test(@projects/@magic-civilization): ⛵ p3-18 P5b — GUT proof the rendered pathfinder embark gate works

test_pathfinder_embark.gd: over an ocean-column map, a land unit finds no path
without embark (embark_level 0), fords the column with embark (level > 0) and
reaches the far landmass; naval movement is unaffected by the embark arg.

Verified headless against the rebuilt dylib: GUT 732 passing / 0 failed (+3 from
729 — these tests; no regression). UI embark now matches the authoritative
headless sim.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/game/engine/tests/unit/test_pathfinder_embark.gd

@@ -0,0 +1,53 @@
+extends GutTest
+## p3-18 — the rendered pathfinder (`pathfinder.gd`) lets a land unit enter water
+## only when its owner can embark (`embark_level > 0`). The embark level itself is
+## computed in Rust (`GdTechWeb.embark_level`, data-driven from tech mechanics);
+## this verifies the thin GDScript gate consumes it so UI movement matches the
+## authoritative headless sim's embark rule.
+
+const GameMapScript: GDScript = preload("res://engine/src/map/game_map.gd")
+const TileScript: GDScript = preload("res://engine/src/map/tile.gd")
+const PathfinderScript: GDScript = preload("res://engine/src/map/pathfinder.gd")
+
+
+## A vertical ocean wall: col 0 land | col 1 ocean (all rows) | col 2 land. Any
+## path from col 0 to col 2 must cross the ocean column.
+func _ocean_wall_map() -> GameMap:
+	var m: GameMap = GameMapScript.new()
+	m.initialize(3, 3, 0)  # WrapMode.NONE
+	for q: int in range(3):
+		for r: int in range(3):
+			var t: Tile = TileScript.new()
+			t.position = Vector2i(q, r)
+			t.biome_id = "ocean" if q == 1 else "plains"
+			m.tiles[Vector2i(q, r)] = t
+	return m
+
+
+func test_land_unit_blocked_by_water_without_embark() -> void:
+	var m: GameMap = _ocean_wall_map()
+	var path: Array[Vector2i] = PathfinderScript.find_path(
+		m, Vector2i(0, 0), Vector2i(2, 0), 20, "land", 0
+	)
+	assert_eq(path.size(), 0, "no embark → the ocean column blocks the land unit")
+
+
+func test_land_unit_crosses_water_with_embark() -> void:
+	var m: GameMap = _ocean_wall_map()
+	var path: Array[Vector2i] = PathfinderScript.find_path(
+		m, Vector2i(0, 0), Vector2i(2, 0), 20, "land", 1
+	)
+	assert_gt(path.size(), 0, "embark_level > 0 → land unit fords the ocean column")
+	assert_eq(
+		path[path.size() - 1], Vector2i(2, 0), "embarked land unit reaches the far landmass"
+	)
+
+
+func test_naval_unit_ignores_embark_level() -> void:
+	# Naval movement is unchanged by the embark arg (it always needs water).
+	var m: GameMap = _ocean_wall_map()
+	# A naval unit can sit on / traverse the ocean column regardless of embark.
+	var on_water: Array[Vector2i] = PathfinderScript.find_path(
+		m, Vector2i(1, 0), Vector2i(1, 2), 20, "naval", 0
+	)
+	assert_gt(on_water.size(), 0, "naval unit traverses water with embark_level 0")