## Selection

```csharp
.UseStorage(s => s
    .Prefer("opfs")
    .Fallback("indexeddb")
    .Fallback("in-memory")
    .AllowNonPersistentFallback()
    .WithMigrationMode(BsqliteStorageMigrationMode.KeepExisting))
```

Two rules shape everything:

1. **Existing data outranks preference.** A database created on IndexedDB stays on IndexedDB when OPFS later becomes available. If the backend that holds the data cannot be reached, the open fails rather than producing an empty database elsewhere. The binding is recorded in `IBsqliteStorageBindingStore` (in `localStorage` by default) only after the open succeeds. A database with no binding - after an application clears `localStorage` on sign-out, say - is looked for on every available persistent backend before it is treated as new; found, it opens there, is bound again (`Resolution.WasFoundWithoutBinding`), and a warning is logged.
2. **Nothing is substituted silently.** A fallback is logged. Falling back to a non-persistent backend needs `AllowNonPersistentFallback()`, and is never bound: the data is gone by the next load, so the binding would protect nothing, and would keep every later visit off a persistent backend that has come back. Total failure throws `BsqliteStorageUnavailableException` listing every candidate and why it was rejected.

`session.Resolution` records the decision: the chosen provider, the probe, every attempt, whether it was the first choice, and whether a better backend is available for an existing database.