[bug] E3-2: avg_duration_sec hardcoded to 0 — active data quality bug

[OneStepAt4time]

Finding

ID: OBS-4 | Severity: 🟠 MEDIUM

getGlobalMetrics hardcodes avg_duration_sec: 0. Session duration is tracked but never aggregated. This is an active data quality bug.

Fix Required

Aggregate durationSec across all sessions in getGlobalMetrics().

Files: src/metrics.ts

Acceptance Criteria

After completing sessions, /v1/health shows a non-zero avg_duration_sec.

Milestone

M-E3: Observability