fix: align MCP 2026 transport interoperability

[MaazAhmed47]

Scope

This draft repairs and verifies Interlock's deliberately scoped MCP 2026-07-28 transport profile. It does not claim full MCP 2026 support or protection for direct MCP connections that bypass the gateway.

Pinned authoritative inputs:

• MCP specification release 2026-07-28, commit 5f5440bb26a62e2cf3440b92da5a667efa03b267
• Python SDK mcp==2.0.0, commit 6f69a3758ebf2ee55ce050f58b470ce11af71133, wheel SHA-256 1cb4c75d2d2c7b8c1d756355e5d82a39f2822cc7f13e22a2051d7ca3592349d6
• TypeScript client/server 2.0.0, commit cc4b41617ce3601b1290d67216ea0b194a3cd9ac, with npm integrity values recorded in the compatibility matrix
• Conformance 0.2.0-alpha.10, commit a9896553900a2ef61787b57adfcbbe936a8ab1f9, as supplemental evidence only

Findings and fixes

• The official specification now has a separate non-prerelease 2026-07-28 release. The old RC status and Python b2 incompatibility are historical, not the current SDK result.
• The outbound modern adapter accepted malformed JSON-RPC envelopes and missing or invalid required cache metadata. It now rejects those responses, invalid optional identity metadata, and unsupported response media types without downgrade.
• Header/body protocol-version conflicts returned the unsupported-version error. They now return the specified header-mismatch error while matching unsupported versions remain rejected separately.
• Unknown or unavailable tools were represented as tool execution failures. They now produce a generic protocol error before upstream execution without exposing eligibility state.
• SDK wire probes retain an allowlisted structural view only; arguments, request IDs, client-info values, capability contents, credentials, unknown metadata, and response bodies are not retained.
• No duplicate serverInfo, SDK fingerprint, User-Agent branch, legacy fallback, required-capability tool, or production SDK dependency was added.

Interoperability evidence

• Python mcp==2.0.0, automatic discovery: server/discover, tools/list, and tools/call passed against Interlock.
• Python mcp==2.0.0, explicit 2026-07-28: tools/list, tools/call, and no-fallback rejection passed. This SDK mode adopts the pinned version without discovery.
• TypeScript client 2.0.0, explicit pin: discovery, list, call, identity parsing, and no-fallback rejection passed.
• Interlock explicit modern profile against TypeScript server 2.0.0 with legacy rejection and JSON responses: discovery, list, call, exact headers, and per-request metadata passed.
• Legacy upstream byte-shape regression, malformed response rejection, pagination containment, unsupported parameter-header containment, and gateway identity stamping passed.
• Alpha conformance result: 21 successes, 4 failures for absent scenario diagnostic tools, and 5 subscription skips. One absent diagnostic tool is the required-client-capability probe. Interlock currently declares no capability-gated tool, so -32021 remains unimplemented and unexercised. This is not a conformance-suite pass.

Unsupported behavior remains unadvertised and fail-closed: SSE response parsing, pagination, MRTR/input-required, subscriptions, tasks, and x-mcp-header forwarding. Required-client-capability behavior and -32021 are unsupported/unimplemented rather than claimed supported.

Verification

• Focused SDK/profile/eligibility suite: 42 passed
• Full pytest with both official SDK probes and alpha conformance probe enabled: 1,789 passed, 126 skipped, 6 xfailed, 4 warnings
• PostgreSQL-gated suite on disposable PostgreSQL 16.14: 131 passed, 0 skipped, 3 warnings
• Changed-Python Black: PASS, 5 files
• Changed-Python Ruff: PASS, 5 files
• Targeted mypy: PASS, 3 Python files
• compileall: PASS
• Node syntax checks: PASS, 2 fixtures
• Prettier: PASS, 2 fixtures
• git diff --check: PASS
• Secret and artifact sanitization scan: PASS

With INTERLOCK_TEST_DATABASE_URL set to a disposable PostgreSQL 16 database, the exact 131-test selection is:

python -m pytest -q tests/test_policy_postgres_boolean.py tests/test_audit_chain_concurrency.py::test_concurrent_replica_appends_cannot_fork_the_chain tests/test_postgres_api_key_revocation.py tests/test_postgres_audit_v3.py tests/test_postgres_ci_boundary_review_gate.py tests/test_postgres_obsolete_api_key_credential_compatibility.py tests/test_postgres_rebaseline_cas.py tests/test_postgres_registry_migration.py tests/test_postgres_usage_boolean.py

This selection comprises five Postgres-adapter boolean regressions, both parametrized real-Postgres concurrent-replica cases, and the seven environment-gated Postgres files. It does not include unrelated schema-conversion unit tests to inflate the database count.

No production dependency or configuration changed. No production deployment occurred. An automatic Vercel preview exists for the branch; production remains unchanged.

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Project	Deployment	Actions	Updated (UTC)
interlock-web	Ready	Preview, Comment	Jul 29, 2026 4:09pm