[enhancement] E3-4: OpenTelemetry tracing — research spike

[OneStepAt4time]

Finding

ID: Enterprise Gap | Severity: 🟠 MEDIUM

No distributed tracing. Request flows through Fastify → session.ts → tmux.ts → monitor.ts cannot be correlated by a tracing backend.

Fix Required

Evaluate: instrument with @opentelemetry/sdk-node auto-instrumentation for Fastify + HTTP. Create spans for the session create/send/monitor cycle.

Output

ADR documenting sampling strategy, exporter choice (Jaeger/OTLP).

Milestone

M-E3: Observability