adventure: route round-end concentration kill through enemyDown (P8)

The T6 Valdris phylactery rebirth (and the pre-existing survive_at_1
one-shot) live in enemyDown, on the premise that it is the single death
chokepoint. It isn't: the round-end concentration pulse ended the fight
on a raw enemyHP<=0 read, so a cleric's Spirit Guardians landing the
lethal blow robbed a revive-armed boss of its rebirth — exactly the
cleric-party arm P8 is tuned around. Route that win-check through
enemyDown so the boss gets its chance to stand back up. Regression test
covers both the armed (revives) and charge-less (still wins) paths.

Claude-Session: https://claude.ai/code/session_0156WqjgsbmSY2U8eQ3Kkb1s

internal/plugin/combat_turn_engine.go

@@ -842,7 +842,12 @@ func (te *turnEngine) stepRoundEnd() {
 			Round: st.round, Phase: CombatPhaseRoundEnd, Actor: "player", Action: "concentration_tick",
 			Damage: st.concentrationDmg, PlayerHP: st.playerHP, EnemyHP: st.enemyHP, Seat: i,
 		})
-		if st.enemyHP <= 0 {
+		// Route the kill through enemyDown, not a raw HP read: a boss that cheats
+		// death (survive_at_1) or holds a phylactery rebirth (T6 Valdris) must get
+		// that chance even when the lethal blow is a lingering concentration pulse.
+		// enemyDown restores its HP and returns false, so the next seat's pulse (or
+		// the following round) resolves against the revived pool.
+		if enemyDown(st, CombatPhaseRoundEnd) {
 			te.finish(CombatStatusWon)
 			return
 		}

internal/plugin/combat_turn_party_test.go

@@ -275,3 +275,57 @@ func TestTurnEngine_CommitPersistsSeatZeroNotTheCursor(t *testing.T) {
 		t.Error("seat 1's consumed Lucky reroll leaked onto the session row")
 	}
 }
+
+// A lingering concentration pulse that lands the killing blow must still give a
+// revive-armed boss (survive_at_1 / T6 Valdris's phylactery rebirth) its chance
+// to stand back up — the round-end tick routes the kill through enemyDown, not a
+// raw enemyHP<=0 read. Regression for the concentration-bypass gap found in the
+// P8 Layer-2 review.
+func TestTurnEngine_ConcentrationKillHonorsRebirth(t *testing.T) {
+	// A charged rebirth: the pulse drops the enemy, a charge spends, it revives.
+	sess := turnSession(CombatPhaseRoundEnd, 500, 30)
+	p := basePlayer()
+	e := baseEnemy()
+	te := resumeTurnEngine(sess, []*Combatant{&p}, &e, combatSessionStepRNG(sess, enemySeat))
+	te.st.concentrationDmg = 100 // lethal against 30 HP
+	te.st.enemyReviveCharges = 1
+	te.st.enemyReviveHP = 40
+	if _, err := te.step(PlayerAction{}); err != nil {
+		t.Fatal(err)
+	}
+	te.commit()
+
+	if !sess.IsActive() {
+		t.Fatalf("a concentration kill ended the fight (%q) while a rebirth charge was armed", sess.Status)
+	}
+	if sess.EnemyHP != 40 {
+		t.Errorf("revived EnemyHP = %d, want the 40-HP revive pool", sess.EnemyHP)
+	}
+	if sess.Statuses.EnemyReviveCharges != 0 {
+		t.Errorf("post-revive charges = %d, want 0 (one spent)", sess.Statuses.EnemyReviveCharges)
+	}
+	rebirths := 0
+	for _, ev := range sess.TurnLog {
+		if ev.Action == "phylactery_rebirth" {
+			rebirths++
+		}
+	}
+	if rebirths != 1 {
+		t.Errorf("phylactery_rebirth events = %d, want 1", rebirths)
+	}
+
+	// With no charge left, the same pulse ends the fight cleanly (the win path
+	// is not broken by the enemyDown routing).
+	mortal := turnSession(CombatPhaseRoundEnd, 500, 30)
+	p2 := basePlayer()
+	e2 := baseEnemy()
+	te2 := resumeTurnEngine(mortal, []*Combatant{&p2}, &e2, combatSessionStepRNG(mortal, enemySeat))
+	te2.st.concentrationDmg = 100
+	if _, err := te2.step(PlayerAction{}); err != nil {
+		t.Fatal(err)
+	}
+	te2.commit()
+	if mortal.Status != CombatStatusWon {
+		t.Errorf("charge-less concentration kill status = %q, want %q", mortal.Status, CombatStatusWon)
+	}
+}