tests: add Hugging Face corpus audit lane

Package.swift

@@ -66,6 +66,10 @@ let package = Package(
             dependencies: ["FetchCore"],
             path: "Tests/SwiftlyFetchTestFixtures"
         ),
+        .executableTarget(
+            name: "SwiftlyFetchCorpusAudit",
+            dependencies: ["FetchCore", "FetchKit"]
+        ),
         .testTarget(
             name: "RAGCoreTests",
             dependencies: ["RAGCore"]

ROADMAP.md

@@ -191,6 +191,7 @@ In Progress
 - [x] Refine the default in-memory all-term ranker so tighter evidence beats scattered term mentions instead of falling through to document ID tie-breaking.
 - [x] Add a second checked-in text source for corpus-based tests so fixture coverage is not only Gutenberg-derived.
 - [x] Add a Hugging Face-derived audit micro-corpus that combines short stories, markdown reference records, and line-oriented literary text across the default in-memory and macOS SearchKit-backed paths.
+- [x] Add an opt-in Hugging Face corpus audit lane that downloads bounded Dataset Viewer slices, indexes a larger temporary corpus locally, and reports ranking/snippet checks without making default CI network-dependent.
 - [ ] Audit larger app-like corpus result quality now that field-aware ranking, compact all-term evidence, phrase weighting, truncation cues, multi-term snippets, and field-evidence metadata are in place.
 - [ ] Keep the persistent `FetchKitLibrary` construction and search API surface under review as real callers exercise the current design.
 - [ ] Explore an opt-in extended snippet surface that can use idle time to precompute short document summaries for larger records, with Apple's [`FoundationModels`](https://developer.apple.com/documentation/foundationmodels) or another local summarization path as the first candidate instead of making foreground full-text search wait on summarization.