ActorDB protocol

proto/meta.proto is the canonical peer schema, preserving all existing message numbers and actordb::proto reexports. Peer protocol v3 remains separate from proto/client.proto, application protocol v1. Rust bindings are committed so normal client builds do not compile protobuf or RocksDB.

Regenerate bindings:

cargo run -p actordb-protocol --features codegen --bin generate
cargo run -p actordb-protocol --features codegen --bin generate -- --check

The optional codegen feature builds bundled protoc for reproducible generation; it is unnecessary for consumers. Other language SDKs should generate bindings from these packaged schemas. Integers in query cells are canonical signed decimal strings, preserving i128 precision. Keys are UTF-8 strings; values are arbitrary bytes. Framing is a four-byte big-endian body length, capped at 16 MiB.

Application Hello/Auth negotiate version and optional capabilities before requests. Challenge proofs use actordb-client-proof-v1\0, proving role, and both ordered Hello offers; they are independent of peer credentials and membership. Byte lengths are u64 big-endian, versions u32 big-endian, capabilities u64 big-endian. Unknown operations must fail explicitly. Never recycle retired field numbers or silently change enum/absence meanings. New peer scan/query messages require their negotiated capability bits before sending to old v3 nodes.