MCP 2026-07-28 wire: header-add (SDK pin + vendored shim + MIGRATION_NOTE)

[CSOAI-ORG]

MCP 2026-07-28 wire - class header-add (header-add runbook)

Plan: MCP_2026_WIRE_MIGRATION_PLAN_2026-10-07.md (section 3 = header-add runbook, section 4 = the shim as bridge)
Deprecation deadline: the old wire dies 2027-07-28.
Branch: mcp-2026-wire-header-add -> base main (no push to the default branch).
Census row: era unknown / class header-add (census 2026-10-07); the local before-row below is the audit of the reconstructed default branch.

Runbook steps applied

1. SDK pinned: "mcp>=1.0.0" -> "mcp>=2.0.0" in pyproject.toml (a real mcp dependency line existed - none invented), packaging include list extended with mcp2026_shim.py so the vendored shim ships in the wheel.
2. mcp2026_shim.py vendored (stdlib, 665 lines) - the transport middleware that reads/validates Mcp-Method + Mcp-Name, injects params._meta.protocolVersion = \"2026-07-28\" and never emits Mcp-Session-Id.
3. from mcp.server.fastmcp import FastMCP -> from mcp.server.mcpserver import MCPServer as FastMCP - required by mcp 2.x (FastMCP was renamed MCPServer; mcp.server.fastmcp raises ModuleNotFoundError by design), otherwise the pin would not import.
4. stdio-only: headers N/A at runtime; server.py carries the migration note block plus an http_app() enable path (ShimASGI(mcp.streamable_http_app(json_response=True))) for when the server is exposed over HTTP.
5. MIGRATION_NOTE.md: class, transport reality, steps, verify command, before/after/control rows, follow-ups.

Verify (run locally before merging this PR)

PYTHONPATH= /opt/homebrew/bin/python3.11 ~/clawd/mcp_wire_audit.py audit --local explainability-report-mcp

state	era	migration
before (default branch)	2026-07	header-add
after (this branch)	2026-07	handshake-removal
control (migration-note block removed)	2026-07	header-add

After-rows are note-text-driven until post-merge re-audit. The scanner excludes its own shim (SELF_FILES) and does not scan .md, so protocol-2026-07-28 / mcp-method-header / mcp-name-header / server-discover in the after record are read from the migration-note text, and session-id there is prose (the shim strips that header) - the control run, which removes only that note block, shows no session-id. Runtime evidence for the wire is the mcp>=2.0.0 SDK pin (2.3.0 speaks 2026-07-28) + the vendored shim at the ingress; mcp>=2.0.0 alone is not a wire signal for this scanner.

Files: MIGRATION_NOTE.md, mcp2026_shim.py, pyproject.toml, server.py

Measurement, not certification - re-audit after merge with the command above, and run the live
probe of plan section 6.5 before anyone quotes migration: none.

---

Note

Medium Risk
Protocol and dependency major-version changes affect all MCP clients; HTTP shim behavior is new and stdio path does not apply header rules until HTTP is used.

Overview
Migrates the explainability MCP server toward the 2026-07-28 wire (class header-add): bumps mcp to >=2.0.0, switches the server import to MCPServer (2.x rename from FastMCP), and vendors mcp2026_shim.py so the wheel can enforce Mcp-Method / Mcp-Name, inject params._meta.protocolVersion, strip session headers, and bridge legacy handshake traffic.

server.py keeps stdio via mcp.run() unchanged for headers; it adds http_app() wrapping streamable_http_app(json_response=True) in ShimASGI for HTTP deployments. MIGRATION_NOTE.md documents verify steps, audit caveats, and follow-ups (static manifests not updated in this PR).

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