Decision Contracts

A decision contract is a ruleset's "type signature": it declares which fields the rule expects to read, which result codes it must emit, and which fields each result carries.

Contracts decouple rules from callers — apps call against the contract, authors write against it, and the platform validates both ends agree before each release.

Contract Shape

// POST /api/v1/projects/:pid/contracts
{
  "name": "discount-check",
  "version": "1.0.0",
  "input": {
    "fields": [
      { "name": "user.age", "type": "number", "required": true },
      { "name": "user.vip", "type": "boolean", "required": false, "default": false },
      { "name": "order.amount", "type": "number", "required": true }
    ]
  },
  "outputs": [
    { "code": "VIP", "fields": [{ "name": "discount", "type": "number" }] },
    { "code": "NORMAL", "fields": [{ "name": "discount", "type": "number" }] },
    { "code": "DENY", "fields": [{ "name": "reason", "type": "string" }] }
  ]
}

When Validation Runs

Trigger	Checks
Studio live editing	Expressions reference fields declared in the contract input
Draft save	Each Terminal's code is in the contract's outputs list
Test run	Test inputs satisfy the contract's input.required
Pre-release	Contract diff against the previous release; breaking changes need higher-tier approval

Relationship with the Fact Catalog

The contract's input.fields reference names and types from the fact catalog. If a field's type changes in the catalog, contracts that depend on it are flagged as "needs migration."

API

Operation	Endpoint
List	GET /api/v1/projects/:pid/contracts
Create	POST /api/v1/projects/:pid/contracts
Update/delete	PUT/DELETE /api/v1/projects/:pid/contracts/:name

Versioning & Breaking Changes

Contracts carry a version field that follows SemVer:

• patch / minor — adding optional fields, adding output.code, relaxing validation: non-breaking.
• major — removing fields, type changes, removing output codes: breaking. Release requests will require an explicit ack.