feat: add STEP-113 Android PBF fast gate diagnostics

include/mln/renderer/render_segment.hpp

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <array>
 #include <cstdint>
 #include <optional>
 #include <set>
@@ -237,6 +238,72 @@ struct RenderSegmentDiagnosticsEntry {
     std::optional<RenderSegmentCacheDiagnostics> cache;
 };
 
+// Platform-neutral, bounded diagnostic samples. No pointers to mutable renderer objects.
+struct FastGateRetainedSample {
+    uint32_t segmentIndex = 0;
+    RenderSegmentCacheDiagnostics cache;
+    bool placementGatePassed = false;
+    std::string actualExecution;
+};
+
+struct FastGateCacheInputSample {
+    uint32_t segmentIndex = 0;
+    bool exists = false;
+    bool valid = false;
+    uint64_t buildRevision = 0;
+    uint64_t staticRevision = 0;
+};
+
+struct FastGatePhaseSample {
+    // Placement changed/fade come from the last completed render-tree snapshot
+    // in pre-fast. Fast tree flags do not imply a fresh Placement calculation.
+    // They are never substituted for the current controller gate #13.
+    bool hasPlacementSnapshot = false;
+    bool placementChanged = false;
+    float symbolFadeChange = 0;
+    bool placementTransitionActive = false;
+    bool retainedSamplesTruncated = false;
+    uint64_t contentRevision = 0;
+    uint64_t topologyRevision = 0;
+    uint64_t configRevision = 0;
+    uint64_t fullCpuFrame = 0;
+    std::optional<uint64_t> processSimulationAdvance;
+    std::vector<FastGateRetainedSample> retained;
+};
+
+struct FastGateFrameSample {
+    uint64_t sequence = 0;
+    uint64_t frame = 0;
+    int64_t updateTimeNs = 0;
+    uint32_t failMask = 0;
+    uint32_t knownMask = 0x00ffffff;
+    std::string firstFailure;
+    bool decisionConsistent = true;
+    bool candidate = false;
+    bool preFastPlacementTransition = false;
+    bool placementTransitionsEnabled = true;
+    bool completed = false;
+    std::string outcome{"pending"};
+    bool cacheInputsTruncated = false;
+    std::vector<FastGateCacheInputSample> cacheInputs;
+    FastGatePhaseSample pre;
+    FastGatePhaseSample post;
+};
+
+struct FastGateTraceDiagnostics {
+    uint32_t schemaVersion = 1;
+    uint64_t lifecycle = 0;
+    uint64_t attempts = 0;
+    uint64_t overwritten = 0;
+    uint64_t decisionMismatch = 0;
+    uint64_t fullRendered = 0;
+    uint64_t fastRendered = 0;
+    uint64_t noRender = 0;
+    std::array<uint64_t, 24> failureCounts{};
+    std::array<uint64_t, 24> firstFailureCounts{};
+    std::vector<FastGateFrameSample> frames;
+};
+
 struct RenderSegmentDiagnostics {
     uint32_t schemaVersion = 1;
     bool enabled = true;
@@ -274,6 +341,7 @@ struct RenderSegmentDiagnostics {
     RenderMutationDiagnostics lastMutation;
     std::vector<StyleLayerDiagnostics> styleLayers;
     std::vector<RenderSegmentDiagnosticsEntry> segments;
+    std::optional<FastGateTraceDiagnostics> fastGateTrace;
 };
 
 struct ResolvedRenderSegment {