feat(@projects/@magic-civilization): ⛵ p3-18 P5b(2) — rendered movement is embark-aware (UI)

Wires the rendered game's GDScript movement to the data-driven embark capability,
so a human playing the UI can cross water when teched (previously embark worked
headless only):
- pathfinder.gd: find_path / movement_range / find_path_with_fog gain a defaulted
  embark_level param (non-breaking for all existing callers); _is_passable lets a
  land unit enter water when embark_level > 0. Single-tier UI gate — the precise
  coast-vs-ocean tier stays authoritative in the Rust sim; the gate avoids
  hardcoding the biome→tier map in GDScript (Rail 1).
- KnowledgeWeb + TechWeb: embark_level(researched) passthroughs to the Rust
  GdTechWeb.embark_level (the tech→level mapping stays in Rust, data-driven).
- world_map.gd: _current_embark_level() (defensive) feeds the active player's
  level into all four pathfinder call sites (move, range overlay, fog previews).

gdlint clean. Verifies via dylib rebuild + GUT (next).

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

src/game/engine/scenes/world_map/world_map.gd

@@ -1028,12 +1028,26 @@ func _deselect_unit() -> void:
 	EventBus.unit_deselected.emit()
 
 
+## p3-18 — the active player's embarkation level (0 none / 1 coast / 2 ocean) for
+## movement gating. Computed in Rust (GdTechWeb.embark_level, data-driven); the
+## GDScript pathfinder uses it to allow land units onto water when teched.
+## Defensive: returns 0 (no embark) if the tech web or player is unavailable.
+func _current_embark_level() -> int:
+	var tw: RefCounted = TurnManager.get_tech_web()
+	if tw == null or not tw.has_method(&"embark_level"):
+		return 0
+	var player: RefCounted = GameState.get_current_player()
+	if player == null:
+		return 0
+	return int(tw.embark_level(PackedStringArray(player.researched_techs)))
+
+
 func _compute_movement_range(unit: RefCounted) -> void:
 	var game_map: RefCounted = GameState.get_game_map()
 	if game_map == null:
 		return
 	_reachable_hexes = PathfinderScript.movement_range(
-		game_map, unit.position, unit.movement_remaining, unit.unit_type
+		game_map, unit.position, unit.movement_remaining, unit.unit_type, _current_embark_level()
 	)
 	_unit_renderer.show_movement_range(_reachable_hexes)
 
@@ -1060,7 +1074,8 @@ func _move_unit_to(unit: RefCounted, target: Vector2i) -> void:
 	if game_map == null:
 		return
 	var path: Array[Vector2i] = PathfinderScript.find_path(
-		game_map, unit.position, target, unit.movement_remaining, unit.unit_type
+		game_map, unit.position, target, unit.movement_remaining, unit.unit_type,
+		_current_embark_level()
 	)
 	if path.is_empty():
 		return
@@ -1787,6 +1802,7 @@ func update_path_preview(hovered_axial: Vector2i) -> void:
 		preview_budget,
 		_selected_unit.unit_type,
 		scouted,
+		_current_embark_level(),
 	)
 	if path.is_empty():
 		_unit_renderer.clear_path_preview()
@@ -1833,6 +1849,7 @@ func _path_preview_for_target(target: Vector2i) -> Array[Vector2i]:
 		9999,
 		_selected_unit.unit_type,
 		scouted,
+		_current_embark_level(),
 	)
 
 

src/game/engine/src/map/pathfinder.gd

@@ -23,7 +23,12 @@ const LOS_BLOCKING_BIOMES: Array[String] = ["mountain", "dense_forest"]
 
 
 static func find_path(
-	map: RefCounted, start: Vector2i, goal: Vector2i, movement_budget: int, unit_type: String
+	map: RefCounted,
+	start: Vector2i,
+	goal: Vector2i,
+	movement_budget: int,
+	unit_type: String,
+	embark_level: int = 0,
 ) -> Array[Vector2i]:
 	## A* pathfinding from start to goal on the hex grid.
 	## Returns the path as an array of axial positions (start excluded, goal included).
@@ -35,7 +40,7 @@ static func find_path(
 	var goal_tile: Resource = map.get_tile(goal)
 	if goal_tile == null:
 		return [] as Array[Vector2i]
-	if not _is_passable(goal_tile, unit_type):
+	if not _is_passable(goal_tile, unit_type, embark_level):
 		return [] as Array[Vector2i]
 
 	# Open set: Array of [f_score, g_score, position] sorted by f_score ascending.
@@ -76,7 +81,7 @@ static func find_path(
 			var neighbor_tile: Resource = map.get_tile(neighbor)
 			if neighbor_tile == null:
 				continue
-			if not _is_passable(neighbor_tile, unit_type):
+			if not _is_passable(neighbor_tile, unit_type, embark_level):
 				continue
 
 			var move_cost: int = _get_effective_cost(neighbor_tile, unit_type)
@@ -96,7 +101,11 @@ static func find_path(
 
 
 static func movement_range(
-	map: RefCounted, start: Vector2i, movement_budget: int, unit_type: String
+	map: RefCounted,
+	start: Vector2i,
+	movement_budget: int,
+	unit_type: String,
+	embark_level: int = 0,
 ) -> Dictionary:
 	## Dijkstra flood-fill: all hexes reachable within movement_budget.
 	## Returns Dictionary mapping Vector2i (axial) -> int (cost spent to reach).
@@ -125,7 +134,7 @@ static func movement_range(
 			var neighbor_tile: Resource = map.get_tile(neighbor)
 			if neighbor_tile == null:
 				continue
-			if not _is_passable(neighbor_tile, unit_type):
+			if not _is_passable(neighbor_tile, unit_type, embark_level):
 				continue
 
 			var move_cost: int = _get_effective_cost(neighbor_tile, unit_type)
@@ -149,6 +158,7 @@ static func find_path_with_fog(
 	movement_budget: int,
 	unit_type: String,
 	scouted: Dictionary,
+	embark_level: int = 0,
 ) -> Array[Vector2i]:
 	## p0-35: fog-aware path preview. A* through tiles the player has scouted
 	## (`scouted[axial] == true`), straight `HexUtilsScript.hex_line()` through
@@ -163,7 +173,7 @@ static func find_path_with_fog(
 		return [] as Array[Vector2i]
 	var goal_scouted: bool = bool(scouted.get(goal, false))
 	if goal_scouted:
-		return find_path(map, start, goal, movement_budget, unit_type)
+		return find_path(map, start, goal, movement_budget, unit_type, embark_level)
 
 	var line: Array[Vector2i] = HexUtilsScript.hex_line(start, goal)
 	## Walk the straight line backwards from goal until we hit a scouted hex.
@@ -182,7 +192,9 @@ static func find_path_with_fog(
 		return fog_only
 
 	var pivot: Vector2i = line[pivot_idx]
-	var scouted_path: Array[Vector2i] = find_path(map, start, pivot, movement_budget, unit_type)
+	var scouted_path: Array[Vector2i] = find_path(
+		map, start, pivot, movement_budget, unit_type, embark_level
+	)
 	if scouted_path.is_empty() and start != pivot:
 		## A* failed in scouted territory (impassable goal-tile, etc.); fall
 		## back to the straight line so the renderer at least shows intent.
@@ -242,8 +254,13 @@ static func has_line_of_sight(map: RefCounted, start: Vector2i, goal: Vector2i)
 # -- Private helpers --
 
 
-static func _is_passable(tile: Resource, unit_type: String) -> bool:
+static func _is_passable(tile: Resource, unit_type: String, embark_level: int = 0) -> bool:
 	## Check if a tile is passable for the given unit type.
+	## `embark_level` (p3-18): the owner's embarkation capability, computed in Rust
+	## (`GdTechWeb.embark_level`) — 0 none / 1 coast / 2 ocean. When > 0 a land unit
+	## may enter water (it embarks). The precise coast-vs-ocean tier is enforced
+	## authoritatively by the Rust sim; this rendered gate is single-tier (any
+	## embark tech opens water) to avoid hardcoding the biome→tier map in GDScript.
 	var flags: Array = tile.get_terrain_flags()
 	match unit_type:
 		"flying":
@@ -253,10 +270,13 @@ static func _is_passable(tile: Resource, unit_type: String) -> bool:
 			# Naval units require water
 			return "water" in flags
 		_:
-			# Land units: blocked by water, naval_only, impassable
-			for flag: String in LAND_IMPASSABLE_FLAGS:
-				if flag in flags:
-					return false
+			# Land units: never cross truly-impassable terrain.
+			if "impassable" in flags:
+				return false
+			# Water / naval_only blocks land units UNLESS they can embark (p3-18).
+			var is_water: bool = "water" in flags or "naval_only" in flags
+			if is_water:
+				return embark_level > 0
 			return true
 
 

src/game/engine/src/modules/tech/knowledge_web.gd

@@ -95,6 +95,15 @@ func is_researched(node_id: String, player_index: int) -> bool:
 	return researched.has(node_id)
 
 
+## p3-18 — embarkation level (0 none / 1 coast / 2 ocean) granted by the given
+## researched tech ids, computed in Rust (`GdTechWeb.embark_level`, data-driven).
+## `0` when the bridge is not built.
+func embark_level(researched: PackedStringArray) -> int:
+	if _bridge == null:
+		return 0
+	return int(_bridge.embark_level(researched))
+
+
 func can_research(node_id: String, player_index: int) -> bool:
 	if _bridge == null or node_id.is_empty():
 		return false

src/game/engine/src/modules/tech/tech_web.gd

@@ -52,6 +52,13 @@ func process_research(player_json: String, yield_json: String, sci_modifier: flo
 	return _web.process_research(player_json, yield_json, sci_modifier)
 
 
+## p3-18 — embarkation level (0 none / 1 coast / 2 ocean) granted by a set of
+## researched tech ids. Delegates to the Rust GdTechWeb (data-driven mapping);
+## consumed by world_map to make rendered movement embark-aware.
+func embark_level(researched: PackedStringArray) -> int:
+	return _web.embark_level(researched)
+
+
 func apply_heritage_tech(player: RefCounted) -> void:
 	## Grant the player's race origin tech (cost 0 by convention).
 	if player == null: