There are no implementations yet but the usage pattern will be something
like:

```javascript
// unixfs cat command
export async function * cat (cid: CID, blockstore: Blocks, options: Partial<CatOptions> = {}): AsyncIterable<Uint8Array> {
  // create a session for the CID if support is available
  const blocks = await (blockstore.createSession != null ? blockstore.createSession(cid) : blockstore)
  const opts: CatOptions = mergeOptions(defaultOptions, options)

  // resolve and export using the session, if created, otherwise fall back to regular blockstore access
  const resolved = await resolve(cid, opts.path, blocks, opts)
  const result = await exporter(resolved.cid, blocks, opts)

  if (result.type !== 'file' && result.type !== 'raw') {
    throw new NotAFileError()
  }

  if (result.content == null) {
    throw new NoContentError()
  }

  yield * result.content(opts)
}
```

…ifferent metadata

Co-authored-by: Russell Dempsey <[email protected]>

…interface

Implements blockstore sessions for trustless gateways.

- Queries the Helia routing for block providers
- Creates a set of trustless gateways from routing results
- Uses only these gateways to fetch session blocks

…teway-sessions