Manifest chunk resolution still signed proxied downloads with the
process-wide read key, so a source filer requiring its own key 401'd on
manifest-bearing files. A side security file that set only one access
level also produced empty tokens for the other instead of inheriting the
process-wide key, and the side file loader ignored the WEED_ environment
overrides the filer itself honors.
ResolveChunkManifest/ResolveOneChunkManifest keep their signatures;
FilerJwt-aware variants thread the provider down to fetchWholeChunk,
which prefers it on proxy URLs. The side loader now applies the same
environment precedence and falls back to the process-wide signer per
missing access level.
Chris Lu
aa48658739