fix(runtime-admin): swap dead agent.mcp_registry import for plugin helper (Phase 5)

[deestax]

The runtime-admin POST /myah/v1/admin/mcp/disconnect/{name} handler imported disconnect_mcp_server from agent.mcp_registry — a module that does not exist anywhere in the repo (or upstream). Every request hit the except Exception fallback and returned 500 "MCP registry module not available".

The dashboard's DELETE /mcp/<name> route (in myah_admin.dashboard._skills_plugins_mcp) delegates to this endpoint over HTTP. The dashboard captured the 500 and fell through to its own config.yaml mutation, so users saw "disconnect succeeded" while the gateway kept the stale reference in tools.mcp_tool._servers until process restart. Toolset cache + MCP-aware tool routing kept treating the server as connected until then.

The fix

Swap the import to the real plugin-side helper at myah_hermes_plugin.runtime_extensions.mcp_disconnect.disconnect_mcp_server. That module has shipped since PR NousResearch#106 (Phase E) — it uses upstream's tools.mcp_tool private state + the _run_on_mcp_loop cross-loop bridge, exactly the pattern upstream's "shutdown ALL servers" helper uses.

One-line swap + a longer comment block explaining the resolution chain so future maintainers don't undo it.

Regression test

tests/test_runtime_admin_mcp_disconnect.py drives the real handler from _make_handlers() against a mocked tools.mcp_tool state (servers dict + threading lock + _run_on_mcp_loop) and asserts:

1. Endpoint returns 200 + {ok: True, name: "..."} (NOT the 500 import-error fallback)
2. The plugin-side helper actually pops the server from tools.mcp_tool._servers (cross-checks the chain end-to-end)
3. Idempotent: unknown server name → still 200 + ok=True (matches dashboard's evict-all chain pattern)

Pre-fix: both tests fail with ModuleNotFoundError: No module named 'agent.mcp_registry' (TDD).
Post-fix: both tests pass.

The existing test_mcp_disconnect.py covers the plugin helper in isolation; this new file covers the runtime-admin handler that calls into it — closes the integration gap.

Companion PR ordering

Parent-repo submodule bump PR follows on T3-Venture-Labs-Limited/myah. Merge this first.

Refs docs/superpowers/plans/2026-05-11-no-fork-vendoring-respec.md (Task 2: Phase 5 fix, ~0.5h estimate).

[github-actions]

🔎 Lint report: fix/runtime-admin-mcp-disconnect-import vs origin/main

ruff

Total: 0 on HEAD, 0 on base (➖ 0)

🆕 New issues: none

✅ Fixed issues: none

Unchanged: 0 pre-existing issues carried over.

ty (type checker)

Total: 8004 on HEAD, 8003 on base (🆕 +1)

🆕 New issues (2):

Rule	Count
unresolved-import	2

First entries

plugins/myah-hermes-plugin/tests/test_runtime_admin_mcp_disconnect.py:32: [unresolved-import] unresolved-import: Cannot resolve imported module `pytest`
plugins/myah-hermes-plugin/tests/test_runtime_admin_mcp_disconnect.py:33: [unresolved-import] unresolved-import: Cannot resolve imported module `aiohttp.test_utils`

✅ Fixed issues: none

Unchanged: 4193 pre-existing issues carried over.

Diagnostics are surfaced as warnings — this check never fails the build.