fix(core): prevent bots from invading/attacking themselves (#3865) (#4014)

Resolves #4094

## Description:

In Free-For-All (FFA) mode where teams default to 0, player isOnSameTeam
checks returned false for oneself, allowing players to attack
themselves. Consequently, if a bot conquered the targeted tile between
queueing a transport ship action and its actual initialization, the
target became itself, causing the bot to execute a self-invasion.

This fix adds a reflexive check in PlayerImpl.ts's isFriendly method to
always treat oneself as friendly. It also adds a safety guard in
TransportShipExecution.ts's init method to abort ship execution if the
target has shifted to the attacker.

## Please complete the following:

- [X] I have added screenshots for all UI updates
- [X] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [X] I have added relevant tests to the test directory
- [X] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

barfires

src/core/execution/TransportShipExecution.ts

@@ -91,6 +91,11 @@ export class TransportShipExecution implements Execution {
       }
     }
 
+    if (this.target === this.attacker) {
+      this.active = false;
+      return;
+    }
+
     if (this.target.isPlayer() && !this.attacker.canAttackPlayer(this.target)) {
       this.active = false;
       return;

src/core/game/PlayerImpl.ts

@@ -776,6 +776,9 @@ export class PlayerImpl implements Player {
   }
 
   canDonateGold(recipient: Player): boolean {
+    if (recipient === this) {
+      return false;
+    }
     if (
       !this.isAlive() ||
       !recipient.isAlive() ||
@@ -803,6 +806,9 @@ export class PlayerImpl implements Player {
   }
 
   canDonateTroops(recipient: Player): boolean {
+    if (recipient === this) {
+      return false;
+    }
     if (
       !this.isAlive() ||
       !recipient.isAlive() ||
@@ -830,6 +836,9 @@ export class PlayerImpl implements Player {
   }
 
   donateTroops(recipient: Player, troops: number): boolean {
+    // Defense-in-depth: canDonateTroops already checks this, but guard here too
+    // to prevent self-donation if the method is called directly.
+    if (recipient === this) return false;
     if (troops <= 0) return false;
     const removed = this.removeTroops(troops);
     if (removed === 0) return false;
@@ -847,6 +856,9 @@ export class PlayerImpl implements Player {
   }
 
   donateGold(recipient: Player, gold: Gold): boolean {
+    // Defense-in-depth: canDonateGold already checks this, but guard here too
+    // to prevent self-donation if the method is called directly.
+    if (recipient === this) return false;
     if (gold <= 0n) return false;
     const removed = this.removeGold(gold);
     if (removed === 0n) return false;
@@ -969,6 +981,9 @@ export class PlayerImpl implements Player {
   }
 
   isFriendly(other: Player, treatAFKFriendly: boolean = false): boolean {
+    if (other === this) {
+      return true;
+    }
     if (other.isDisconnected() && !treatAFKFriendly) {
       return false;
     }

tests/Attack.test.ts

@@ -527,4 +527,19 @@ describe("Attack immunity", () => {
     constructionExecution(game, playerA, 0, 11, UnitType.AtomBomb, 3);
     expect(playerA.units(UnitType.AtomBomb)).toHaveLength(1);
   });
+
+  test("Should abort TransportShipExecution when target is the attacker itself", async () => {
+    // Wait for spawn immunity to end to ensure it doesn't prematurely abort the execution
+    waitForImmunityToEnd();
+
+    // playerA tries to send a transport ship targeting one of playerA's own tiles (spawn tile at 7, 0)
+    const selfTarget = game.ref(7, 0);
+    const exec = new TransportShipExecution(playerA, selfTarget, 10);
+    game.addExecution(exec);
+    game.executeNextTick();
+
+    // Verify it aborted immediately: active is false, and no transport ship unit spawned
+    expect(exec.isActive()).toBe(false);
+    expect(playerA.units(UnitType.TransportShip)).toHaveLength(0);
+  });
 });

tests/Donate.test.ts

@@ -239,3 +239,51 @@ describe("Donate Gold to a non ally", () => {
     expect(recipient.gold() >= recipientGoldBefore).toBe(true);
   });
 });
+
+describe("Self donation prevention", () => {
+  it("Should evaluate isFriendly(this) to true but disallow donating to self", async () => {
+    const game = await setup("ocean_and_land", {
+      infiniteGold: false,
+      infiniteTroops: false,
+      donateGold: true,
+      donateTroops: true,
+    });
+    const gameID: GameID = "game_id";
+
+    // Create a player with team=0/null (default/FFA)
+    const playerInfo = new PlayerInfo(
+      "player_self",
+      PlayerType.Human,
+      null,
+      "self_id",
+    );
+    game.addPlayer(playerInfo);
+
+    const player = game.player(playerInfo.id);
+    const spawnA = game.ref(0, 10);
+
+    game.addExecution(new SpawnExecution(gameID, playerInfo, spawnA));
+    game.executeNextTick();
+
+    // Assert player.isFriendly(player) === true
+    expect(player.isFriendly(player)).toBe(true);
+
+    // Assert canDonateGold and canDonateTroops return false for self
+    expect(player.canDonateGold(player)).toBe(false);
+    expect(player.canDonateTroops(player)).toBe(false);
+
+    // Try executing DonateGoldExecution and DonateTroopsExecution on self
+    player.addGold(1000n);
+    player.addTroops(1000);
+    const goldBefore = player.gold();
+    const troopsBefore = player.troops();
+
+    game.addExecution(new DonateGoldExecution(player, player.id(), 500));
+    game.addExecution(new DonateTroopsExecution(player, player.id(), 500));
+    game.executeNextTick();
+
+    // Verify no changes occurred to gold or troops (execution failed/aborted)
+    expect(player.gold()).toBeGreaterThanOrEqual(goldBefore);
+    expect(player.troops()).toBeGreaterThanOrEqual(troopsBefore);
+  });
+});