fix(engine,wasm,web): detect no-legal-moves correctly and surface banner

Engine: replace broken has_legal_moves loop (which checked buried
mid-column cards without sequence validation) with a delegation to
possible_instructions(), mirroring the hint system's logic exactly.

WASM: add has_moves: bool to GameSnapshot, computed in snap() using the
same stock/waste/possible_instructions check so the web client gets the
flag in every state update at no extra round-trip cost.

Web: show a non-blocking no-moves banner (slide-up toast) with Undo and
New Game actions when has_moves is false and the game is not won. Banner
hides automatically once a move restores legal play (e.g. after undo).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_engine/src/game_plugin.rs

@@ -1045,9 +1045,7 @@ pub fn record_replay_on_win(
 /// previous heuristic incorrectly did (Quat hit this with 4 cards
 /// remaining and the game just sat there).
 pub fn has_legal_moves(game: &GameState) -> bool {
-    use solitaire_core::card::Card;
     use solitaire_core::pile::PileType;
-    use solitaire_core::rules::{can_place_on_foundation, can_place_on_tableau};
 
     // Drawing from a non-empty stock, and recycling a non-empty waste back to
     // stock, are always legal moves in standard Klondike (unlimited recycles).
@@ -1058,40 +1056,14 @@ pub fn has_legal_moves(game: &GameState) -> bool {
         return true;
     }
 
-    // Stock and waste exhausted — check whether any visible card can be placed.
-    let mut sources: Vec<Card> = Vec::new();
-    // Top waste card (waste is empty here, but included for completeness).
-    if let Some(p) = game.piles.get(&PileType::Waste)
-        && let Some(top) = p.cards.last()
-    {
-        sources.push(top.clone());
-    }
-    // Any face-up card in a tableau column can be the base of a movable run.
-    for i in 0..7_usize {
-        if let Some(t) = game.piles.get(&PileType::Tableau(i)) {
-            for card in t.cards.iter().filter(|c| c.face_up) {
-                sources.push(card.clone());
-            }
-        }
-    }
-
-    for card in &sources {
-        for slot in 0..4_u8 {
-            if let Some(dest) = game.piles.get(&PileType::Foundation(slot))
-                && can_place_on_foundation(card, dest)
-            {
-                return true;
-            }
-        }
-        for i in 0..7_usize {
-            if let Some(dest) = game.piles.get(&PileType::Tableau(i))
-                && can_place_on_tableau(card, dest)
-            {
-                return true;
-            }
-        }
-    }
-    false
+    // Stock and waste both exhausted — delegate to the authoritative move
+    // enumeration in core, which validates tableau sequence structure and
+    // foundation placement correctly. The previous hand-rolled loop only
+    // checked can_place_on_tableau(card, dest) for individual face-up cards
+    // without verifying that the cards above them form a valid alternating run,
+    // causing false positives when a useful-looking card was buried under an
+    // invalid sequence.
+    !game.possible_instructions().is_empty()
 }
 
 /// After each `StateChangedEvent`, check if the game has no legal moves.

solitaire_server/web/game.css

@@ -355,6 +355,67 @@ main {
     animation: illegal-shake 320ms ease;
 }
 
+/* ── No-moves banner ─────────────────────────────────────────────────── */
+
+#no-moves-banner {
+    position: fixed;
+    bottom: 24px;
+    left: 50%;
+    transform: translateX(-50%);
+    z-index: 900;
+    animation: slide-up 240ms ease;
+}
+
+#no-moves-banner.hidden { display: none; }
+
+.no-moves-card {
+    background: var(--panel);
+    border: 1px solid rgba(255,255,255,0.15);
+    border-radius: 12px;
+    padding: 20px 32px;
+    text-align: center;
+    display: flex;
+    flex-direction: column;
+    gap: 12px;
+    box-shadow: 0 8px 32px rgba(0,0,0,0.7);
+    min-width: 300px;
+}
+
+.no-moves-title {
+    font-size: 18px;
+    font-weight: 700;
+    color: var(--accent);
+}
+
+.no-moves-detail {
+    font-size: 13px;
+    color: var(--text-muted);
+    margin: 0;
+    line-height: 1.5;
+}
+
+.no-moves-actions {
+    display: flex;
+    gap: 10px;
+    justify-content: center;
+    margin-top: 4px;
+}
+
+.no-moves-actions button.secondary {
+    background: transparent;
+    border: 1px solid rgba(255,255,255,0.2);
+    color: var(--text-muted);
+}
+
+.no-moves-actions button.secondary:hover {
+    background: rgba(255,255,255,0.05);
+}
+
+@keyframes slide-up {
+    from { opacity: 0; transform: translateX(-50%) translateY(12px); }
+    to   { opacity: 1; transform: translateX(-50%) translateY(0); }
+}
+
 /* ── Foundation slot suit hints ──────────────────────────────────────────── */
 
 .slot-hint {

solitaire_server/web/game.html

@@ -77,6 +77,17 @@
         </div>
     </div>
 
+    <div id="no-moves-banner" class="hidden">
+        <div class="no-moves-card">
+            <div class="no-moves-title">No Moves Available</div>
+            <p class="no-moves-detail">No legal moves remain. Undo to go back or start a new game.</p>
+            <div class="no-moves-actions">
+                <button id="btn-no-moves-undo">↩ Undo</button>
+                <button id="btn-no-moves-new" class="secondary">↺ New Game</button>
+            </div>
+        </div>
+    </div>
+
     <script type="module" src="/web/game.js"></script>
 </body>
 </html>

solitaire_server/web/game.js

@@ -141,6 +141,7 @@ const winScore   = document.getElementById("win-score");
 const winMoves      = document.getElementById("win-moves");
 const winTime       = document.getElementById("win-time");
 const btnWinNew     = document.getElementById("btn-win-new");
+const noMovesBanner = document.getElementById("no-moves-banner");
 
 // ── Scale to fit ─────────────────────────────────────────────────────────────
 // Scales #card-area to fill #board without overflowing either dimension.
@@ -391,9 +392,12 @@ function render(s) {
         clearSave();
         stopTimer();
         if (acTimer) { clearInterval(acTimer); acTimer = null; }
+        if (noMovesBanner) noMovesBanner.classList.add("hidden");
         showWin(s);
     } else {
         saveState();
+        const noMoves = !s.has_moves && !s.is_auto_completable;
+        if (noMovesBanner) noMovesBanner.classList.toggle("hidden", !noMoves);
     }
 }
 
@@ -479,6 +483,8 @@ function attachHandlers() {
     btnUndo.addEventListener("click", doUndo);
     btnBoardUndo.addEventListener("click", doUndo);
     btnNew.addEventListener("click", () => startGame(randomSeed()));
+    document.getElementById("btn-no-moves-undo")?.addEventListener("click", doUndo);
+    document.getElementById("btn-no-moves-new")?.addEventListener("click", () => startGame(randomSeed()));
     btnWinNew.addEventListener("click", () => startGame(randomSeed()));
     chkDraw3.addEventListener("change", () => {
         drawThree = chkDraw3.checked;

solitaire_wasm/src/lib.rs

@@ -241,6 +241,8 @@ pub struct GameSnapshot {
     pub move_count: u32,
     pub is_won: bool,
     pub is_auto_completable: bool,
+    /// `false` when stock, waste, and all pile-to-pile moves are exhausted.
+    pub has_moves: bool,
     pub undo_count: u32,
     /// Number of snapshots currently on the undo stack; 0 means undo is unavailable.
     pub undo_stack_len: usize,
@@ -279,11 +281,17 @@ impl SolitaireGame {
                 .map(|p| p.cards.iter().map(CardSnapshot::from).collect())
                 .unwrap_or_default()
         };
+        let has_moves = {
+            let stock_empty = self.game.piles.get(&PileType::Stock).is_none_or(|p| p.cards.is_empty());
+            let waste_empty = self.game.piles.get(&PileType::Waste).is_none_or(|p| p.cards.is_empty());
+            !stock_empty || !waste_empty || !self.game.possible_instructions().is_empty()
+        };
         GameSnapshot {
             score: self.game.score,
             move_count: self.game.move_count,
             is_won: self.game.is_won,
             is_auto_completable: self.game.is_auto_completable,
+            has_moves,
             undo_count: self.game.undo_count,
             undo_stack_len: self.game.undo_stack_len(),
             stock: cards(PileType::Stock),