Add bounded CPU reference for temporal resolve

include/faset/render/temporal_reference.hpp

@@ -0,0 +1,45 @@
+#pragma once
+#include <array>
+#include <cstdint>
+#include <vector>
+
+namespace faset::render {
+
+// CPU-only 1:1 oracle for the temporal resolve shader. Color is already
+// display-referred; motion is current-minus-previous normalized scene UV.
+// The renderer does not call this per-pixel path in production.
+struct TemporalReferencePixel {
+    std::array<float, 4> color{0, 0, 0, 1};
+    float depth{1};
+    std::array<float, 2> motion{};
+    float previous_depth{1};
+    bool motion_valid{};
+    float reactive{};
+};
+
+struct TemporalReferenceFrame {
+    std::uint32_t width{}, height{};
+    std::vector<TemporalReferencePixel> pixels;
+};
+
+struct TemporalReferenceHistory {
+    std::uint32_t width{}, height{};
+    std::vector<std::array<float, 4>> color;
+    std::vector<float> depth;
+};
+
+struct TemporalReferenceResult {
+    TemporalReferenceHistory history;
+    std::vector<std::uint8_t> accepted;
+    std::uint32_t accepted_count{};
+};
+
+// A null previous history is the first-frame/cut fallback. Extents must agree
+// when history is supplied; reset it instead of reprojecting stale dimensions.
+// Input is bounded to four million pixels so synthetic tests cannot consume
+// unbounded memory. Invalid motion rejects history for that pixel.
+TemporalReferenceResult temporal_reference_resolve(
+    const TemporalReferenceFrame& current,
+    const TemporalReferenceHistory* previous = nullptr);
+
+} // namespace faset::render