Add hand-entered (custom) MCP servers not listed in any registry

[yh928]

Summary

Let users add an MCP server they run themselves — a local stdio command or a remote HTTP(S) endpoint — from the desktop UI, for servers that no registry (mcp_official / Smithery) lists. Surfaces as a "Custom servers" pane on the MCP Servers tab (Connections → MCP Servers).

Problem

The MCP Servers tab today can only install servers a registry lists. There is no way from the UI to connect a server you host yourself: a local npx/uvx command, or a private/internal HTTP MCP endpoint. The only workaround is hand-editing config outside the app, which doesn't integrate with the registry UI, the connection health toolbar, or the OAuth flow. The store schema already carries the needed columns (command, args_json, transport, deployment_url, enabled) — only the add/edit path and UI are missing.

Solution (optional)

Scope: core + app.

• Core RPCs mcp_clients_add_custom / mcp_clients_update_custom writing an ordinary InstalledServer with a new ServerProvenance (registry vs hand-entered) column, reusing the existing MCP transport / OAuth / tool-safety code paths — no second MCP client.
• UI: a side pane + add/edit modal on the MCP Servers tab.
• Credentials are scope-bound (write-only env; stored secrets, including the OAuth bundle, are dropped and must be re-entered when the credential scope changes — transport switch or HTTP origin change — never carried across).

Acceptance criteria

• Add local (stdio) server — command + args, launched and connectable
• Add remote (HTTP) server — http/https URL, connectable including OAuth
• Edit / remove a custom server; identity stable across a rename
• Provenance — legacy rows backfill to registry; install cannot clobber a custom row
• Diff coverage ≥ 80% — the implementing PR meets the changed-lines coverage gate (Vitest + cargo-llvm-cov, enforced by .github/workflows/ci-lite.yml).

Related

Implementation ready on a fork; PR to follow. That PR also carries a small, related MCP fix (cancelling the OAuth sign-in wait), tracked separately.