profile: in-process SIGPROF sampler + exclusive route/phase census (L77); closes to 0.1%

Opt-in (L77 build + --linux77-profile; compiled out by default, 0.02% handler cost).
FI/TN cost account closes against direct grid-fill timing within 0.15% (LOD0-2 bins within 1.4%).
Passage carving = 66% of LOD0-2 CPU (52-54% whole view), passage support 10-14%, base packed
+ analytic field ~3%. Hotspots: value noise 17%, lower_bound in VisitNearestPassageSpatialNode
14%, ApplyResolvedStratePassageCarves 6.5%. LOD0/1 complete LAST (4.1/4.6 s) while LOD2 is
ready at 2.2 s.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Standalone/Source/StreamingWorld.h

@@ -714,6 +714,8 @@ public:
     {bProfileMesherStages=Enabled;}
     void SetTileDrainInstrumentationEnabled(bool Enabled)
     {bInstrumentTileDrain=Enabled;}
+    void SetLinux77ProfileEnabled(bool Enabled)
+    {bLinux77Profile=Enabled;}
     void SetPassageComposerProfilingEnabled(bool Enabled)
     {bProfilePassageComposer=Enabled;}
     void SetExactMidpointDensityMemoEnabled(bool Enabled)
@@ -902,6 +904,7 @@ private:
             Options.profileMesherStages=(bProfileMesherStages||bInstrumentTileDrain)&&!ForceGenerate;
             Options.profilePassageComposer=bProfilePassageComposer;
             Options.instrumentTileDrain=bInstrumentTileDrain&&!ForceGenerate;
+            Options.linux77Profile=bLinux77Profile;
             Options.exactMidpointDensityMemo=bExactMidpointDensityMemo&&!ForceGenerate;
             Options.activeLaneBatching=bActiveLaneBatching&&!ForceGenerate;
             Options.proofBlockCells=static_cast<std::uint32_t>(ProofBlockCells);
@@ -1195,6 +1198,7 @@ private:
     int32 Lod8HorizonInteriorStepVoxels=0;
     bool bProfileMesherStages=false;
     bool bInstrumentTileDrain=false;
+    bool bLinux77Profile=false;
     bool bProfilePassageComposer=false;
     bool bExactMidpointDensityMemo=false;
     bool bActiveLaneBatching=false;