Fix findCounter infinite loop; corpus filter skips chunks past 256 MB

lastIndexOf('(', -1) searches from 0 again, so a subject starting with a "("
that isn't a counter, without a quote, looped forever. The corpus filter hit
it at 11:23 on Oct 24: the coordinator (and corpus:filter) spun at 100% CPU
for 10 hours and no range finished. The Rust find_counter stops at 0 already.

A chunk inflating past V8's longest string can't be filtered as text; such a
chunk is now stored unfiltered instead of throwing.

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

app/services/corpus.ts

@@ -9,6 +9,8 @@ import type { ChunkSpan } from '#services/spool'
 const inflate = promisify(unzip)
 const deflate = promisify(deflateCb)
 const gzip = promisify(gzipCb)
+/** The largest inflated chunk the filter reads as one string (V8's limit is 0x1fffffe8 characters). */
+const MAX_FILTER_BYTES = 256 * 1024 * 1024
 
 /** What a filtered chunk was filtered with (CORPUS_FILTER): the rule set and the group priorities of its lease. */
 export interface CorpusFilter {
@@ -91,7 +93,9 @@ class Corpus {
     const file = this.path(range, span)
     await mkdir(dir, { recursive: true })
     let stored = data
-    if (filter) {
+    // Past V8's longest string (0x1fffffe8) the text can't be filtered; such a chunk is stored as it came (the
+    // worker drops the same lines itself). Seen once: a chunk inflating past 512 MB (LOG.md 2026-10-24 (102)).
+    if (filter && raw.length < MAX_FILTER_BYTES) {
       // Latin-1 both ways: every byte back as it was.
       const { kept, drops } = filterOverviews(raw.toString('latin1'), range.group, filter.priorities, filter.ruleVersion)
       stored = await deflate(Buffer.from(kept, 'latin1'), { level: 9 })