fix(storage): treat dedupe-candidate cache miss as no candidates, not an error (#4122)

GetAllDedupeReposCandidates propagated zerr.ErrCacheMiss from the cache's
GetAllBlobs verbatim. But a cache miss is the normal case for a not-yet-cached
blob — the first push of a new blob, or a cross-repo mount check during a push
— and semantically means "no dedupe/mount candidates", not a failure.

Propagating it caused canMount (used by the CheckBlob and CreateBlobUpload
handlers) to surface the error, which the route handlers log as an
"unexpected error". With remote (e.g. S3) storage a cache is always present
(dedupe:false does not disable it), so this logs an error-level line for every
fresh blob digest on every push — significant log spam during bulk pushes and
cross-repo mounts, with no functional impact (the push still succeeds via a
normal upload).

Handle ErrCacheMiss the same way as the existing nil-cache branch above:
return no candidates and no error.

Signed-off-by: Janko Thyson <janko@kaosmaps.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

pkg/storage/imagestore/imagestore.go

@@ -1388,6 +1388,16 @@ func (is *ImageStore) GetAllDedupeReposCandidates(digest godigest.Digest) ([]str
 
 	blobsPaths, err := is.cache.GetAllBlobs(digest)
 	if err != nil {
+		// A cache miss means the digest is not present in the cache yet, so there
+		// are simply no dedupe/mount candidates for it — that is the normal case
+		// for a not-yet-cached blob, not a failure. Treat it like the nil-cache
+		// case above and return no candidates rather than propagating the error
+		// (which callers log as an "unexpected error", spamming the logs on every
+		// fresh blob during pushes/cross-repo mount checks).
+		if errors.Is(err, zerr.ErrCacheMiss) {
+			return nil, nil //nolint:nilnil
+		}
+
 		return nil, err
 	}
 

pkg/storage/storage_test.go

@@ -644,6 +644,18 @@ func TestGetAllDedupeReposCandidates(t *testing.T) {
 				slices.Sort(repos)
 				So(repoNames, ShouldResemble, repos)
 			})
+
+			Convey("A digest with no cached blob returns no candidates and no error", t, func(c C) {
+				// A cache miss is the normal case for a not-yet-cached blob (e.g. the
+				// first push of a new blob, or a cross-repo mount check during a push).
+				// It must surface as "no dedupe/mount candidates", NOT as an error the
+				// caller logs as "unexpected error".
+				uncachedDigest := godigest.FromBytes([]byte("blob that was never pushed to any repo"))
+
+				repos, err := imgStore.GetAllDedupeReposCandidates(uncachedDigest)
+				So(err, ShouldBeNil)
+				So(repos, ShouldBeEmpty)
+			})
 		})
 	}
 }