The least-privilege half of the criterion could not hold as built.
provision_mcp.py creates the endpoint owner's workspace through
CoreHandler().create_workspace, which makes that account its ADMIN, and
2.3.3 knows only ADMIN and MEMBER - both write table data. There is no
read-only workspace role to demote to, so mutating_tools_enabled: false
bounded nothing while create_rows, update_rows and delete_rows sat in the
served allowlist.
The adapter's contract simply omits them: a client calling one is refused
with DENY_UNKNOWN_TOOL. Omission is the mechanism, since passthrough.py
refuses to load a contract that lists a mutating tool while mutations are
off. The other ten stay recorded under upstream_serves so a version bump
enabling one shows up as drift rather than as a silently wider surface.
The transport was what reverted this twice. Baserow speaks classic
HTTP+SSE, where a GET opens the response stream and the stream names a
second URL for requests, while the adapter only ever spoke Streamable
HTTP. adapter.upstream_transport selects sse.py and defaults to
streamable_http, so no existing provider changes.
The endpoint key stops being a client credential. Clients present
credentials.mcp_bearer to the sidecar; the key reaches the sidecar as
ADAPTER_UPSTREAM_PATH_KEY and is spliced in percent-encoded, so it never
enters the rendered contract and a key carrying a separator cannot open a
path of its own.
Deploy is green: the probe reached list_databases over SSE, the served
surface matched the contract, and the sidecar proved it reaches only its
provider.
