[BuildStream] Coping with partial artifacts

[Sander Striker <s striker striker nl>]

Hi,

I expect CAS and ArtifactCache (and ActionCache) to contain partial artifacts at some point due to different retention policies for different parts.  For example, build trees might expire much faster than the core artifact (the part that is staged when depended upon).  Similarly logs may expire as well.

This is all policy based, and very much use case specific.  I do not wish for us to design or implement how partial expiry of artifacts might work, I merely want us to acknowledge that artifacts may become partial in the future.  And with that acknowledgement consider future proofing buildstream to gracefully deal with partial artifacts.

Thoughts?

Cheers,

Sander

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Cheers,

Sander