fix(engine): double-click moves exactly the clicked run (#158)

Double-click/tap auto-move previously tried the run's top card alone
before the full run headed by the clicked card, so a top card with a
foundation move hijacked the intended whole-stack move. Both handlers
now share auto_move_for_run: a lone top card goes foundation-first, a
multi-card run moves whole to a tableau or not at all. The double-click
key is now the clicked card, so two clicks on different cards of the
same stack no longer register as a double-click.

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

solitaire_engine/src/input_plugin/tests.rs

@@ -429,6 +429,118 @@ fn best_tableau_destination_for_stack_returns_none_when_no_legal_move() {
     );
 }
 
+// -----------------------------------------------------------------------
+// auto_move_for_run pure-function tests (issue #158)
+// -----------------------------------------------------------------------
+//
+// These need real positions — `can_move_cards` validates against the live
+// session, not the `set_test_*` overlays. Seeds 51 and 145 both deal an
+// Ace and its Two on tableau tops plus an opposite-color Three elsewhere,
+// letting two moves build a face-up [Three, Two] run whose top card is
+// foundation-eligible (the bait the pre-#158 code would take).
+
+/// Deal `seed`, send the Ace on tableau 1 to its foundation, then stack the
+/// matching Two from `two_from` onto the opposite-color Three on `run_on`.
+/// Returns the game with a 2-card face-up run on `run_on`.
+fn deal_run_with_foundation_bait(seed: u64, two_from: Tableau, run_on: Tableau) -> GameState {
+    let mut game = GameState::new(seed, DrawStockConfig::DrawOne);
+    let (ace, _) = game
+        .pile(KlondikePile::Tableau(Tableau::Tableau1))
+        .last()
+        .cloned()
+        .expect("seed deals a card on tableau 1");
+    let foundation = best_destination(&ace, &game).expect("ace has a foundation home");
+    game.move_cards(KlondikePile::Tableau(Tableau::Tableau1), foundation, 1)
+        .expect("ace moves to foundation");
+    game.move_cards(
+        KlondikePile::Tableau(two_from),
+        KlondikePile::Tableau(run_on),
+        1,
+    )
+    .expect("two stacks onto three");
+    game
+}
+
+#[test]
+fn auto_move_for_run_moves_exact_clicked_run_not_top_card() {
+    let game = deal_run_with_foundation_bait(51, Tableau::Tableau6, Tableau::Tableau5);
+    let run_pile = KlondikePile::Tableau(Tableau::Tableau5);
+    let cards = game.pile(run_pile);
+    let (top, _) = cards.last().cloned().expect("run pile has cards");
+    let (clicked, _) = cards[cards.len() - 2].clone();
+
+    // The bait: the lone top card has a foundation move available.
+    assert!(
+        matches!(
+            best_destination(&top, &game),
+            Some(KlondikePile::Foundation(_))
+        ),
+        "precondition: run top card must be foundation-eligible"
+    );
+
+    // Clicking the run base must move exactly the 2-card run to a tableau.
+    match auto_move_for_run(&clicked, &run_pile, &game, 2) {
+        Some((KlondikePile::Tableau(dest), 2)) => assert_ne!(dest, Tableau::Tableau5),
+        other => panic!("expected a whole-run tableau move, got {other:?}"),
+    }
+}
+
+#[test]
+fn auto_move_for_run_rejects_when_clicked_run_cannot_move() {
+    let game = deal_run_with_foundation_bait(145, Tableau::Tableau4, Tableau::Tableau7);
+    let run_pile = KlondikePile::Tableau(Tableau::Tableau7);
+    let cards = game.pile(run_pile);
+    let (top, _) = cards.last().cloned().expect("run pile has cards");
+    let (clicked, _) = cards[cards.len() - 2].clone();
+
+    assert!(
+        matches!(
+            best_destination(&top, &game),
+            Some(KlondikePile::Foundation(_))
+        ),
+        "precondition: run top card must be foundation-eligible"
+    );
+
+    // The 2-card run has no legal home — the top card's foundation move
+    // must NOT be taken as a substitute.
+    assert_eq!(
+        auto_move_for_run(&clicked, &run_pile, &game, 2),
+        None,
+        "an immovable clicked run must not fall back to a top-card move"
+    );
+}
+
+#[test]
+fn auto_move_for_run_single_card_prefers_foundation() {
+    // Seed 51 after the Ace reaches the foundation: the Two on tableau 6
+    // is a lone face-up card that could go to the foundation OR onto the
+    // Three on tableau 5. Foundation must win.
+    let mut game = GameState::new(51, DrawStockConfig::DrawOne);
+    let (ace, _) = game
+        .pile(KlondikePile::Tableau(Tableau::Tableau1))
+        .last()
+        .cloned()
+        .expect("seed 51 deals a card on tableau 1");
+    let foundation = best_destination(&ace, &game).expect("ace has a foundation home");
+    game.move_cards(KlondikePile::Tableau(Tableau::Tableau1), foundation, 1)
+        .expect("ace moves to foundation");
+
+    let two_pile = KlondikePile::Tableau(Tableau::Tableau6);
+    let (two, _) = game.pile(two_pile).last().cloned().expect("two on top");
+    assert!(
+        game.can_move_cards(&two_pile, &KlondikePile::Tableau(Tableau::Tableau5), 1),
+        "precondition: a tableau destination also exists"
+    );
+
+    assert!(
+        matches!(
+            auto_move_for_run(&two, &two_pile, &game, 1),
+            Some((KlondikePile::Foundation(_), 1))
+        ),
+        "a lone top card still prefers the foundation"
+    );
+}
+
 // -----------------------------------------------------------------------
 // Task #28 — find_hint pure-function tests
 // -----------------------------------------------------------------------