refactor(M03): extract WMO render build queue

src/render/wmo/wmo_render_build_queue.gd

@@ -0,0 +1,88 @@
+class_name WmoRenderBuildQueue
+extends RefCounted
+
+## Owns pending lightweight-WMO job records and FIFO placement keys.
+
+const JOB_SCRIPT := preload("res://src/render/wmo/wmo_render_build_job.gd")
+
+var _jobs_by_placement_key: Dictionary = {}
+var _queued_placement_keys: Array[String] = []
+
+
+## Enqueues a new typed job. Duplicate placement keys replace the keyed job but
+## append another FIFO entry, preserving the loader's historical behavior.
+func enqueue(placement_key: String, root: Node3D, render_resource: Resource) -> bool:
+	if placement_key.is_empty() or root == null or render_resource == null:
+		return false
+	_jobs_by_placement_key[placement_key] = JOB_SCRIPT.new(
+		placement_key,
+		root,
+		render_resource
+	)
+	_queued_placement_keys.append(placement_key)
+	return true
+
+
+## Returns whether at least one FIFO key, including a stale key, is pending.
+func has_pending() -> bool:
+	return not _queued_placement_keys.is_empty()
+
+
+## Returns the front FIFO key, or an empty String when the queue is empty.
+func front_key() -> String:
+	if _queued_placement_keys.is_empty():
+		return ""
+	return _queued_placement_keys.front()
+
+
+## Returns the current typed job for a placement key, or null for a stale key.
+func job_for(placement_key: String) -> WmoRenderBuildJob:
+	return _jobs_by_placement_key.get(placement_key, null) as WmoRenderBuildJob
+
+
+## Pops and returns the front FIFO key, or an empty String when already empty.
+func pop_front() -> String:
+	if _queued_placement_keys.is_empty():
+		return ""
+	return _queued_placement_keys.pop_front()
+
+
+## Cancels the keyed job and erases only the first matching FIFO key. Returns
+## whether an active job record existed. Engine objects are never freed here.
+func cancel(placement_key: String) -> bool:
+	var had_job := _jobs_by_placement_key.has(placement_key)
+	_jobs_by_placement_key.erase(placement_key)
+	_queued_placement_keys.erase(placement_key)
+	return had_job
+
+
+## Releases all job/key references without freeing referenced engine objects.
+func clear() -> void:
+	_jobs_by_placement_key.clear()
+	_queued_placement_keys.clear()
+
+
+## Returns FIFO entry count, including duplicate and stale keys.
+func pending_count() -> int:
+	return _queued_placement_keys.size()
+
+
+## Returns active keyed job count, excluding stale FIFO keys.
+func active_job_count() -> int:
+	return _jobs_by_placement_key.size()
+
+
+## Returns detached FIFO order and placement-key-sorted scalar job diagnostics.
+func diagnostic_snapshot() -> Dictionary:
+	var placement_keys: Array = _jobs_by_placement_key.keys()
+	placement_keys.sort()
+	var jobs: Array[Dictionary] = []
+	for placement_key_variant in placement_keys:
+		var placement_key := String(placement_key_variant)
+		var job := job_for(placement_key)
+		if job != null:
+			jobs.append(job.diagnostic_snapshot())
+	return {
+		"queued_placement_keys": _queued_placement_keys.duplicate(),
+		"jobs": jobs,
+	}