RpcCallId

A transport-agnostic identifier for an in-flight RPC call.

Each transport that supports cancellation (or other features keyed by an original request) provides its own subtype to carry the identifier in whatever native form the wire protocol requires (PacketCallId(channelId, messageId) for packet transports, JsonRpcCallId(JsonPrimitive) for json-rpc, etc.).

Not declared sealed because the known subtypes live in sibling transport modules (ksrpc-packets, ksrpc-jsonrpc), which Kotlin does not permit for sealed hierarchies — a sealed hierarchy would have to collapse them into a single module. Consumers that need to inspect a transport-specific shape should is / cast to the subtype they expect.

Subtypes MUST be data classes / objects with stable equals and hashCode implementations so they can be used as keys in cancellation-tracking maps and compared in tests.