Ingest a ThreadView, check several invariants, and produce a list of prev pointers to not-yet-pointed-to messages.

Returns the zero time if there is no recorded last send time (either because the device has never sent a message, or because it hasn't sent one since we started recording).

NewAttachmentStore creates a standard AttachmentStore that uses a real S3 connection.

NewKeyFinder creates a KeyFinder.

Preview creates preview assets from src.

If no first query time is found in the local db, this function writes the current time.

ErrAbortOnPartMismatch is returned when there is a mismatch between a current part and a previous attempt part.

All devices are presumed active for the first 24 hours.

FetchRetrier is responsible for tracking any nonblock fetch failures, and retrying them automatically.

PutS3Result is the success result of calling PutS3.

KeyFinder remembers results from previous calls to CryptKeys().