restore full TAA accumulation

[MichaelFisher1997]

Problem

TAA is currently in pass-through mode and only samples the current HDR buffer. That keeps the world visible, but temporal anti-aliasing is effectively disabled.

Why

We temporarily bypassed TAA while debugging the render pipeline and left a TODO in assets/shaders/vulkan/taa.frag.

Follow-up

• Revalidate the TAA output path against the post-process chain
• Restore temporal accumulation in assets/shaders/vulkan/taa.frag
• Confirm history textures and present/layout transitions remain correct across resize and Wayland fullscreen changes
• Remove the passthrough TODO once restored

[opencode-agent]

Based on my analysis, here's what I found:

Classification

Bug - TAA is disabled by default and may have incomplete integration.

Analysis

The shader code at assets/shaders/vulkan/taa.frag appears to have full temporal accumulation logic including:

• Velocity-based reprojection (line 22-23)
• History sampling (line 32)
• Neighborhood clamping with 3x3 cross pattern (lines 34-42)
• Velocity rejection and blending (lines 44-47)

However, I found these issues:

1. TAA defaults to disabled (src/game/settings/data.zig:64): taa_enabled: bool = false
2. Cannot locate the TODO mentioned in the issue - the shader appears complete but may have been fixed already
3. Velocity buffer validation needed - The G-pass creates a velocity buffer (rhi_resource_setup.zig:221-287) but I need confirmation it's being written correctly by geometry shaders

Missing Information Needed

To properly diagnose this issue, please provide:

1. The actual TODO comment - Can you paste the specific TODO text that should be in taa.frag? The current shader doesn't show any passthrough TODO.

2. Reproduction steps - When you enable TAA in settings, what behavior do you observe? Is there no temporal accumulation at all?

3. Velocity buffer verification - Is the velocity buffer actually being populated in the G-pass? Check if geometry shaders are outputting motion vectors.

4. Screenshot comparison - A frame with TAA enabled vs disabled would help confirm if accumulation is working.

The code structure looks correct, but TAA being opt-in rather than default may be causing confusion. If the TODO was already removed, this issue can likely be closed after verifying the velocity buffer writes are functioning.

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