--- a/store/src/lib.rs
+++ b/store/src/lib.rs
@@ -21,3 +21,6 @@ pub mod training_common;
 
 // python interface "trictrac_engine" (for AI training..)
 mod pyengine;
+
+// C++ interface via cxx.rs (for OpenSpiel C++ integration)
+pub mod cxxengine;