rnd(M03): extract streaming target planner

Work-Package: M03-RND-STREAMING-PLANNER-001
Agent: sindo-main-codex
Tests: planner/facade/focus/coordinate/manifest/shutdown contracts, seven-checkpoint dry-run, repository gates
Fidelity: preserves wanted/retained radii, boundary prefetch, editor preview, queue priority and cache/render behavior

src/render/streaming/streaming_target_plan.gd

@@ -0,0 +1,37 @@
+class_name StreamingTargetPlan
+extends RefCounted
+
+## Immutable result of one runtime or editor target-planning operation.
+## Tile-key sets use the streamer's existing `<tile_x>_<tile_y>` representation.
+
+var focus_tile: AdtTileCoordinate:
+	get:
+		return _focus_tile
+
+var _focus_tile: AdtTileCoordinate
+var _wanted_tile_keys: Dictionary
+var _retained_tile_keys: Dictionary
+
+
+## Takes ownership of planner-created sets and freezes them. The planner creates
+## these dictionaries independently from its catalog input, so no copy is needed.
+func _init(
+		focus_tile_value: AdtTileCoordinate,
+		wanted_tile_keys_value: Dictionary,
+		retained_tile_keys_value: Dictionary
+) -> void:
+	_focus_tile = focus_tile_value
+	_wanted_tile_keys = wanted_tile_keys_value
+	_retained_tile_keys = retained_tile_keys_value
+	_wanted_tile_keys.make_read_only()
+	_retained_tile_keys.make_read_only()
+
+
+## Returns the immutable wanted tile-key set.
+func wanted_tile_keys() -> Dictionary:
+	return _wanted_tile_keys
+
+
+## Returns the immutable retained tile-key set.
+func retained_tile_keys() -> Dictionary:
+	return _retained_tile_keys