> Possibilistic authorization engine: graph indices, relation/reachability queries, rule evaluation over a DSL, and lossless condensed snapshots.
## Why
Authorization policies live on a graph: users hold relations to objects, groups, and roles, and rules derive decisions from those relations. `@arbiter/core` answers one question — *may user U perform relation R on object O?* — with a **possibility** ranking, not a boolean. Callers supply evidence with strengths; the engine fuses it through rule operators (`union`, `intersection`, `exclusion`, `defeasible`, chain, multi-hop, relational comparator) and returns the strongest derivable possibility, the reliability of the decision, and the validity provenance of the ranking.
The engine does not police caller-supplied evidence: you supply validated relation strengths and proofs; the engine derives and fuses. It is a library, not a service — no storage, no transport, no policy source of truth.
## Install
```bash
npm install @arbiter/core
```
The package is ESM-only and requires Node 22 or newer.
## Quick Start
```js
import{Arbiter}from'@arbiter/core';
constarbiter=newArbiter();
// Nodes: an id and a type.
arbiter.addNode('user:1','user');
arbiter.addNode('doc:9','doc');
// Relations: a config says how decisions for that relation are derived.
Every check returns a `possibility` in `[0, 1]` — a maxitive ranking supplied by the caller through relation strengths. `1` means derivable, `0` means not derivable. Fusions take the maximum under `union`, and enforce thresholds and conflicts under `intersection`, `exclusion`, and `defeasible` operators.
### Result shape
Every check result carries the same four fields:
| Field | Type | Meaning |
|-------|------|---------|
| `possibility` | `number` in `[0,1]` | Derived possibility of the decision |
| `reliability` | `number` in `[0,1]` | Reliability of the decision; always `0` for denials |
Denied decisions never leak a source's reliability. `includeMeta: true` adds `meta` with the full provenance (allow/deny blocks, rule traces, thresholds) and the full validity block (`sources`, `conflictMass`, `validifiedPossibility`, `nonMaxitive`).
### The caller owns evidence and time
- **Evidence**: relation strengths and validity labels come from the caller. The engine derives and fuses but never judges.
- **Time**: TTL-gated evidence uses the caller's clock. Pass `{ now }` (or `partialGraph.now`) to pin the temporal context; a rerun with the same context reproduces the decision.
**TTL is a value-freshness gate, not an access-expiry mechanism.**`valueManager.setTTL(relation, ms)` controls how long a relation's *value* stays fresh for value-consuming paths (relational comparators, chain/multi-hop value collection): once `age > TTL` the value is treated as absent, which denies the comparator and drops the value from collected values. Possibility-based grants — a direct relation's allow/deny, union disjunction, chain traversal — are **timeless**: an edge grants regardless of its age. If you need access to expire, express it in the policy (e.g. a comparator over a time-carrying value), not via `setTTL`.
**Clocks and caches.** The decision caches (direct-check, rule-result, chain) are keyed on the meta-less decision form only: `includeMeta` callers and pinned-clock callers always get a fresh evaluation, and value-carrying results are never cached (values are TTL-gated evidence). Unpinned callers share wall-clock cache entries — the correct default for timeless decisions. Pin `{ now }` whenever the answer depends on when you ask; every cache bypasses itself for pinned-clock callers, so a rerun with the same `{ now }` reproduces the decision exactly.
`check` accepts a `PartialGraphContext` overlay. Overlay relations take precedence over the base graph, letting you answer "what changes if this evidence appears?" without mutating the graph.
- **Reachability**: `isReachable`, `getReachableNodes`, `getReachingNodes`, `shortestPathLength`, `estimateGraphDistance` (`isReachable` returns `null` when no PLTC index is available — a signal to defer to rule evaluation)
- **Snapshots**: `enableCondensedSnapshot`, `toSnapshotBinary`, `Arbiter.fromSnapshotBinary` (lossless: carries relation metadata, TTLs, and validity; malformed buffers fail fast with clean errors)
| `partialGraphContext` | `PartialGraphContext` | none | Overlay taking precedence over the base graph |
## Development
```bash
npm install # install dependencies
npm test# full suite
npm run test:rigor # js-rigor campaigns (property-based + fuzzing)
npm run benchmark # compare against the committed perf baseline
npm run benchmark:save # record a new perf baseline
```
CI runs the full suite, the rigor campaigns, and the benchmark on every push; `v*` tags additionally publish the package to the `@arbiter` registry.
## Design Notes
- **Possibility is a maxitive ranking.** Fusions preserve the weakest validity label under arbitrary dependence; conjunctive operators surface conflict mass instead of silently averaging it.
- **One evaluation path.** The rule engine has a single, uncompiled evaluator — parity between normal, binary, partial-graph, and snapshot-restored checks is structural, and the rigor campaigns enforce it.
- **Snapshots are a trust boundary.** Restoring untrusted bytes must produce a clean, bounded error — never a hang, a crash, or silently corrupted data. The deserializer cross-validates every count field before use.
