Vulkan PostFX 1.9.1

Fixed

• Improved failure handling for external VPFX post chains.
• External VPFX pack execution failures are now caught during both:
  • PostChain.addToFrame(...)
  • frame graph execution
• Fixed a state issue where an internally failed external VPFX chain could still be marked as successfully applied.
• Failed external VPFX packs are now marked unavailable for the current runtime session.
• When an external VPFX pack fails, Vulkan PostFX now falls back to vanilla rendering instead of allowing invalid pipelines to crash the client.
• Preserved minecraft:scene_color external target support for the minecraft_postchain backend.
• Preserved sampler_name = "In" / InSampler compatibility for VPFX Minimal Showcase.

Notes

This is a stability patch for VPFX v1 alpha.
VPFX v1 remains experimental, and the current backend is still Minecraft PostChain.