protocol

const (
	// Gateway is the business MCP Security Gateway surface (Capability B).
	Gateway Capability = iota
	// Management is the read-only + draft/validate/simulate surface (Capability A).
	Management
)

const (
	// ClientOriginated — the natural client→server request flow (the client, or
	// Culvert acting as a client toward an upstream server, is the requestor).
	ClientOriginated Direction = iota
	// ServerOriginated — the reverse channel (the server is the requestor). In V1
	// server-originated requests are rejected at admission.
	ServerOriginated
)

const (
	// HandlingRejected — the method is not admitted; there is no dispatch path.
	HandlingRejected Handling = iota
	// HandlingKernelTerminal — the kernel handles and answers the method itself and
	// never dispatches it downstream.
	HandlingKernelTerminal
	// HandlingDecisionPoint — the method is admitted and dispatched to exactly one
	// named downstream decision point (implemented in a later slice, not PR-1).
	HandlingDecisionPoint
)

const (
	// ClientFacing — the agent → Culvert leg (TB-1 / TB-7).
	ClientFacing PeerRole = iota
	// UpstreamFacing — the Culvert ↔ upstream-MCP-server leg (TB-2).
	UpstreamFacing
)

const (
	// StateNew — created, not yet initialized. Only initialize is admissible.
	StateNew State = iota
	// StateInitializing — initialize accepted, awaiting notifications/initialized.
	StateInitializing
	// StateInitialized — steady state; all admitted non-handshake methods allowed.
	StateInitialized
	// StateClosed — terminal; nothing is admissible.
	StateClosed
)

const (
	// CondSessionlessMissingVersion — a sessionless / first request with no
	// MCP-Protocol-Version header. D-1 CLOSED: reject with 400 (never silently
	// assume 2025-03-26).
	CondSessionlessMissingVersion TransportCondition = iota
	// CondInvalidVersionHeader — an invalid or unsupported MCP-Protocol-Version
	// header on a subsequent request → 400.
	CondInvalidVersionHeader
	// CondMissingSessionID — a required session identifier is missing → 400.
	CondMissingSessionID
	// CondUnknownOrTerminatedSession — an unknown or terminated session → 404.
	CondUnknownOrTerminatedSession
	// CondDeleteUnsupported — an unsupported DELETE → 405.
	CondDeleteUnsupported
	// CondGetWithoutNegotiatedContext — a GET without a valid negotiated context →
	// terminal 405, and NO text/event-stream is opened (no legacy SSE, no
	// pre-negotiation held stream).
	CondGetWithoutNegotiatedContext
	// CondInitializeVersionUnsupported — an initialize whose requested version is
	// unsupported. Preferred handling is a 200 InitializeResult counter-offer of a
	// supported version — NOT a 4xx — so a spec-conformant or catch-any SDK client
	// is never recruited into the legacy 2024-11-05 probe.
	CondInitializeVersionUnsupported
)

const (
	// VersionPrimary is the primary supported revision.
	VersionPrimary Version = "2025-11-25"
	// VersionFloor is the compatibility floor.
	VersionFloor Version = "2025-06-18"
)