Mission-critical audit fixes: MLX test gating, sendability, and registry test drift

[christopherkarani]

Summary

This automation run performed a mission-critical audit focused on correctness and test reliability, then implemented and verified fixes.

1) Fixed hard test compile break (MLX gating mismatch)

• Problem: DiffusionModelDownloaderTests was compiled under #if canImport(Hub) while production diffusion types are only compiled under CONDUIT_TRAIT_MLX && canImport(MLX) (+ backend imports).
• Impact: Default test runs failed with unresolved symbols (DiffusionModelDownloader, DiffusionModelRegistry, DownloadedDiffusionModel).
• Fix: Aligned test compile gate with production conditions:
  • #if CONDUIT_TRAIT_MLX && canImport(MLX) && (canImport(Hub) || canImport(HuggingFace))
• File: Tests/ConduitTests/ImageGeneration/DiffusionModelDownloaderTests.swift

2) Removed deprecated + less-safe chip type decoding path

• Problem: DeviceCapabilities.getChipType() used deprecated String(cString:) and ignored sysctlbyname return values.
• Risk: Reduced robustness on failed sysctl calls; persistent deprecation warnings.
• Fix:
  • Guard sysctlbyname return codes and size validity.
  • Decode null-terminated buffer explicitly via UTF-8 bytes.
• File: Sources/Conduit/Core/Types/DeviceCapabilities.swift

3) Resolved Swift 6 Sendable warning in schema encoding error path

• Problem: internal EncodingError.invalidValue stored Any, causing Sendable diagnostics.
• Fix: narrowed payload to String, preserving behavior while removing non-Sendable payload.
• File: Sources/Conduit/Core/Types/GenerationSchema.swift

4) Fixed stale unit tests after provider/model catalog expansion

• Problem: ModelIdentifierTests and ProtocolCompilationTests had hard-coded expectations that no longer matched current catalog/provider surface (Kimi and MiniMax additions).
• Impact: Full test suite exited with failures despite implementation being valid.
• Fixes:
  • Updated provider/model/capability/cloud assertions to current expected totals.
  • Extended ProviderType coverage to include kimi and minimax plus network/display checks.
• Files:
  • Tests/ConduitTests/Core/ModelIdentifierTests.swift
  • Tests/ConduitTests/Core/ProtocolCompilationTests.swift

Verification

• swift build ✅
• swift test ✅
  • Full run passes (XCTest + Swift Testing)

Notes

• Planning artifacts in tasks/ were intentionally not committed per repo guidance.