Fix MCP tool call attribute selection

[MrAlias]

Motivation

• A recent change captured MCP tool-call arguments and results but these sensitive payloads were gated by broad GenAI input/output selection, preventing operators from independently including or excluding gen_ai.tool.call.arguments and gen_ai.tool.call.result.
• The goal is to restore per-attribute control so tool-call payloads cannot be exported implicitly when operators opt into other GenAI data.

Description

• Add attr.GenAIToolCallArguments and attr.GenAIToolCallResult to the trace attribute selector definitions so they appear in attributes.select configuration (pkg/export/attributes/attr_defs.go).
• Change MCP span emission to gate tool-call arguments/results on their own optional attribute names instead of GenAIInput/GenAIOutput (pkg/export/otel/tracesgen/tracesgen.go).
• Add selector tests to verify inclusion/exclusion behavior for gen_ai.tool.call.* (pkg/export/attributes/attr_selector_test.go).
• Add trace tests to ensure gen_ai.tool.call.arguments/gen_ai.tool.call.result are not emitted via GenAIInput/GenAIOutput and are emitted when their own selectors are enabled (pkg/export/otel/tracesgen/tracesgen_test.go).

Testing

• go test ./pkg/export/attributes ./pkg/export/otel/tracesgen

[codecov]

Codecov Report

❌ Patch coverage is 92.59259% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.18%. Comparing base (914ffa4) to head (8c337e2).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/export/attributes/attr_select.go	83.33%	1 Missing ⚠️
pkg/export/attributes/attr_selector.go	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2518      +/-   ##
==========================================
- Coverage   69.24%   69.18%   -0.07%     
==========================================
  Files         345      345              
  Lines       46747    46811      +64     
==========================================
+ Hits        32372    32384      +12     
- Misses      12330    12394      +64     
+ Partials     2045     2033      -12     

Flag	Coverage Δ
integration-test	50.66% <70.83%> (-0.26%)	⬇️
integration-test-arm	27.13% <66.66%> (-1.18%)	⬇️
integration-test-vm-5.15-lts	?
integration-test-vm-6.18-lts	?
k8s-integration-test	36.04% <70.83%> (+0.34%)	⬆️
oats-test	35.38% <70.83%> (+0.01%)	⬆️
unittests	63.40% <100.00%> (+0.08%)	⬆️

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[grcevski]

LGTM! Looks great