serverCapabilities

recordSubtitleProviderStatus: Store a reply's answer on m.global.server.

An unknown answer is NOT stored, so a failed check is retried by the next consumer instead of being remembered for the rest of the session.

shouldOfferSubtitleSearch: Whether to offer Manage Subtitles once the provider check has settled.

This capability FAILS OPEN: only a definite "unavailable" hides the button, and an unknown result here (the check failed) offers it. Safe for this feature specifically — a search without a provider returns an empty success, the panel says so and points at provider setup, and nothing is changed on the server. A transport error is not evidence the plugin is missing, so hiding a working feature on a network blip would be the worse outcome. Not a default for other capabilities; see the header.

subtitleProviderStatusFrom: What a /Libraries/AvailableOptions reply says about subtitle providers.

SubtitleFetchers lists every installed subtitle provider plugin by name. It cannot tell whether a provider has CREDENTIALS — an installed but unconfigured provider counts as available, and the panel's empty-state message covers that.

the reply does not answer the question (non-ok, malformed)