What
When Claude Code publishes changes to an artifact as a patch (only the changed parts), it can now send a precondition for each file. A precondition is a check saying "only apply this if the file still looks the way I expect."
If the server refuses with a conflict (HTTP status 409) and the reason precondition_failed, Claude Code now works out which files caused it. For each conflicting path it records:
- the expected sha256, a fingerprint of the file contents Claude Code thought was there
- the actual sha256, the fingerprint of what the server really had
The conflicting paths are also reported in usage data as conflict_paths. Upload calls take one extra parameter as well.
Why
A failed publish can now name the exact files that changed underneath it, instead of failing as a whole with no detail. This makes it easier to see which files someone else edited in the meantime.
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
The finding does not say what the extra upload parameter does.