Hub character swapping, XP percentage, passive health regeneration

Character swapping is hub-only, and refused by the SERVER rather than merely
greyed out in the menu. Allowing it inside a dungeon would be an instant,
uninterruptible exit from danger -- strictly better than the one-second escape
channel, which would make that channel pointless. Creating a character in a
dungeon is refused for the same reason. Both are covered by diag_progression.

Health regenerates at 0.5% of MAXIMUM per second. A percentage rather than a
flat rate so it does not become irrelevant at level 15: a capped character
regains 1.2 hp/s against a level 1's 0.5, and both take about 200 seconds to
heal from nothing. No out-of-combat gate -- at this rate it cannot out-heal
anything actually shooting at you, and a trickle that never stops is easier to
reason about than a timer players have to learn. A fractional carry is needed
because a tick heals well under one hit point, so truncating each tick would
heal exactly nothing; there is a test for that specifically.

The XP bar now states the percentage and the level it leads to, since a bar
answers "how far" vaguely and a number answers it exactly.

Recorded the two Stage 3 answers: 4 inventory slots, and the boss's food item
is player-instanced now so the mechanism gets exercised rather than deferred.

Writing the swap guard's test caught my own mistake: the first version created
its spare character through the store, which has no opinion about where you
are, so it bypassed the guard it was meant to prove and left a stray character
behind that broke a later assertion.

200 tests. check.sh, test.sh, smoke.sh and both diagnostics pass.

src/ui/character_select.gd

@@ -8,12 +8,14 @@ extends CanvasLayer
 
 signal select_requested(character_id: String)
 signal create_requested(character_name: String)
+signal closed
 
 var _list: VBoxContainer
 var _name_field: LineEdit
 var _create_button: Button
 var _status: Label
 var _title: Label
+var _close_button: Button
 var _known: Array[Dictionary] = []
 var _selected: String = ""
 
@@ -63,6 +65,11 @@ func _ready() -> void:
 	_create_button.pressed.connect(_on_create)
 	row.add_child(_create_button)
 
+	_close_button = Button.new()
+	_close_button.text = "Back to the hub"
+	_close_button.pressed.connect(func() -> void: closed.emit())
+	panel.add_child(_close_button)
+
 	_status = Label.new()
 	_status.add_theme_font_size_override("font_size", 12)
 	_status.add_theme_color_override("font_color", Color(1.0, 0.6, 0.5))
@@ -144,3 +151,9 @@ func _row_for(c: Dictionary) -> Control:
 	play.pressed.connect(func() -> void: select_requested.emit(String(c["id"])))
 	row.add_child(play)
 	return row
+
+
+## Whether the player may dismiss this screen. False when they have nothing to
+## play, in which case there is nowhere to dismiss it to.
+func set_dismissible(can_close: bool) -> void:
+	_close_button.visible = can_close

src/ui/game_menu.gd

@@ -9,9 +9,11 @@ extends CanvasLayer
 signal resumed
 signal return_to_hub_requested
 signal disconnect_requested
+signal characters_requested
 
 var _panel: VBoxContainer
 var _hub_button: Button
+var _characters_button: Button
 var _disconnect_button: Button
 var _note: Label
 var _in_dungeon: bool = false
@@ -55,6 +57,9 @@ func _ready() -> void:
 	_hub_button = _button("Return to hub", func() -> void:
 		return_to_hub_requested.emit()
 		close())
+	_characters_button = _button("Change character", func() -> void:
+		characters_requested.emit()
+		close())
 	_button("Resume", func() -> void: close())
 	_disconnect_button = _button("Disconnect to menu", func() -> void:
 		disconnect_requested.emit()
@@ -108,6 +113,12 @@ func set_in_dungeon(in_dungeon: bool) -> void:
 		return
 	_in_dungeon = in_dungeon
 	_hub_button.disabled = not in_dungeon
+	# Swapping is hub-only, and the server enforces that regardless of what
+	# this button does -- but a disabled button explains the rule, where a
+	# refusal after the fact just looks broken.
+	_characters_button.disabled = in_dungeon
+	_characters_button.text = "Change character  (hub only)" if in_dungeon \
+		else "Change character"
 	if in_dungeon:
 		# Disconnecting is not an escape: the server keeps the body in the
 		# world, channelling out, for the same second the escape button costs.

src/ui/hud.gd

@@ -156,10 +156,17 @@ func _draw_xp_bar(at: Vector2) -> void:
 	if who.is_empty():
 		return
 	var level := int(who["level"])
-	var progress: float = who["progress"] if level < Progression.MAX_LEVEL else 1.0
-	_canvas.draw_rect(Rect2(at, Vector2(BAR_W, 4.0)), Color(0.1, 0.12, 0.18))
-	_canvas.draw_rect(Rect2(at, Vector2(BAR_W * progress, 4.0)),
-		Color(0.6, 0.55, 1.0) if level < Progression.MAX_LEVEL else Color(1.0, 0.85, 0.4))
+	var capped := level >= Progression.MAX_LEVEL
+	var progress: float = 1.0 if capped else who["progress"]
+	var tint := Color(1.0, 0.85, 0.4) if capped else Color(0.6, 0.55, 1.0)
+	_canvas.draw_rect(Rect2(at, Vector2(BAR_W, 5.0)), Color(0.1, 0.12, 0.18))
+	_canvas.draw_rect(Rect2(at, Vector2(BAR_W * progress, 5.0)), tint)
+	# The number as well as the bar: "how far to the next level" is a question
+	# a bar answers vaguely and a percentage answers exactly.
+	var text := "MAX" if capped else "%d%% to level %d" % [
+		int(floor(progress * 100.0)), level + 1]
+	_canvas.draw_string(ThemeDB.fallback_font, at + Vector2(BAR_W + 10.0, 6.0),
+		text, HORIZONTAL_ALIGNMENT_LEFT, -1, 12, tint)
 
 
 ## Shown after the boss dies, so the victory lap has a visible clock on it.