feat(core): reachable SW landmark chamber demo with a reachability audit (L45); research R12

Stamp vocabulary v2; the flagged SW demo opens through a side-facing portal and a bent ramp (max 14 deg,
two landings) into a 17 x 15 m chamber with a rock dais. New reachability audit: a capsule surface search
from walkable ground near the arrival mouth to the chamber floor (66 samples, 0 blocked/unsupported); the
buried L43 layout fails it. Demo off: owner hashes identical to L44. fast/medium/full PASS (Clang+GCC).
Research R12 (read-only): composite cavern-graph generator design and slices.

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

Standalone/Core/src/ResolvedLayoutInternal.h

@@ -830,8 +830,9 @@ bool ResolvedLayoutSnapshotV3::validate(ResolvedLayoutValidationModeV3 mode,
         if(stampVocabularyVersion!=0)
             add("stamp_vocabulary_version","stamp vocabulary version is set without any stamp records");
     }
-    else if(stampVocabularyVersion!=ResolvedLayoutStampVocabularyVersionV1)
-        add("stamp_vocabulary_version","resolved stamps require vocabulary version 1");
+    else if(stampVocabularyVersion!=ResolvedLayoutStampVocabularyVersionV1
+        &&stampVocabularyVersion!=ResolvedLayoutStampVocabularyVersionV2)
+        add("stamp_vocabulary_version","resolved stamps require supported vocabulary version 1 or 2");
     std::vector<std::string> stampIds;
     for(const auto& stamp:stamps)
     {
@@ -1065,6 +1066,20 @@ bool ResolveResolvedLayoutStampsV1(ResolvedLayoutSnapshotV3& layout,std::int32_t
     layout=std::move(candidate);return true;
 }
 
+bool ResolveResolvedLayoutStampsV2(ResolvedLayoutSnapshotV3& layout,std::int32_t seed,
+    std::span<const ResolvedLayoutStampRequestV1> requests,std::string& error)
+{
+    if(!ResolveResolvedLayoutStampsV1(layout,seed,requests,error))return false;
+    if(requests.empty())return true;
+    ResolvedLayoutSnapshotV3 candidate=layout;
+    candidate.stampVocabularyVersion=ResolvedLayoutStampVocabularyVersionV2;
+    if(!candidate.finalize(error))return false;
+    std::vector<ResolvedLayoutIssueV2> issues;std::string strictError;
+    if(!candidate.validate(ResolvedLayoutValidationModeV3::strict,issues,strictError))
+    {error="strict stamp vocabulary-2 validation failed: "+strictError;return false;}
+    layout=std::move(candidate);return true;
+}
+
 ResolvedLayoutStampPlacementAuditV1 AuditResolvedLayoutStampPlacementV1(
     const ResolvedLayoutSnapshotV3& layout)
 {