* PVF: Don't dispute on missing artifact
A dispute should never be raised if the local cache doesn't provide a certain
artifact. You can not dispute based on this reason, as it is a local hardware
issue and not related to the candidate to check.
Design:
Currently we assume that if we prepared an artifact, it remains there on-disk
until we prune it, i.e. we never check again if it's still there.
We can change it so that instead of artifact-not-found triggering a dispute, we
retry once (like we do for AmbiguousWorkerDeath, except we don't dispute if it
still doesn't work). And when enqueuing an execute job, we check for the
artifact on-disk, and start preparation if not found.
Changes:
- [x] Integration test (should fail without the following changes)
- [x] Check if artifact exists when executing, prepare if not
- [x] Return an internal error when file is missing
- [x] Retry once on internal errors
- [x] Document design (update impl guide)
* Add some context to wasm error message (it is quite long)
* Fix impl guide
* Add check for missing/inaccessible file
* Add comment referencing Substrate issue
* Add test for retrying internal errors
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Co-authored-by: parity-processbot <>