Lone articles under scrambled names are per-article; inactive groups get no corpus fill

One article of a multi-part file under a name like "nYDeXeF49dieZ1J7flK-JFzZ3j.ZEDsr" or
"bslXlwgPiqZadhRa" (a random subject and poster per article, with fake counters) was a release:
looksRandom misses these names for their separators. 160k of alt.binaries.storage's 162k
non-Bob releases, and about 60% of all single-article releases in a 2% sample.

looks_scrambled / isScrambledFile: at least half the stem's letters and digits in tokens of 5+
that switch case or letter/digit 3 times or more (93% of the storage spam). Used for lone
articles given up before the block's end only; at the end the strict looksRandom stays, as the
rest of such a file can be in the next block. The namer's re-index (partialFiles) does the same.

The prefetcher's corpus fill skips groups that aren't active.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

edge/src/names.rs

@@ -1065,6 +1065,22 @@ pub fn is_random_file(name: &str) -> bool {
     looks_random(&file_stem(name))
 }
 
+/// looksScrambled: at least half the letters and digits of a file's stem in tokens of 5 or more that switch case
+/// (lower to upper) or between letters and digits 3 times or more ("nYDeXeF49dieZ1J7flK-JFzZ3j.ZEDsr", "bslXlwgPiqZadhRa").
+/// The names a random-subject-per-article upload gives each article that looksRandom misses for their separators.
+pub fn looks_scrambled(name: &str) -> bool {
+    let stem = file_stem(name);
+    let (mut total, mut scrambled) = (0, 0);
+    for token in stem.as_bytes().split(|c| !c.is_ascii_alphanumeric()).filter(|t| !t.is_empty()) {
+        total += token.len();
+        let switches = token.windows(2).filter(|w| (w[0].is_ascii_lowercase() && w[1].is_ascii_uppercase()) || w[0].is_ascii_digit() != w[1].is_ascii_digit()).count();
+        if token.len() >= 5 && switches >= 3 {
+            scrambled += token.len();
+        }
+    }
+    total >= 8 && scrambled * 2 >= total
+}
+
 static SEVEN_SPLIT: LazyLock<Regex> = LazyLock::new(|| re(r"(?i)\.7z\.([0-9]{1,4})$"));
 static SEVEN: LazyLock<Regex> = LazyLock::new(|| re(r"(?i)\.7z$"));
 static PART1: LazyLock<Regex> = LazyLock::new(|| re(r"(?i)\.part0*1\.rar$"));
@@ -1376,6 +1392,17 @@ mod tests {
         assert_eq!(file_stem_re("Morning Lovers.wmv.058"), "Morning Lovers");
     }
 
+    #[test]
+    fn scrambled_names() {
+        for n in ["nYDeXeF49dieZ1J7flK-JFzZ3j.ZEDsr", "bslXlwgPiqZadhRa", "PNSVWSV-xLaNv6o5qS840e3lwSZyH", "Biq-YsXu8G33ktt"] {
+            assert!(looks_scrambled(n), "{n}");
+        }
+        // Short ones of the spam too (8% of alt.binaries.storage's): too few switches to tell.
+        for n in ["A1Monitor v6.2.2", "PDF2Word v1.3", "Some.Show.S01E01.1080p.WEB.part1.rar", "MacGyver.S01E01.mkv", "Jimmy and the Crawler (mobi)", "Q25m.PDUYtbA", "82WH.2iuTK"] {
+            assert!(!looks_scrambled(n), "{n}");
+        }
+    }
+
     #[test]
     fn display_names() {
         let porn4you = "webmaster@hdbangvidz.com (Porn4You)";