Rebuild: strings that outlive their chunk are copied (worker 1.14 → 0.66 GB)

A slice of a chunk's text keeps the whole text alive (tens of MB) for as
long as the file it belongs to stays open: message-ids, file details and
cache keys are now copies. edge:bench on boneless: peak RSS 1,137 → ~660
MB, external memory 570 → 40–75 MB, the same speed (~190k headers/s);
the same results on 800k real lines. edge:bench prints the breakdown.

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

lib/edge/scan.ts

@@ -26,6 +26,16 @@ export interface EdgeSegment {
   file: FileMeta
 }
 
+/**
+ * A copy of a string that doesn't keep the string it was cut from alive: a
+ * slice of a chunk's text otherwise holds on to the whole text (tens of MB)
+ * for as long as the file it belongs to stays open. External memory was
+ * ~570 MB of a worker's 1.1 GB (LOG.md 2026-10-09).
+ */
+function own(text: string): string {
+  return (' ' + text).slice(1)
+}
+
 interface Counter {
   index: number
   length: number
@@ -110,14 +120,14 @@ export class SegmentScanner {
     let file = this.files.get(key)
     if (file === undefined) {
       file = this.describe(subject, nameEnd, counter, from, xref, group)
-      this.files.set(key, file)
+      this.files.set(own(key), file)
     }
     if (!file || counter.segment < 1 || counter.segment > file.totalParts) return null
     return {
       fileKey: file.fileKey,
       number: counter.segment,
       totalParts: file.totalParts,
-      messageId: messageId.charCodeAt(0) === 60 ? messageId.slice(1, -1) : messageId,
+      messageId: own(messageId.charCodeAt(0) === 60 ? messageId.slice(1, -1) : messageId),
       bytes: Number.parseInt(bytes, 10) || 0,
       articleNumber,
       postedAt: Date.parse(date),
@@ -129,17 +139,18 @@ export class SegmentScanner {
   private describe(subject: string, nameEnd: number, counter: Counter, from: string, xref: string, group: string): FileMeta | null {
     const nameStart = subject.lastIndexOf('"', nameEnd - 1)
     if (nameStart === -1) return null
-    const name = subject.slice(nameStart + 1, nameEnd)
+    const name = own(subject.slice(nameStart + 1, nameEnd))
     if (!name || counter.total < 1) return null
-    const base = (subject.slice(0, counter.index) + subject.slice(counter.index + counter.length)).replace(/\s+/g, ' ').trim()
+    const base = own((subject.slice(0, counter.index) + subject.slice(counter.index + counter.length)).replace(/\s+/g, ' ').trim())
+    const poster = own(from)
     return {
-      fileKey: fileKey(from, base, counter.total),
+      fileKey: fileKey(poster, base, counter.total),
       name,
-      poster: from,
+      poster,
       subject: base,
       totalParts: counter.total,
       groups: xrefGroups(xref, group),
-      release: releaseIdentity({ poster: from, subject: base, name, weak: false }),
+      release: releaseIdentity({ poster, subject: base, name, weak: false }),
     }
   }
 }
@@ -149,7 +160,7 @@ function xrefGroups(xref: string, group: string): string[] {
   const tokens = xref.trim().split(/\s+/)
   for (let i = 1; i < tokens.length; i++) {
     const colon = tokens[i].lastIndexOf(':')
-    if (colon > 0) groups.push(tokens[i].slice(0, colon))
+    if (colon > 0) groups.push(own(tokens[i].slice(0, colon)))
   }
   return groups.length > 0 ? groups : [group]
 }