---
type: overview
summary: What an application may rely on from @ng-eventually/sdk, and what it will have to delete
triggers:
  keywords: [polyfill, sdk, surface, contract, publish, published, entry, export, migration, unlearn, consumer, app-facing]
  paths:
    - "packages/sdk/src/index.ts"
    - "packages/sdk/src/surface/**"
    - "packages/sdk/README.md"
    - "examples/notebook/**"
    - "docs/api-contract.md"
vocabulary:
  - term: reference
    gloss: a NURI that names a document and grants nothing — what an application circulates
    not: [link, lien, share-link]
    see: contract_sdk-surface
  - term: ReadCap
    gloss: upstream's word for what opens a document — a reference carrying its secret
    not: [token, credential, permission]
  - term: polyfill-era
    gloss: a published symbol with no counterpart in the target SDK, deleted at migration
    not: [transitional, shim-only]
    see: knowledge_what-an-app-deletes-at-migration
---

# app-contract — the boundary between this library and the applications that use it

This library exists so an application can be **written today against the NextGraph that does not ship yet**, and keep its code when it does. Everything under this concept governs that boundary: what the package publishes, what a caller may rely on, what it must not, and what disappears at migration.

The distinguishing question, asked at every surface choice: **would this make a caller learn something it has to UNLEARN?** If yes it is a deviation, whatever it buys — see `rule_would-the-caller-unlearn-it`.

This repo is the **provider** of `contract_sdk-surface`; consuming applications live in other repos and pull it. The per-symbol ruling, with an epistemic label on every target-side claim, stays here in `docs/api-contract.md` — that is maintainer material, not the engagement.

## Read first

- `contract_sdk-surface` — the engagement itself, written from the caller's point of view.
- `rule_would-the-caller-unlearn-it` — the test that decides what may be published.
- `knowledge_what-an-app-deletes-at-migration` — the two fates a published symbol can have.