Phase 2 / Task 3: Move LPVSystem ownership into render graph

[MichaelFisher1997]

Goal

Move LPV ownership out of RenderSystem and into the render-graph setup path.

Scope

• src/engine/graphics/render_system.zig
• src/engine/graphics/render_graph.zig

Work

• Rework LPV initialization and storage so the graph owns the dependency explicitly
• Update SceneContext fields that carry LPV textures
• Keep feature flags and fallback behavior intact

Acceptance criteria

• LPV setup is isolated from the rest of RenderSystem
• Rendering output remains unchanged

Parallel-safe

Yes

[github-actions]

Classification: Refactoring/Architecture task.

Analysis:

Current state:

• LPVSystem is owned directly by RenderSystem (render_system.zig:33), initialized at lines 195-204 and deinitialized at line 246.
• LPV texture handles flow through SceneContext (render_graph.zig:86-88) to passes that need them (OpaquePass at lines 352-354, WaterReflectionPass at lines 522-524).
• In world.zig:326-328, the SceneContext is populated with LPV handles via lpv_system.getTextureHandle().

The refactoring is well-scoped with a clear two-file scope. The render graph already receives LPV texture handles via SceneContext, but RenderSystem currently owns the LPVSystem lifecycle. Moving ownership means:

1. Initialization: LPVSystem.init() should move from RenderSystem.init() into the render graph setup path (likely after RenderGraph.init() but before addPass() calls).
2. Teardown: LPVSystem.deinit() should move from RenderSystem.deinit() to RenderGraph.deinit() or a new cleanup path.
3. SceneContext population: The LPV texture handles currently fetched in world.zig:326-328 should instead be obtained from the render graph's own LPV storage.
4. Accessor removal: RenderSystem.getLPVSystem() at line 313 and the .lpv_system field at line 33 become unnecessary.

One consideration: The LPV system update logic (LPVSystem.update()) is called in world.zig:228 based on camera position. This update call should remain functional since the world/chunk data it needs will still be accessible. If the update requires world context, the render graph may need to expose a update-style method or receive the world reference.

The acceptance criteria appear achievable - the LPV textures are already bound through SceneContext in the render passes, so once ownership moves and texture handles are populated by the graph, rendering output should be unchanged.

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