Fix AI eval thread races (timeout cancellation, parallel mustAttack Combat mutation) (#11161)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: Blackvipe99

forge-ai/src/main/java/forge/ai/AiAttackController.java

@@ -940,7 +940,12 @@ && isEffectiveAttacker(ai, attacker, combat, finalDefender)) {
                         }
                     }
                     if (mustAttackDef != null) {
-                        combat.addAttacker(attacker, mustAttackDef);
+                        // combat is shared across these parallel futures and its attacker
+                        // multimap is not thread-safe; unsynchronized addAttacker calls
+                        // collide (ConcurrentModificationException, dropped attackers)
+                        synchronized (combat) {
+                            combat.addAttacker(attacker, mustAttackDef);
+                        }
                         attackersLeft.remove(attacker);
                         numForcedAttackers.incrementAndGet();
                     }

forge-ai/src/main/java/forge/ai/AiController.java

@@ -98,7 +98,7 @@ public class AiController {
     private int lastAttackAggression;
     private boolean useLivingEnd;
     private List<SpellAbility> skipped;
-    private boolean timeoutReached;
+    private volatile boolean timeoutReached;
 
     public AiController(final Player computerPlayer, final Game game0) {
         player = computerPlayer;
@@ -1601,7 +1601,7 @@ private SpellAbility chooseSpellAbilityToPlayFromList(final List<SpellAbility> a
                     continue;
                 }
 
-                if (timeoutReached) {
+                if (timeoutReached || Thread.currentThread().isInterrupted()) {
                     timeoutReached = false;
                     break;
                 }
@@ -1681,16 +1681,36 @@ else if (!sa.getHostCard().isPermanent() && sa.canCastTiming(player)
         try {
             return future.get(game.getAITimeout(), TimeUnit.SECONDS);
         } catch (InterruptedException | ExecutionException | TimeoutException e) {
+            e.printStackTrace();
+            if (e instanceof TimeoutException) {
+                // log where the eval thread currently is - each timeout doubles as a
+                // profiler sample for diagnosing remaining AI slowdowns from user logs
+                StringBuilder sb = new StringBuilder("AI eval thread at timeout:");
+                StackTraceElement[] evalStack = t.getStackTrace();
+                for (int i = 0; i < Math.min(30, evalStack.length); i++) {
+                    sb.append("\n\tat ").append(evalStack[i]);
+                }
+                System.out.println(sb);
+            }
+            // ask the eval thread to exit at the next SpellAbility check first: a brutal
+            // Thread.stop() mid-evaluation can leave partially mutated shared state behind
+            timeoutReached = true;
+            future.cancel(true);
             try {
-                e.printStackTrace();
-                t.stop();
-            } catch (UnsupportedOperationException | NoSuchMethodError ex) {
-                // Stop support: dropped by Android and Java 20 / 26 removed it completely - so sadly thread will keep running
-                timeoutReached = true;
-                future.cancel(true);
-                // TODO wait a few more seconds to try and exit at a safe point before letting the engine continue
-                // TODO mark some as skipped to increase chance to find something playable next priority
+                t.join(500);
+            } catch (InterruptedException ie) {
+                Thread.currentThread().interrupt();
+            }
+            if (t.isAlive()) {
+                // last resort, see #8302: the eval thread may be stuck inside a single
+                // evaluation or an infinite loop and never reach the cooperative exit
+                try {
+                    t.stop();
+                } catch (UnsupportedOperationException | NoSuchMethodError ex) {
+                    // Stop support: dropped by Android and Java 20 / 26 removed it completely - so sadly thread will keep running
+                }
             }
+            // TODO mark some as skipped to increase chance to find something playable next priority
             return null;
         }
     }