Adds langfuseMiddleware in internal/shared so every daemon's
shared.Run gets free production-traffic trace visibility when
LANGFUSE_URL + LANGFUSE_PUBLIC_KEY + LANGFUSE_SECRET_KEY are set.
Same env names + file shape as the multi_coord_stress driver, so
operators ship one /etc/lakehouse/langfuse.env across the deploy.
Wiring is auth-gated: middleware runs INSIDE the RequireAuth group,
so 401s from credential-stuffing don't pollute traces. /health is
exempt so LB probes don't either. Missing env vars → nil client →
middleware is a passthrough no-op (fail-open per ADR-005 5.1).
Bundled deploy:
- langfuse.env.example template (mode 0640, root:lakehouse)
- 11 systemd units gain `EnvironmentFile=-/etc/lakehouse/langfuse.env`
(leading - so missing file = OK)
- REPLICATION.md bootstrap section documents setup
Tests (4): nil passthrough, /health bypass, real-request emission,
status-writer wrapping. All green.
STATE_OF_PLAY OPEN list: 5 rows → 4 rows.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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