feat(@projects/@magic-civilization): ✅ improve land tile handling for demo

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

src/game/engine/scenes/tests/gameplay_arc_proof.gd

@@ -88,8 +88,14 @@ func _ready() -> void:
 
 	_p1 = GameState.players[0] as PlayerScript
 	_p2 = GameState.players[1] as PlayerScript
-	_p1_pos = _p1.units[0].position
-	_p2_pos = _p2.units[0].position
+	# Honour FORBIDDEN_BIOMES — relocate any founder that the harness dropped
+	# onto ocean/coast/mountains to the nearest land tile so cities never
+	# get founded on water in the demo (matches the production game's
+	# `mc-mapgen::spawn_box` gate). See the user-reported issue.
+	_p1_pos = _find_land_tile_near(_p1.units[0].position, 12)
+	_p2_pos = _find_land_tile_near(_p2.units[0].position, 12)
+	_p1.units[0].position = _p1_pos
+	_p2.units[0].position = _p2_pos
 
 	_setup_renderers()
 	_setup_camera_fit()
@@ -131,8 +137,18 @@ func _ready() -> void:
 	_c1.set_population(7)
 	await _capture("07_capital_pop7", "focus", _p1_pos, 6.0)
 
-	# Add placed buildings around the capital
-	var ring1: Array[Vector2i] = _hex_ring(_p1_pos, 1)
+	# Add placed buildings around the capital. Filter the ring to land
+	# tiles only so the building icons never overlap ocean/coast hexes —
+	# the visual demo should respect the same constraints the production
+	# city-tile picker enforces (mc-city::tile_picker rejects water tiles).
+	var ring1: Array[Vector2i] = _filter_land(_hex_ring(_p1_pos, 1))
+	if ring1.size() < 4:
+		# Top up from ring 2 if ring 1 had ocean/coast hexes pruned out.
+		var ring2_land: Array[Vector2i] = _filter_land(_hex_ring(_p1_pos, 2))
+		for r2: Vector2i in ring2_land:
+			if ring1.size() >= 4:
+				break
+			ring1.append(r2)
 	_c1.placed_buildings = {
 		"dwarf_granary": ring1[0] if ring1.size() > 0 else _p1_pos,
 		"dwarf_forge": ring1[1] if ring1.size() > 1 else _p1_pos,
@@ -164,9 +180,12 @@ func _ready() -> void:
 	await _capture("12_two_culture_zones_wide", "fit")
 
 	# ── ACT IV: Military buildup ───────────────────────────────────────────
+	# Filter the ring to land tiles so warriors never spawn on ocean —
+	# matches `pathfinder.gd::_is_passable` rejecting `water` in the
+	# unit's terrain flags for land units.
 	var spawned: int = 0
 	for n_pos: Vector2i in ring1:
-		if not _game_map.tiles.has(n_pos):
+		if not _is_land_tile(n_pos):
 			continue
 		var u: UnitScript = UnitScript.new("dwarf_warrior", 0, n_pos)
 		u.id = "p1_army_%d" % spawned
@@ -176,24 +195,22 @@ func _ready() -> void:
 			break
 	await _capture("13_p1_army_3warriors", "focus", _p1_pos, 7.0)
 
-	# Add a mixed army: archer + scout
-	var ring2: Array[Vector2i] = _hex_ring(_p1_pos, 2)
-	if ring2.size() > 1 and _game_map.tiles.has(ring2[0]):
-		var arch: UnitScript = UnitScript.new("dwarf_archer", 0, ring2[0])
+	# Add a mixed army: archer + scout — same land-only filter.
+	var ring2_land: Array[Vector2i] = _filter_land(_hex_ring(_p1_pos, 2))
+	if ring2_land.size() > 0:
+		var arch: UnitScript = UnitScript.new("dwarf_archer", 0, ring2_land[0])
 		arch.id = "p1_archer"
 		_p1.units.append(arch)
-	if ring2.size() > 2 and _game_map.tiles.has(ring2[1]):
-		var sct: UnitScript = UnitScript.new("dwarf_scout", 0, ring2[1])
+	if ring2_land.size() > 1:
+		var sct: UnitScript = UnitScript.new("dwarf_scout", 0, ring2_land[1])
 		sct.id = "p1_scout"
 		_p1.units.append(sct)
 	await _capture("14_mixed_army", "focus", _p1_pos, 9.0)
 
-	# P2 puts up a defensive force too
-	for j: int in range(2):
-		var n2: Vector2i = _hex_ring(_p2_pos, 1)[j] if _hex_ring(_p2_pos, 1).size() > j else _p2_pos
-		if not _game_map.tiles.has(n2):
-			continue
-		var u2: UnitScript = UnitScript.new("dwarf_warrior", 1, n2)
+	# P2 puts up a defensive force too — land-only.
+	var p2_ring1_land: Array[Vector2i] = _filter_land(_hex_ring(_p2_pos, 1))
+	for j: int in range(min(2, p2_ring1_land.size())):
+		var u2: UnitScript = UnitScript.new("dwarf_warrior", 1, p2_ring1_land[j])
 		u2.id = "p2_army_%d" % j
 		_p2.units.append(u2)
 	await _capture("15_p2_defenders", "focus", _p2_pos, 7.0)
@@ -518,3 +535,54 @@ func _hex_ring(centre: Vector2i, radius: int) -> Array[Vector2i]:
 			result.append(current)
 			current = current + dirs[side]
 	return result
+
+
+## True when `pos` is a land tile a city or land unit can occupy. Mirrors
+## `mc_mapgen::spawn_box::FORBIDDEN_BIOMES` (ocean / coast / mountains)
+## and the GDScript `pathfinder.gd::_is_passable` water/impassable gates.
+## Defensive: missing tile, missing biome string, or non-land biome all
+## return false so demo placements never land in the sea.
+func _is_land_tile(pos: Vector2i) -> bool:
+	if not _game_map.tiles.has(pos):
+		return false
+	var tile: Resource = _game_map.tiles[pos]
+	if tile == null:
+		return false
+	var biome: String = ""
+	if "biome_id" in tile:
+		biome = String(tile.biome_id)
+	elif "biome_label_id" in tile:
+		biome = String(tile.biome_label_id)
+	if biome.is_empty():
+		return false
+	# Forbidden biomes for cities + land-unit footprints. Mountains are
+	# walkable in some game modes but never a valid capital site, so we
+	# treat them as forbidden for the demo's placement helpers.
+	const FORBIDDEN: Array[String] = [
+		"ocean", "deep_ocean", "coast", "inland_sea", "lake",
+		"mountains", "volcano", "ice",
+	]
+	return biome not in FORBIDDEN
+
+
+## Pick the first land tile in concentric rings expanding outward from
+## `centre`, scanning up to `max_radius`. Returns `centre` when nothing
+## land-eligible is found so the demo still proceeds (the projector will
+## render the city dot regardless).
+func _find_land_tile_near(centre: Vector2i, max_radius: int) -> Vector2i:
+	if _is_land_tile(centre):
+		return centre
+	for r: int in range(1, max_radius + 1):
+		for candidate: Vector2i in _hex_ring(centre, r):
+			if _is_land_tile(candidate):
+				return candidate
+	return centre
+
+
+## Filter `positions` down to land-only tiles. Order-preserving.
+func _filter_land(positions: Array[Vector2i]) -> Array[Vector2i]:
+	var out: Array[Vector2i] = []
+	for p: Vector2i in positions:
+		if _is_land_tile(p):
+			out.append(p)
+	return out