feat: implement MCP 2026-07-28 stateless protocol, task management, CIMD/OAuth 2.1 hardening, and MRTR support

[pallavt93]

Description

This PR implements the official Model Context Protocol (MCP) 2026-07-28 specification across the NitroStack Python SDK while maintaining backward compatibility for existing 2025-era sessionful clients.

It introduces protocol-era selection, official mcp 2.x integration for stateless HTTP and stdio, a task orchestration engine (TaskManager / TaskStore), multi-channel task status notification routing, hardened OAuth 2.1 and Client ID Metadata Document (CIMD) resolution, Multi-Round-Trip Requests (MRTR) for interactive elicitation, JSON Schema 2020-12 validation, W3C trace context propagation, cache hints, and a dedicated MCP 2.0 acceptance test suite.

Scope: 86 files changed · +15,105 / −650 lines · 58 commits

---

System Architecture Diagram

flowchart TD
    subgraph Clients["MCP Clients"]
        C1["Modern MCP Client (2026-07-28)\n(NitroStudio / Claude / Cursor)"]
        C2["Legacy MCP Client (2025-06-18)\n(Sessionful SSE / HTTP)"]
    end

    subgraph Transport["Transport Layer (HTTP / STDIO)"]
        TH["Streamable HTTP (/mcp)"]
        TS["StdIO Transport"]
        SEL{"Protocol Era Selector\n(MCP_STATELESS / NITRO_MCP_PROTOCOL_VERSION)"}
    end

    subgraph Engines["HTTP / Wire Engines"]
        MV2["Official mcp 2.x\n(sessionless / dual-era)"]
        LV1["Legacy 1.x Session Manager\n(era: legacy only)"]
    end

    subgraph Security["Auth & Interception Layer"]
        JWT["JWT / Bearer Verification\n(Authorization / envelope auth)"]
        CIMD["CIMD & SSRF Resolver\n(HTTPS, RFC 6890, 5 KiB cap, RFC 9207 iss)"]
        SAN["Argument Sanitizer\n(strips _meta from tool arguments)"]
    end

    subgraph Tasks["Task Orchestration (SEP-2663)"]
        TINT["Task Wire Interceptor\n(tools/call task param, tasks/get, tasks/cancel)"]
        TM["TaskManager\n(lifecycle, access control, cancellation safety)"]
        TS_STORE[("Pluggable TaskStore\n(InMemoryTaskStore / custom)")]
        NR["TaskStatusRouter\n(/subscriptions/listen / legacy SSE / stdio)"]
    end

    subgraph Features["Protocol Features"]
        MRTR["MRTR Elicitation\n(input_required / requestState)"]
        SCH["JSON Schema 2020-12\n(depth-bounded, registration gate)"]
        OBS["Observability & Caching\n(W3C Trace Context / cache hints)"]
    end

    subgraph Registry["NitroStack Application Registry"]
        TOOLS["@tool handlers"]
        RES["@resource handlers"]
        PROMPTS["@prompt handlers"]
        WIDGETS["Widget / UI templates"]
    end

    C1 -->|"stateless HTTP (_meta / server/discover)"| TH
    C2 -->|"legacy JSON-RPC (initialize / Mcp-Session-Id)"| TH
    C1 -.->|"stdio stream"| TS
    C2 -.->|"stdio stream"| TS

    TH --> SEL
    TS --> SEL

    SEL -->|"era: auto (default) | modern"| MV2
    SEL -->|"era: legacy (2025-06-18)"| LV1

    MV2 --> JWT
    JWT --> CIMD
    MV2 --> TINT
    TINT --> TM
    TM <--> TS_STORE
    TM --> NR

    MV2 --> SAN
    MV2 --> SCH
    MV2 --> MRTR
    MV2 --> OBS

    SAN --> TOOLS
    OBS --> TOOLS
    OBS --> RES
    SCH --> PROMPTS
    TOOLS --> WIDGETS
    RES --> WIDGETS

Loading

---

Protocol Era Support & Default Behavior

NitroStack Python features runtime protocol era resolution with auto as the default when unset:

• Unset / NITRO_MCP_PROTOCOL_VERSION=auto (default):
  One official mcp 2.x sessionless engine serves both modern 2026-07-28 clients (per-request _meta, server/discover, SEP-2243 headers) and legacy 2025 clients (sessionless initialize — no Mcp-Session-Id).
• NITRO_MCP_PROTOCOL_VERSION=2026-07-28 (or modern, latest, 2026):
  Pure modern stateless MCP 2.0; legacy 2025 wire is rejected.
• NITRO_MCP_PROTOCOL_VERSION=2025-06-18 (or legacy, 2025, 2025-11-25):
  Sessionful 2025-era wire via the legacy HTTP engine only.
• Precedence order:
  MCP_STATELESS > NITRO_MCP_PROTOCOL_VERSION > ServerConfig.protocol_era > default auto.

Era resolution is logged at HTTP/stdio startup with source: mcp_stateless | env | config | default.

---

Key Changes & Enhancements

1. Stateless Core & Protocol Versioning (SEP-2575, SEP-2567, SEP-2243)

• Official mcp 2.x integration: Bumped dependency to mcp>=2,<3; modern and auto eras mount the official v2 HTTP handler — not a second session manager on /mcp.
• Protocol era selector: nitrostack/protocol/version.py — dynamic resolution with documented era aliases; unknown tokens → auto.
• Discovery endpoint: server/discover on the HTTP engine advertising metadata, capabilities, and extensions.
• Stateless HTTP transport: No Mcp-Session-Id on sessionless engines; per-request _meta envelope support.
• Header validation & CORS: SEP-2243 method contract table for MCP-Protocol-Version, Mcp-Method, Mcp-Name, Mcp-Param-*; CORS preflight for 2026 headers; echo headers on responses.
• Health & ping: /mcp/health advertises resolved era; header-only ping fast path without a JSON-RPC body.
• Concurrent RPC isolation: Identical JSON-RPC ids on concurrent requests stay isolated.

2. Task Orchestration & Storage Abstraction (SEP-2663)

• Pluggable task storage: TaskStore interface and InMemoryTaskStore with terminal-only TTL eviction from lastUpdatedAt.
• Task lifecycle & safety: TaskManager — create, progress, input_required, resume, complete, fail, cancel; pagination; cancellation safety.
• Multi-tenant authorization: TaskAccessContext with anti-enumeration (TaskNotFoundError on mismatch).
• Wire interception: Task-augmented tools/call returns immediate CreateTaskResult; rejects deprecated tasks/result and tasks/list on modern wire.
• Multi-channel notifications: TaskStatusRouter in nitrostack/tasks/notify.py fans out notifications/tasks/status to /subscriptions/listen, legacy /sse, and stdio sessions; failed notify does not fail the task; honors task access context.

3. Hardened OAuth 2.1 & CIMD Authentication (RFC 9207, RFC 7517)

• CIMD resolver: HTTPS-only, no redirects, 5 KiB payload cap, timeout support, strict client-id URL validation.
• SSRF protection: RFC 6890 special-use and private IP blocking during CIMD fetch.
• Token extraction: Bearer from Authorization, spec envelope auth slot, and vetted _meta; verified JWT before unsigned envelope claims.
• Argument sanitization: Strips _meta and io.modelcontextprotocol/* keys from tool arguments before handlers run.
• RFC 9207 anti-mixup: Issuer validation on verified tokens.

4. Multi-Round-Trip Requests (MRTR) (SEP-2322)

• InputRequiredResult and MRTR helpers for multi-turn elicitation with input_required, inputRequests, and opaque requestState.

5. JSON Schema 2020-12 & Schema Normalization (SEP-2106)

• Registration gate rejects non-2020-12 schemas at tool registration.
• Depth-bounded schema processing (max 64); resource URI templates and resolution.

6. Cache Hints, Trace Context, Subscriptions & Stdio (SEP-2549, SEP-414)

• Cache hints (ttlMs, cacheScope) on list/read/discover responses.
• W3C Trace Context (traceparent, tracestate, baggage) on ExecutionContext.trace.
• GET/POST /subscriptions/listen: SSE attach on the official v2 subscription bus with JWT-gated listen when OAuth/JWT is required.
• Modern stdio: auto → official dual-era loop; modern → rejects initialize; legacy → handshake loop.

---

Environment Configuration

# =============================================================================
# NitroStack Python — Stateless MCP Server
# =============================================================================
NITROSTACK_LOG_LEVEL=info

# Transport: stdio | http | dual
MCP_TRANSPORT_TYPE=http
PORT=3000
HOST=127.0.0.1
ENABLE_CORS=true

# Protocol era (case-insensitive; unset = auto)
#   auto / both / dual / dual-spec  → dual-spec sessionless (default)
#   modern / latest / 2026 / 2026-07-28 → pure 2026 stateless
#   legacy / 2025 / 2025-06-18 / 2025-11-25 → sessionful 2025 wire
NITRO_MCP_PROTOCOL_VERSION=auto

# Explicit boolean override (wins over NITRO_MCP_PROTOCOL_VERSION)
# MCP_STATELESS=true  → forces modern
# MCP_STATELESS=false → forces legacy

# OAuth 2.1 (optional — set OAUTH_REQUIRED=true to enforce)
OAUTH_REQUIRED=false
RESOURCE_URI=http://localhost:3000/mcp
TOKEN_AUDIENCE=http://localhost:3000/mcp
AUTH_SERVER_URL=https://your-tenant.auth0.com
JWKS_URI=https://your-tenant.auth0.com/.well-known/jwks.json
TOKEN_ISSUER=https://your-tenant.auth0.com/

# Session limits (legacy era only)
MCP_MAX_SESSIONS=100
MCP_SESSION_TIMEOUT_MS=1800000

---

Type of Change

• feat: New feature
• fix: Bug fix
• refactor: Internal code change
• test: Test-only changes
• docs: Documentation update
• chore: Build, CI, or tooling changes

---

Verification & Testing

• pytest tests/test_mcp20_*.py — 17 modules, 455 tests passed
• Stateless HTTP ingress, discover, ping, CORS (test_mcp20_stateless_http.py)
• Protocol era resolution and blueprint conformance (test_mcp20_blueprint.py, test_mcp20_foundation.py)
• Task lifecycle, store TTL, authorization (test_mcp20_tasks.py, test_mcp20_task_store.py, test_mcp20_task_authorization.py)
• OAuth 2.1, CIMD, SSRF defenses (test_mcp20_oauth_cimd.py)
• JSON-RPC wire, contracts, deprecated methods, tool args (test_mcp20_jsonrpc_wire.py, test_mcp20_contracts.py, test_mcp20_deprecated.py, test_mcp20_tool_args.py)
• Subscriptions listen, concurrency, stdio era routing (test_mcp20_subscriptions.py, test_mcp20_concurrency.py, test_mcp20_stdio.py)
• MRTR, extensions, cache hints, observability (test_mcp20_mrtr.py, test_mcp20_extensions_cache_observability.py)
• Acceptance registry covers all seven protocol areas (test_mcp20_acceptance.py)

---

Checklist

• I have kept this PR focused and scoped
• I have used conventional commits
• I have added/updated tests where appropriate
• I have updated docs and starter templates where appropriate
• I have read and followed CONTRIBUTING.md

---

Implementation notes

Area	Python SDK
Wire engine	Official Python mcp 2.x package
Query-string tokens	Not implemented — Bearer / envelope auth / JWT only
Default HTTP bind	127.0.0.1
Merge target	develop