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_policy.gd

@@ -0,0 +1,108 @@
+class_name StreamingTargetPolicy
+extends RefCounted
+
+## Immutable runtime tile-radius and boundary-prefetch policy consumed by
+## [StreamingTargetPlanner]. Values preserve scene configuration exactly;
+## effective radii and thresholds apply the existing renderer clamps.
+
+const CHUNKS_PER_ADT_TILE := 16
+
+var lod2_radius_chunks: int:
+	get:
+		return _lod2_radius_chunks
+
+var lod2_tile_radius: int:
+	get:
+		return _lod2_tile_radius
+
+var warm_tile_margin: int:
+	get:
+		return _warm_tile_margin
+
+var prewarm_tile_margin: int:
+	get:
+		return _prewarm_tile_margin
+
+var retain_tile_margin: int:
+	get:
+		return _retain_tile_margin
+
+var boundary_prefetch_threshold: float:
+	get:
+		return _boundary_prefetch_threshold
+
+var _lod2_radius_chunks: int
+var _lod2_tile_radius: int
+var _warm_tile_margin: int
+var _prewarm_tile_margin: int
+var _retain_tile_margin: int
+var _boundary_prefetch_threshold: float
+
+
+## Captures one renderer configuration snapshot for a deterministic plan.
+func _init(
+		lod2_radius_chunks_value: int,
+		lod2_tile_radius_value: int,
+		warm_tile_margin_value: int,
+		prewarm_tile_margin_value: int,
+		retain_tile_margin_value: int,
+		boundary_prefetch_threshold_value: float
+) -> void:
+	_lod2_radius_chunks = lod2_radius_chunks_value
+	_lod2_tile_radius = lod2_tile_radius_value
+	_warm_tile_margin = warm_tile_margin_value
+	_prewarm_tile_margin = prewarm_tile_margin_value
+	_retain_tile_margin = retain_tile_margin_value
+	_boundary_prefetch_threshold = boundary_prefetch_threshold_value
+
+
+## Returns the current visible ADT radius derived from chunk and tile settings.
+func visible_tile_radius() -> int:
+	return calculate_visible_tile_radius(_lod2_radius_chunks, _lod2_tile_radius, _warm_tile_margin)
+
+
+## Returns the visible radius plus the non-negative prewarm margin.
+func load_tile_radius() -> int:
+	return calculate_load_tile_radius(
+		_lod2_radius_chunks,
+		_lod2_tile_radius,
+		_warm_tile_margin,
+		_prewarm_tile_margin
+	)
+
+
+## Returns the load radius plus the non-negative hysteresis margin.
+func retained_tile_radius() -> int:
+	return load_tile_radius() + maxi(0, _retain_tile_margin)
+
+
+## Returns the edge fraction accepted by the existing prefetch policy.
+func clamped_boundary_prefetch_threshold() -> float:
+	return clampf(_boundary_prefetch_threshold, 0.0, 0.49)
+
+
+## Calculates the visible radius without allocating a policy. The streamer uses
+## this hot-path form while finalizing tiles between planning refreshes.
+static func calculate_visible_tile_radius(
+		lod2_radius_chunks_value: int,
+		lod2_tile_radius_value: int,
+		warm_tile_margin_value: int
+) -> int:
+	var chunk_tile_radius := int(ceil(
+		float(lod2_radius_chunks_value) / float(CHUNKS_PER_ADT_TILE)
+	)) + warm_tile_margin_value
+	return maxi(chunk_tile_radius, lod2_tile_radius_value)
+
+
+## Calculates the load radius without allocating a policy.
+static func calculate_load_tile_radius(
+		lod2_radius_chunks_value: int,
+		lod2_tile_radius_value: int,
+		warm_tile_margin_value: int,
+		prewarm_tile_margin_value: int
+) -> int:
+	return calculate_visible_tile_radius(
+		lod2_radius_chunks_value,
+		lod2_tile_radius_value,
+		warm_tile_margin_value
+	) + maxi(0, prewarm_tile_margin_value)