---
type: knowledge
summary: The two fates a published symbol can have, and why the deletion list is now carried by a block and a test rather than by an import path
---

# What an application deletes at migration, and what it keeps

Every published symbol has exactly one of two fates, and knowing which is the whole point of this boundary.

**Replaced in place.** The build alias resolving `@ng-eventually/polyfill` is removed, the import resolves to the real SDK, and the application's code is unchanged. This is almost everything: `ng`, `useShape`, `watchShape`, `init`, `initNg`, `readUnion`, `subscribeDoc(s)`, `docs.*`, `inbox.*`, `storeRegistry.*`, and the types.

**Deleted.** The symbol has no counterpart at any level of the target, exists only because one shared wallet hosts every user, and goes with its call site. Today that is `configure` and its config type.

`ensureIdentity` sits between the two and is worth stating precisely: its **substance** is scaffolding — a barrier that hands out a shared wallet file and takes an identifier, a step that exists only because users share a wallet — while its **call site survives**, because an application still awaits a session before it renders. Its signature was designed for that: it takes no identifier, so the line does not change the day the wallet supplies the identity and the barrier stops appearing.

## Why the deletion list is not an import path any more

There were two entry points until 2026-08-07, `.` and `./polyfill`, and the second one carried a signal worth naming: *what you import from that path is exactly what you will delete*. That was a mechanical guarantee — the compiler produced the list.

Merging them lost it. Nothing at an import line now distinguishes `configure`, which goes away, from `docs`, which is replaced. Three things carry it instead, and it is worth knowing that only the last two are enforced:

- the **`POLYFILL-ERA` block** in the package's entry module, which is the deletion list, kept short by construction;
- **`docs/api-contract.md`**, which rules on every symbol with an epistemic label (PASSTHROUGH / LEVEL-1 SHAPE / ASSUMPTION / NO COUNTERPART) and whose export inventory is pinned by a test — so it cannot go stale quietly, which a hand-kept list would;
- the **names themselves**, each built from the target's own vocabulary or carrying a marker saying why it exists only here, pinned by the same test.

The trade was deliberate and it is a real reduction in enforcement: a documentary signal where a mechanical one used to be. To verify the pinning is doing its job, look for the vocabulary test beside the package's other tests — it compares the contract's inventory against the entry's real exports, in both directions, and it caught five drifted sections the day it was extended to the rulings.

## The direction of travel

The polyfill-era list only shrinks. It has gone from four published calls to one, and each removal was a symbol an application should never have had: naming its own identity, awaiting the connection, wiring a second bootstrap, reaching a machinery accessor. A symbol added to that block is a promise to delete it later — so the question at every addition is whether the application genuinely needs it, or whether the library is passing on a problem of its own.