Feature/issue 24 wire alignment

[jpsiddharth2008]

Closes #24
Builds on #34 (#22) and #36 (#23) — this branch is stacked on top of feature/issue-23-http-factory, since neither has merged to develop yet. Please merge those first.

Summary

• After [mcp-2026] Remove JSON-RPC sidecar; one /mcp owner (official mcp 2.x) #22 removed the JSON-RPC sidecar, several 2026-07-28 wire behaviors were left half-finished — written assuming the sidecar would enforce them, and silently dead once it was gone.
• ping is retired for auto/modern (only legacy keeps it) — the official mcp SDK answers ping by default on every era unless explicitly told not to; NitroStack now opts out via NitroStackMcpServer.set_protocol_era().
• Added -32021 (MISSING_REQUIRED_CLIENT_CAPABILITY) to JsonRpcErrorCode — unused until the Tasks issue wires a live path for it, per [mcp-2026] Align 2026 wire: drop ping, add -32021, discover _meta, MUST headers #24's own acceptance criteria.
• server/discover's result _meta now carries serverInfo, in addition to the existing top-level copy (kept for auto/legacy back-compat).
• resultType is now stamped on tools/list, tools/call, resources/list, resources/templates/list, resources/read, prompts/list, prompts/get — not only discover/task-create/MRTR as before.
• Deleted dead sidecar-era code discovered while implementing this: build_sessionless_initialize_result, handle_sessionless_initialize (both copies), discover_handler/initialize_handler attributes on NitroStackMcpServer, the old optional-header validators in jsonrpc.py, and the unused MethodContract/MODERN_METHOD_CONTRACTS machinery in method_contract.py (kept only the still-used DEPRECATED_MODERN_METHODS/rejects_deprecated_method).
• Important finding that changed scope mid-implementation: the official mcp SDK already fully implements SEP-2243 MUST-header validation itself (mcp.shared.inbound.classify_inbound_request), triggered automatically whenever a client sends an MCP-Protocol-Version header the 2025 handshake doesn't recognize — independent of NitroStack's own protocol_era. I initially built a duplicate NitroStack-level validator per the issue's literal wording, then found this and removed it rather than ship a second implementation of the same ladder (exactly the anti-pattern [mcp-2026] Remove JSON-RPC sidecar; one /mcp owner (official mcp 2.x) #22/[mcp-2026] Unify HTTP factory: CORS once, subscribe flag, public stdio APIs #23 already removed). The new tests prove the SDK's existing behavior instead of re-testing NitroStack code that no longer exists.

Test plan

• pytest tests/test_mcp24_wire_alignment.py tests/test_mcp23_http_factory.py tests/test_mcp22_official_http_owner.py tests/test_transport_http.py tests/test_lifecycle_http.py tests/test_mcp20_stdio.py tests/test_transports.py — new tests covering the issue's full "Test / verify" table, plus every existing mcp-2026 regression file → 58 passed
• Full suite → 573 passed, 0 failed (excluded items independently confirmed pre-existing on the base branch or flaky Windows socket tests, not regressions from this branch — same exclusion list as [mcp-2026] Unify HTTP factory: CORS once, subscribe flag, public stdio APIs #23)
• Manual: booted examples/calculator_server.py and a scaffolded python-pizzaz project over HTTP, confirmed /mcp/health, tools/list, and widget metadata all work end-to-end

Note for reviewers

Filed a separate follow-up investigation (not part of this PR): server/discover returns "method not found" when called via the plain 2025-shaped stateless dispatch path with no MCP-Protocol-Version header — root cause is the official SDK's own spec-version gate (_methods.validate_client_request) rejecting NitroStack's extension method at the default negotiated version. Confirmed unrelated to this PR's changes; needs its own fix in the sidecar-free architecture.