MiniClient: negotiate optional media capabilities

[jzhvymetal]

Summary

• add explicit capability negotiation for optional media state, DVD navigation and disc policy, playback rate, and caption state
• require negotiated support before sending new commands
• preserve legacy behavior when a client or server does not recognize a capability
• add focused protocol tests

Validation

• Focused Java protocol tests passed in the Vibe extraction workspace.

Review state

Draft protocol proposal: identifiers, versioning, fallback behavior, and cross-client compatibility require OpenSageTV design approval before merge.

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This replaces OpenSageTV#10, which was opened against an intermediate fork instead of the canonical SageTV repository. The topic was replayed without patch changes onto the current canonical master.

Maintenance triage (2026-09-29)

Disposition: draft protocol proposal; not requested for merge.

This is not a correction for an existing stock-client failure. It defines optional capabilities used by newer clients while preserving legacy fallback. The focused protocol tests demonstrate internal compatibility, but they do not establish that upstream should adopt the names, command, state ownership, or versioning model.

Do not merge without an upstream design discussion covering identifiers, negotiation/versioning, old-client and old-server behavior, every supported MiniClient implementation, and which capabilities are general SageTV contracts rather than Vibe features.

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