Sisense MCP Server — Repo Guide

Use this skill whenever you're about to add a tool, touch session state, generate artifact IDs, or handle credentials. It captures lessons learned from real bugs in this codebase.

Project Commands

bun run test                # unit tests (bun + preloaded setup.ts)
bun run test:e2e            # end-to-end tests (requires built server)
bun run build               # vite view build + bun SSE server bundle
bun run dev                 # watch mode (no build needed)
bun run type-check          # tsc --noEmit (run before committing)
bun run lint                # eslint src/**/*.ts

Commit Messages — Conventional Commits

Format: <type>[(optional scope)]: <description> (SNS-XXXXX)

The Jira ticket (SNS-xxx) is mandatory at the end of the header line.

fix(buildChart): use crypto.randomUUID() for toolCallId (SNS-128032)

Replace requestId with randomUUID so chartIds are unique per tool call.
JSON-RPC requestId is always 1 from Claude, causing every chart to get
the same ID.

Supported <type> values:

Changelog follows common-changelog.org conventions.

Architecture at a Glance

HTTP request → sse-server.ts
                 ├── credential hash → persistentStates Map
                 │     (survives client reconnects for same user)
                 └── MCP session ID → sessions Map (transport + state ref)
                       └── setupMcpServer(sessionState) → mcp-server.ts
                             ├── tools/build-chart.ts
                             ├── tools/get-data-sources.ts
                             └── tools/get-data-source-fields.ts

`SessionState = Map<string, unknown>` — the single source of truth per session.

SessionState Key Taxonomy

Pitfall: extra.requestId Is NOT a Unique Tool Call ID

The MCP SDK exposes extra.requestId in tool handlers, but Claude sends requestId=1 for every invocation — it's a JSON-RPC correlation ID, not a per-call unique ID. Never use it to identify artifacts.

Use generateArtifactId() instead:

import { generateArtifactId } from '../utils/string-utils.js';

const toolCallId = generateArtifactId('chart'); // → 'chart-3f2504e0'

First 8 hex chars of a UUID — short enough for LLMs to reference, unique enough in practice.

Pitfall: Global Sisense SDK Client Fallback

Bug hit in SNS-128031: Tools without credentials were silently falling through to the global Sisense SDK httpClient, causing requests to succeed under the wrong user context.

Always get clients from session — never assume a global fallback:

import { getSessionHttpClient, getSessionOpenAIClient } from '../utils/sisense-session.js';

const httpClient = getSessionHttpClient(sessionState); // throws MISSING_SISENSE_SESSION_MESSAGE if absent
const openAIClient = getSessionOpenAIClient(sessionState);

These functions throw explicitly. That's intentional — a missing client is a bug, not a fallback case.

Pitfall: Large Payloads in _meta Break Clients

Bug hit in SNS-128032: Chart payload (serialized widget props + credentials) was returned in the _meta field of the tool response. Cursor and ChatGPT couldn't handle it.

>

Follow-up (SNS-129470): Replacing _meta with an MCP ResourceTemplate + readServerResource() fixed Cursor but broke ChatGPT — its MCP App host doesn't proxy resources/read. Claude.ai also has a dual-session issue where the Model session stores the payload but the AppBridge session can't find it.

Current pattern — inline `artifactPayload` in `structuredContent`:

1. buildChart sets artifactPayload: { type: 'chart', sisenseUrl, sisenseToken, serializedWidgetProps } on structuredContent (not in LLM-visible content[0].text).
2. The analytics app reads toolResult.structuredContent.artifactPayload from the postMessage toolresult event and renders directly — no HTTP fetch, works across ChatGPT (CSP), Claude dual-session, Goose, and Cursor.

Adding a new artifact type (e.g. buildDashboard): set artifactPayload in the tool's structuredContent, add the type to the BiArtifact union in analytics-app.tsx, and handle it in renderArtifact.

MCP App Mode vs Tool Mode

Controlled by MCP_APP_ENABLED env var. The feature flag pattern used throughout:

function isMcpAppEnabled(): boolean {
  return process.env.MCP_APP_ENABLED !== 'false' && process.env.MCP_APP_ENABLED !== '0';
}

Feature flags are enabled by default (opt-out, not opt-in). Check both 'false' and '0'.

When adding a new tool, decide up-front which mode applies and wire it conditionally if needed.

Pitfall: MCP App resize loop (analytics view)

ext-apps ≥ 1.7.2: Unbounded ChartWidget layout + autoResize causes infinite loading / host-context-changed spam.

Do: Keep default autoResize: true. Wrap ChartWidget in .chartContainer (width: 100%, tuned min-height) so CSDK has a stable size anchor.

Don't: min-height: 100vh on #root or .main; autoResize: false without sendSizeChanged; gate render on hostContext (gate on !app only).

See src/analytics-view/.

Adding a New Tool — Checklist

1. Get credentials from session — use getSessionHttpClient(), getSessionOpenAIClient(), getSessionSisenseUrl(), getSessionSisenseToken() from src/utils/sisense-session.ts. Never touch globals.
2. Generate session artifact IDs with `generateArtifactId(type)` — not Date.now(), not extra.requestId, not session counters. Same rule applies to S3 filenames (randomUUID() not Date.now()).
3. Wrap CSDK calls in csdkBrowserMock.withBrowserEnvironment(async () => { ... }).
4. Wrap engine calls in runWithUserAction('MCP', 'ASSISTANT', () => ...) for telemetry.
5. Sanitize errors before logging — console.warn(sanitizeError(err).message). Never log raw errors; they may contain tokens in URLs.
6. Sanitize user input — sanitizeForText(userPrompt) for prompts, sanitizeForDescription() for short strings.
7. Return `isError: true` in catch blocks alongside structured content (see buildChart error path).
8. Register in `mcp-server.ts` — add tool registration in setupMcpServer().
9. Write unit tests with bun test preload (src/__test-helpers__/setup.ts mocks browser globals).
10. Query cache — stored under queryId in build-query.ts; trimmed via trimQueryCache in session-query-cache.ts. Do not clear on MCP re-initialize.

Pitfall: ChatGPT multiple MCP sessions (re-initialize)

ChatGPT opens several MCP HTTP sessions per chat (model tools, MCP app iframe, resources/read). Each sends initialize without mcp-session-id. That is not a new user conversation.

Do not clone/clear persistentStates on re-init — it breaks buildQuery → buildChart (retrieveQuery_miss). Re-init only calls refreshSessionBaseUrl() and reuses the same SessionState Map (sse-server.ts).

Debug with NODE_ENV=development and [mcp-session] logs from devDebug. Expect initialize_reuse with conversationKeys still containing the queryId after buildQuery_stored.

Query cache size: MCP_QUERY_CACHE_MAX_ENTRIES (default 10) — oldest query-* keys evicted on each new buildQuery.

AJV / Bun Compatibility

The MCP SDK's JSON Schema validation is bypassed with a no-op validator because AJV has compatibility issues with Bun:

const noOpValidator: any = {
  getValidator: () => (input: unknown) => ({ valid: true, data: input, errorMessage: undefined }),
};
new McpServer({ ... }, { jsonSchemaValidator: noOpValidator });

Zod handles all validation internally. Don't remove this or try to wire in AJV — it will break.

Credential Key (Persistent State)

The persistentStates Map is keyed by a 16-char hex credential hash:

createHash('sha256').update(`${sisenseUrl}:${sisenseToken}`).digest('hex').slice(0, 16);

This means: same user with same credentials → same persistent state, regardless of how many times they reconnect. New conversation resets per-conversation keys but preserves credentials and reusable payloads.