Lobby barrel-smash reward + roll/slam barrel destruction

Bull's boulder roll now homes on and ploughs through lobby barrels, and
the slam shockwave bursts them within its radius. HUD tallies barrels on
load and fires a confetti "WOooOoW!" + two gold bonus HP pips when the
last one breaks; gates open from run state as fights are cleared.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

levels/run_state.gd

@@ -34,11 +34,20 @@ var pending_col: int = -1
 ## Debug override — when set, active_level() returns this regardless of map state.
 ## Set via the console `level` command; cleared on start_new_run().
 var debug_level_override: LevelDef = null
-## The lobby is an interstitial hub between fights, not a map node: the player is sent
-## here after clearing a level (go_to_lobby()) to move around freely before choosing the
-## next node. While set, active_level() serves the lobby; cleared once a node is picked
-## (select_node) or a fresh run begins.
+## The lobby is the hub the run starts and returns to: a walk-around room whose gates lead
+## into the fights. While set, active_level() serves the lobby; cleared once a gate is
+## entered (choose_level) and set again on a win (return_to_lobby).
 var enter_lobby: bool = false
+## Level picked at a lobby gate and being fought now — active_level() serves it while
+## enter_lobby is false. Null in the lobby itself.
+var lobby_choice: LevelDef = null
+## Ids of levels the player has cleared this run (StringName -> true). Drives which lobby
+## gates are open: the bear gate stays shut until the arena is beaten.
+var cleared: Dictionary = {}
+## Run-long bonus health (yellow pips) earned from lobby rewards. Persists across level
+## loads — the player reads it on spawn — and is capped so it can't stack past BONUS_HP_CAP.
+var bonus_hp: int = 0
+const BONUS_HP_CAP: int = 2
 
 # Level catalog. Every level shares the shell scene; what changes is the level module
 # (its geometry + spawners) and the opponent. The arena (matador wave, normal + boss
@@ -85,6 +94,8 @@ func active_level() -> LevelDef:
 		return debug_level_override
 	if enter_lobby:
 		return _lobby
+	if lobby_choice != null:
+		return lobby_choice
 	var n := node_at(pending_row, pending_col)
 	if n == null:
 		n = current_node()
@@ -115,7 +126,11 @@ func start_new_run() -> void:
 	pending_row = -1
 	pending_col = -1
 	debug_level_override = null
-	enter_lobby = false
+	# The run opens in the lobby hub; its gates lead into the fights.
+	enter_lobby = true
+	lobby_choice = null
+	cleared = {}
+	bonus_hp = 0
 	run_started.emit()
 
 
@@ -177,10 +192,42 @@ func select_node(node: MapNode) -> void:
 
 
 ## Send the player to the lobby hub instead of a fight — active_level() serves the lobby
-## until a node is picked. Called after clearing a level so the player lands in the lobby
-## rather than jumping straight to the next fight.
+## until a gate is entered.
 func go_to_lobby() -> void:
 	enter_lobby = true
+	lobby_choice = null
+
+
+## Enter the fight behind a lobby gate: active_level() serves it until the player wins and
+## returns to the lobby. Ignored for an unknown id.
+func choose_level(id: StringName) -> void:
+	var l := get_level(id)
+	if l == null:
+		return
+	enter_lobby = false
+	lobby_choice = l
+
+
+## Land back in the lobby after a win, banking the cleared level so its follow-on gates
+## open (clearing the arena unlocks the bear gate).
+func return_to_lobby() -> void:
+	if lobby_choice != null:
+		cleared[lobby_choice.id] = true
+	go_to_lobby()
+
+
+## Whether the bear gate should be open — the arena must be cleared first.
+func bear_gate_open() -> bool:
+	return cleared.has(&"arena")
+
+
+## Bank bonus health for the rest of the run, clamped to BONUS_HP_CAP. Returns how many
+## pips were actually added (0 once the cap is reached) so the HUD only heals the bull when
+## there's headroom — a repeat barrel clear still cheers but grants nothing.
+func add_bonus_hp(amount: int) -> int:
+	var before := bonus_hp
+	bonus_hp = clampi(bonus_hp + amount, 0, BONUS_HP_CAP)
+	return bonus_hp - before
 
 
 ## Commit the level just won: move the player onto the pending node (or leave them at the