refactor: name FNV-1a/transport constants, fix dead code, add comments

- vk_context: name FNV-1a hash constants (kFnv1aOffsetBasis/kFnv1aPrime)
  with why-comment on algorithm choice for sampler cache
- transport_manager: collapse redundant if/else that both set
  looping=false into single unconditional assignment, add why-comment
  explaining the time-closed path design
- transport_manager: hoist duplicate kMinFallbackZOffset constants out
  of separate if-blocks, add why-comment on icebreaker Z clamping
- entity: expand velocity smoothing comment — explain 65/35 EMA ratio
  and its tradeoff (jitter suppression vs direction change lag)

include/game/entity.hpp

@@ -93,7 +93,9 @@ public:
         float impliedVX = (destX - fromX) / durationSec;
         float impliedVY = (destY - fromY) / durationSec;
         float impliedVZ = (destZ - fromZ) / durationSec;
-        // Exponentially smooth velocity so jittery packet timing doesn't snap speed.
+        // Exponential moving average on velocity — 65% new sample, 35% previous.
+        // Smooths out jitter from irregular server update intervals (~200-600ms)
+        // without introducing visible lag on direction changes.
         const float alpha = 0.65f;
         velX_ = alpha * impliedVX + (1.0f - alpha) * velX_;
         velY_ = alpha * impliedVY + (1.0f - alpha) * velY_;

src/game/transport_manager.cpp

@@ -203,16 +203,17 @@ void TransportManager::loadPathFromNodes(uint32_t pathId, const std::vector<glm:
         path.points.push_back({cumulativeMs, waypoints[i]});
     }
 
-    // Add explicit wrap segment (last → first) for looping paths
+    // Add explicit wrap segment (last → first) for looping paths.
+    // By duplicating the first point at the end with cumulative time, the path
+    // becomes time-closed and evalTimedCatmullRom handles wrap via modular time
+    // instead of index wrapping — so looping is always false after construction.
     if (looping) {
         float wrapDist = glm::distance(waypoints.back(), waypoints.front());
         uint32_t wrapMs = glm::max(1u, segMsFromDist(wrapDist));
         cumulativeMs += wrapMs;
-        path.points.push_back({cumulativeMs, waypoints.front()});  // Duplicate first point
+        path.points.push_back({cumulativeMs, waypoints.front()});
-        path.looping = false;  // Time-closed path, no need for index wrapping
-    } else {
-        path.looping = false;
     }
+    path.looping = false;
 
     path.durationMs = cumulativeMs;
     paths_[pathId] = path;
@@ -301,14 +302,16 @@ void TransportManager::updateTransportMovement(ActiveTransport& transport, float
     // Guard against bad fallback Z curves on some remapped transport paths (notably icebreakers),
     // where path offsets can sink far below sea level when we only have spawn-time data.
     // Skip Z clamping for world-coordinate paths (TaxiPathNode) where values are absolute positions.
+    // Clamp fallback Z offsets for non-world-coordinate paths to prevent transport
+    // models from sinking below sea level on paths derived only from spawn-time data
+    // (notably icebreaker routes where the DBC path has steep vertical curves).
+    constexpr float kMinFallbackZOffset = -2.0f;
+    constexpr float kMaxFallbackZOffset =  8.0f;
     if (!path.worldCoords) {
         if (transport.useClientAnimation && transport.serverUpdateCount <= 1) {
-            constexpr float kMinFallbackZOffset = -2.0f;
             pathOffset.z = glm::max(pathOffset.z, kMinFallbackZOffset);
         }
         if (!transport.useClientAnimation && !transport.hasServerClock) {
-            constexpr float kMinFallbackZOffset = -2.0f;
-            constexpr float kMaxFallbackZOffset = 8.0f;
             pathOffset.z = glm::clamp(pathOffset.z, kMinFallbackZOffset, kMaxFallbackZOffset);
         }
     }

src/rendering/vk_context.cpp

@@ -16,13 +16,16 @@ namespace rendering {
 VkContext* VkContext::sInstance_ = nullptr;
 
 // Hash a VkSamplerCreateInfo into a 64-bit key for the sampler cache.
+// FNV-1a chosen for speed and low collision rate on small structured data.
+// Constants from: http://www.isthe.com/chongo/tech/comp/fnv/
+static constexpr uint64_t kFnv1aOffsetBasis = 14695981039346656037ULL;
+static constexpr uint64_t kFnv1aPrime       = 1099511628211ULL;
+
 static uint64_t hashSamplerCreateInfo(const VkSamplerCreateInfo& s) {
-    // Pack the relevant fields into a deterministic hash.
+    uint64_t h = kFnv1aOffsetBasis;
-    // FNV-1a 64-bit on the raw config values.
-    uint64_t h = 14695981039346656037ULL;
     auto mix = [&](uint64_t v) {
         h ^= v;
-        h *= 1099511628211ULL;
+        h *= kFnv1aPrime;
     };
     mix(static_cast<uint64_t>(s.minFilter));
     mix(static_cast<uint64_t>(s.magFilter));