KPMG found 49% of leaders scaled back an agent deployment over cost and 7% report established ROI — so nine in ten of the organisations that cut did it without a denominator. Cost is metered by a vendor that needs to bill you; value stays at zero until someone builds it. The measurement you cannot add later is the pre-agent baseline.
The feature grids converged, so the decision is licence and billing meter — and every meter prices the trace archive that becomes your golden set, regression baseline and fine-tuning corpus. Instrument against OpenTelemetry, dual-write the stream somewhere you own, and the platform becomes a swappable backend.
Every coding agent leaves a different telemetry trail — JSONL transcripts, a SQLite store, or only a prose log — so the open-source tracker worth installing depends on which trail your agent leaves. Four trackers, four trails, plus the levers that actually cut the bill.
All four ship traces, datasets, and evaluators — the feature lists nearly match. What separates them is which feedback loop they were built to close: the dev loop, CI, the production gateway, or model-monitoring drift.