feat(assets): replace is_procedural/is_gpu_procedural bools with AssetType enum, add MP3 type

- Add AssetType enum {STATIC, PROC, PROC_GPU, MP3} to AssetRecord
- Add GetAssetType() API to asset_manager.h/cc
- asset_packer: parse 'MP3' compression keyword in assets.txt
- tracker: remove magic-byte is_mp3_asset(); use GetAssetType() instead
- assets.txt: NEVER_MP3 now uses 'MP3' compression type
- doc/ASSET_SYSTEM.md: rewritten to document new types and API

handoff(Gemini): AssetType enum landed; MP3 detection is now explicit via asset metadata.

3 files changed, 24 insertions, 24 deletions

diff --git a/src/audio/tracker.cc b/src/audio/tracker.cc
index 333a337..7ce96fc 100644
--- a/src/audio/tracker.cc
+++ b/src/audio/tracker.cc
@@ -44,15 +44,6 @@ static bool g_cache_initialized = false;
 // Forward declarations
 static int get_free_pool_slot();
 
-// Returns true if the asset blob looks like an MP3 file.
-static bool is_mp3_asset(const uint8_t* data, size_t size) {
-  if (!data || size < 3) return false;
-  // ID3v2 tag prefix
-  if (data[0] == 'I' && data[1] == 'D' && data[2] == '3') return true;
-  // Raw MP3 sync word: 0xFF followed by 0xE0-0xFF
-  if (size >= 2 && data[0] == 0xFF && (data[1] & 0xE0) == 0xE0) return true;
-  return false;
-}
 
 #if !defined(STRIP_ALL)
 // Decode an in-memory MP3 blob to a heap-allocated spectrogram (caller owns).
@@ -147,7 +138,7 @@ void tracker_init() {
         size_t size;
         const uint8_t* data = GetAsset(aid, &size);
 #if !defined(STRIP_ALL)
-        if (data && size > 0 && is_mp3_asset(data, size)) {
+        if (data && size > 0 && GetAssetType(aid) == AssetType::MP3) {
           int num_frames = 0;
           float* spec_data =
               convert_mp3_to_spectrogram(data, size, &num_frames);
@@ -165,7 +156,7 @@ void tracker_init() {
           }
         } else
 #else
-        FATAL_CHECK(data == nullptr || !is_mp3_asset(data, size),
+        FATAL_CHECK(data == nullptr || GetAssetType(aid) != AssetType::MP3,
                     "MP3 assets not supported in STRIP_ALL builds\n");
 #endif
         if (data && size >= sizeof(SpecHeader)) {
diff --git a/src/util/asset_manager.cc b/src/util/asset_manager.cc
index a606b46..2285f3a 100644
--- a/src/util/asset_manager.cc
+++ b/src/util/asset_manager.cc
@@ -37,7 +37,7 @@ static const size_t kNumProcGenFuncs =
     sizeof(kAssetManagerProcGenFuncs) / sizeof(kAssetManagerProcGenFuncs[0]);
 
 // Array-based cache for assets.
-// Initialized to all zeros (nullptr data, 0 size, false is_procedural)
+// Initialized to all zeros (nullptr data, 0 size, AssetType::STATIC)
 // The size is derived from the generated ASSET_LAST_ID enum value.
 static AssetRecord g_asset_cache[(size_t)AssetId::ASSET_LAST_ID] = {};
 
@@ -78,7 +78,8 @@ const uint8_t* GetAsset(AssetId asset_id, size_t* out_size) {
 
   AssetRecord cached_record = source_record;
 
-  if (source_record.is_procedural) {
+  if (source_record.type == AssetType::PROC ||
+      source_record.type == AssetType::PROC_GPU) {
     // Dynamically generate the asset
     ProcGenFunc proc_gen_func_ptr = nullptr;
     for (size_t i = 0; i < kNumProcGenFuncs; ++i) {
@@ -131,13 +132,8 @@ const uint8_t* GetAsset(AssetId asset_id, size_t* out_size) {
 
     cached_record.data = generated_data;
     cached_record.size = data_size;
-    cached_record.is_procedural = true;
-    // proc_gen_func, proc_params, num_proc_params already copied from
+    // type, proc_gen_func, proc_params, num_proc_params already copied from
     // source_record
-
-  } else {
-    // Static asset (copy from g_assets)
-    cached_record.is_procedural = false;
   }
 
   // Store in cache for future use
@@ -187,7 +183,8 @@ void DropAsset(AssetId asset_id, const uint8_t* asset) {
   // Check if the asset is in cache and is procedural, and if the pointer
   // matches. This prevents accidentally freeing static data or freeing twice.
   if (g_asset_cache[index].data == asset &&
-      g_asset_cache[index].is_procedural) {
+      (g_asset_cache[index].type == AssetType::PROC ||
+       g_asset_cache[index].type == AssetType::PROC_GPU)) {
     delete[] g_asset_cache[index].data;
     g_asset_cache[index] = {}; // Zero out the struct to force re-generation
   }
@@ -203,7 +200,9 @@ bool ReloadAssetsFromFile(const char* config_path) {
 
   // Clear cache to force reload
   for (size_t i = 0; i < (size_t)AssetId::ASSET_LAST_ID; ++i) {
-    if (g_asset_cache[i].is_procedural && g_asset_cache[i].data) {
+    if ((g_asset_cache[i].type == AssetType::PROC ||
+         g_asset_cache[i].type == AssetType::PROC_GPU) &&
+        g_asset_cache[i].data) {
       delete[] g_asset_cache[i].data;
     }
     g_asset_cache[i] = {};
@@ -213,3 +212,10 @@ bool ReloadAssetsFromFile(const char* config_path) {
   return true;
 }
 #endif // !defined(STRIP_ALL)
+
+AssetType GetAssetType(AssetId asset_id) {
+  uint16_t index = (uint16_t)asset_id;
+  if (index >= (uint16_t)AssetId::ASSET_LAST_ID)
+    return AssetType::STATIC;
+  return GetAssetRecordTable()[index].type;
+}
diff --git a/src/util/asset_manager.h b/src/util/asset_manager.h
index 1714c21..09483e5 100644
--- a/src/util/asset_manager.h
+++ b/src/util/asset_manager.h
@@ -5,12 +5,12 @@
 #pragma once
 #include "asset_manager_dcl.h"
 
+enum class AssetType : uint8_t { STATIC, PROC, PROC_GPU, MP3 };
+
 struct AssetRecord {
   const uint8_t* data; // Pointer to asset data (static or dynamic)
   size_t size;         // Size of the asset data
-  bool is_procedural;  // True if data was dynamically allocated by a procedural
-                       // generator
-  bool is_gpu_procedural; // True if GPU compute shader generates texture
+  AssetType type;
   const char* proc_func_name_str; // Name of procedural generation function
                                   // (string literal)
   const float* proc_params; // Parameters for procedural generation (static,
@@ -30,6 +30,9 @@ void DropAsset(AssetId asset_id, const uint8_t* asset);
 // found.
 AssetId GetAssetIdByName(const char* name);
 
+// Returns the AssetType for a given asset id.
+AssetType GetAssetType(AssetId asset_id);
+
 #if !defined(STRIP_ALL)
 // Hot-reload: Parse and reload assets from config file (debug only)
 bool ReloadAssetsFromFile(const char* config_path);