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/BuildLinux.sh

@@ -86,6 +86,10 @@ fi
 if [[ "${VOXELFORGE_PROFILE_LEGACY_TERMS:-0}" == "1" ]]; then
     FLAGS+=(-DVF_L76_PROFILE_LEGACY_TERMS=1)
 fi
+if [[ "${VOXELFORGE_PROFILE_L77:-0}" == "1" ]]; then
+    FLAGS+=(-DVF_L77_PROFILE=1 -g)
+    LINK_FLAGS+=(-no-pie)
+fi
 if [[ "$($COMPILER --version | head -n 1)" == *clang* ]]; then
     FLAGS+=(-Wno-c++11-narrowing)
 else
@@ -142,6 +146,11 @@ done < "$ROOT/Core/core_sources.txt"
 headless_object="$BUILD_DIR/objects/StreamBenchmarkHeadless.o"
 compile_background "$ROOT/Source/StreamBenchmarkHeadless.cpp" "$headless_object"
 LEGACY_OBJECTS+=("$headless_object")
+if [[ "${VOXELFORGE_PROFILE_L77:-0}" == "1" ]]; then
+    l77_profiler_object="$BUILD_DIR/objects/Linux77Profiler.o"
+    compile_background "$ROOT/Source/Linux77Profiler.cpp" "$l77_profiler_object"
+    LEGACY_OBJECTS+=("$l77_profiler_object")
+fi
 
 for pid in "${PIDS[@]}"; do wait "$pid"; done
 PIDS=()