Limit the number of unpack retries

[tmshort]

Clarification: Is this a statement or something that needs to be done in the future?

// There must be a limit to number of entries if status is stuck at
// unpack pending.

Originally posted by @everettraven in #846 (comment)

[joelanford]

No I don't think we should have a limit. Let exponential back off do its thing.

[tmshort]

So we should close this?

[everettraven]

IIRC this was from a PR comment I made about a code comment. I'm fine with closing this, but maybe we should make sure we clean that comment up as well if it is not applicable.