fix(extract): handle singleton collections in getCollectionItems (#144)

[zerothirteenstudio]

Fixes #144.

extract (with content) crashes when the source instance has singleton collections, because getCollectionItems assumes readItems() always returns an array:

const response = (await api.client.request(readItems(collection, {limit, page}))) as Record<string, unknown>[]
items.push(...response)            // singleton → object, not iterable
if (response.length < PAGE_SIZE) break

For a singleton, the SDK resolves to the single item object, so ...response throws Spread syntax requires ...iterable[Symbol.iterator] to be a function and response.length is undefined. The extract aborts at the first singleton (alphabetically) and writes no content for it or any collection after it.

Fix

Guard the non-array response — wrap a singleton object in an array:

const rows = Array.isArray(response) ? response : response ? [response] : []
items.push(...rows)
if (rows.length < PAGE_SIZE) break

Verification

• tsc -b builds clean.
• With this change, a full extract with content completes on an instance that has singleton collections (reproduced with Agency OS's globals, os_settings, pages_blog, pages_projects). The crash was independently confirmed by another reporter in extract crashes on singleton collections (getCollectionItems spreads a non-array response) #144 on a different Node version.

Single-file change; non-singleton collections keep the existing array path unchanged.

[alexvdvalk]

This writes the output into an array in the json which may impact the loading function too

[zerothirteenstudio]

You're completely right. I went and checked on a real instance and it's actually a bit worse than the crash: with the array wrap, loadSingletons reads the file back as an object, so the array comes through as updateSingleton(collection, {0: {…}}) and the singleton's data just quietly gets dropped on apply, no error at all.

So I've switched it to write the singleton as an object instead, and normalise to an array only for the relation-stripping pass. On a test instance that gives a clean extract (the singleton as an object, array collections untouched) and the apply round-trips fine.

Does that approach look right to you, or would you rather handle singletons a different way, like detecting them and using readSingleton?