fix(crash): EndPlay tore the world down under live workers -- the cache made it lethal

PIE crashed with EXCEPTION_ACCESS_VIOLATION reading 0xffffffffffffffff:

  FRoomGraphSource::Eval()   VoxelDensityOpStack.cpp:3056  (Manager->GetLayoutVersion())
  UVoxelGenerator::GetDensityAt()  VoxelGenerator.cpp:1103 (ActiveOpStack->EvalMC)
  ...  AVoxelWorld::LoadTile lambda, on a task-graph worker

Two lifetime bugs, combined:

1. EndPlay gave up after a 3-second deadline and destroyed UObjects while workers
   were still inside GenerateTileResult. The crash log records 4, 3 and 7 tasks
   still running during teardown. ARCHITECTURE has always said EndPlay blocks on
   ActiveTaskCount -> 0; it did not.
2. e08b49a's worker-local cache keeps 128 built op stacks alive per thread, and
   those stacks hold a raw UVoxelStrateManager*. Before the cache, a stack was
   rebuilt at every chunk crossing and never outlived its owner for long. After
   it, a freed manager stayed reachable and got dereferenced.

The cache did not create the teardown race. It made an existing one lethal.

Fixes:
- EndPlay now waits unconditionally for ActiveTaskCount == 0. The 3s deadline is
  demoted to a log line: a slow drain is reported, teardown is never torn out
  from under a reader.
- UVoxelStrateManager carries a process-unique CacheLifetimeId, folded into the
  cache key. Deliberately not a UObject pointer: allocator address reuse must not
  let a stale worker-local stack look current across PIE sessions. PassagesVersion
  restarts per layout and cannot make that distinction.
- Cached passage/room manager references are weak pointers, fail-closed.
- Verified FStrateGenerationParams is copied BY VALUE into tunnel operators, and
  stack moves preserve owned operator allocations, so no operator references a
  previous cache entry's parameters.

  TunnelNetwork mesh  342.332 s -> 16.199 s   (21.1x)
  per tile, 64 tiles    5.349 s ->  0.253 s

NOT verified, and it matters here:
- No PIE measurement. The owner restricted this session to analysis and fixes, so
  the numbers above are the commandlet's direct-mesher path, NOT the streaming
  path the game uses. They are not game timings and are not presented as such.
- The 128-slot cache may churn at distance: an L0 tile crosses at most 27 exact
  chunks, but L2/L3/L4 tiles touch 216 / 1,000 / 6,859 chunk keys. Whether that
  helps or hurts in game is unmeasured.
- EndPlay waiting forever converts a crash into a hang if a task never observes
  bShuttingDown. Workers do check it, but this trade is deliberate and worth
  watching.

Named, not changed: the straight "roads" the owner still sees are inter-strate
passages. FStratePassageConfig defaults Connections=1 and Style=Straight
(VoxelStrateTypes.h:1781); GeneratePassages maps Straight -> SlopedTunnel and
builds a two-leg switchback that FPassageCarveOp carves
(VoxelStrateManager.cpp:819). d97373c removed the landing-to-hub radial roads; it
did not touch these. FLatticeCorridorSource also still emits axis-aligned capsule
edges for Maze (VoxelDensityOpStack.cpp:548). Awaiting the owner's call on what
should replace them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012aheo2crrZmHuYtPpdY2Cb

Source/VoxelForge/Private/VoxelWorld.cpp

@@ -857,17 +857,18 @@ void AVoxelWorld::EndPlay(const EEndPlayReason::Type EndPlayReason)
     // Signal all async tasks to bail out ASAP
     bShuttingDown.store(true, std::memory_order_release);
 
-    // Wait for all running tasks to finish before destroying UObjects.
-    // Tasks check bShuttingDown and exit early, so this should be fast.
-    // Timeout after 3 seconds to avoid hanging the editor.
+    // Wait for every running task before destroying UObjects. A timeout here is unsafe: a task
+    // already inside GenerateTileResult may still be evaluating a cached op stack that points at
+    // this world's manager. Log a slow drain, but never tear the world down underneath a reader.
     const double Deadline = FPlatformTime::Seconds() + 3.0;
+    bool bReportedSlowDrain = false;
     while (ActiveTaskCount.load(std::memory_order_relaxed) > 0)
     {
-        if (FPlatformTime::Seconds() > Deadline)
+        if (!bReportedSlowDrain && FPlatformTime::Seconds() > Deadline)
         {
-            UE_LOG(LogTemp, Warning, TEXT("[VoxelWorld] EndPlay: %d tasks still running after 3s timeout"),
+            UE_LOG(LogTemp, Warning, TEXT("[VoxelWorld] EndPlay: waiting for %d tasks after 3s; UObject teardown is deferred"),
                 ActiveTaskCount.load(std::memory_order_relaxed));
-            break;
+            bReportedSlowDrain = true;
         }
         FPlatformProcess::Yield();  // Give CPU to other threads
     }