Add Chat service API schemas (proto + OpenAPI)

[rowan-stein]

User Request

Add proto and OpenAPI schemas for the Chat service to agynio/api. Chat is a data-plane service that wraps Threads for the built-in web/mobile app chat experience.

Specification

Proto: proto/agynio/api/chat/v1/chat.proto

5 RPCs in ChatService:

• CreateChat — Create a new chat thread between participants. Authenticated user auto-added.
• GetChats — List chats for the authenticated user with cursor-based pagination.
• GetMessages — List messages in a chat with pagination + unread count (from Threads GetUnackedMessages).
• SendMessage — Send a message. Sender = authenticated identity_id from gRPC metadata.
• MarkAsRead — Mark messages as read (delegates to Threads AckMessages). Idempotent.

Entities: Chat, ChatParticipant, ChatMessage

Conventions:

• Package: agynio.api.chat.v1
• Go package: github.com/agynio/api/gen/agynio/api/chat/v1;chatv1
• google.protobuf.Timestamp, cursor-based pagination
• Identity from gRPC metadata (no user_id in request bodies)
• Must pass buf lint (STANDARD rules)

OpenAPI: openapi/chat/v1/ (16 files)

Modular YAML structure matching existing specs (files/v1, team/v1, llm/v1):

Endpoint	Method	Proto RPC
/chats	GET	GetChats
/chats	POST	CreateChat
/chats/{chatId}/messages	GET	GetMessages
/chats/{chatId}/messages	POST	SendMessage
/chats/{chatId}/read	POST	MarkAsRead

• OpenAPI 3.0.3, RFC 7807 Problem, cursor-based pagination (pageSize/pageToken/nextPageToken)
• No user_id in request bodies — Gateway authenticates and resolves identity

File List

proto/agynio/api/chat/v1/chat.proto
openapi/chat/v1/openapi.yaml
openapi/chat/v1/paths/chats.yaml
openapi/chat/v1/paths/chat-messages.yaml
openapi/chat/v1/paths/chat-read.yaml
openapi/chat/v1/components/parameters/ChatIdPath.yaml
openapi/chat/v1/components/responses/ProblemResponse.yaml
openapi/chat/v1/components/schemas/Problem.yaml
openapi/chat/v1/components/schemas/Chat.yaml
openapi/chat/v1/components/schemas/ChatParticipant.yaml
openapi/chat/v1/components/schemas/ChatCreateRequest.yaml
openapi/chat/v1/components/schemas/PaginatedChats.yaml
openapi/chat/v1/components/schemas/ChatMessage.yaml
openapi/chat/v1/components/schemas/ChatMessageCreateRequest.yaml
openapi/chat/v1/components/schemas/PaginatedChatMessages.yaml
openapi/chat/v1/components/schemas/MarkAsReadRequest.yaml
openapi/chat/v1/components/schemas/MarkAsReadResponse.yaml

References

• Architecture: agynio/architecture/architecture/chat.md, authn.md, tenancy.md
• Pattern: proto/agynio/api/threads/v1/threads.proto (proto conventions)
• Pattern: openapi/llm/v1/ (OpenAPI modular structure)