KV capacity normalization

Provider and runtime KV-cache metrics use different native units. internal/modelperfobs.NormalizeKVCapacity converts explicit observations into a comparable fak-kv-capacity/1 snapshot without erasing the source values.

What the normalizer accepts

The normalizer covers both shipped dialects:

• Block-oriented runtimes report total/free/used blocks plus block geometry.
• Direct runtimes report token and byte capacity directly.

It derives three comparable unit families when the inputs support them: resident tokens, resident bytes, and occupancy. Reusable/high-water token counters and between-scrape deltas remain separate from capacity.

Honesty floor

A derived value is emitted only when its denominator and unit are explicit. Missing block geometry, counter resets, runtime-identity changes, impossible occupancy, and disagreeing native units produce typed diagnostics instead of invented values. Observed byte counters take precedence over geometry estimates, and every rendered report places native observations before normalized values.

Use the Go seam

snapshot := modelperfobs.NormalizeKVCapacity(current, previous)
err := modelperfobs.WriteKVCapacityMarkdown(w, snapshot)

current and previous are modelperfobs.KVMetricSample values. Use previous == nil for a point-in-time snapshot. The normalization floor and exact dialect fixtures are pinned by internal/modelperfobs/kv_capacity_test.go.