Removes pins added while making the auto-default suite pass that weren't
actually testing older-protocol-only behavior, and keeps (with a stated
reason) the ones that are. Along the way, fixes two real defects the audit
surfaced in the modern protocol path: PingMiddleware could leak a
_active_sessions entry when a connection's exit_stack closed before its
keepalive task got its first scheduler turn, and FastMCP(experimental_
capabilities=...) was silently dropped from server/discover responses
(it only ever reached the legacy initialize handshake).
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.
* Reapply span attributes after creation to survive non-forwarding samplers
Tracer.start_span builds the span from sampling_result.attributes, not
the attributes kwarg — a custom Sampler that returns
SamplingResult(RECORD_AND_SAMPLE) without forwarding attributes
silently drops everything FastMCP passed at creation time. Reapply the
same attributes immediately after span creation (guarded by
is_recording()) so on_start hooks and samplers still see them, while
the finished span is guaranteed to carry FastMCP's telemetry
regardless of sampler behavior.
* Restore only missing span attributes, not a blanket reapply
Reapplying all attributes after span creation overwrote values a
sampler deliberately set (e.g. a redacted mcp.method.name) and
inflated dropped-attribute counts when the SDK's attribute limit was
hit. Compare against the span's existing attributes and restore only
the keys a non-forwarding sampler actually dropped, via a shared
restore_missing_attributes() helper in fastmcp.telemetry.
* Gate attribute restore on all-or-nothing, not per-key
Restoring only missing keys reinserted attributes the SDK's bounded
attribute map had already evicted under a low
OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT, evicting a different retained key and
inflating dropped_attributes beyond what the sampler actually dropped.
Gate on none of our attributes being present (plus dropped_attributes
== 0) instead — the regression this exists to fix is a sampler
dropping everything, and eviction under a limit always leaves some.
Renamed restore_missing_attributes to restore_dropped_attributes to
match.
* Gate attribute restore on empty span, not per-key presence
A sampler that intentionally supplies only its own attributes (e.g. to
strip component names or resource URIs for privacy/cardinality
control) left none of FastMCP's keys on the span, so the previous
all-or-nothing gate treated it identically to a bare non-forwarding
sampler and restored everything, defeating the filter. Key off the
span having no attributes at all instead — a bare sampler leaves it
empty, a filtering sampler doesn't.
