The Files tab was the only payload path not on object storage, violating the
2026-10-06 directive (object storage is the ONLY media I/O path) — and oCIS's
WebDAV surface is currently 500ing server-side, which made every upload fail.
Uploads now seal + dedupe into R2 via StorageService (SPENC1, content-
addressed); downloads read R2 when storage_key is set, falling back to oCIS
for legacy rows. Share-into-library copies oCIS Drive sources into R2 and
records the real sha256 instead of a placeholder. Migration 041 adds
chat_media_archive.storage_key.
