Completes User Story 4's eleven named metrics: first-response-time
(messages.service.ts's post(), guarded against double-counting a
ticket's second agent message), SLA compliance (sla.service.ts's
complete()/runBreachDetectionSweep(), with a guard so a run already
breached by the sweep is never also counted "met" when it later
resolves), most-common-errors (error-codes.service.ts, counted only
once a code is confirmed real), and tool-failure-rate/knowledge-
effectiveness (tools.service.ts's single executeTool call site).
Verified end-to-end against real Postgres/Redis by scraping the real
/metrics endpoint before and after driving each metric's actual
underlying event through the real service layer — including a genuine
tool-execution failure (a nonexistent ticket ID) rather than a
simulated one.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
