* Separate proxy protocol policy from client construction
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* Strip connection-owned request metadata at the proxy backend boundary
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
* Sanitize forwarded request metadata where the proxy copies it
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
* Forward hop-safe request metadata for proxied resources, templates, and prompts
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Most pins in tests/server/providers/proxy/ were added only to keep tests
green while unpinning changed which protocol era the proxy's backend
connection used, not because the test's subject cared about the era. With
proxy era-mirroring (#4573) landed, a front client on auto correctly moves
the whole chain to the modern protocol, so plain tool/resource/prompt calls
through a proxy no longer need a pin.
Kept pins fall into three buckets, each commented at the call site: tests
whose subject is genuinely handshake-only (sampling, roots, elicitation
push-forwarding, ping, initialize handshake mechanics); tests whose backend
is a directly-constructed ProxyClient/StatefulProxyClient, which always
defaults to legacy independent of the front era; and two tests left pinned
with a TODO documenting a real defect this audit surfaced (upstream
instructions not forwarded to a modern-era client through a proxy, and
ProxyProvider.list_tools leaking an unwrapped connection error instead of
an MCPError).
Client negotiates the newest mutual protocol era by default (probe
server/discover, fall back to the initialize handshake). ProxyClient and the
inspect utility explicitly pin the handshake era so proxy forwarding and
server_info reads are unchanged. SSE and multi-server config transports are
legacy-only. extensions= and result_claims= (SEP-2133) are thin passthroughs
to the SDK session.
Replaces FastMCP.as_proxy() helper calls with create_proxy(), rewrites the
mount() as_proxy=/prefix= kwarg tests to plain mount() (the params are gone),
and deletes deprecation-only tests for as_proxy() and remove_tool().
