Module messaging_plugin_protocol 

JSON-over-stdio protocol types for external messaging adapter plugins.

Messaging adapter plugins communicate with TA using a request/response protocol over stdin/stdout. TA spawns the plugin process, writes one JSON request line to stdin, reads one JSON response line from stdout.

Protocol overview

Every exchange is a single JSON line in each direction:

TA → plugin: {"op":"<name>",...params...}
plugin → TA: {"ok":true,...result...}   or   {"ok":false,"error":"..."}

Operations

Op	Description
fetch	Fetch messages since a watermark timestamp
create_draft	Write a draft to the provider’s native Drafts folder
draft_status	Poll whether a draft was sent, discarded, or still open
health	Connectivity + credential check
capabilities	Advertise which optional ops this plugin supports

Safety invariant — send is absent by design

The send operation is intentionally absent from this protocol. TA never sends messages on behalf of the user. Plugins expose only create_draft; the user sends from their native email client. This is a deliberate safety boundary enforced at the type level.

Structs

CapabilitiesParams

Parameters for the capabilities operation.

CreateDraftParams

Parameters for the create_draft operation.

DraftEnvelope

The content of a draft message to be created.

DraftStatusParams

Parameters for the draft_status operation.

FetchParams

Parameters for the fetch operation.

FetchedMessage

A single fetched message.

HealthParams

Parameters for the health operation.

MessagingPluginResponse

Response sent from a messaging plugin to TA over stdout.

Enums

DraftState

Current state of a draft as reported by the provider.

MessagingPluginError

Errors from messaging plugin operations.

MessagingPluginRequest

Request sent from TA to a messaging plugin over stdin.

Constants

MESSAGING_PROTOCOL_VERSION

Protocol version implemented by this TA build.