Persistent store of MCP server names the user has disabled.
Disabled servers are skipped at config merge time so their tools never
reach the agent and no connection is attempted. State lives under
[mcp_disabled] in ~/.deepagents/config.toml, mirroring the layout
used by mcp_trust.py.
The store keys on server name alone. Two configs that both declare a
github server will both be disabled by a single entry — intentional,
since the agent cannot distinguish overlapping names at runtime anyway
(later configs in the merge order win).
Return the set of server names the user has disabled.
Return True when server_name is in the disabled set.
Add or remove server_name from the persistent disabled set.
Refuses to write when the existing config cannot be parsed so a
corrupt or permission-denied file is not silently overwritten —
that would discard sibling sections such as [mcp_trust].
