capabilities

Honest self-report for a capability-aware caller: whether this backend genuinely streams tokens and accepts images, which GenerationConfig fields it reads, and — when it can't run — the real AiFailure reason instead of a bare false. Default answer is conservative (no streaming, no honored config) and derives AiCapabilities.unavailableReason from isAvailable alone; a backend with a more specific gate (model residency, OS feature status) overrides this to report why.