# Datetime Capability — Spec Delta (datetime-spec-conformance)

## MODIFIED Requirements

Each requirement in `openspec/specs/datetime/spec.md` gains a `**Verified by:**` line naming the test cases that pin it. No requirement text is changed; only verification metadata is added.

DT-01..DT-11 are amended in-place. See the folded spec for the canonical Verified-by lines.

## ADDED Requirements

### DT-09a — Output-size histograms (clarifies DT-09)

`expandRecurrence` MUST record an `expandRecurrenceSize` histogram (unit `{occurrences}`) in addition to its duration histogram. `businessDaysBetween` MUST record `businessDaysBetweenSize` (unit `{days}`) and `businessDaysBetweenDuration` (unit `ms`) histograms in addition to the cumulative `businessDaysBetweenTotal` counter. All four histograms are no-ops when no `MeterProvider` is registered.

**Verified by:** `src/datetime.spec-conformance.test.ts::"expandRecurrence + businessDaysBetween expose duration + size histograms"` AND `src/otel/datetime-otel.test.ts::"recordExpandRecurrence with size does not throw"` AND `src/otel/datetime-otel.test.ts::"recordBusinessDaysBetween with duration does not throw"`.