Deluan Quintão 0a55cc8caf
docs(plugins): document how a metadata agent signals "not found" (#6001)
A MetadataAgent plugin reports "I have no data for this item" by returning an empty response
with a nil error. Any error it returns instead is treated as a plugin fault and retried with
backoff. That rule was not documented anywhere, so an author naturally returns an error for a
missing item, and Navidrome then retries every item the plugin's source does not cover.

This is not hypothetical: the artist-nfo-metadata plugin returned an error for every artist
without an artist.nfo, which kept those artists in the artwork retry queue for hours and
tripped the artwork circuit breaker for the plugin as a whole.

Document the rule on the capability interface, which ndpgen copies into the Go PDK, and in the
MetadataAgent section of the plugin README.
2026-08-20 22:48:26 -04:00
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