Summary

The OTEL Collector file exporter hardcoded /tmp/claude-code-{events,metrics}.jsonl inside the distroless container. The default uid (10001) cannot write to the container's /tmp on macOS bind-mount setups, producing:

can't open new logfile: open /tmp/claude-code-metrics.jsonl: permission denied

Host-side chmod or symlinking does not reach the container filesystem, so this needs a config + compose fix rather than a host workaround.

Changes

• otel-collector/config.yaml, otel-collector/config-with-prometheus.yaml — Replace hardcoded /tmp/... with ${env:OTEL_FILE_EXPORT_DIR}/... so the in-container target is configurable instead of baked into a checked-in file.
• docker-compose.yml (otel-collector service):
  • OTEL_FILE_EXPORT_DIR=/var/log/otel (in-container mount point — fixed).
  • Bind-mount ${CLAUDE_CODE_TMPDIR:-./otel-collector/data}/otel:/var/log/otel. The /otel sub-namespace prevents collector output from sharing a directory with Claude Code's per-uid runtime tmpdir (claude-<uid>/).
  • user: "0:0" so writes succeed regardless of bind-mount ownership on macOS.
• otel-collector/enable-telemetry.sh — Default CLAUDE_CODE_TMPDIR to project-local ./otel-collector/data when not already exported.
• .gitignore — Ignore otel-collector/data/.

Behavior

Test plan

• docker compose up -d otel-collector starts cleanly with no logfile error
• OTLP HTTP POSTs to localhost:4318/v1/metrics return 200 partialSuccess: {}
• File exporter writes to the configured host path; size grows under load
• Sub-namespace (/otel/) keeps output isolated from claude-<uid>/
• Verified via lsof that there is one writer and one active file (no duplicate writes)

Notes

• docker-compose interpolates ${CLAUDE_CODE_TMPDIR} from the shell that invokes it, not from Claude Code's settings.json. Users who want the override to apply automatically should export it from their shell rc, an .env file, or enable-telemetry.sh.
• For Cloud Run / stateless deployments, the file exporter remains a footgun — an OTLP exporter to a managed sink is the right move there. Out of scope for this PR.