Step 9 of docs/plan/derived-blobs.md. content_derived_blobs holds bytes
that are a pure function of a file's content, so they are keyed by that
content and shared by every file holding it. This table holds the
opposite: bytes a user supplied or chose, which must never be shared
across files. The key is what enforces it.
That difference is a security boundary, not a modelling preference. A
content-keyed client preview would let user A upload a file plus a
preview that misrepresents it; when user B later uploads the same bytes,
dedup matches and B is served A's preview. Content-keying is only safe
when the server can derive the bytes — there is nothing to poison,
because the same input yields the same output for everyone.
Required now rather than deferred: the SPA already generates and PUTs
previews for PDFs, and there is no server-side regeneration path for
them, so the sidecar migration has nowhere else to put those bytes.
uploaded_by is NOT NULL with no foreign key, per the provenance
convention rather than the plan's sketch. A FK with ON DELETE SET NULL
discards the audit trail exactly when it matters, and without an
ON DELETE clause it would block deleting a user outright. Deleting the
uploader must not rewrite history.
FileAttachedReferenceSource is registered in built_in_registry before
anything writes to the table, so dedup_gc's reap predicate already knows
it exists — otherwise the first sweep after the first attachment would
delete it. Manifest level only, like the derived source: these blobs are
almost always single-chunk, so contributing at chunk level would
double-count against the aliased hash.
copy_file_satellites gains one arm: attachments are DUPLICATED, since
the key is file_id and the copy is a different file, with uploaded_by
carried over — the person who supplied the bytes did not change because
someone copied the file. Each duplicate takes its own reference, so the
bytes stay deduplicated while the mapping does not.
Both golden SQL tests updated: the new fragment lands inside the reap
predicate's NOT(...) group and as a summed term in the manifest
recompute. Verified on a scratch PG with every migration applied — the
attachment duplicates to 2 rows holding 2 references with provenance
intact, while the content-keyed thumbnail stays 1 row reachable from
both files.
Edouard Vanbelle