feat(combat): forest concealment roll, only on Forest terrain

src/Domain/CombatEngine.php

@@ -15,6 +15,7 @@ final class CombatEngine
     public const CRIT_THRESHOLD = 95;
     public const DAMAGE_VARIANCE_MIN_PCT = 85;
     public const DAMAGE_VARIANCE_MAX_PCT = 115;
+    public const FOREST_CONCEALMENT_MISS_CHANCE = 15;
 
     public function move(MatchState $match, string $unitId, Position $destination): MatchState
     {
@@ -85,20 +86,17 @@ final class CombatEngine
             return $next->copy(actionLog: [...$next->actionLog, implode(' ', $logParts)]);
         }
 
-        // Forest concealment: independent 15% miss roll.
+        // Forest concealment: independent 15% miss roll after to-hit passes.
-        if ($match->battlefield->terrainAt($target->position)->movementCost() === 2) {
+        $targetTerrain = $match->battlefield->terrainAt($target->position);
-            // Forest and rough both have cost 2; only forest has concealment. Distinguish by name.
+        if ($targetTerrain === \BattleForge\Domain\Terrain::Forest) {
-            $terrainName = $match->battlefield->terrainAt($target->position)->name;
-            if ($terrainName === 'Forest') {
             $concealmentRoll = random_int(1, 100);
-                if ($concealmentRoll <= 15) {
+            if ($concealmentRoll <= self::FOREST_CONCEALMENT_MISS_CHANCE) {
                 $logParts[] = 'for 0 damage';
                 $logParts[] = '— miss — concealed';
                 $next = $match->withUnit($updatedAttacker);
                 return $next->copy(actionLog: [...$next->actionLog, implode(' ', $logParts)]);
             }
         }
-        }
 
         $isCrit = $roll >= self::CRIT_THRESHOLD;
         $base = max(1, ($attacker->attack + $attacker->attackBonus) - ($target->defense + $terrainDefense));

tests/Unit/Domain/CombatEngineTest.php

@@ -1656,4 +1656,85 @@ final class CombatEngineTest extends TestCase
         self::assertContains(19, $unique, 'three allies should cap at +30 flanking, threshold 19');
         self::assertNotContains(4, $unique, 'flanking should not exceed +30');
     }
+
+    public function testAttackForestDefenderCarriesConcealedMissOnLowRoll(): void
+    {
+        // Force a concealment miss: target is on forest. Run 200 attacks; the
+        // engine rolls the concealment die; we observe at least one log entry
+        // containing " — miss — concealed" and confirm the damage is 0.
+        $concealSeen = false;
+        for ($i = 0; $i < 200; $i += 1) {
+            $match = $this->freshMatch();
+            $matchArray = ScenarioSerializer::matchToArray($match);
+            $matchArray['units'][0]['position'] = ['x' => 0, 'y' => 0];
+            $matchArray['units'][0]['attack'] = 3;
+            $matchArray['units'][0]['defense'] = 0;
+            $matchArray['units'][1]['position'] = ['x' => 1, 'y' => 0];
+            $matchArray['units'][1]['attack'] = 1;
+            $matchArray['units'][1]['defense'] = 1;
+            // (no-op, kept for clarity)
+            $match = ScenarioSerializer::matchFromArray($matchArray);
+            // Stamp forest terrain on the target's tile.
+            $matchArray['battlefield']['terrain'] = ['1:0' => 'forest'];
+            $match = ScenarioSerializer::matchFromArray($matchArray);
+
+            // Brief uses 'm' for matchId; TurnToken requires 16+ lowercase hex chars.
+            // Use a valid matchId (the smallest deviation).
+            $matchId = '0123456789abcdef';
+            $token = TurnToken::issue('s', $matchId, 'alpha', 1, 0);
+            $req = $this->buildRequest($match, $token, [
+                'matchId' => $matchId,
+                'match' => $matchArray,
+                'attackerId' => 'alpha-1',
+                'targetId' => 'bravo-1',
+            ]);
+            $result = (new PostMatchAttack('s'))->handle($req, []);
+            $body = json_decode($result->body, true);
+            $log = $body['match']['actionLog'];
+            if (str_contains($log[0], ' — miss — concealed')) {
+                $concealSeen = true;
+                preg_match('/for (\d+) damage/', $log[0], $m);
+                self::assertSame('0', $m[1], 'concealed miss should record 0 damage');
+                break;
+            }
+        }
+        self::assertTrue($concealSeen, 'expected at least one concealed miss in 200 trials against a forest defender');
+    }
+
+    public function testAttackNonForestTerrainDoesNotRollConcealment(): void
+    {
+        // Same as above but target is on rough terrain (cost 2, no concealment).
+        // No log entry should contain " — concealed" in 200 trials.
+        $concealSeen = false;
+        for ($i = 0; $i < 200; $i += 1) {
+            $match = $this->freshMatch();
+            $matchArray = ScenarioSerializer::matchToArray($match);
+            $matchArray['units'][0]['position'] = ['x' => 0, 'y' => 0];
+            $matchArray['units'][0]['attack'] = 3;
+            $matchArray['units'][0]['defense'] = 0;
+            $matchArray['units'][1]['position'] = ['x' => 1, 'y' => 0];
+            $matchArray['units'][1]['attack'] = 1;
+            $matchArray['units'][1]['defense'] = 1;
+            $match = ScenarioSerializer::matchFromArray($matchArray);
+            $matchArray['battlefield']['terrain'] = ['1:0' => 'rough'];
+            $match = ScenarioSerializer::matchFromArray($matchArray);
+
+            $matchId = '0123456789abcdef';
+            $token = TurnToken::issue('s', $matchId, 'alpha', 1, 0);
+            $req = $this->buildRequest($match, $token, [
+                'matchId' => $matchId,
+                'match' => $matchArray,
+                'attackerId' => 'alpha-1',
+                'targetId' => 'bravo-1',
+            ]);
+            $result = (new PostMatchAttack('s'))->handle($req, []);
+            $body = json_decode($result->body, true);
+            $log = $body['match']['actionLog'];
+            if (str_contains($log[0], ' — concealed')) {
+                $concealSeen = true;
+                break;
+            }
+        }
+        self::assertFalse($concealSeen, 'rough terrain should never produce a concealed-miss log entry');
+    }
 }