> ## Documentation Index
> Fetch the complete documentation index at: https://headgate.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Atomic admission

> The store-side decision that combines policy, claim, and lease.

Admission is the defining operation in headgate. A worker provides its queue set and free
capacity. The store evaluates every configured policy using store-owned time, then writes
the claim and lease in the same atomic operation.

```mermaid theme={"system"}
sequenceDiagram
  participant W as Worker
  participant S as Store
  W->>S: admit(queues, capacity, lease, quantum)
  Note over S: store clock<br/>queue pause + weight<br/>fairness<br/>rate limits<br/>concurrency<br/>quarantine
  S-->>W: admission units with fenced leases
```

## Non-negotiable properties

* Policy-rejected jobs remain visible and unlocked.
* The lease is written by the same statement or Lua script that claims the job.
* Store time controls refill, scheduling, and lease expiry.
* Candidate selection draws per partition so one flooding tenant cannot hide quiet ones.
* Fairness is work-conserving: spare capacity never idles to punish a noisy tenant.
* Rate-limited work is requeued without consuming an attempt.

<Note>
  PostgreSQL uses one admission query, MySQL uses its matching atomic transaction path, and
  Redis uses one Lua script. Their behavior is compared by cross-language conformance.
</Note>

## Admission units

Claims are returned in groups called admission units. Units normally contain one job today,
but the shape reserves correct accounting for future store-side aggregation without
reopening the hardest boundary in the system.