Rebuild: phase 1 modules from the current app, ordered by pipeline stage

lib/nntp (XOVER client, Xref, GROUP), lib/headers (subjects, file keys,
segments from overview lines; the yEnc path stays behind for phase 2),
lib/release (identity, random names, now in lib), lib/files (aggregator,
volume names), lib/rules (posting tools, owner by priority, release
verdicts), lib/chunks (release chunk codec). Their unit tests came along;
new ones for codec, rules and volumes.

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

lib/chunks/codec.ts

@@ -0,0 +1,45 @@
+import { constants, zstdCompressSync, zstdDecompressSync } from 'node:zlib'
+
+/** A file of a release chunk: what an NZB needs, once per file, and its segments as [part, message-id, bytes]. */
+export interface ChunkFile {
+  name: string
+  poster: string
+  subject: string
+  /** Earliest post date of its articles, ms since 1970 (null when no article had a valid date). */
+  postedAt: number | null
+  groups: string[]
+  segments: [number, string, number][]
+}
+
+const VERSION = 1
+
+/**
+ * A release chunk's payload (REBUILD.md, chunk store): a version byte, then
+ * zstd of a JSON line with the files (name, poster, subject, date, groups,
+ * sizes, and part numbers unless they are 1..N) followed by one message-id
+ * per line, in file order. Message-ids are mostly random, so this is close
+ * to what plain compression gets (LOG.md 2026-10-08 (3)).
+ */
+export function encodeChunk(files: ChunkFile[]): Buffer {
+  const head = files.map((f) => {
+    const sequential = f.segments.every(([n], i) => n === i + 1)
+    return { n: f.name, p: f.poster, j: f.subject, d: f.postedAt, g: f.groups, s: f.segments.map(([, , b]) => b), ...(sequential ? {} : { k: f.segments.map(([n]) => n) }) }
+  })
+  const ids = files.flatMap((f) => f.segments.map(([, id]) => id))
+  const text = Buffer.from([JSON.stringify(head), ...ids].join('\n'), 'utf8')
+  return Buffer.concat([Buffer.from([VERSION]), zstdCompressSync(text, { params: { [constants.ZSTD_c_compressionLevel]: 3 } })])
+}
+
+export function decodeChunk(data: Buffer): ChunkFile[] {
+  if (data[0] !== VERSION) throw new Error(`Unknown chunk version ${data[0]}`)
+  const [head, ...ids] = zstdDecompressSync(data.subarray(1)).toString('utf8').split('\n')
+  let at = 0
+  return (JSON.parse(head) as any[]).map((f) => ({
+    name: f.n,
+    poster: f.p,
+    subject: f.j,
+    postedAt: f.d,
+    groups: f.g,
+    segments: (f.s as number[]).map((bytes, i) => [f.k?.[i] ?? i + 1, ids[at++], bytes] as [number, string, number]),
+  }))
+}