feat(benchmark): fetch AMI corpus from HuggingFace mirror, Edinburgh as fallback

Sources/FluidAudioCLI/DatasetParsers/DatasetDownloader.swift

@@ -111,16 +111,22 @@ struct DatasetDownloader {
     ) async
         -> Bool
     {
-        // Try multiple URL patterns - the AMI corpus mirror structure has some variations
-        let baseURLs = [
-            "https://groups.inf.ed.ac.uk/ami/AMICorpusMirror//amicorpus",  // Double slash pattern (from user's working example)
-            "https://groups.inf.ed.ac.uk/ami/AMICorpusMirror/amicorpus",  // Single slash pattern
-            "https://groups.inf.ed.ac.uk/ami/AMICorpusMirror//amicorpus",  // Alternative with extra slash
+        // Prefer the HuggingFace mirror (hosts the official 16-meeting SDM test
+        // split), then fall back to the intermittently-available Edinburgh
+        // server. Meetings or variants absent from the mirror 404 and fall
+        // through to upstream.
+        let mirrorURL =
+            "https://huggingface.co/datasets/FluidInference/ami-corpus-mirror/resolve/main/\(variant.rawValue)/\(meetingId).\(variant.filePattern)"
+        // Both slash patterns of the upstream corpus mirror have been seen working.
+        let upstreamBases = [
+            "https://groups.inf.ed.ac.uk/ami/AMICorpusMirror//amicorpus",
+            "https://groups.inf.ed.ac.uk/ami/AMICorpusMirror/amicorpus",
         ]
+        let candidateURLs =
+            [mirrorURL]
+            + upstreamBases.map { "\($0)/\(meetingId)/audio/\(meetingId).\(variant.filePattern)" }
 
-        for (_, baseURL) in baseURLs.enumerated() {
-            let urlString = "\(baseURL)/\(meetingId)/audio/\(meetingId).\(variant.filePattern)"
-
+        for urlString in candidateURLs {
             guard let url = URL(string: urlString) else {
                 continue
             }
@@ -192,19 +198,23 @@ struct DatasetDownloader {
         }
 
         // Download and extract AMI manual annotations v1.6.2.
-        // The Edinburgh server is occasionally flaky, so retry with backoff —
-        // a single transient failure here once poisoned a CI benchmark run
-        // with placeholder ground truth (issue #752).
-        let zipURL =
-            "https://groups.inf.ed.ac.uk/ami/AMICorpusAnnotations/ami_public_manual_1.6.2.zip"
+        // Prefer the HuggingFace mirror — the upstream Edinburgh server is
+        // intermittently down, and a single transient failure here once
+        // poisoned a CI benchmark run with placeholder ground truth (#752).
+        let zipURLs = [
+            "https://huggingface.co/datasets/FluidInference/ami-corpus-mirror/resolve/main/annotations/ami_public_manual_1.6.2.zip",
+            "https://groups.inf.ed.ac.uk/ami/AMICorpusAnnotations/ami_public_manual_1.6.2.zip",
+        ]
         let zipFile = annotationsDir.appendingPathComponent("ami_public_manual_1.6.2.zip")
 
         var zipSuccess = false
         let maxAttempts = 3
-        for attempt in 1...maxAttempts {
-            zipSuccess = await downloadAnnotationFile(from: zipURL, to: zipFile)
-            if zipSuccess { break }
-            logger.warning("Annotation download attempt \(attempt)/\(maxAttempts) failed")
+        attempts: for attempt in 1...maxAttempts {
+            for zipURL in zipURLs {
+                zipSuccess = await downloadAnnotationFile(from: zipURL, to: zipFile)
+                if zipSuccess { break attempts }
+            }
+            logger.warning("Annotation download attempt \(attempt)/\(maxAttempts) failed for all sources")
             if attempt < maxAttempts {
                 try? await Task.sleep(nanoseconds: UInt64(attempt) * 2_000_000_000)
             }