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/StreamBenchmarkHeadless.cpp

@@ -49,6 +49,7 @@ namespace
         bool ProfileLodWork=false;
         bool ProfilePassageComposer=false;
         bool InstrumentTileDrain=false;
+        bool Linux77Profile=false;
         bool ExactMidpointDensityMemo=false;
         bool ActiveLaneBatching=false;
         bool ParallelSignEdgeRepair=false;
@@ -1442,6 +1443,7 @@ namespace
                     "  --audit-uniform-block-proofs (fill and check every interval-certified block)\n"
                     "  --profile-lod-work (report per-LOD density sample counts)\n"
                     "  --instrument-tile-drain (opt-in CpuTileTimeline and per-tile stages/counters)\n"
+                    "  --linux77-profile (Linux-only SIGPROF stack and route census)\n"
                     "  --profile-passage-composer (emit per-tile passage work counters)\n"
                     "  --exact-midpoint-density-memo (exact-input midpoint query memo A/B)\n"
                     "  --active-lane-batching --proof-block-cells=N (proof-masked density fill A/B)\n"
@@ -1500,6 +1502,8 @@ namespace
             else if(arg=="--audit-uniform-block-proofs")options.AuditUniformBlockProofs=true;
             else if(arg=="--profile-lod-work")options.ProfileLodWork=true;
             else if(arg=="--instrument-tile-drain")options.InstrumentTileDrain=true;
+            else if(arg=="--linux77-profile")
+            {options.Linux77Profile=true;options.ProfileLodWork=true;}
             else if(arg=="--profile-passage-composer")
             {options.ProfilePassageComposer=true;options.InstrumentTileDrain=true;}
             else if(arg=="--exact-midpoint-density-memo")options.ExactMidpointDensityMemo=true;
@@ -2224,5 +2228,5 @@ int main(int argc,char** argv)
             ?options.ParallelSignEdgeRepair:options.FloatingIslandsRecipe,
         options.AuditNativeLattice,options.LatticeOrphanControl,
         options.CaptureSkipWalkability,options.ProfilePassageComposer,
-        options.StreamHashAllowUniformSkips);
+        options.StreamHashAllowUniformSkips,options.Linux77Profile);
 }