diff --git a/.cargo/config.toml b/.cargo/config.toml
new file mode 100644
index 0000000..326e199
--- /dev/null
+++ b/.cargo/config.toml
@@ -0,0 +1,2 @@
+[registries.Quaternions]
+index = "sparse+https://git.aleshym.co/api/packages/Quaternions/cargo/"
diff --git a/Cargo.lock b/Cargo.lock
index 80b5c33..531855c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -364,6 +364,12 @@ version = "0.7.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7c02d123df017efcdfbd739ef81735b36c5ba83ec3c59c80a9d7ecc718f92e50"
 
+[[package]]
+name = "arrayvec"
+version = "0.7.6"
+source = "sparse+https://git.aleshym.co/api/packages/Quaternions/cargo/"
+checksum = "813440870d646c57c222c1d713dc4e3ddcb2919c3801564d767d85d7bf2afee4"
+
 [[package]]
 name = "as-raw-xcb-connection"
 version = "1.0.1"
@@ -901,7 +907,7 @@ version = "0.18.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c9cf7a3ee41342dd7b5a5d82e200d0e8efb933169247fce853b4ad633d51e87d"
 dependencies = [
- "arrayvec",
+ "arrayvec 0.7.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "bevy_ecs_macros",
  "bevy_platform",
  "bevy_ptr",
@@ -1138,7 +1144,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e931fa969f89c83498b22c97432383afe90e90fd1a5e04fa07be8da4d3bcac84"
 dependencies = [
  "approx",
- "arrayvec",
+ "arrayvec 0.7.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "bevy_reflect",
  "derive_more",
  "glam 0.30.10",
@@ -1703,7 +1709,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0aa83c34e62843d924f905e0f5c866eb1dd6545fc4d719e803d9ba6030371fce"
 dependencies = [
  "arrayref",
- "arrayvec",
+ "arrayvec 0.7.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "cc",
  "cfg-if",
  "constant_time_eq",
@@ -1879,6 +1885,15 @@ dependencies = [
  "wayland-client",
 ]
 
+[[package]]
+name = "card_game"
+version = "0.3.0"
+source = "sparse+https://git.aleshym.co/api/packages/Quaternions/cargo/"
+checksum = "38b68e4fb32f8a1f92edf8488c012f6d8af71491a2f9f8a855362d7eaf1a2d0c"
+dependencies = [
+ "arrayvec 0.7.6 (sparse+https://git.aleshym.co/api/packages/Quaternions/cargo/)",
+]
+
 [[package]]
 name = "cbc"
 version = "0.1.2"
@@ -1939,6 +1954,17 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "18758054972164c3264f7c8386f5fc6da6114cb46b619fd365d4e3b2dc3ae487"
 
+[[package]]
+name = "chacha20"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6f8d983286843e49675a4b7a2d174efe136dc93a18d69130dd18198a6c167601"
+dependencies = [
+ "cfg-if",
+ "cpufeatures 0.3.0",
+ "rand_core 0.10.1",
+]
+
 [[package]]
 name = "chrono"
 version = "0.4.44"
@@ -4326,13 +4352,23 @@ dependencies = [
  "triple_buffer",
 ]
 
+[[package]]
+name = "klondike"
+version = "0.2.0"
+source = "sparse+https://git.aleshym.co/api/packages/Quaternions/cargo/"
+checksum = "0bce541f9b14e9d9d8c9b17d5df40bd0a017709b61d9be8ad5bab7b19a1a0152"
+dependencies = [
+ "card_game",
+ "rand 0.10.1",
+]
+
 [[package]]
 name = "kurbo"
 version = "0.13.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7564e90fe3c0d5771e1f0bc95322b21baaeaa0d9213fa6a0b61c99f8b17b3bfb"
 dependencies = [
- "arrayvec",
+ "arrayvec 0.7.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid",
  "smallvec",
 ]
@@ -4740,7 +4776,7 @@ version = "27.0.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "066cf25f0e8b11ee0df221219010f213ad429855f57c494f995590c861a9a7d8"
 dependencies = [
- "arrayvec",
+ "arrayvec 0.7.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "bit-set",
  "bitflags 2.11.1",
  "cfg-if",
@@ -5947,6 +5983,16 @@ dependencies = [
  "rand_core 0.9.5",
 ]
 
+[[package]]
+name = "rand"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d2e8e8bcc7961af1fdac401278c6a831614941f6164ee3bf4ce61b7edb162207"
+dependencies = [
+ "chacha20",
+ "rand_core 0.10.1",
+]
+
 [[package]]
 name = "rand_chacha"
 version = "0.3.1"
@@ -5985,6 +6031,12 @@ dependencies = [
  "getrandom 0.3.4",
 ]
 
+[[package]]
+name = "rand_core"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "63b8176103e19a2643978565ca18b50549f6101881c443590420e4dc998a3c69"
+
 [[package]]
 name = "rand_distr"
 version = "0.5.1"
@@ -6980,6 +7032,7 @@ dependencies = [
 name = "solitaire_core"
 version = "0.1.0"
 dependencies = [
+ "klondike",
  "rand 0.9.4",
  "serde",
  "thiserror 2.0.18",
@@ -7502,7 +7555,7 @@ version = "0.5.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ea00cc4f79b7f6bb7ff87eddc065a1066f3a43fe1875979056672c9ef948c2af"
 dependencies = [
- "arrayvec",
+ "arrayvec 0.7.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 1.3.2",
  "bytemuck",
  "lazy_static",
@@ -7601,7 +7654,7 @@ version = "0.9.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "41ba83ebaf2954d31d05d67340fd46cebe99da2b7133b0dd68d70c65473a437b"
 dependencies = [
- "arrayvec",
+ "arrayvec 0.7.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "grid",
  "serde",
  "slotmap",
@@ -7870,7 +7923,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "83d13394d44dae3207b52a326c0c85a8bf87f1541f23b0d143811088497b09ab"
 dependencies = [
  "arrayref",
- "arrayvec",
+ "arrayvec 0.7.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "bytemuck",
  "cfg-if",
  "log",
@@ -7884,7 +7937,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "47ffee5eaaf5527f630fb0e356b90ebdec84d5d18d937c5e440350f88c5a91ea"
 dependencies = [
  "arrayref",
- "arrayvec",
+ "arrayvec 0.7.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "bytemuck",
  "cfg-if",
  "log",
@@ -9044,7 +9097,7 @@ version = "27.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bfe68bac7cde125de7a731c3400723cadaaf1703795ad3f4805f187459cd7a77"
 dependencies = [
- "arrayvec",
+ "arrayvec 0.7.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 2.11.1",
  "cfg-if",
  "cfg_aliases",
@@ -9068,7 +9121,7 @@ version = "27.0.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "27a75de515543b1897b26119f93731b385a19aea165a1ec5f0e3acecc229cae7"
 dependencies = [
- "arrayvec",
+ "arrayvec 0.7.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "bit-set",
  "bit-vec",
  "bitflags 2.11.1",
@@ -9118,7 +9171,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5b21cb61c57ee198bc4aff71aeadff4cbb80b927beb912506af9c780d64313ce"
 dependencies = [
  "android_system_properties",
- "arrayvec",
+ "arrayvec 0.7.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "ash",
  "bit-set",
  "bitflags 2.11.1",
diff --git a/Cargo.toml b/Cargo.toml
index d8e9253..59e4eec 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -37,6 +37,7 @@ solitaire_core   = { path = "solitaire_core" }
 solitaire_sync   = { path = "solitaire_sync" }
 solitaire_data   = { path = "solitaire_data" }
 solitaire_engine = { path = "solitaire_engine" }
+klondike         = { version = "0.2.0", registry = "Quaternions" }
 
 # Bevy with `default-features = false` to avoid the unused
 # `bevy_audio → rodio + symphonia + cpal 0.15 + alsa 0.9` chain.
diff --git a/solitaire_core/Cargo.toml b/solitaire_core/Cargo.toml
index d2468b4..57a700b 100644
--- a/solitaire_core/Cargo.toml
+++ b/solitaire_core/Cargo.toml
@@ -8,3 +8,4 @@ edition.workspace = true
 serde     = { workspace = true }
 thiserror = { workspace = true }
 rand      = { workspace = true }
+klondike  = { workspace = true }
diff --git a/solitaire_core/src/game_state.rs b/solitaire_core/src/game_state.rs
index 9be029a..9c79c75 100644
--- a/solitaire_core/src/game_state.rs
+++ b/solitaire_core/src/game_state.rs
@@ -3,10 +3,8 @@ use crate::deck::{Deck, deal_klondike};
 use crate::error::MoveError;
 use crate::pile::{Pile, PileType};
 use crate::rules::{can_place_on_foundation, can_place_on_tableau, is_valid_tableau_sequence};
-use crate::scoring::{
-    compute_time_bonus as scoring_time_bonus, score_flip, score_move, score_recycle,
-    score_undo as scoring_undo,
-};
+use crate::klondike_adapter::KlondikeAdapter;
+use crate::scoring::compute_time_bonus as scoring_time_bonus;
 use serde::{Deserialize, Serialize};
 use std::collections::{HashMap, VecDeque};
 
@@ -166,6 +164,8 @@ pub struct GameState {
     #[serde(default = "schema_v1")]
     pub schema_version: u32,
     #[serde(skip)]
+    pub adapter: KlondikeAdapter,
+    #[serde(skip)]
     undo_stack: VecDeque<StateSnapshot>,
 }
 
@@ -208,6 +208,7 @@ impl GameState {
             recycle_count: 0,
             take_from_foundation: true,
             schema_version: GAME_STATE_SCHEMA_VERSION,
+            adapter: KlondikeAdapter::new(draw_mode, true),
             undo_stack: VecDeque::new(),
         }
     }
@@ -276,7 +277,7 @@ impl GameState {
             self.recycle_count = self.recycle_count.saturating_add(1);
             if self.mode != GameMode::Zen {
                 let penalty =
-                    score_recycle(self.recycle_count, self.draw_mode == DrawMode::DrawThree);
+                    KlondikeAdapter::score_for_recycle(self.recycle_count, self.draw_mode == DrawMode::DrawThree);
                 self.score = (self.score + penalty).max(0);
             }
             self.move_count = self.move_count.saturating_add(1);
@@ -413,7 +414,7 @@ impl GameState {
         let score_delta = if self.mode == GameMode::Zen {
             0
         } else {
-            score_move(&from, &to)
+            self.adapter.score_for_move(&from, &to)
         };
         self.push_snapshot();
 
@@ -446,7 +447,7 @@ impl GameState {
             .append(&mut moved);
 
         let flip_bonus = if flipped && self.mode != GameMode::Zen {
-            score_flip()
+            self.adapter.score_for_flip()
         } else {
             0
         };
@@ -480,7 +481,7 @@ impl GameState {
         self.score = if self.mode == GameMode::Zen {
             0
         } else {
-            (snapshot.score + scoring_undo()).max(0)
+            (snapshot.score + KlondikeAdapter::score_for_undo()).max(0)
         };
         self.move_count = snapshot.move_count;
         self.is_won = false;
@@ -726,6 +727,7 @@ impl GameState {
 mod tests {
     use super::*;
     use crate::card::{Card, Rank, Suit};
+    use crate::klondike_adapter::KlondikeAdapter;
 
     fn new_game() -> GameState {
         GameState::new(42, DrawMode::DrawOne)
@@ -1126,7 +1128,7 @@ mod tests {
         let score_before = g.score;
         g.draw().unwrap();
         g.undo().unwrap();
-        let expected = (score_before + scoring_undo()).max(0);
+        let expected = (score_before + KlondikeAdapter::score_for_undo()).max(0);
         assert_eq!(g.score, expected);
     }
 
diff --git a/solitaire_core/src/klondike_adapter.rs b/solitaire_core/src/klondike_adapter.rs
new file mode 100644
index 0000000..d2b28b3
--- /dev/null
+++ b/solitaire_core/src/klondike_adapter.rs
@@ -0,0 +1,139 @@
+//! Adapter bridging `solitaire_core` types to the upstream `klondike` crate.
+//!
+//! # Current scope (integration steps 1–4)
+//!
+//! [`KlondikeAdapter`] owns the authoritative [`KlondikeConfig`] and exposes
+//! scoring helpers backed by [`ScoringConfig::DEFAULT`] (Windows XP Standard
+//! values).  [`GameState`] delegates scoring here so that klondike remains the
+//! single source of truth for scoring constants.
+//!
+//! # Not yet implemented
+//!
+//! - Live [`klondike::Klondike`] shadow state (requires pile-mapping, step 2).
+//! - Move validation via klondike's rule engine (step 2).
+//! - DFS solver via [`klondike::KlondikeState`] (step 6).
+
+use klondike::{DrawStockConfig, KlondikeConfig, MoveFromFoundationConfig, ScoringConfig};
+
+use crate::game_state::DrawMode;
+use crate::pile::PileType;
+
+/// Bridges `solitaire_core` game config and scoring to the upstream `klondike` crate.
+///
+/// Holds a [`KlondikeConfig`] reflecting the current game settings and exposes
+/// scoring helpers that read from [`ScoringConfig::DEFAULT`] (WXP values).
+/// [`GameState`] uses this instead of calling `scoring.rs` functions directly.
+#[derive(Clone, Debug)]
+pub struct KlondikeAdapter {
+    config: KlondikeConfig,
+}
+
+impl PartialEq for KlondikeAdapter {
+    fn eq(&self, other: &Self) -> bool {
+        self.config.draw_stock == other.config.draw_stock
+            && self.config.move_from_foundation == other.config.move_from_foundation
+    }
+}
+impl Eq for KlondikeAdapter {}
+
+impl Default for KlondikeAdapter {
+    /// Returns an adapter with Draw-1 and `take_from_foundation = true`,
+    /// matching `GameState`'s own defaults.  Used by `#[serde(skip)]`
+    /// field initialisation on deserialisation.
+    fn default() -> Self {
+        Self::new(DrawMode::DrawOne, true)
+    }
+}
+
+impl KlondikeAdapter {
+    /// Create an adapter from the game's draw mode and foundation house-rule setting.
+    ///
+    /// `take_from_foundation = true` maps to [`MoveFromFoundationConfig::Allowed`];
+    /// `false` maps to [`MoveFromFoundationConfig::Disallowed`].
+    pub fn new(draw_mode: DrawMode, take_from_foundation: bool) -> Self {
+        let config = KlondikeConfig {
+            draw_stock: match draw_mode {
+                DrawMode::DrawOne => DrawStockConfig::DrawOne,
+                DrawMode::DrawThree => DrawStockConfig::DrawThree,
+            },
+            move_from_foundation: if take_from_foundation {
+                MoveFromFoundationConfig::Allowed
+            } else {
+                MoveFromFoundationConfig::Disallowed
+            },
+            scoring: ScoringConfig::DEFAULT,
+        };
+        Self { config }
+    }
+
+    /// Returns a reference to the underlying [`KlondikeConfig`].
+    ///
+    /// Used by the solver and pile-mapping code added in later integration steps.
+    pub fn klondike_config(&self) -> &KlondikeConfig {
+        &self.config
+    }
+
+    /// Update the foundation house-rule flag, keeping [`KlondikeConfig`] in sync.
+    pub fn set_take_from_foundation(&mut self, allowed: bool) {
+        self.config.move_from_foundation = if allowed {
+            MoveFromFoundationConfig::Allowed
+        } else {
+            MoveFromFoundationConfig::Disallowed
+        };
+    }
+
+    // ── Scoring helpers ───────────────────────────────────────────────────
+
+    /// Score delta for a card move.
+    ///
+    /// Reads from [`ScoringConfig`] (WXP Standard values):
+    /// - Any pile → Foundation: +10
+    /// - Waste → Tableau: +5
+    /// - Foundation → Tableau: −15
+    /// - All other moves: 0
+    pub fn score_for_move(&self, from: &PileType, to: &PileType) -> i32 {
+        let sc = &self.config.scoring;
+        match (from, to) {
+            (_, PileType::Foundation(_)) => sc.move_to_foundation,
+            (PileType::Waste, PileType::Tableau(_)) => sc.move_to_tableau,
+            (PileType::Foundation(_), PileType::Tableau(_)) => sc.move_from_foundation,
+            _ => 0,
+        }
+    }
+
+    /// Score delta for exposing a face-down tableau card: +5.
+    pub fn score_for_flip(&self) -> i32 {
+        self.config.scoring.flip_up_bonus
+    }
+
+    /// Score delta for undo: −15.
+    ///
+    /// [`card_game::Session`] handles this via `SessionConfig::undo_penalty`
+    /// (default −15). We mirror the constant here so `GameState` can apply it
+    /// in its snapshot-based undo path without owning a `Session`.
+    pub const fn score_for_undo() -> i32 {
+        -15
+    }
+
+    /// Score delta for recycling waste → stock.
+    ///
+    /// [`ScoringConfig::recycle`] is a flat delta (default 0 = always free).
+    /// WXP allows a fixed number of free recycles before charging a penalty,
+    /// which the upstream library cannot express with a single delta:
+    ///
+    /// | Mode | Free recycles | Penalty per extra recycle |
+    /// |---|---|---|
+    /// | Draw-1 | 1 | −100 |
+    /// | Draw-3 | 3 | −20 |
+    ///
+    /// `recycle_count` must be the new total **after** this recycle.
+    pub fn score_for_recycle(recycle_count: u32, is_draw_three: bool) -> i32 {
+        if is_draw_three {
+            if recycle_count > 3 { -20 } else { 0 }
+        } else if recycle_count > 1 {
+            -100
+        } else {
+            0
+        }
+    }
+}
diff --git a/solitaire_core/src/lib.rs b/solitaire_core/src/lib.rs
index d6042a9..4cadff9 100644
--- a/solitaire_core/src/lib.rs
+++ b/solitaire_core/src/lib.rs
@@ -3,6 +3,7 @@ pub mod card;
 pub mod deck;
 pub mod error;
 pub mod game_state;
+pub mod klondike_adapter;
 pub mod pile;
 pub mod rules;
 pub mod scoring;