fix(benchmarks-migrate): route 2-part random-access to Skip, not Unknown

The post-alpha cleanup made `bin_random_access` reject 2-part legacy
shapes by returning None, but `classify_outcome` mapped any None bin
to `Outcome::Unknown`, so those records counted against the 5%
uncategorized gate. Intentional drops must Skip; only truly
unrecognized shapes are Unknown.

Reuses the existing `Skip::UnsupportedShape` variant, originally
added for "get_group succeeded but classify_v2 didn't" — same
semantic shape (recognized but unsupported).

Regression test in `tests/classifier.rs` exercises `classify_outcome`
(not just the top-level `classify`) so Skip vs Unknown is observable.

Signed-off-by: Claude <noreply@anthropic.com>

Author: claude

benchmarks-website/migrate/src/classifier.rs

@@ -537,7 +537,16 @@ pub fn classify_outcome(record: &V2Record) -> Outcome {
         return Outcome::Skip(Skip::DerivedRatio);
     }
     let bin = match &cls.group {
-        V2Group::RandomAccess => bin_random_access(record),
+        V2Group::RandomAccess => match bin_random_access(record) {
+            Some(b) => Some(b),
+            // Legacy 2-part `random-access/<format>-…` records carry
+            // no dataset and are intentionally dropped by
+            // `bin_random_access`. Route them to Skip so the
+            // `Outcome::Unknown` arm below — and the 5%
+            // uncategorized gate in `migrate::run` — don't trip on
+            // them.
+            None => return Outcome::Skip(Skip::UnsupportedShape),
+        },
         V2Group::Compression => bin_compression_time(&cls, record),
         V2Group::CompressionSize => bin_compression_size(&cls, record),
         V2Group::Query { .. } => bin_query(&cls, record),

benchmarks-website/migrate/tests/classifier.rs

@@ -271,6 +271,23 @@ fn unmapped_records_yield_none(#[case] name: &str) {
     );
 }
 
+#[test]
+fn random_access_2_part_legacy_is_skip_not_unknown() {
+    // The 2-part legacy shape `random-access/<format>-tokio-local-disk`
+    // carries no dataset, so `bin_random_access` returns None. That
+    // None must route through `Outcome::Skip` (an intentional drop),
+    // NOT `Outcome::Unknown`, otherwise these records count against
+    // the 5% uncategorized gate in `migrate::run`. Top-level
+    // `classify()` returns None for both Skip and Unknown, so this
+    // assertion has to go through `classify_outcome`.
+    let r = record("random-access/parquet-tokio-local-disk");
+    let outcome = classify_outcome(&r);
+    assert!(
+        matches!(outcome, Outcome::Skip(_)),
+        "2-part legacy random-access must Skip, not Unknown; got {outcome:?}"
+    );
+}
+
 #[test]
 fn parquet_zstd_size_is_deprecated() {
     // `parquet-zstd` is not on the v3 emitter's format allowlist, so