refactor(core): align Spider with upstream card_game idioms

Addresses upstream author review of the Spider core (PR #157):

- RNG: drop the hand-rolled SplitMix64 + Fisher-Yates; deals now use
  rand::rngs::StdRng seeded via seed_from_u64 + SliceRandom::shuffle,
  exactly like klondike::with_seed. solitaire_core gains the same
  pinned rand dep klondike uses (0.10.1, std_rng only — already in the
  lock, no new transitive deps). Deals for a given seed change; Spider
  has no persisted games yet, so nothing breaks.
- Enums over integers: pile indices and card counts in the instruction
  type are now SpiderTableau (Tableau1..Tableau10, with an ALL const)
  and RunLength (Run1..Run13); out-of-range piles and zero-card moves
  are unrepresentable. Rank comparisons use Rank::checked_add instead
  of u8 arithmetic.
- Fixed-size containers: build_deck returns Stack<104> instead of
  Vec<Card>; possible_instructions is a const-iterated SpiderIter +
  validity filter (klondike's KlondikeIter pattern) instead of
  collecting into a Vec.
- Upstream naming: SpiderGame -> Spider (matches Klondike),
  tableau_face_up/_down -> tableau_face_up_cards/_down_cards,
  stock_len -> stock() accessor, with_rng added alongside with_seed.
- Solver access: SpiderGameState now exposes session(), the same
  escape hatch GameState has — the wrapper no longer pretends to hide
  solve(), which SessionConfig budgets already gate.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Cargo.lock

@@ -7331,6 +7331,7 @@ dependencies = [
  "card_game",
  "klondike",
  "proptest",
+ "rand 0.10.1",
  "serde",
  "thiserror 2.0.18",
 ]

solitaire_core/Cargo.toml

@@ -16,6 +16,11 @@ serde     = { workspace = true }
 thiserror = { workspace = true }
 klondike  = { workspace = true }
 card_game = { workspace = true }
+# Deliberately NOT the workspace rand (0.9): this pins the exact dep the
+# upstream `klondike` crate uses, so `SeedableRng`/`SliceRandom` resolve
+# against the same crate version as `klondike::Rng` and Spider deals go
+# through the identical shuffle stack as Klondike deals.
+rand      = { version = "0.10.1", default-features = false, features = ["std_rng"] }
 
 [lints]
 workspace = true

solitaire_core/src/lib.rs

@@ -25,8 +25,8 @@ pub use game_state::{DEFAULT_SOLVE_MOVES_BUDGET, DEFAULT_SOLVE_STATES_BUDGET, So
 // Spider rules (second `card_game::Game` implementation; engine UI is a
 // later phase — nothing outside solitaire_core consumes these yet).
 pub use spider::{
-    SpiderConfig, SpiderGame, SpiderGameState, SpiderInstruction, SpiderScoring, SpiderStats,
+    RunLength, Spider, SpiderConfig, SpiderGameState, SpiderInstruction, SpiderIter, SpiderMove,
-    SpiderSuits,
+    SpiderScoring, SpiderStats, SpiderSuits, SpiderTableau,
 };
 
 /// All four foundation slots, in slot order.

solitaire_core/src/spider.rs

@@ -22,11 +22,10 @@
 //!
 //! ## Determinism
 //!
-//! Deals are seeded with an inline SplitMix64 + Fisher–Yates shuffle:
+//! Deals are seeded exactly like upstream Klondike: [`Rng`] is the same
-//! `solitaire_core` has no `rand` dependency (and adding one needs
+//! `rand::rngs::StdRng` alias `klondike` exports, seeded through
-//! explicit approval), so Spider's seed space is deliberately
+//! `SeedableRng::seed_from_u64` and applied with a `SliceRandom`
-//! self-contained rather than shared with Klondike's `StdRng` seeds.
+//! shuffle. The same seed + suit count always produces the same deal.
-//! The same seed + suit count always produces the same deal.
 //!
 //! ## Card identity caveat (engine integration, later phase)
 //!
@@ -43,6 +42,10 @@ use serde::{Deserialize, Serialize};
 
 use crate::error::MoveError;
 
+/// The RNG Spider deals with — the same alias upstream `klondike`
+/// exports, so both games share one shuffle stack.
+pub type Rng = rand::rngs::StdRng;
+
 /// Number of tableau piles.
 pub const SPIDER_TABLEAUS: usize = 10;
 /// Total cards in play (two decks).
@@ -146,24 +149,212 @@ impl SpiderStats {
 }
 
 // ---------------------------------------------------------------------------
-// Instruction
+// Piles, run lengths, and instructions
 // ---------------------------------------------------------------------------
 
+/// One of the ten Spider tableau piles, in layout order.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub enum SpiderTableau {
+    /// Leftmost pile (opens with 6 cards).
+    Tableau1,
+    /// Second pile (opens with 6 cards).
+    Tableau2,
+    /// Third pile (opens with 6 cards).
+    Tableau3,
+    /// Fourth pile (opens with 6 cards).
+    Tableau4,
+    /// Fifth pile (opens with 5 cards).
+    Tableau5,
+    /// Sixth pile (opens with 5 cards).
+    Tableau6,
+    /// Seventh pile (opens with 5 cards).
+    Tableau7,
+    /// Eighth pile (opens with 5 cards).
+    Tableau8,
+    /// Ninth pile (opens with 5 cards).
+    Tableau9,
+    /// Rightmost pile (opens with 5 cards).
+    Tableau10,
+}
+
+impl SpiderTableau {
+    /// All ten piles, in layout order — the canonical iteration source,
+    /// following `Suit::SUITS` / `Rank::RANKS` upstream.
+    pub const ALL: [Self; SPIDER_TABLEAUS] = [
+        Self::Tableau1,
+        Self::Tableau2,
+        Self::Tableau3,
+        Self::Tableau4,
+        Self::Tableau5,
+        Self::Tableau6,
+        Self::Tableau7,
+        Self::Tableau8,
+        Self::Tableau9,
+        Self::Tableau10,
+    ];
+    const ITER_BEGIN: Self = Self::Tableau1;
+    const fn next(self) -> Option<Self> {
+        use SpiderTableau::*;
+        Some(match self {
+            Tableau1 => Tableau2,
+            Tableau2 => Tableau3,
+            Tableau3 => Tableau4,
+            Tableau4 => Tableau5,
+            Tableau5 => Tableau6,
+            Tableau6 => Tableau7,
+            Tableau7 => Tableau8,
+            Tableau8 => Tableau9,
+            Tableau9 => Tableau10,
+            Tableau10 => return None,
+        })
+    }
+    /// Zero-based position in layout order.
+    const fn index(self) -> usize {
+        self as usize
+    }
+}
+
+/// How many cards a [`SpiderMove`] picks up — at most 13, since a
+/// movable run is same-suit strictly-descending.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub enum RunLength {
+    /// A single card.
+    Run1 = 1,
+    /// The top 2 cards.
+    Run2 = 2,
+    /// The top 3 cards.
+    Run3 = 3,
+    /// The top 4 cards.
+    Run4 = 4,
+    /// The top 5 cards.
+    Run5 = 5,
+    /// The top 6 cards.
+    Run6 = 6,
+    /// The top 7 cards.
+    Run7 = 7,
+    /// The top 8 cards.
+    Run8 = 8,
+    /// The top 9 cards.
+    Run9 = 9,
+    /// The top 10 cards.
+    Run10 = 10,
+    /// The top 11 cards.
+    Run11 = 11,
+    /// The top 12 cards.
+    Run12 = 12,
+    /// A full K→A run.
+    Run13 = 13,
+}
+
+impl RunLength {
+    const ITER_BEGIN: Self = Self::Run1;
+    const fn next(self) -> Option<Self> {
+        use RunLength::*;
+        Some(match self {
+            Run1 => Run2,
+            Run2 => Run3,
+            Run3 => Run4,
+            Run4 => Run5,
+            Run5 => Run6,
+            Run6 => Run7,
+            Run7 => Run8,
+            Run8 => Run9,
+            Run9 => Run10,
+            Run10 => Run11,
+            Run11 => Run12,
+            Run12 => Run13,
+            Run13 => return None,
+        })
+    }
+    /// Number of cards in the run.
+    pub const fn len(self) -> usize {
+        self as usize
+    }
+    /// True only for [`Self::Run1`]; provided because clippy expects an
+    /// `is_empty` alongside `len`, and a run is never actually empty.
+    pub const fn is_empty(self) -> bool {
+        false
+    }
+}
+
+/// Move the top [`RunLength`] cards (a same-suit descending run) from
+/// one pile to another.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub struct SpiderMove {
+    /// Source pile.
+    pub from: SpiderTableau,
+    /// Number of cards picked up from the top of `from`.
+    pub run: RunLength,
+    /// Destination pile.
+    pub to: SpiderTableau,
+}
+
+impl SpiderMove {
+    const ITER_BEGIN: Self = Self {
+        from: SpiderTableau::ITER_BEGIN,
+        run: RunLength::ITER_BEGIN,
+        to: SpiderTableau::ITER_BEGIN,
+    };
+    const fn next(self) -> Option<Self> {
+        let Self { from, run, to } = self;
+        if let Some(to) = to.next() {
+            return Some(Self { from, run, to });
+        }
+        let to = SpiderTableau::ITER_BEGIN;
+        if let Some(run) = run.next() {
+            return Some(Self { from, run, to });
+        }
+        let run = RunLength::ITER_BEGIN;
+        if let Some(from) = from.next() {
+            return Some(Self { from, run, to });
+        }
+        None
+    }
+}
+
 /// One atomic Spider action (the `Game::Instruction` type).
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub enum SpiderInstruction {
+    /// Move a run between tableau piles.
+    Move(SpiderMove),
     /// Deal one card from the stock onto every tableau pile.
     Deal,
-    /// Move the top `count` face-up cards (a same-suit descending run)
+}
-    /// from pile `from` to pile `to`. Pile indices are `0..10`.
+
-    Move {
+impl SpiderInstruction {
-        /// Source pile index.
+    const ITER_BEGIN: Self = Self::Move(SpiderMove::ITER_BEGIN);
-        from: u8,
+    const fn next(self) -> Option<Self> {
-        /// Destination pile index.
+        Some(match self {
-        to: u8,
+            Self::Move(spider_move) => match spider_move.next() {
-        /// Number of cards in the moved run (≥ 1).
+                Some(spider_move) => Self::Move(spider_move),
-        count: u8,
+                None => Self::Deal,
             },
+            Self::Deal => return None,
+        })
+    }
+}
+
+/// Exhaustive walk of the Spider instruction space, mirroring
+/// `klondike::KlondikeIter`.
+pub struct SpiderIter {
+    instruction: Option<SpiderInstruction>,
+}
+
+impl SpiderIter {
+    const fn new() -> Self {
+        Self {
+            instruction: Some(SpiderInstruction::ITER_BEGIN),
+        }
+    }
+}
+
+impl Iterator for SpiderIter {
+    type Item = SpiderInstruction;
+    fn next(&mut self) -> Option<Self::Item> {
+        let instruction = self.instruction;
+        self.instruction = instruction?.next();
+        instruction
+    }
 }
 
 // ---------------------------------------------------------------------------
@@ -174,45 +365,22 @@ pub enum SpiderInstruction {
 /// of completed runs. Everything else (undo, score bookkeeping) lives
 /// in the wrapping [`Session`].
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
-pub struct SpiderGame {
+pub struct Spider {
     tableaus: [Pile<MAX_FACE_DOWN, SPIDER_DECK_SIZE>; SPIDER_TABLEAUS],
     stock: Stack<STOCK_SIZE>,
     completed_runs: u8,
 }
 
-/// SplitMix64 step — small, well-known, and dependency-free. Spider
-/// only needs a deterministic shuffle, not cryptographic quality.
-const fn splitmix64(state: u64) -> (u64, u64) {
-    let state = state.wrapping_add(0x9E37_79B9_7F4A_7C15);
-    let mut z = state;
-    z = (z ^ (z >> 30)).wrapping_mul(0xBF58_476D_1CE4_E5B9);
-    z = (z ^ (z >> 27)).wrapping_mul(0x94D0_49BB_1331_11EB);
-    (state, z ^ (z >> 31))
-}
-
-/// In-place Fisher–Yates driven by SplitMix64. The modulo bias is
-/// astronomically small for n ≤ 104 and irrelevant for gameplay.
-fn shuffle(cards: &mut [Card], seed: u64) {
-    let mut state = seed;
-    for i in (1..cards.len()).rev() {
-        let (next_state, r) = splitmix64(state);
-        state = next_state;
-        #[allow(clippy::cast_possible_truncation)]
-        let j = (r % (i as u64 + 1)) as usize;
-        cards.swap(i, j);
-    }
-}
-
 /// Builds the 104-card Spider deck for a suit-count difficulty.
 ///
 /// Deck ids spread copies apart where possible (`Deck1..Deck4`), but
 /// 1- and 2-suit games necessarily contain identical `Card` values —
 /// see the module docs.
-fn build_deck(suits: SpiderSuits) -> Vec<Card> {
+fn build_deck(suits: SpiderSuits) -> Stack<SPIDER_DECK_SIZE> {
     let suit_set = suits.suits();
     let copies = SPIDER_DECK_SIZE / (suit_set.len() * RUN_LEN);
     let decks = [Deck::Deck1, Deck::Deck2, Deck::Deck3, Deck::Deck4];
-    let mut cards = Vec::with_capacity(SPIDER_DECK_SIZE);
+    let mut cards = Stack::new();
     for copy in 0..copies {
         for &suit in suit_set {
             for rank in Rank::RANKS {
@@ -223,15 +391,24 @@ fn build_deck(suits: SpiderSuits) -> Vec<Card> {
     cards
 }
 
-impl SpiderGame {
+impl Spider {
     /// Deals a new seeded game at the given suit difficulty.
     pub fn with_seed(seed: u64, suits: SpiderSuits) -> Self {
+        use rand::SeedableRng;
+        let mut rng = Rng::seed_from_u64(seed);
+        Self::with_rng(&mut rng, suits)
+    }
+
+    /// Deals a new game from a caller-supplied RNG.
+    pub fn with_rng(rng: &mut Rng, suits: SpiderSuits) -> Self {
+        // shuffle a new two-deck spread
         let mut deck = build_deck(suits);
-        shuffle(&mut deck, seed);
+        use rand::seq::SliceRandom;
+        deck.shuffle(rng);
         let mut cards = deck.into_iter();
 
         let tableaus = core::array::from_fn(|index| {
-            // Piles 0–3 open with 5 face-down cards, piles 4–9 with 4;
+            // Piles 1–4 open with 5 face-down cards, piles 5–10 with 4;
             // one face-up card lands on each afterwards.
             let down_count = if index < 4 { 5 } else { 4 };
             let stack: Stack<MAX_FACE_DOWN> = cards.by_ref().take(down_count).collect();
@@ -250,22 +427,24 @@ impl SpiderGame {
         }
     }
 
-    /// Face-up cards of pile `index` (bottom → top). Empty slice for
+    /// Face-up cards of a pile (bottom → top).
-    /// out-of-range indices.
+    pub fn tableau_face_up_cards(&self, tableau: SpiderTableau) -> &[Card] {
-    pub fn tableau_face_up(&self, index: usize) -> &[Card] {
+        self.tableaus[tableau.index()].face_up()
-        self.tableaus.get(index).map_or(&[], |pile| pile.face_up())
     }
 
-    /// Face-down cards of pile `index` (bottom → top).
+    /// Face-down cards of a pile (bottom → top).
-    pub fn tableau_face_down(&self, index: usize) -> &[Card] {
+    pub fn tableau_face_down_cards(&self, tableau: SpiderTableau) -> &[Card] {
-        self.tableaus
+        self.tableaus[tableau.index()].face_down()
-            .get(index)
-            .map_or(&[], |pile| pile.face_down())
     }
 
-    /// Cards remaining in the stock.
+    /// Topmost face-up card of a pile.
-    pub fn stock_len(&self) -> usize {
+    pub fn tableau_top_card(&self, tableau: SpiderTableau) -> Option<&Card> {
-        self.stock.len()
+        self.tableaus[tableau.index()].face_up().last()
+    }
+
+    /// The stock (deals come off the top).
+    pub const fn stock(&self) -> &Stack<STOCK_SIZE> {
+        &self.stock
     }
 
     /// Completed K→A runs removed from play so far.
@@ -273,19 +452,16 @@ impl SpiderGame {
         self.completed_runs
     }
 
-    /// Length of the longest movable run on top of pile `index`: the
+    /// Length of the longest movable run on top of a pile: the maximal
-    /// maximal same-suit, strictly-descending face-up suffix.
+    /// same-suit, strictly-descending face-up suffix.
-    fn movable_run_len(&self, index: usize) -> usize {
+    fn movable_run_len(&self, tableau: SpiderTableau) -> usize {
-        let Some(pile) = self.tableaus.get(index) else {
+        let up = self.tableau_face_up_cards(tableau);
-            return 0;
-        };
-        let up = pile.face_up();
         let mut len = usize::from(!up.is_empty());
         while len < up.len() {
             let above = &up[up.len() - len];
             let below = &up[up.len() - len - 1];
             let descends =
-                below.suit() == above.suit() && below.rank() as u8 == above.rank() as u8 + 1;
+                below.suit() == above.suit() && above.rank().checked_add(1) == Some(below.rank());
             if !descends {
                 break;
             }
@@ -294,27 +470,27 @@ impl SpiderGame {
         len
     }
 
-    /// Whether `Move { from, to, count }` is legal in this position.
+    /// Whether a run move is legal in this position.
-    fn is_move_valid(&self, from: u8, to: u8, count: u8) -> bool {
+    fn is_move_valid(&self, spider_move: SpiderMove) -> bool {
-        let (from, to, count) = (from as usize, to as usize, count as usize);
+        let SpiderMove { from, run, to } = spider_move;
-        if from == to || from >= SPIDER_TABLEAUS || to >= SPIDER_TABLEAUS || count == 0 {
+        if from == to {
             return false;
         }
-        if count > self.movable_run_len(from) {
+        if run.len() > self.movable_run_len(from) {
             return false;
         }
-        let src_up = self.tableaus[from].face_up();
+        let src_up = self.tableau_face_up_cards(from);
-        // Bottom card of the moved run; `count <= movable_run_len <=
+        // Bottom card of the moved run; `run.len() <= movable_run_len
-        // src_up.len()` guarantees the index is in range.
+        // <= src_up.len()` guarantees the index is in range.
-        let Some(moved_bottom) = src_up.get(src_up.len() - count) else {
+        let Some(moved_bottom) = src_up.get(src_up.len() - run.len()) else {
             return false;
         };
-        match self.tableaus[to].face_up().last() {
+        match self.tableau_top_card(to) {
             // Build down regardless of suit.
-            Some(dest_top) => dest_top.rank() as u8 == moved_bottom.rank() as u8 + 1,
+            Some(dest_top) => moved_bottom.rank().checked_add(1) == Some(dest_top.rank()),
             // Empty pile accepts anything (face-down remnant can't
             // exist without a face-up card — Pile flips eagerly).
-            None => self.tableaus[to].is_empty(),
+            None => self.tableaus[to.index()].is_empty(),
         }
     }
 
@@ -323,22 +499,24 @@ impl SpiderGame {
         !self.stock.is_empty() && self.tableaus.iter().all(|pile| !pile.is_empty())
     }
 
-    /// Removes a completed K→A same-suit run from the top of pile
+    /// Removes a completed K→A same-suit run from the top of a pile,
-    /// `index`, if one is present. Returns `true` when a run was
+    /// if one is present. Returns `true` when a run was removed (and
-    /// removed (and the next face-down card, if any, was flipped).
+    /// the next face-down card, if any, was flipped).
-    fn sweep_completed_run(&mut self, index: usize) -> bool {
+    fn sweep_completed_run(&mut self, tableau: SpiderTableau) -> bool {
-        let Some(pile) = self.tableaus.get_mut(index) else {
+        let pile = &mut self.tableaus[tableau.index()];
-            return false;
-        };
         let up = pile.face_up();
         if up.len() < RUN_LEN {
             return false;
         }
         let run = &up[up.len() - RUN_LEN..];
         let suit = run[0].suit();
-        let is_complete = run.iter().enumerate().all(|(offset, card)| {
+        // The run sits bottom-first (K → A); reversed, it must read
-            card.suit() == suit && card.rank() as u8 == (RUN_LEN - offset) as u8
+        // exactly Ace → King in one suit.
-        });
+        let is_complete = run
+            .iter()
+            .rev()
+            .zip(Rank::RANKS)
+            .all(|(card, rank)| card.suit() == suit && card.rank() == rank);
         if !is_complete {
             return false;
         }
@@ -348,7 +526,7 @@ impl SpiderGame {
     }
 }
 
-impl Game for SpiderGame {
+impl Game for Spider {
     type Score = i32;
     type Stats = SpiderStats;
     type Config = SpiderConfig;
@@ -365,34 +543,16 @@ impl Game for SpiderGame {
         &self,
         config: &Self::Config,
     ) -> impl Iterator<Item = Self::Instruction> + use<> {
-        let mut out = Vec::new();
+        let state = self.clone();
-        if self.is_deal_valid() {
+        let config = config.clone();
-            out.push(SpiderInstruction::Deal);
+        SpiderIter::new()
-        }
+            .filter(move |&instruction| state.is_instruction_valid(&config, instruction))
-        for from in 0..SPIDER_TABLEAUS {
-            let max_run = self.movable_run_len(from);
-            for count in 1..=max_run {
-                for to in 0..SPIDER_TABLEAUS {
-                    #[allow(clippy::cast_possible_truncation)]
-                    let instruction = SpiderInstruction::Move {
-                        from: from as u8,
-                        to: to as u8,
-                        count: count as u8,
-                    };
-                    if self.is_move_valid(from as u8, to as u8, count as u8) {
-                        out.push(instruction);
-                    }
-                }
-            }
-        }
-        let _ = config;
-        out.into_iter()
     }
 
     fn is_instruction_valid(&self, _config: &Self::Config, instruction: Self::Instruction) -> bool {
         match instruction {
             SpiderInstruction::Deal => self.is_deal_valid(),
-            SpiderInstruction::Move { from, to, count } => self.is_move_valid(from, to, count),
+            SpiderInstruction::Move(spider_move) => self.is_move_valid(spider_move),
         }
     }
 
@@ -413,24 +573,24 @@ impl Game for SpiderGame {
         match instruction {
             SpiderInstruction::Deal => {
                 stats.deals += 1;
-                for index in 0..SPIDER_TABLEAUS {
+                for tableau in SpiderTableau::ALL {
                     match self.stock.pop() {
-                        Some(card) => self.tableaus[index].push(card),
+                        Some(card) => self.tableaus[tableau.index()].push(card),
                         None => break,
                     }
                 }
-                for index in 0..SPIDER_TABLEAUS {
+                for tableau in SpiderTableau::ALL {
-                    if self.sweep_completed_run(index) {
+                    if self.sweep_completed_run(tableau) {
                         self.completed_runs += 1;
                         stats.runs_completed += 1;
                     }
                 }
             }
-            SpiderInstruction::Move { from, to, count } => {
+            SpiderInstruction::Move(SpiderMove { from, run, to }) => {
-                let (from, to, count) = (from as usize, to as usize, count as usize);
+                let src_len = self.tableaus[from.index()].face_up().len();
-                let src_len = self.tableaus[from].face_up().len();
+                let (cards, _flipped) =
-                let (cards, _flipped) = self.tableaus[from].take_range_flip_up(src_len - count..);
+                    self.tableaus[from.index()].take_range_flip_up(src_len - run.len()..);
-                self.tableaus[to].extend(cards);
+                self.tableaus[to.index()].extend(cards);
                 if self.sweep_completed_run(to) {
                     self.completed_runs += 1;
                     stats.runs_completed += 1;
@@ -455,7 +615,7 @@ impl Game for SpiderGame {
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct SpiderGameState {
     seed: u64,
-    session: Session<SpiderGame>,
+    session: Session<Spider>,
 }
 
 impl SpiderGameState {
@@ -478,7 +638,7 @@ impl SpiderGameState {
         };
         Self {
             seed,
-            session: Session::new(SpiderGame::with_seed(seed, suits), config),
+            session: Session::new(Spider::with_seed(seed, suits), config),
         }
     }
 
@@ -493,10 +653,18 @@ impl SpiderGameState {
     }
 
     /// Current position (read-only).
-    pub fn game(&self) -> &SpiderGame {
+    pub fn game(&self) -> &Spider {
         self.session.state().state()
     }
 
+    /// The underlying upstream session, for solver access and replay —
+    /// the same escape hatch [`crate::game_state::GameState::session`]
+    /// provides (`session().solve()` honours the budgets configured in
+    /// [`SessionConfig`]).
+    pub const fn session(&self) -> &Session<Spider> {
+        &self.session
+    }
+
     /// In-play score, clamped at 0 like the Klondike wrapper.
     pub fn score(&self) -> i32 {
         self.session
@@ -563,7 +731,7 @@ impl SpiderGameState {
 // ---------------------------------------------------------------------------
 
 #[cfg(any(test, feature = "test-support"))]
-impl SpiderGame {
+impl Spider {
     /// Builds an arbitrary position for tests: per-pile
     /// `(face_down, face_up)` card lists plus stock and completed-run
     /// count. No card-count invariants are enforced — stacked
@@ -592,7 +760,7 @@ impl SpiderGame {
 #[cfg(any(test, feature = "test-support"))]
 impl SpiderGameState {
     /// Wraps an arbitrary position in a fresh session (empty history).
-    pub fn from_test_game(game: SpiderGame, suits: SpiderSuits) -> Self {
+    pub fn from_test_game(game: Spider, suits: SpiderSuits) -> Self {
         let config = SessionConfig {
             inner: SpiderConfig {
                 suits,
@@ -614,6 +782,8 @@ impl SpiderGameState {
 
 #[cfg(test)]
 mod tests {
+    use super::RunLength::*;
+    use super::SpiderTableau::*;
     use super::*;
 
     /// `Card::new` shorthand for stacked positions.
@@ -621,6 +791,11 @@ mod tests {
         Card::new(Deck::Deck1, suit, rank)
     }
 
+    /// `SpiderMove` shorthand for rule tests.
+    const fn mv(from: SpiderTableau, run: RunLength, to: SpiderTableau) -> SpiderMove {
+        SpiderMove { from, run, to }
+    }
+
     /// K→A same-suit run, bottom (King) first — the face-up order a
     /// completed run occupies on a pile.
     fn full_run(suit: Suit) -> Vec<Card> {
@@ -643,21 +818,25 @@ mod tests {
 
     #[test]
     fn opening_deal_shape_is_4x6_6x5_with_50_in_stock() {
-        let game = SpiderGame::with_seed(42, SpiderSuits::Four);
+        let game = Spider::with_seed(42, SpiderSuits::Four);
-        for index in 0..SPIDER_TABLEAUS {
+        for (index, tableau) in SpiderTableau::ALL.into_iter().enumerate() {
             let expected_down = if index < 4 { 5 } else { 4 };
-            assert_eq!(game.tableau_face_down(index).len(), expected_down);
+            assert_eq!(game.tableau_face_down_cards(tableau).len(), expected_down);
-            assert_eq!(game.tableau_face_up(index).len(), 1, "one card face-up");
+            assert_eq!(
+                game.tableau_face_up_cards(tableau).len(),
+                1,
+                "one card face-up"
+            );
         }
-        assert_eq!(game.stock_len(), STOCK_SIZE);
+        assert_eq!(game.stock().len(), STOCK_SIZE);
         assert_eq!(game.completed_runs(), 0);
     }
 
     #[test]
     fn same_seed_same_deal_different_seed_different_deal() {
-        let a = SpiderGame::with_seed(7, SpiderSuits::Four);
+        let a = Spider::with_seed(7, SpiderSuits::Four);
-        let b = SpiderGame::with_seed(7, SpiderSuits::Four);
+        let b = Spider::with_seed(7, SpiderSuits::Four);
-        let c = SpiderGame::with_seed(8, SpiderSuits::Four);
+        let c = Spider::with_seed(8, SpiderSuits::Four);
         assert_eq!(a, b);
         assert_ne!(a, c);
     }
@@ -691,15 +870,21 @@ mod tests {
         let mut layout = empty_layout();
         layout[0].1 = vec![card(Suit::Hearts, Rank::Five)];
         layout[1].1 = vec![card(Suit::Spades, Rank::Six)];
-        let game = SpiderGame::from_test_layout(layout, Vec::new(), 0);
+        let game = Spider::from_test_layout(layout, Vec::new(), 0);
-        assert!(game.is_move_valid(0, 1, 1), "5♥ onto 6♠ is legal");
+        assert!(
-        assert!(!game.is_move_valid(1, 0, 1), "6♠ onto 5♥ is not");
+            game.is_move_valid(mv(Tableau1, Run1, Tableau2)),
+            "5♥ onto 6♠ is legal"
+        );
+        assert!(
+            !game.is_move_valid(mv(Tableau2, Run1, Tableau1)),
+            "6♠ onto 5♥ is not"
+        );
     }
 
     #[test]
     fn only_same_suit_runs_are_movable_as_a_group() {
         let mut layout = empty_layout();
-        // Pile 0: 7♠ 6♠ (movable run of 2). Pile 1: 7♥ 6♠ (mixed).
+        // Pile 1: 7♠ 6♠ (movable run of 2). Pile 2: 7♥ 6♠ (mixed).
         layout[0].1 = vec![
             card(Suit::Spades, Rank::Seven),
             card(Suit::Spades, Rank::Six),
@@ -711,10 +896,19 @@ mod tests {
         // Destinations: 8♣ (for the pair), 7♦ (for a lone six).
         layout[2].1 = vec![card(Suit::Clubs, Rank::Eight)];
         layout[3].1 = vec![card(Suit::Diamonds, Rank::Seven)];
-        let game = SpiderGame::from_test_layout(layout, Vec::new(), 0);
+        let game = Spider::from_test_layout(layout, Vec::new(), 0);
-        assert!(game.is_move_valid(0, 2, 2), "same-suit pair moves");
+        assert!(
-        assert!(!game.is_move_valid(1, 2, 2), "mixed-suit pair does not");
+            game.is_move_valid(mv(Tableau1, Run2, Tableau3)),
-        assert!(game.is_move_valid(1, 3, 1), "its top card alone does");
+            "same-suit pair moves"
+        );
+        assert!(
+            !game.is_move_valid(mv(Tableau2, Run2, Tableau3)),
+            "mixed-suit pair does not"
+        );
+        assert!(
+            game.is_move_valid(mv(Tableau2, Run1, Tableau4)),
+            "its top card alone does"
+        );
     }
 
     #[test]
@@ -724,27 +918,40 @@ mod tests {
             card(Suit::Spades, Rank::Nine),
             card(Suit::Spades, Rank::Eight),
         ];
-        // Pile 1 deliberately left empty.
+        // Pile 2 deliberately left empty.
         layout[2].1 = vec![card(Suit::Hearts, Rank::Nine)];
-        let game = SpiderGame::from_test_layout(layout, Vec::new(), 0);
+        let game = Spider::from_test_layout(layout, Vec::new(), 0);
-        assert!(game.is_move_valid(0, 1, 2), "run onto empty pile");
-        assert!(game.is_move_valid(2, 1, 1), "single onto empty pile");
         assert!(
-            !game.is_move_valid(0, 2, 2),
+            game.is_move_valid(mv(Tableau1, Run2, Tableau2)),
+            "run onto empty pile"
+        );
+        assert!(
+            game.is_move_valid(mv(Tableau3, Run1, Tableau2)),
+            "single onto empty pile"
+        );
+        assert!(
+            !game.is_move_valid(mv(Tableau1, Run2, Tableau3)),
             "9♠8♠ cannot land on 9♥ (needs a 10)"
         );
     }
 
     #[test]
-    fn invalid_moves_rejected_out_of_range_zero_count_self_move() {
+    fn invalid_moves_rejected_self_move_and_overlong_run() {
+        // Out-of-range piles and zero-card runs are unrepresentable in
+        // `SpiderMove` — the enums only span legal values — so the only
+        // structurally invalid shapes left are self-moves and runs
+        // longer than the movable suffix.
         let mut layout = empty_layout();
         layout[0].1 = vec![card(Suit::Spades, Rank::Five)];
-        let game = SpiderGame::from_test_layout(layout, Vec::new(), 0);
+        let game = Spider::from_test_layout(layout, Vec::new(), 0);
-        assert!(!game.is_move_valid(0, 0, 1), "self-move");
+        assert!(
-        assert!(!game.is_move_valid(0, 1, 0), "zero count");
+            !game.is_move_valid(mv(Tableau1, Run1, Tableau1)),
-        assert!(!game.is_move_valid(0, 10, 1), "destination out of range");
+            "self-move"
-        assert!(!game.is_move_valid(10, 0, 1), "source out of range");
+        );
-        assert!(!game.is_move_valid(0, 1, 2), "count exceeds run");
+        assert!(
+            !game.is_move_valid(mv(Tableau1, Run2, Tableau2)),
+            "count exceeds run"
+        );
     }
 
     // -- dealing from stock -------------------------------------------------
@@ -752,31 +959,35 @@ mod tests {
     #[test]
     fn deal_requires_stock_and_no_empty_pile() {
         let stock = vec![card(Suit::Spades, Rank::Ace); 10];
-        let game = SpiderGame::from_test_layout(junk_layout(), stock.clone(), 0);
+        let game = Spider::from_test_layout(junk_layout(), stock.clone(), 0);
         assert!(game.is_deal_valid());
 
         let mut with_gap = junk_layout();
         with_gap[3].1.clear();
-        let game = SpiderGame::from_test_layout(with_gap, stock, 0);
+        let game = Spider::from_test_layout(with_gap, stock, 0);
         assert!(!game.is_deal_valid(), "empty pile blocks the deal");
 
-        let game = SpiderGame::from_test_layout(junk_layout(), Vec::new(), 0);
+        let game = Spider::from_test_layout(junk_layout(), Vec::new(), 0);
         assert!(!game.is_deal_valid(), "empty stock blocks the deal");
     }
 
     #[test]
     fn deal_puts_one_card_on_every_pile() {
         let mut state = SpiderGameState::new_with_suits(3, SpiderSuits::Two);
-        let before: Vec<usize> = (0..SPIDER_TABLEAUS)
+        let before: Vec<usize> = SpiderTableau::ALL
-            .map(|i| state.game().tableau_face_up(i).len())
+            .into_iter()
+            .map(|tableau| state.game().tableau_face_up_cards(tableau).len())
             .collect();
         state
             .apply_instruction(SpiderInstruction::Deal)
             .expect("deal is legal on a fresh game");
-        for (index, previous) in before.iter().enumerate() {
+        for (tableau, previous) in SpiderTableau::ALL.into_iter().zip(before) {
-            assert_eq!(state.game().tableau_face_up(index).len(), previous + 1);
+            assert_eq!(
+                state.game().tableau_face_up_cards(tableau).len(),
+                previous + 1
+            );
         }
-        assert_eq!(state.game().stock_len(), STOCK_SIZE - SPIDER_TABLEAUS);
+        assert_eq!(state.game().stock().len(), STOCK_SIZE - SPIDER_TABLEAUS);
     }
 
     #[test]
@@ -787,7 +998,7 @@ mod tests {
                 .apply_instruction(SpiderInstruction::Deal)
                 .expect("five deals must all be legal on untouched piles");
         }
-        assert_eq!(state.game().stock_len(), 0);
+        assert_eq!(state.game().stock().len(), 0);
         assert!(matches!(
             state.apply_instruction(SpiderInstruction::Deal),
             Err(MoveError::RuleViolation(_))
@@ -799,30 +1010,26 @@ mod tests {
     #[test]
     fn completing_a_run_removes_it_and_flips_the_card_beneath() {
         let mut layout = empty_layout();
-        // Pile 0: one face-down card under K..2 of spades; the ace
+        // Pile 1: one face-down card under K..2 of spades; the ace
-        // arrives from pile 1.
+        // arrives from pile 2.
         let mut run = full_run(Suit::Spades);
         let ace = run.pop().unwrap_or(card(Suit::Spades, Rank::Ace));
         layout[0] = (vec![card(Suit::Hearts, Rank::Nine)], run);
         layout[1].1 = vec![ace];
-        let game = SpiderGame::from_test_layout(layout, Vec::new(), 0);
+        let game = Spider::from_test_layout(layout, Vec::new(), 0);
         let mut state = SpiderGameState::from_test_game(game, SpiderSuits::One);
 
         state
-            .apply_instruction(SpiderInstruction::Move {
+            .apply_instruction(SpiderInstruction::Move(mv(Tableau2, Run1, Tableau1)))
-                from: 1,
-                to: 0,
-                count: 1,
-            })
             .expect("ace onto two completes the run");
 
         assert_eq!(state.game().completed_runs(), 1);
         assert_eq!(
-            state.game().tableau_face_up(0),
+            state.game().tableau_face_up_cards(Tableau1),
             &[card(Suit::Hearts, Rank::Nine)],
             "run removed and the buried card flipped face-up"
         );
-        assert!(state.game().tableau_face_up(1).is_empty());
+        assert!(state.game().tableau_face_up_cards(Tableau2).is_empty());
     }
 
     #[test]
@@ -832,16 +1039,12 @@ mod tests {
         let ace = run.pop().unwrap_or(card(Suit::Spades, Rank::Ace));
         layout[0].1 = run;
         layout[1].1 = vec![ace];
-        let game = SpiderGame::from_test_layout(layout, Vec::new(), TOTAL_RUNS - 1);
+        let game = Spider::from_test_layout(layout, Vec::new(), TOTAL_RUNS - 1);
         let mut state = SpiderGameState::from_test_game(game, SpiderSuits::One);
 
         assert!(!state.is_won());
         state
-            .apply_instruction(SpiderInstruction::Move {
+            .apply_instruction(SpiderInstruction::Move(mv(Tableau2, Run1, Tableau1)))
-                from: 1,
-                to: 0,
-                count: 1,
-            })
             .expect("winning move is legal");
         assert!(state.is_won());
         assert!(matches!(
@@ -882,11 +1085,7 @@ mod tests {
     #[test]
     fn rule_violation_surfaces_move_error() {
         let mut state = SpiderGameState::new_with_suits(9, SpiderSuits::One);
-        let result = state.apply_instruction(SpiderInstruction::Move {
+        let result = state.apply_instruction(SpiderInstruction::Move(mv(Tableau1, Run1, Tableau1)));
-            from: 0,
-            to: 0,
-            count: 1,
-        });
         assert!(matches!(result, Err(MoveError::RuleViolation(_))));
     }
 
@@ -905,6 +1104,13 @@ mod tests {
             assert!(state.game().is_instruction_valid(&config, instruction));
         }
     }
+
+    #[test]
+    fn instruction_iter_walks_the_full_space_once() {
+        // 10 sources × 13 run lengths × 10 destinations, plus Deal.
+        let count = SpiderIter::new().count();
+        assert_eq!(count, SPIDER_TABLEAUS * RUN_LEN * SPIDER_TABLEAUS + 1);
+    }
 }
 
 #[cfg(test)]
@@ -915,11 +1121,15 @@ mod proptests {
     /// Total cards across tableaus + stock + removed runs must always
     /// equal 104, and every generated instruction must validate — for
     /// any seed, difficulty, and random walk through legal moves.
-    fn card_conservation(game: &SpiderGame) -> usize {
+    fn card_conservation(game: &Spider) -> usize {
-        let on_piles: usize = (0..SPIDER_TABLEAUS)
+        let on_piles: usize = SpiderTableau::ALL
-            .map(|i| game.tableau_face_up(i).len() + game.tableau_face_down(i).len())
+            .into_iter()
+            .map(|tableau| {
+                game.tableau_face_up_cards(tableau).len()
+                    + game.tableau_face_down_cards(tableau).len()
+            })
             .sum();
-        on_piles + game.stock_len() + usize::from(game.completed_runs()) * RUN_LEN
+        on_piles + game.stock().len() + usize::from(game.completed_runs()) * RUN_LEN
     }
 
     proptest! {