6.0.0

Removed

• BREAKING — the calls that answer "what is on disk" and "how much memory is there" now throw
  instead of guessing. LocalModelInventory, ModelRegistry, AdapterRegistry, MLXBackend,
  DestinationHubDownloader and LLMLocalService gained throwing initializers;
  MemoryProvider.availableMemoryBytes() throws; DownloadState.paused carries Data?;
  DownloadedModel.sizeInBytes is no longer optional.
• StubDownloadDelegate and StubAdapterNetworkDelegate are gone. They were the injected
  defaults, and they reported a completed 1 MB download of a model that was never fetched and
  recorded a 13-byte text file as a cached adapter. A caller who forgot to wire a delegate was told
  the work succeeded. The delegates are now optional, and the two calls that actually need bytes
  moved — downloadWithProgress and a remote AdapterRegistry.resolve — fail without one. The uses
  that never needed a delegate keep working.

Fixed

• An unreadable model directory reported as "not downloaded". isDownloaded used
  try? contentsOfDirectory, so a permission error looked like an absent model — and
  DestinationHubDownloader responded by re-fetching a multi-gigabyte model already on disk.
  snapshotState(at:) now distinguishes complete, incomplete and absent, and throws when it cannot
  tell.
• Storage size understated without saying so. The directory walk used errorHandler: nil and
  try? per file, so an unreadable subtree silently contributed zero — producing a plausible short
  number that a user acts on when deciding what to delete.
• The backup-exclusion flag dropped silently. try? on setResourceValues meant multi-gigabyte
  weights could end up in iCloud backup with no signal, contradicting the doc comment directly
  above it.
• A fabricated memory measurement. host_page_size's return code was discarded, and a failed
  host_statistics64 returned physicalMemory / 2 — a made-up number indistinguishable from a
  real one.
• A download that could not be cancelled reported as stopped. try? on the delegate call, then
  bookkeeping torn down regardless, so the transfer kept running while isDownloading said false.
  A pause with no resume data stored Data(), so hasResumeData said true and resume restarted
  from byte 0.
• Eviction reported storage freed when the files were still there. deleteCache dropped the entry
  whether or not the delete succeeded — and that entry was the last thing pointing at the
  gigabytes, so nothing could find them to try again. The entry is now kept and the failure
  reported; clearAllCache saves what it did manage to free.
• Application Support resolution had two opposite policies in three files — .first! in two
  (a crash the caller cannot catch) and ?? temporaryDirectory in the third (a purgeable directory,
  so "downloaded" quietly stops being true). One throwing helper now serves all three.