[FEATURE] skill.name tag in claude_code.cost.usage should reflect actual skill name for marketplace plugin skills

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Marketplace plugin skills (loaded from .claude/plugins/marketplaces/) are tagged as skill.name:third-party in claude_code.cost.usage metric in datadog, making it impossible to attribute token cost to individual skills. Native/built-in skills (e.g. update-config) correctly appear under their own skill.name tag.

Proposed Solution

When a skill from a plugin marketplace is invoked, tag skill.name with the actual skill name (e.g. review-pr) rather than third-party.

Alternative Solutions

• Add a separate plugin.skill.name tag that carries the skill name, leaving skill.name unchanged
• Tag plugin.name with the plugin identifier (e.g. cambia-janus-dev-assistant) so cost can at least be attributed at plugin level — currently this also shows as third-party

Priority

Medium - Would be very helpful

Feature Category

Configuration and settings

Use Case Example

We built a review-pr skill distributed via the claude plugin marketplace. We want a Datadog widget showing token cost per skill invocation to track ROI. Currently all marketplace skill cost is lumped under third-party, making per-skill cost tracking impossible.

Additional Context

• Confirmed via Datadog Metrics Explorer: skill.name:third-party and plugin.name:third-party are the only values appearing for marketplace skills
• Native skills like update-config do receive proper skill.name tagging
• OTEL config is set via managed-settings.json — the tagging behavior appears hardcoded in the Claude Code binary, not configurable