AT-360 Added Diagram Chat Functionality To Mermaid/sdk So MCP Server Can Directly Access Mermaid AI

[Prashant-7718]

This pull request adds a diagramChat method to the @mermaidchart/sdk, enabling external clients such as MCP servers to chat directly with Mermaid AI without handling streaming internals themselves.

These changes also expose the necessary types (DiagramChatRequest, DiagramChatResponse) so consumers get full TypeScript support for the new chat capability.

New diagramChat method in SDK:

• Added MermaidChart.diagramChat() which posts a single user message to the collab chat endpoint with autoFetchHistory: true, so callers never need to track or resend previous messages.
• Used responseType: 'text' on the axios request to buffer the full Vercel AI data-stream body as a plain string, then parsed it with two dedicated helpers: parseVercelAIStreamText (extracts AI reply from 0: lines) and parseVercelAIStreamData (extracts documentChatThreadID from 2: data lines).
• Returns a clean { text, documentChatThreadID, documentID } object — the resolved thread ID falls back to the caller-supplied one if the backend did not return a new one.
• Added DiagramChatRequest and DiagramChatResponse interfaces to types.ts covering message, code, documentID, documentChatThreadID, and the full response shape.

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
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[Copilot]

Pull request overview

Adds SDK support for a new Mermaid AI “diagram chat” endpoint so consumers (e.g., an MCP server) can send a user prompt + optional diagram context and receive streamed AI output.

Changes:

• Added /rest-api/openai/chat URL constant.
• Introduced DiagramChatRequest / DiagramChatResponse public types.
• Implemented MermaidChart.diagramChat() including parsing of Vercel AI SDK data-stream output.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
packages/sdk/src/urls.ts	Adds the REST URL for the new OpenAI chat endpoint.
packages/sdk/src/types.ts	Defines request/response types for diagram chat.
packages/sdk/src/index.ts	Implements diagramChat() and helpers to parse the streamed response body.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Comments suppressed due to low confidence (1)

packages/sdk/src/index.ts:24

• The PR description says the new DiagramChatRequest/DiagramChatResponse types are exposed for SDK consumers, but the entrypoint doesn’t re-export them. Since this package’s public surface is src/index.ts (and dist/index.d.ts), consider adding explicit export type { DiagramChatRequest, DiagramChatResponse } from './types.js' so consumers can import them from @mermaidchart/sdk without deep imports.

import type {
  AuthState,
  AuthorizationData,
  DiagramChatRequest,
  DiagramChatResponse,
  Document,
  InitParams,
  MCDocument,
  MCProject,
  MCUser,
  RepairDiagramRequest,
  RepairDiagramResponse,
  AICreditsUsage,
} from './types.js';
import { URLS } from './urls.js';

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[Copilot]

DiagramChatResponse.documentID is marked optional, but MermaidChart.diagramChat() always returns documentID and the request requires it. Making this required (or omitting it entirely from the response type) would avoid confusing consumers and better reflect the actual behavior.

Suggested change

	documentID?: string;
	documentID: string;

[Copilot]

This test doesn’t exercise the 402-handling logic in diagramChat() because it mocks client.diagramChat() itself to reject. Instead, mock the underlying axios .post() to reject with a { response: { status: 402, data: ... } } shape and assert that diagramChat() maps it to AICreditsLimitExceededError.

Suggested change

	vi.spyOn(client, 'diagramChat').mockRejectedValue(
	new AICreditsLimitExceededError('AI credits limit exceeded'),
	);
	// Mock the underlying axios call to simulate a 402 response from the API.
	// eslint-disable-next-line @typescript-eslint/no-explicit-any
	vi.spyOn((client as any).axios, 'post').mockRejectedValue({
	response: {
	status: 402,
	data: {
	message: 'AI credits limit exceeded',
	},
	},
	});