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>

lib/rules/index.ts

@@ -1,2 +1,2 @@
 export { uploadTool, signatureGroup, signatureKey, explored } from './upload_tools.js'
-export { RuleSet, DEFAULT_RULES, isRandomFile, ownerOf, posterWords, type Rules, type Verdict } from './rule_set.js'
+export { RuleSet, DEFAULT_RULES, isRandomFile, isScrambledFile, ownerOf, posterWords, type Rules, type Verdict } from './rule_set.js'

lib/rules/rule_set.ts

@@ -56,6 +56,26 @@ export function isRandomFile(name: string) {
   return looksRandom(fileStem(name))
 }
 
+/**
+ * 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.
+ */
+export function isScrambledFile(name: string) {
+  let total = 0
+  let scrambled = 0
+  for (const token of fileStem(name).split(/[^A-Za-z0-9]+/)) {
+    total += token.length
+    let switches = 0
+    for (let i = 1; i < token.length; i++) {
+      const [a, b] = [token[i - 1], token[i]]
+      if ((/[a-z]/.test(a) && /[A-Z]/.test(b)) || /\d/.test(a) !== /\d/.test(b)) switches++
+    }
+    if (token.length >= 5 && switches >= 3) scrambled += token.length
+  }
+  return total >= 8 && scrambled * 2 >= total
+}
+
 /** The owner of an article posted to `groups` (its Xref), or null when none of them is indexed. */
 export function ownerOf(groups: string[], priorities: Record<string, number>): string | null {
   let owner: string | null = null