# Memory System Status & Migration Plan

## Completed Work

### Core Systems
- **MemoryArena**: Implemented linear allocator with alignment, markers, and reset support.
- **Global Arenas**:
  - `ScratchArena` (64MB): Transient per-frame memory.
  - `EngineArena` (256MB): Persistent engine memory (internal).
  - `GameArena` (512MB): Persistent game memory (exported to Game DLL).
- **Helpers**: Added `ArenaPushType<T>` and `ArenaPushArray<T>` with automatic zero-initialization.

### Migrated Subsystems
- **Display**: `Win32Window` and `Win32DisplayDevice` now use `EngineArena`.
- **Game Entities**: `Entity.h` uses `GameArena` for entity allocation; manual `free` calls removed from `game.cpp`.
- **Hot Reload**: `HotReload.cpp` (persistent paths to `EngineArena`) and `Win32HotReload.cpp` (temp paths to `ScratchArena`).

## Remaining Work

The following subsystems still use legacy `malloc`/`calloc`/`realloc`/`free` and need to be migrated.



### IO System
- **Files**: `Core/HAL/IO/IOStream.cpp`, `Core/HAL/IO/Win32/Win32IOStream.cpp`
- **Allocations**: `IOStream` instance, data buffers, `Win32IOStreamDataPayload`.
- **Challenge**: `Realloc` is used for growing buffers.
- **Strategy**: 
  - `IOStream` struct -> `ScratchArena` (if transient) or `EngineArena`.
  - Buffers: Evaluate if `ArenaPush` with large enough capacity is sufficient, or implement a growable buffer on top of arena (or use `std::vector` with custom allocator if absolutely needed, but prefer simple fixed max size if possible).

### Graphics / Debug
- **Files**: `Graphics/DebugDisplayRenderer.cpp`
- **Allocations**: `DepthTestedVertices`, `OverlayVertices`.
- **Strategy**: Use `EngineArena` or a dedicated `RenderArena` if these are persistent. If per-frame, move to `ScratchArena`.

### Shader Compiler
- **Files**: `JulietShaderCompiler/ShaderCompiler.cpp`
- **Allocations**: Argument arrays, file buffers.
- **Strategy**: Use `ScratchArena` for all compilation tasks as they are transient.

### Filesystem
- **Files**: `Core/HAL/Filesystem/Filesystem.cpp`
- **Allocations**: `CachedBasePath`.
- **Strategy**: Migrate to `EngineArena` (persistent).
