Missing Conformance Tests

Traces (blocked — all runners unimplemented)

traces_event_attribute — match on span event attributes (all runners return nil for event_attribute)
traces_link_trace_id — match spans by linked trace ID (all runners return nil for link_trace_id)

compound_all_keep_types — all/none/sample/rate_limit(N/s)/rate_limit(N/m) under one policy set
compound_rate_limit_most_restrictive — rate_limit vs none precedence; confirms none > rate_limit

compound_sampling_interactions — trace sampling with fail_closed contrast, drop (0%) overriding sampling, mixed fail_closed=true/false with missing trace_id

compound_regex_edge_cases — character classes, anchoring, alternation, UUID patterns, escaped brackets, case-insensitive regex
compound_double_negation — exists: false + negate: true (FAILS Go — ENG-229)
compound_empty_vs_missing — empty string vs null/absent field behavior
compound_nested_attributes — nested attribute paths across all signal types

compound_transform_chain — cross-policy transform visibility (confirmed: transforms applied after all matching)
compound_scope_isolation — resource/scope attribute transform isolation

compound_datapoint_attr_types — datapoint attribute matching across histogram, summary, gauge

~~traces_sampling_hash_seed~~ — removed; non-zero hash_seed produces different FNV inputs across runners
~~*_no_matchers~~ — removed; match: [] is not a valid policy
ENG-228: Rust evaluates policies in array order instead of alphanumeric (fails compound_conflicting_keeps)
ENG-229: Go ignores negate flag on existence checks — exists: false, negate: true should mean "field exists" but Go treats it as "field absent" (fails compound_double_negation)