MCP: Support the 2026-07-28 protocol without legacy sessions #2625

Part of #2408: the protocol implementation for release gate L2. It implements the contract agreed in #2624.

Goal

Serve only MCP 2026-07-28 at the Data API MCP endpoint. Upgrading the framework is necessary but not sufficient: Quarkiverse MCP Server 2.0.3 still accepts and advertises older revisions, so version admission and server/discover must be restricted explicitly.

Status

• MCP: upgrade framework and test stateless tools/list #2644 upgrades the BOM from 1.13.0 to 2.0.3 and tests stateless tools/list.
• Upstream #1078 merged on October 19, 2026. The latest published release checked is still 2.0.3 and does not contain the merge. Track the first release containing configurable supported versions, adopt it, and verify version admission and advertised versions together.

Required changes

Each item links the changelog entry it implements and is written as behavior a test can check. Within each group, items follow changelog order; uppercase M marks a major change and lowercase m a minor one.

Prerequisite

• Upgrade to 2.0.3 on Quarkus 3.38.1 (MCP: upgrade framework and test stateless tools/list #2644), changing the platform only for a demonstrated incompatibility. Pin test-client revisions.

Version, session and transport

• M1 No MCP session is created and no Mcp-Session-Id is issued. An obsolete session header on an otherwise valid request is ignored.
• M2 initialize and notifications/initialized are removed. A request is rejected unless its _meta carries io.modelcontextprotocol/protocolVersion and io.modelcontextprotocol/clientCapabilities, with no fallback to a default version. Omitted clientInfo is accepted; a present one is validated.
• M3 server/discover advertises exactly the supported set (initially 2026-07-28, not a >= comparison) and only the capabilities we implement.
• M5 ping, logging/setLevel and notifications/roots/list_changed are removed, along with unsolicited log notifications.
• M9 No SSE event IDs are emitted, and Last-Event-ID is ignored without replaying anything.
• m4 A POST without Mcp-Method, or a tools/call without Mcp-Name, is rejected.
• m12 Errors use the final codes: HeaderMismatch -32020, MissingRequiredClientCapability -32021, UnsupportedProtocolVersion -32022.
• D2 Only the Streamable HTTP flow is exposed; the legacy HTTP+SSE entry points are removed.

Results

• M8 Discovery, tools/list and completed tool calls (including isError results) carry resultType: "complete" and serverInfo.
• m3 tools/list returns tools in a deterministic order that stays stable across pages.
• m5 Complete server/discover and tools/list results include ttlMs and cacheScope. Start with private scope and ttlMs: 0 until a cache policy is reviewed.

Schemas (audit; change only what fails)

• m1 Capability serialization accepts the extensions map.
• m10 Generated tool schemas validate as JSON Schema 2020-12, and structuredContent handling makes no object-only assumption. Data API's object responses stay as they are.
• S1 A regression test shows fractional minimum, maximum and default values survive.

Integration

• The endpoint is OAuth-only, integrated with MCP: Add OAuth authentication and discovery #2642. MCP gets no custom token-header fallback; ordinary Data API HTTP authentication is unchanged.
• Regression tests cover optional and null tool arguments, and request-context teardown with asynchronous tools. The upstream fixes ship in 2.0.3; Data API's own context cleanup is MCP: Keep request IDs and logs separate between tool calls #2629.

Deliberately not implemented

This is a tools-only launch, so these stay unadvertised:

• M4 POST subscriptions: only needed if we advertise listChanged.
• M6 tasks, M7 multi round-trip requests, m11 URL elicitation completion, D1 roots, sampling and logging, D3 sampling includeContext values: no current tool needs them.
• m6 resource-not-found -32602: only if resources are exposed.

The remaining changelog entries are tracked elsewhere: m2 (trace context) in #2629, and m7–m9 and D4 (authorization) in the authorization-service work under #2408.

Done when

• Build, package, focused tests and the existing DSE/HCD MCP suites pass against 2026-07-28.
• The dependency tree, built artifact version and test results are attached here.

Close on that evidence. Raw wire conformance (#2626), client qualification (#2633) and deployment (#2634) are verified separately and don't block closing this ticket.

Normative detail: Streamable HTTP, authorization, caching.