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It looks to me like Firestore's API doesn't include a "default" way to upload user edits to documents. Conflict detection is possible using the transactions - https://cloud.google.com/firestore/docs/manage-data/update-d... - you can do something like HTTP's PUT If-Unmodified-Since (or PUT If-Match).

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Good point. read-modify-write transactions are a good way to detect conflicts and get a chance to handle them, but they're unfortunately limited to while the client is online. If the client is offline, the transaction will fail so they're not useful for general conflict resolution. This was an intentional decision because there's not a straightforward way to preserve the intent of the transaction across app restarts. But there may be options for adding some sort of conflict resolution strategy in the future that leverages the same underlying primitives that transactions use today.

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