Relocated onto the decomposed module layout and hardened:
- Trigger covers the rejection CLASS, not just literal 400: SSE-only
servers' load balancers answer the chunked Streamable HTTP initialize
POST with 400/405/406/411, and the mcp>=2.0 SDK surfaces many such
rejections as an opaque -32603 'Server returned an error response'
(error class per #104363 by @RohithPariki). Timeouts and 5xx never
trigger the fallback: they are not transport mismatches.
- Reconnect exclusion via _ever_connected instead of _ready: run()
clears _ready before re-entering the transport, so the original guard
also fired on reconnects after a proven session.
- Successful fallback latches _sse_fallback so reconnects go straight
to SSE, and logs a warning suggesting the user pin transport: sse.
- Both transports failing raises a ConnectionError naming both errors
and suggesting transport: sse / checking the URL.
- No fallback with strict_redirect_headers (SSE cannot enforce that
boundary) or when transport is explicitly configured.
- Tests trimmed to 3 invariant contracts (proven red on base): fallback
connects + latches; no fallback on reconnect/timeout/5xx; both-fail
error is actionable.
The extracted SSE path reuses _sse_transport/_serve_transport from main,
preserving the bounded handshake timeout and reconnect-retry semantics.
Fixes#53676
mcp.servers.status now rides the shared _mcp_rpc decorator (profile scope, 4064,
5024 with the real message) instead of a hand-rolled try/finally with a blanket
except. Drop the _MCPConnectErrorText str subclass and reason taxonomy: the
existing status/error fields already carry the state, and a whitelist on the RPC
keeps error text out of the wire. The Desktop connections.health contribution
contract is held back until its consumer plugin is public. Tests trimmed to the
scope invariants (per-profile runtime visibility, scoped shutdown clears only its
own status, launch runtime never leaks into another profile).
For each issue anchor present in BASE 63279301bc non-test .py and absent on HEAD, the BASE comment/docstring block was re-attached at the HEAD location of the code it explained (matched by the distinctive code line / enclosing def). Sentences already covered by an existing HEAD comment were deduped; the issue number always survives. Insert-only: no code lines changed.
