refactor(M03): extract terrain quality mesh cache

src/render/terrain/terrain_quality_mesh_cache.gd

@@ -0,0 +1,73 @@
+class_name TerrainQualityMeshCache
+extends RefCounted
+
+## Session-memory LRU owner for full-quality terrain Mesh references retained
+## across tile unload/revisit. It owns no tile state, Node, RID, task or file.
+
+const EXCLUDED_QUALITY_SOURCES: Array[String] = [
+	"control_splat_cache",
+	"splat_cache",
+	"splat",
+]
+
+var _entries_by_tile_key: Dictionary = {}
+var _tile_keys_oldest_to_newest: Array[String] = []
+
+
+## Stores an admitted Mesh reference, touches it as newest and trims oldest
+## entries to the supplied non-negative capacity. Returns false when rejected.
+func store(tile_key: String, mesh: Mesh, source: String, capacity: int) -> bool:
+	if tile_key.is_empty() or mesh == null or EXCLUDED_QUALITY_SOURCES.has(source):
+		return false
+	_entries_by_tile_key[tile_key] = {"mesh": mesh, "source": source}
+	_touch(tile_key)
+	_trim(maxi(0, capacity))
+	return _entries_by_tile_key.has(tile_key)
+
+
+## Returns a fresh record containing the retained Mesh/source and touches the key
+## as newest. Missing or invalid records return empty and are removed.
+func restore(tile_key: String) -> Dictionary:
+	if not _entries_by_tile_key.has(tile_key):
+		return {}
+	var entry: Dictionary = _entries_by_tile_key[tile_key]
+	var source := String(entry.get("source", "baked_full"))
+	var mesh := entry.get("mesh") as Mesh
+	if mesh == null or EXCLUDED_QUALITY_SOURCES.has(source):
+		_remove(tile_key)
+		return {}
+	_touch(tile_key)
+	return {"mesh": mesh, "source": source}
+
+
+## Releases every retained Mesh reference and resets LRU order.
+func clear() -> void:
+	_entries_by_tile_key.clear()
+	_tile_keys_oldest_to_newest.clear()
+
+
+## Returns detached scalar diagnostics without exposing retained Mesh references.
+func diagnostic_snapshot() -> Dictionary:
+	var entries: Array[Dictionary] = []
+	for tile_key in _tile_keys_oldest_to_newest:
+		var entry: Dictionary = _entries_by_tile_key.get(tile_key, {})
+		entries.append({"tile_key": tile_key, "source": String(entry.get("source", ""))})
+	return {
+		"entry_count": entries.size(),
+		"entries_oldest_to_newest": entries,
+	}
+
+
+func _touch(tile_key: String) -> void:
+	_tile_keys_oldest_to_newest.erase(tile_key)
+	_tile_keys_oldest_to_newest.append(tile_key)
+
+
+func _trim(capacity: int) -> void:
+	while _tile_keys_oldest_to_newest.size() > capacity:
+		_remove(_tile_keys_oldest_to_newest.front())
+
+
+func _remove(tile_key: String) -> void:
+	_entries_by_tile_key.erase(tile_key)
+	_tile_keys_oldest_to_newest.erase(tile_key)

src/render/terrain/terrain_quality_mesh_cache.gd.uid

@@ -0,0 +1 @@
+uid://y576l2omqwox