Module domain 

Domain layer: value objects, aggregates and pure functions.

This layer has zero I/O dependencies. Time, randomness and session-id generation are injected from outside it rather than called globally, so every function here is deterministic and testable.

Populated by T04 (protocol version value objects), T05-T08 (feature profile, negotiation, canonical IR, per-revision codecs), T10 (the session aggregate: lifecycle, in-flight requests, cancellation, progress) and T11 (the registry’s pure half: primitives, visibility, snapshots).

Re-exports

pub use bridge::Agreement;

pub use bridge::Leg;

pub use bridge::RefusedBy;

pub use bridge::Withheld;

pub use bridge::agree;

pub use feature::DegradePolicy;

pub use feature::FEATURES;

pub use feature::Feature;

pub use feature::FeatureProfile;

pub use feature::FeatureSpec;

pub use feature::Negotiation;

pub use feature::resolve;

pub use idempotency::Claim;

pub use idempotency::ClaimToken;

pub use idempotency::CompletedResults;

pub use idempotency::IdempotencyError;

pub use idempotency::IdempotencyKey;

pub use idempotency::StaleClaim;

pub use mcp::AuthorizationModel;

pub use mcp::BearerMethod;

pub use mcp::ClientRegistration;

pub use mcp::MCP_METHOD_HEADER;

pub use mcp::MCP_NAME_HEADER;

pub use mcp::McpSessionId;

pub use mcp::McpSessionIdError;

pub use mcp::ResourceMetadata;

pub use mcp::ResourceUri;

pub use mcp::ResourceUriError;

pub use mcp::RoutingHeaderError;

pub use mcp::RoutingHeaders;

pub use mcp::RoutingName;

pub use mcp::RoutingTarget;

pub use mcp::VISIBLE_ASCII_RANGE;

pub use mcp::WELL_KNOWN;

pub use mcp::authorization_model;

pub use mcp::client_method_defined_in;

Modules

a2a

A2A domain — the version negotiation model, the per-revision A2aFeatureProfile, and the value objects that the wire codecs (T28) lower into.

acp

domain::acp — the protocol-neutral ACP value objects.

bridge

What a bridge can honestly promise.

feature

Feature — the protocol behaviours a session may or may not have, and resolve — the pure function that decides which of them it has.

idempotency

Running a peer-observable side effect at most once per key.

ir

The canonical, version-agnostic IR.

jsonrpc

The protocol-neutral JSON-RPC layer.

mcp

The parts of MCP that exist as wire headers rather than as IR.

names

The event name a legacy-transport frame carries, or the unnamed default.

oauth

OAuth machinery that is not MCP-specific.

registry

The registry’s pure half: what a primitive is, who may see it, and the immutable set a publish hands to readers.

session

The session aggregate: lifecycle, in-flight requests, cancellation, progress.

stateless_meta_keys

The capability names the stateless _meta is allowed to carry.

Structs

CapabilitySet

A set of advertised capabilities.

EventId

A stream event’s position, as a client quotes it back.

EventName

A validated event: value.

EventRing

A bounded, replayable buffer of stream events.

FrameDecoder

Reassembles newline-delimited frames from arbitrarily chopped-up bytes.

MaxFrameSize

The largest frame a decoder will accept, in bytes, excluding the terminator.

MessageEndpoint

The endpoint event’s data, parsed once and used verbatim.

NegotiatedSession

A session that has agreed on a version and a feature profile.

PeerInfo

What a peer calls itself.

RateLimit

A request allowance: limit requests per window.

RecommendedCapacity

A capacity for a stream whose payload size the caller has not measured.

ReleaseDate

A spec revision’s release date.

StatelessRequest

What a stateless 2026-07-28 request said about itself.

StreamEvent

One event, with the id a client would quote to resume after it.

SupportedVersions

A non-empty, sorted, duplicate-free set of protocol versions.

TransportSpec

A transport named at an adapter boundary.

Enums

Capability

A capability name as the specification spells it.

EventNameError

Why a string is not usable as an event: name.

FramingError

A frame that could not be framed.

MaxFrameSizeError

Why a MaxFrameSize could not be built.

MessageEndpointError

Why a string is not a usable message endpoint.

NegotiationError

Why negotiation could not produce a session.

ParseProtocolVersionError

Why a string is not a ProtocolVersion.

ParseReleaseDateError

Why a string is not a YYYY-MM-DD release date.

ProtocolVersion

A published MCP revision, or one published after this build was compiled.

Replay

What a client asking to resume actually gets.

RequestId

A JSON-RPC request id: a number or a string.

ServerDecision

What the server decided to speak.

Side

Which side of the connection a capability is declared on.

SpecError

Why a transport spec could not be read.

SupportedVersionsError

Why a set of supported versions was rejected.

TransportKind

A transport the specification defines.

UnknownVersionError

Why a date cannot become ProtocolVersion::Unknown.

Verdict

What check concluded.

Constants

CAPABILITY_TABLE

A capability and the revisions whose schemas define it.

CLIENT_CAPABILITY_WIRE

How one client capability appears in a ClientCapabilities object.

RECOMMENDED_CAPACITY

Events to retain for a stream whose payload size is unmeasured.

SERVER_CAPABILITY_WIRE

How one server capability appears in a ServerCapabilities object.

Functions

assumed_version

The version a request is assumed to be, given whatever signals it carries.

assumed_version_without_signal

The version a request is assumed to be when it carries no version signal at all.

check_protocol_header

Checks an MCP-Protocol-Version header against the negotiated version.

check_rate_limit

The outcome of one check.

defined_in

Whether version’s schema defines capability.

discover_defined_in

Whether server/discover exists in this revision.

encode_frame

Appends one frame — the document, then the terminator — to out.

handshake_defined_in

Whether version has an initialize handshake at all.

is_reserved_meta_key

Whether a _meta key is one the stateless lifecycle reserves.

negotiate_client

Client-side version negotiation.

negotiate_server

Server-side version negotiation.

negotiate_stateless

Stateless per-request negotiation, as 2026-07-28 defines it.

transport_allowed

Whether the specification defines transport for version.