diff --git a/include/game/game_handler.hpp b/include/game/game_handler.hpp
index 89c518a6..fb5d4ef5 100644
--- a/include/game/game_handler.hpp
+++ b/include/game/game_handler.hpp
@@ -417,7 +417,7 @@ public:
     void castSpell(uint32_t spellId, uint64_t targetGuid = 0);
     void cancelCast();
     void cancelAura(uint32_t spellId);
-    const std::vector<uint32_t>& getKnownSpells() const { return knownSpells; }
+    const std::unordered_set<uint32_t>& getKnownSpells() const { return knownSpells; }
     bool isCasting() const { return casting; }
     uint32_t getCurrentCastSpellId() const { return currentCastSpellId; }
     float getCastProgress() const { return castTimeTotal > 0 ? (castTimeTotal - castTimeRemaining) / castTimeTotal : 0.0f; }
@@ -1315,7 +1315,7 @@ private:
     uint64_t playerTransportStickyGuid_ = 0;       // Last transport player was on (temporary retention)
     float playerTransportStickyTimer_ = 0.0f;      // Seconds to keep sticky transport alive after transient clears
     std::unique_ptr<TransportManager> transportManager_;  // Transport movement manager
-    std::vector<uint32_t> knownSpells;
+    std::unordered_set<uint32_t> knownSpells;
     std::unordered_map<uint32_t, float> spellCooldowns;    // spellId -> remaining seconds
     uint8_t castCount = 0;
     bool casting = false;
diff --git a/include/ui/spellbook_screen.hpp b/include/ui/spellbook_screen.hpp
index 6fac7ba7..1ae5a1f6 100644
--- a/include/ui/spellbook_screen.hpp
+++ b/include/ui/spellbook_screen.hpp
@@ -73,7 +73,7 @@ private:
     void loadSpellDBC(pipeline::AssetManager* assetManager);
     void loadSpellIconDBC(pipeline::AssetManager* assetManager);
     void loadSkillLineDBCs(pipeline::AssetManager* assetManager);
-    void categorizeSpells(const std::vector<uint32_t>& knownSpells);
+    void categorizeSpells(const std::unordered_set<uint32_t>& knownSpells);
     GLuint getSpellIcon(uint32_t iconId, pipeline::AssetManager* assetManager);
     const SpellInfo* getSpellInfo(uint32_t spellId) const;
 };
diff --git a/src/audio/audio_engine.cpp b/src/audio/audio_engine.cpp
index 88f0d8cb..edd60f59 100644
--- a/src/audio/audio_engine.cpp
+++ b/src/audio/audio_engine.cpp
@@ -25,9 +25,25 @@ struct DecodedWavCacheEntry {
 static std::unordered_map<uint64_t, DecodedWavCacheEntry> gDecodedWavCache;
 
 static uint64_t makeWavCacheKey(const std::vector<uint8_t>& wavData) {
-    uint64_t ptr = static_cast<uint64_t>(reinterpret_cast<uintptr_t>(wavData.data()));
-    uint64_t sz = static_cast<uint64_t>(wavData.size());
-    return (ptr * 11400714819323198485ull) ^ (sz + 0x9e3779b97f4a7c15ull + (ptr << 6) + (ptr >> 2));
+    // FNV-1a over the first 256 bytes + last 256 bytes + total size.
+    // Full-content hash would be correct but slow for large files; sampling the
+    // edges catches virtually all distinct files while keeping cost O(1).
+    constexpr uint64_t FNV_OFFSET = 14695981039346656037ull;
+    constexpr uint64_t FNV_PRIME  = 1099511628211ull;
+    uint64_t h = FNV_OFFSET;
+    auto mix = [&](uint8_t b) { h ^= b; h *= FNV_PRIME; };
+
+    const size_t sz = wavData.size();
+    const size_t head = std::min(sz, size_t(256));
+    for (size_t i = 0; i < head; ++i) mix(wavData[i]);
+    if (sz > 256) {
+        const size_t tail_start = sz > 512 ? sz - 256 : 256;
+        for (size_t i = tail_start; i < sz; ++i) mix(wavData[i]);
+    }
+    // Mix in the total size so files with identical head/tail but different
+    // lengths still produce different keys.
+    for (int s = 0; s < 8; ++s) mix(static_cast<uint8_t>(sz >> (s * 8)));
+    return h;
 }
 
 static bool decodeWavCached(const std::vector<uint8_t>& wavData, DecodedWavCacheEntry& out) {
@@ -80,6 +96,12 @@ static bool decodeWavCached(const std::vector<uint8_t>& wavData, DecodedWavCache
     entry.sampleRate = sampleRate;
     entry.frames = framesRead;
     entry.pcmData = pcmData;
+    // Evict oldest half when cache grows too large (keeps ~128 most-recent sounds)
+    if (gDecodedWavCache.size() >= 256) {
+        auto it = gDecodedWavCache.begin();
+        for (size_t n = gDecodedWavCache.size() / 2; n > 0; --n, ++it) {}
+        gDecodedWavCache.erase(gDecodedWavCache.begin(), it);
+    }
     gDecodedWavCache.emplace(key, entry);
     out = entry;
     return true;
diff --git a/src/game/game_handler.cpp b/src/game/game_handler.cpp
index dd59bdbc..76e58b70 100644
--- a/src/game/game_handler.cpp
+++ b/src/game/game_handler.cpp
@@ -96,8 +96,8 @@ GameHandler::GameHandler() {
     wardenModuleManager_ = std::make_unique<WardenModuleManager>();
 
     // Default spells always available
-    knownSpells.push_back(6603);  // Attack
-    knownSpells.push_back(8690);  // Hearthstone
+    knownSpells.insert(6603);  // Attack
+    knownSpells.insert(8690);  // Hearthstone
 
     // Default action bar layout
     actionBar[0].type = ActionBarSlot::SPELL;
@@ -1053,9 +1053,8 @@ void GameHandler::handlePacket(network::Packet& packet) {
 
             // Add to known spells immediately for prerequisite re-evaluation
             // (SMSG_LEARNED_SPELL may come separately, but we need immediate update)
-            bool alreadyKnown = std::find(knownSpells.begin(), knownSpells.end(), spellId) != knownSpells.end();
-            if (!alreadyKnown) {
-                knownSpells.push_back(spellId);
+            if (!knownSpells.count(spellId)) {
+                knownSpells.insert(spellId);
                 LOG_INFO("Added spell ", spellId, " to known spells (trainer purchase)");
             }
 
@@ -7010,21 +7009,17 @@ void GameHandler::handleInitialSpells(network::Packet& packet) {
     InitialSpellsData data;
     if (!InitialSpellsParser::parse(packet, data)) return;
 
-    knownSpells = data.spellIds;
+    knownSpells = {data.spellIds.begin(), data.spellIds.end()};
 
     // Debug: check if specific spells are in initial spells
-    bool has527 = std::find(knownSpells.begin(), knownSpells.end(), 527u) != knownSpells.end();
-    bool has988 = std::find(knownSpells.begin(), knownSpells.end(), 988u) != knownSpells.end();
-    bool has1180 = std::find(knownSpells.begin(), knownSpells.end(), 1180u) != knownSpells.end();
+    bool has527 = knownSpells.count(527u);
+    bool has988 = knownSpells.count(988u);
+    bool has1180 = knownSpells.count(1180u);
     LOG_INFO("Initial spells include: 527=", has527, " 988=", has988, " 1180=", has1180);
 
     // Ensure Attack (6603) and Hearthstone (8690) are always present
-    if (std::find(knownSpells.begin(), knownSpells.end(), 6603u) == knownSpells.end()) {
-        knownSpells.insert(knownSpells.begin(), 6603u);
-    }
-    if (std::find(knownSpells.begin(), knownSpells.end(), 8690u) == knownSpells.end()) {
-        knownSpells.push_back(8690u);
-    }
+    knownSpells.insert(6603u);
+    knownSpells.insert(8690u);
 
     // Set initial cooldowns
     for (const auto& cd : data.cooldowns) {
@@ -7172,7 +7167,7 @@ void GameHandler::handleAuraUpdate(network::Packet& packet, bool isAll) {
 
 void GameHandler::handleLearnedSpell(network::Packet& packet) {
     uint32_t spellId = packet.readUInt32();
-    knownSpells.push_back(spellId);
+    knownSpells.insert(spellId);
     LOG_INFO("Learned spell: ", spellId);
 
     // Check if this spell corresponds to a talent rank
@@ -7192,9 +7187,7 @@ void GameHandler::handleLearnedSpell(network::Packet& packet) {
 
 void GameHandler::handleRemovedSpell(network::Packet& packet) {
     uint32_t spellId = packet.readUInt32();
-    knownSpells.erase(
-        std::remove(knownSpells.begin(), knownSpells.end(), spellId),
-        knownSpells.end());
+    knownSpells.erase(spellId);
     LOG_INFO("Removed spell: ", spellId);
 }
 
@@ -7204,12 +7197,10 @@ void GameHandler::handleSupercededSpell(network::Packet& packet) {
     uint32_t newSpellId = packet.readUInt32();
 
     // Remove old spell
-    knownSpells.erase(
-        std::remove(knownSpells.begin(), knownSpells.end(), oldSpellId),
-        knownSpells.end());
+    knownSpells.erase(oldSpellId);
 
     // Add new spell
-    knownSpells.push_back(newSpellId);
+    knownSpells.insert(newSpellId);
 
     LOG_INFO("Spell superceded: ", oldSpellId, " -> ", newSpellId);
 
@@ -7226,9 +7217,7 @@ void GameHandler::handleUnlearnSpells(network::Packet& packet) {
 
     for (uint32_t i = 0; i < spellCount && packet.getSize() - packet.getReadPos() >= 4; ++i) {
         uint32_t spellId = packet.readUInt32();
-        knownSpells.erase(
-            std::remove(knownSpells.begin(), knownSpells.end(), spellId),
-            knownSpells.end());
+        knownSpells.erase(spellId);
         LOG_INFO("  Unlearned spell: ", spellId);
     }
 
@@ -8300,8 +8289,8 @@ void GameHandler::handleTrainerList(network::Packet& packet) {
     }
 
     // Check if specific prerequisite spells are known
-    bool has527 = std::find(knownSpells.begin(), knownSpells.end(), 527u) != knownSpells.end();
-    bool has25312 = std::find(knownSpells.begin(), knownSpells.end(), 25312u) != knownSpells.end();
+    bool has527 = knownSpells.count(527u);
+    bool has25312 = knownSpells.count(25312u);
     LOG_INFO("Prerequisite check: 527=", has527, " 25312=", has25312);
 
     // Debug: log first few trainer spells to see their state
diff --git a/src/ui/game_screen.cpp b/src/ui/game_screen.cpp
index e09f5754..881cddd5 100644
--- a/src/ui/game_screen.cpp
+++ b/src/ui/game_screen.cpp
@@ -4860,7 +4860,7 @@ void GameScreen::renderTrainerWindow(game::GameHandler& gameHandler) {
             auto isKnown = [&](uint32_t id) {
                 if (id == 0) return true;
                 // Check if spell is in knownSpells list
-                bool found = std::find(knownSpells.begin(), knownSpells.end(), id) != knownSpells.end();
+                bool found = knownSpells.count(id);
                 if (found) return true;
 
                 // Also check if spell is in trainer list with state=2 (explicitly known)
diff --git a/src/ui/spellbook_screen.cpp b/src/ui/spellbook_screen.cpp
index c1a7b8cd..41ccba86 100644
--- a/src/ui/spellbook_screen.cpp
+++ b/src/ui/spellbook_screen.cpp
@@ -136,7 +136,7 @@ void SpellbookScreen::loadSkillLineDBCs(pipeline::AssetManager* assetManager) {
     }
 }
 
-void SpellbookScreen::categorizeSpells(const std::vector<uint32_t>& knownSpells) {
+void SpellbookScreen::categorizeSpells(const std::unordered_set<uint32_t>& knownSpells) {
     spellTabs.clear();
 
     // Only SkillLine category 7 ("Class") gets its own tab (the 3 specialties).