`PostProcessingEffects` renders a garbage frame when FXAA is enabled over `GraphicsCompositorHelper.CreateDefault` (disabled private range passes leave FXAA reading an unwritten render target)

[jpenberthy]

Release Type: Official Release
Version: 4.3.0.2507
Platform(s): All backends (verified Vulkan + D3D11); code-only compositor path

Describe the bug
CreateDefault(enablePostEffects: true) calls PostProcessingEffects.DisableAll(), which also
disables the private rangeCompress/rangeDecompress passes — and nothing can re-enable
them (no public accessor). DrawCore then chooses the "anti-alias before bloom" branch based on

bool stableBloom = Bloom != null && Bloom.StableConvolution;   // Bloom.Enabled is NOT consulted

StableConvolution defaults to true, so the branch is taken even with bloom disabled. Inside
it, rangeCompress.Draw() is a no-op (disabled renderers draw nothing, not even a blit), FXAA
reads the unwritten scoped render target, and currentInput = compressed; discards the real
scene. Everything downstream runs on allocator garbage.

To Reproduce

1. Code-only game, GraphicsCompositorHelper.CreateDefault(enablePostEffects: true).
2. post.Antialiasing = new FXAAEffect { Enabled = true };
3. Frame is garbage/black. Measured on a fixed camera: mean frame luma 0.4775 → 0.0755 with
   FXAA as the only change.

Expected behavior
FXAA over the default compositor antialiases the frame.

Additional context / workaround
One-line app-side workaround (verified: luma unchanged 0.4784 → 0.4807; edge-aliasing metrics
−39% to −52%): set post.Bloom.StableConvolution = false before enabling FXAA — that selects
the other DrawCore branch, which doesn't touch the disabled private passes. Upstream fix
shapes (any one suffices): gate the branch on Bloom.Enabled && Bloom.StableConvolution; have
DrawCore enable the range passes it is about to use (they're private plumbing — their
Enabled flag is meaningless as public state); or make DisableAll() leave them alone. A
defensive log/throw on drawing a disabled internal pass would have made this a one-line
diagnosis instead of a silent black frame. Happy to PR.