# Architecture: hyper-p2p-histogram-gossip

**Category:** measurement-rate-control  
**Protocol:** `histogram-gossip/v1`

## Purpose

Distributed approximate latency/RTT distributions via gossiped histogram buckets.

## Per-metric state

```js
{ min, max, counts: number[], total }
```

## Wire messages

| type | fields | behavior |
|------|--------|----------|
| `histogram-buckets` | `metric`, `min`, `max`, `counts`, `peer`, `at` | `_mergeBuckets` into local histogram; emit `remote-buckets` |

## observe → gossip pipeline

```
_ensure(metric) → update min/max/counts
→ gossipSend full snapshot counts
→ stats.observed++
```

## Percentile estimation

Walk buckets cumulatively until cumulative count ≥ `ceil(p/100 * total)`; return bucket midpoint.

## Composition

- Feed SLI checks from `hyper-p2p-sla-budget` using percentile thresholds
- Pair with `hyper-p2p-percentile-sketch` locally for exact small-sample stats

## Limits

- Merging unlike bucket counts assumes compatible bucket count length
- Min/max drift widens bins over time