Vendored swift-transformers: add Sendable to Hub.Repo / Hub.RepoType (Swift 6 build fix)

[rcfa]

Summary

Under Swift 6 strict concurrency, Hub.RepoType and Hub.Repo (in the vendored swift-transformers
copy under Vendors/) need Sendable to cross actor/task boundaries; without it, builds that touch
these types from concurrent contexts fail.

Both are trivially sendable (a String-raw enum and an all-let struct of Sendable fields). This
adds the conformance to the vendored copy so vmlx-swift builds clean under Swift 6 now, without
waiting on an upstream swift-transformers release + a vendor bump.

The same fix is now merged upstream at huggingface/swift-transformers#374 (merged 2026-06-28) — so
this vendored stopgap matches the accepted upstream change, and can be dropped on the next vendor sync
that picks it up. No behavior change.

[rcfa]

Upstream PR approved

[jjang-ai]

Thanks — the conformance itself is correct (RepoType is a String-raw enum, Repo is all-let over Sendable fields), and it matches what upstream accepted. Two bits of context that aren't visible from outside the repo, though, and they change what we'd want to do with it:

1. We don't vendor from huggingface/swift-transformers. Per Vendors/README.md, Hub/Tokenizers/Generation/Models are copied from osaurus-ai/swift-transformers at revision 087a66b1. So patching the vendored copy in-tree means the next vendor sync overwrites it — the fix would silently disappear on a routine refresh, which is a worse failure than not having it (it'd come back as a mystery build break months later). The durable path is to land it in osaurus-ai/swift-transformers first and then bump the vendored revision here; at that point this diff becomes unnecessary rather than redundant.

2. The stated symptom doesn't reproduce on main. Hub.Repo / Hub.RepoType aren't referenced anywhere under Libraries/ or Sources/, and main builds clean today (MLXLMCommon is deliberately compiled in Swift 5 mode — see the long comment on that target in Package.swift — while the rest is Swift 6). So this isn't fixing a live break here; it's pre-emptive, or fixing something in a downstream consumer. That's fine, but it's worth saying plainly in the PR body, because "Swift 6 build fix" reads like the build is currently red and it isn't.

If you're hitting this from a downstream package, could you paste the actual compiler error and the context it fires in? If it's real for consumers we should fix it in the fork and re-vendor, which helps everyone rather than just this tree.

No objection to the change on its merits — it's the delivery mechanism that needs to move.

[rcfa]

Agreed — closing this. Patching the vendored copy is the wrong delivery (a vendor sync would erase it), and on our side it turns out not to be a live break at all: MLXLMCommon is pinned to .v5, nothing in our tree references Hub.Repo/Hub.RepoType, and a strict-.v6 build compiles clean with the conformance removed (0 errors). The real fix is already merged upstream at huggingface/swift-transformers#374; I'll get it onto osaurus-ai/swift-transformers (currently ~2 months behind and missing it) so it flows in on the next vendored bump. Thanks for the careful trace.