fix: forward trace-related OTEL env vars to Claude Code subprocess

[jeanleeb]

Summary

PR #886 added forwarding for metrics/logs OTEL environment variables to the Claude Code subprocess, but missed several variables required for trace export and content detail:

Trace enablement (without these, no traces are exported):

• CLAUDE_CODE_ENHANCED_TELEMETRY_BETA — required alongside CLAUDE_CODE_ENABLE_TELEMETRY to enable span tracing
• OTEL_TRACES_EXPORTER — selects the traces exporter (e.g. otlp, console); without this, traces are not exported even when the endpoint is configured

Signal-specific transport (takes precedence over generic vars):

• OTEL_EXPORTER_OTLP_TRACES_ENDPOINT — trace-specific endpoint URL (e.g. MLflow requires full /v1/traces path)
• OTEL_EXPORTER_OTLP_TRACES_HEADERS — trace-specific headers (e.g. experiment routing)
• OTEL_EXPORTER_OTLP_TRACES_PROTOCOL — trace-specific protocol override

Trace content detail (without these, traces arrive but are empty):

• OTEL_LOG_TOOL_DETAILS — tool parameters in spans
• OTEL_LOG_TOOL_CONTENT — full tool I/O content in spans (truncated at 60KB)
• OTEL_LOG_USER_PROMPTS — user prompt text in spans

Without these, setting trace-related env vars in the workflow step's env: block has no effect because composite actions only forward explicitly listed variables (same root cause as #887).

Reproduction

- uses: anthropics/claude-code-action@v1
  env:
    CLAUDE_CODE_ENABLE_TELEMETRY: "1"
    CLAUDE_CODE_ENHANCED_TELEMETRY_BETA: "1"    # ❌ silently dropped
    OTEL_TRACES_EXPORTER: otlp                   # ❌ silently dropped
    OTEL_EXPORTER_OTLP_TRACES_ENDPOINT: https://mlflow.example.com/v1/traces  # ❌ dropped
    OTEL_EXPORTER_OTLP_TRACES_HEADERS: "x-mlflow-experiment-id=123"           # ❌ dropped
    OTEL_LOG_TOOL_DETAILS: "1"                   # ❌ silently dropped
    OTEL_LOG_TOOL_CONTENT: "1"                   # ❌ silently dropped
    OTEL_LOG_USER_PROMPTS: "1"                   # ❌ silently dropped

No traces are received at the OTLP endpoint despite all variables being set.

Changes

Added the 8 missing variables to the telemetry section of action.yml and base-action/action.yml, following the same ${{ env.VAR }} pattern used by existing telemetry variables.

Test plan

• Verify bun test and bun run typecheck pass (no TS changes, YAML only)
• Deploy with the fix and confirm OTEL traces arrive at the configured endpoint with full content

🤖 Generated with Claude Code