Streamable HTTP answers a POST on the same request; classic SSE splits the channels, so a GET opens the response stream and that stream announces a second URL as the request channel. The adapter only ever spoke the former, which is what reverted the Baserow migration twice. A contract now selects the transport and defaults to streamable_http, so no existing provider changes, and an unknown value is refused at load rather than at the first tool call.
The stream is opened once and held, because reopening it per call would lose whatever answer is already in flight. A notification carries no id, so it posts without awaiting a response the protocol never sends. A dead stream is now reset alongside the session it belongs to, since rebuilding the handshake over a dead stream would keep using it.
Two things this cleaned up on the way: NoRedirect and OPENER had been copied rather than reused, so server.py now takes the one in sse.py, and decode_jsonrpc moved to passthrough.py where it belongs, since it unwraps MCP responses rather than HTTP, which also brought server.py back under the file-size limit.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Four guarantees the contract made were never applied. concurrent_requests and stream_seconds appeared nowhere but the required-key list: ThreadingHTTPServer starts a thread per connection and asks no contract, so the ceiling only holds if the handler refuses the surplus itself, which it now does with 503 and gives the slot back on the failure path as well. The upstream was opened with urlopen, which follows redirects, and urllib copies the request headers onto the redirect target, so an upstream answering 302 with an off-host location would have handed the adapter's upstream credential to whoever it named.
input_schema was published to clients and never checked, which made it a suggestion: on the openapi path an argument the contract does not name is appended to the upstream request as a query parameter, so a client could add parameters the reviewed operation never granted, and a tool declaring no schema accepted anything. A tool that declares no inputs now takes none, a required input must be present, and the check runs after the size ceiling so a large payload is still refused for being large. No shipped contract regresses: the read tool every deploy probe calls declares no required argument, measured across all fourteen contracts.
sse.py adds a client for the classic HTTP+SSE transport, which splits the response and request channels across two URLs and needs a reader thread because the answer to a POST regularly arrives before the POST returns. It has no caller yet. The deploy probe keeps its own SSE implementation deliberately: it guards every enabled surface today and fails by exit code rather than by exception.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
kevinveenbirkenbachandClaude Opus 5