Type Alias RendererFallbackReason

RendererFallbackReason:
    | "unsupported"
    | "initialization-failed"
    | "missing-capability"

Why "auto" moved past a registered backend (§62's "diagnostics event").

"unsupported"
RendererRegistration.isSupported answered false.
"initialization-failed"
The backend was built, and Renderer.initialize rejected.
"missing-capability"
The backend initialized, but did not answer every RendererCapabilityDeclaration.required capability true (WP-R1.9); it was disposed and the walk moved on.