Part of the StudioMeyer MCP Stack — Built in Mallorca 🌴 · ⭐ if you use it

mcp-tenant-pair

Spec: MCP 2025-06-18 License: MIT Repo layout: monorepo (npm workspaces)

packages/
  lib/        mcp-tenant-pair          (TypeScript library)
  cli/        mcp-tenant-pair-cli      (commander CLI)
  demo/       mcp-tenant-pair-demo     (reference Low-Level MCP server, stdio)

A note from us

We have been building tools and systems for ourselves for the past two years. The fact that this repo is small and has few stars is not because it is new. It is because we only just decided to share what we have built. It is not a fresh experiment, it is a long story with a recent commit.

We love building things and sharing them. We do not love social media tactics, growth hacks, or chasing stars and followers. So this repo is small. The code is real, it gets used, issues get answered. Judge for yourself.

If it helps you, sharing, testing, and feedback help us. If it could be better, an issue is more useful. If you build something with it, tell us at hello@studiomeyer.io. That genuinely makes our day.

From a small studio in Palma de Mallorca.

Related MCP server: Arachne Discord MCP

Why this exists

Most MCP servers today are single-user. The moment you want to share state across two or more humans (couples, families, small groups) you hit the same five sub-problems each time: pair creation, invite flow, identity-separated state, conflict resolution, voluntary leave / kick. This library solves them once, so downstream MCP servers (Pet-Platform, recipe-sharing, household, calendar) do not re-invent them.

5-Minute Quickstart

Library

import { TenantPair, SqliteTenantStore, LWWResolver } from "mcp-tenant-pair";

const tp = new TenantPair({
  store: new SqliteTenantStore({ path: "./tenant-pair.sqlite" }),
  resolver: new LWWResolver(),
});

const { pairId, inviteToken } = await tp.createPair({ creatorMemberId: "alice" });
await tp.acceptInvite({ inviteToken, memberId: "bob" });

await tp.setMemberPreference(pairId, "alice", "allergy", ["nuts"]);
await tp.setSharedState(pairId, "alice", "tonight", "pizza");

const aliceConstraints = await tp.getMemberConstraints(pairId, "alice");
const shared = await tp.getSharedState(pairId);

CLI

npx mcp-tenant-pair-cli pair create --member-id alice
npx mcp-tenant-pair-cli pair invite --pair-id <id> --member-id alice
npx mcp-tenant-pair-cli state set --pair-id <id> --member-id alice --key tonight --value pizza
npx mcp-tenant-pair-cli state get --pair-id <id>

Demo MCP server

node packages/demo/dist/server.js
# or via stdio in your MCP client config

Reads MCP_TENANT_PAIR_DB env (default :memory:).

Tools (12)

Compatibility Matrix

Storage adapters

• SqliteTenantStore — default, embedded, single-process. Uses better-sqlite3 with WAL mode. Pass { path: "./pair.sqlite" } or :memory:.

• PostgresTenantStore — multi-process, multi-tenant. Accepts any pg.Pool-shaped client ({ query<R>(text, params): Promise<{rows: R[]}>, end?(): Promise<void> }). pg is a peer dependency.

Conflict resolution

ConflictResolver is an interface. Two implementations ship:

• LWWResolver — picks the row with the latest validFrom, ties broken by highest version. Throws on empty candidate list.

• ManualResolver — returns no resolutions; conflicts stay pending until a human resolves them externally.

Inject your own by implementing { name: string; resolve(conflicts: Conflict[]): Resolution[] }.

Bi-temporal model

Every overwrite of a (pairId, namespace, key) triple sets valid_to on the previous active row and inserts a new row with a fresh valid_from. version is monotonic per key. This lets you replay history (getPairStateHistory) and detect concurrent writes deterministically.

Identity separation

member_state is per-member (only readable by that member via get_member_constraints). pair_state is shared (all active members can read via get_shared_state).

Writes by a member who later leaves or is kicked stay visible in shared state.

Security notes

• Invite tokens are <uuid v4>.<XXXX-XXXX> — uuid v4 (122 bits CSPRNG entropy via node:crypto) plus a voice-readable base32 short-code (default RNG is node:crypto.randomInt, injectable for tests).

• Per-pair pending-invite cap (default 25, configurable via maxPendingInvites).

• Owner-only kick. Owner cannot kick themselves; use leave instead.

• DSGVO Art. 17 erasure path: forgetMember(pairId, memberId) hard-deletes the member's member_state rows (allergies, dietary preferences) and nulls display_name. Membership trace (left_at) is retained for audit.

• Postgres adapter rejects schema names that don't match /^[a-z_][a-z0-9_]{0,62}$/ at construction time (defense against SQL injection via integrator-supplied schema strings).

• acceptInvite is race-safe — both adapters use atomic transactions (better-sqlite3 immediate transaction; pg BEGIN + SELECT ... FOR UPDATE).

• Time is injectable (now: () => Date) for deterministic tests.

Development

npm install
npm run build
npm test

Tests cover (142 + 1 conditional):

• Pair creation (8)

• Invite flow (10)

• Invite expiry boundary (6) — accept/pending agree at the exact expires_at instant, both adapters

• Member preferences (8)

• Shared state (8)

• Conflict resolution (13)

• Resolvers (11)

• Error handling (17) — exhaustive TenantPairError code coverage

• Store adapters (6)

• Postgres adapter (26) — schema-identifier validation, atomic transaction, fallback paths (mock pool, no live DB)

• Adapter parity (6 + 1) — same operations against SQLite and Postgres produce identical results; the Postgres leg runs only when TENANT_PAIR_TEST_PG_URL/DATABASE_URL points at a reachable database and is skipped otherwise (never false-fails)

• Demo server integration (9)

• Round-1 regression fixes (14) — SQL-injection schema-validation, TOCTOU acceptInvite race, conflict-resolved winner-marker, asOf-clock, DSGVO erasure, CSPRNG-default

Run the cross-adapter parity suite against a real Postgres:

TENANT_PAIR_TEST_PG_URL=postgres://user:pass@host:5432/db npm test

Status

Foundation build. Reviewed (Cold-Cross-Review + MCP Factory Reviewer + Tester) — all HIGH/MEDIUM findings fixed. tsc clean (strict), 142 tests green (+1 Postgres-conditional skip). Prod dependency tree carries 0 known advisories (npm audit --omit=dev).

About StudioMeyer

StudioMeyer is an AI and design studio based in Palma de Mallorca, working with clients worldwide. We build custom websites and AI infrastructure for small and medium businesses. Production stack on Claude Agent SDK, MCP and n8n, with Sentry, Langfuse and LangGraph for observability and an in-house guard layer.