Rebuild: the batch store (catalog upserts, write-once chunks, candidates, rule counts, fragments, resume point)

A batch is stored in one transaction and only at its range's resume
point, so a retried batch can't count twice. Garbage is judged before
per-article: a dropped tool isn't worth reading bodies for either.

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

lib/edge/range_indexer.ts

@@ -20,6 +20,9 @@ export interface ReleaseChunk {
   bytes: number
   firstArticle: number
   lastArticle: number
+  /** A file with a readable name; a par2 file. */
+  readable: boolean
+  hasPar2: boolean
   payload: Buffer
 }
 
@@ -63,6 +66,8 @@ export interface Fragment {
 }
 
 export interface EdgeBatch {
+  /** The range's resume point this batch starts at. */
+  from: number
   /** First article number not covered yet. */
   next: number
   headers: number
@@ -193,8 +198,8 @@ export class RangeIndexer {
     }
   }
 
-  private empty(next: number): EdgeBatch {
-    return { next, headers: 0, releases: [], samples: [], candidates: [], counts: [], fragments: [] }
+  private empty(from: number): EdgeBatch {
+    return { from, next: from, headers: 0, releases: [], samples: [], candidates: [], counts: [], fragments: [] }
   }
 }
 
@@ -247,6 +252,8 @@ function chunkOf(key: string, files: AggregatedFile<IngestSegment>[]): ReleaseCh
     bytes,
     firstArticle,
     lastArticle,
+    readable: chunkFiles.some((f) => !isRandomFile(f.name)),
+    hasPar2: chunkFiles.some((f) => /\.par2$/i.test(f.name)),
     payload: encodeChunk(chunkFiles),
   }
 }