True iff data is a versioned ISPO frame with a string op. Does NOT
validate per-op payload fields — callers switch on op and apply op-specific
checks where it matters (see isRpcCall / isRpcReply). Rejects
runtime-logger frames ({ v, type }), legacy { type: 'ispo:*' } events,
bare { id, method } RPC, null, and arrays.
True iff
datais a versioned ISPO frame with a stringop. Does NOT validate per-op payload fields — callers switch onopand apply op-specific checks where it matters (seeisRpcCall/isRpcReply). Rejects runtime-logger frames ({ v, type }), legacy{ type: 'ispo:*' }events, bare{ id, method }RPC,null, and arrays.