Chapter dates: read date setting and tiered release dates (BL-0047)

- Chapter rows show when you first finished a chapter (setting: date + hour,
  date, off) from a new durable progress doneAt; older reads fall back to the
  reading clock's earliest remembered completion.
- chapter.json keeps added (arrival in this library, now kept on replace) plus
  x-dates.source (source upload, bulk imports flagged), x-dates.release
  (official, for a later metadata job) and x-dates.ecosystem (first entry into
  any Manga Circus library; carried over peering, earliest wins, clamped).
- Rows show one release date by tier: official > source upload > ecosystem >
  library, with all known dates in the tooltip (setting to hide).
- Fixes: WeebCentral dates came from the chapter page, which has none (every
  chapter got the download time); they now come from the full chapter list.
  MangaDex no longer writes a group's publishAt into added. Peering sends dates.
- tools/backfill-chapter-dates.js migrates an existing library (dry run default).
- Coverage dry run on the server: docs/chapter-dates-coverage-2026-10-24.md.

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

peering/gateway.js

@@ -9,6 +9,7 @@ const crypto = require('node:crypto');
 const { once } = require('node:events');
 const { PeeringState, fp, hash, requirePeer, grantStatus } = require('./state');
 const { parseKey, parseSpecialFolder } = require('../chapter-identity');
+const { peerDates } = require('../chapter-dates');
 const { resolveWorkIdentity } = require('../scraper/lib/work-identity');
 
 const DATA = path.resolve(process.env.PEER_DATA || path.join(process.env.DATA || 'data', 'peering'));
@@ -116,12 +117,23 @@ async function mangaIndex(peer, share) {
       if (!pages.length) continue;
       const id = `c${opaque(`${share.id}/${bookName}/${chapterName}`)}`;
       const chapterMeta = await jsonFile(path.join(chapterDir, 'chapter.json'));
+      const dirStat = await fsp.stat(chapterDir);
       const item = { id, number: parsed.key, volume: book.key, title: String(chapterMeta.title || parsed.title || '').slice(0, 200),
-        pageCount: pages.length, chapterDir, pages };
+        pageCount: pages.length, chapterDir, pages, dates: peerDates(chapterMeta, dirStat.mtimeMs) };
       chapters.push(item); byId.set(id, item);
       if (chapters.length > 10000) fail(413, 'Shared manga chapter limit exceeded');
     }
   }
+  // Every version of a chapter number offers the earliest ecosystem date known for it.
+  const earliest = new Map();
+  for (const item of chapters) {
+    const key = `${item.volume}/${item.number}`, at = item.dates.ecosystem;
+    if (at && (!earliest.has(key) || Date.parse(at) < Date.parse(earliest.get(key)))) earliest.set(key, at);
+  }
+  for (const item of chapters) {
+    const at = earliest.get(`${item.volume}/${item.number}`);
+    if (at) item.dates = { ...item.dates, ecosystem: at };
+  }
   const result = { at: Date.now(), mangaDir, meta, chapters, byId };
   indexCache.set(key, result);
   return result;
@@ -147,7 +159,7 @@ async function chapterManifest(peer, share, chapterId) {
       size: stat.size, mtimeMs: stat.mtimeMs, at: Date.now() });
     if (pages.length > 500) fail(413, 'Chapter page limit exceeded');
   }
-  return { id: chapter.id, number: chapter.number, volume: chapter.volume, title: chapter.title, pages };
+  return { id: chapter.id, number: chapter.number, volume: chapter.volume, title: chapter.title, dates: chapter.dates, pages };
 }
 async function streamBlob(req, res, peer, id) {
   const item = blobCache.get(`${peer.id}:${id}`);
@@ -248,7 +260,7 @@ const server = https.createServer({ key: identity.key, cert: identity.cert, requ
       return json(res, 200, { id: share.id, title: String(index.meta.title || share.mangaId).slice(0, 200),
         workIdentity: resolveWorkIdentity(index.meta, share.mangaId, identity.id),
         ...publicMetadata(index.meta), coverAvailable: !!coverFile(index.mangaDir),
-        chapters: index.chapters.slice(cursor, cursor + 100).map(({ id, number, volume, title, pageCount }) => ({ id, number, volume, title, pageCount })),
+        chapters: index.chapters.slice(cursor, cursor + 100).map(({ id, number, volume, title, pageCount, dates }) => ({ id, number, volume, title, pageCount, dates })),
         nextCursor: cursor + 100 < index.chapters.length ? String(cursor + 100) : null });
     }
     const chapterMatch = /^\/peer\/v1\/manga\/(m[0-9a-f]{24})\/chapters\/(c[0-9a-f]{32})$/.exec(url.pathname);