Path-derived tags for nested model layouts (e.g.
models/checkpoints/flux/foo.safetensors) emitted only the slash-joined
shape `["models", "checkpoints/flux"]`, which broke the frontend
combo-widget set-membership filter `include_tags=models,checkpoints` —
the literal `checkpoints` token was no longer present in the asset's
tag set.
Add `expand_bucket_prefixes` at the tag-write layer. When a tag's first
slash segment is a registered model category (or input/output/temp
root), the bucket is inserted as a standalone token immediately after
the slash-joined form. This preserves tag[1] as the slash-joined
positional contract cloud emits while restoring the set-membership
token the frontend filter requires.
The expansion is bounded to known buckets so free-form user labels
with slashes (`my-org/team-a`) pass through unchanged. The helper is
applied uniformly in `set_reference_tags`, `add_tags_to_reference`,
and `batch_insert_seed_assets` so HTTP uploads, user-tag mutations,
and path-scanning ingest all converge on the same canonical shape.
Also align the upload-route category validator with
`resolve_destination_from_tags` by extracting the first slash segment
of tag[1], so HTTP uploads matching cloud's slash-joined emission
shape are no longer rejected as `unknown models category`.
