feat(worker): ranged 7z listing orchestrator + RangeReader

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

worker/src/archive/ranged/sevenz-ranged.ts

@@ -1,3 +1,11 @@
+import type { FileEntry } from "../zip-reader.js";
+import { read7zContents } from "../sevenz-reader.js";
+import { listFromSparse } from "./sparse-list.js";
+import type { RangeReader } from "./range-reader.js";
+import { childLogger } from "../../util/logger.js";
+
+const log = childLogger("sevenz-ranged");
+
 const SEVENZ_MAGIC = Buffer.from([0x37, 0x7a, 0xbc, 0xaf, 0x27, 0x1c]);
 
 export function parseSevenZSignatureHeader(
@@ -10,3 +18,36 @@ export function parseSevenZSignatureHeader(
     nextHeaderSize: Number(buf.readBigUInt64LE(20)),
   };
 }
+
+export interface RangedPart { fileId: string; fileSize: bigint; fileName: string }
+
+export async function readSevenZListingRanged(
+  parts: RangedPart[],
+  read: RangeReader,
+): Promise<FileEntry[] | null> {
+  const part = parts[0];
+  if (!part) return null;
+  const size = Number(part.fileSize);
+  try {
+    const sig = await read(part.fileId, 0, 32, part.fileSize);
+    const parsed = parseSevenZSignatureHeader(sig);
+    if (!parsed) return null;
+    const endStart = 32 + parsed.nextHeaderOffset;
+    if (endStart < 0 || endStart + parsed.nextHeaderSize > size) return null;
+    const endHeader = await read(part.fileId, endStart, parsed.nextHeaderSize, part.fileSize);
+    return listFromSparse(
+      [{
+        fileName: part.fileName,
+        size,
+        regions: [
+          { offset: 0, bytes: sig },
+          { offset: endStart, bytes: endHeader },
+        ],
+      }],
+      read7zContents,
+    );
+  } catch (err) {
+    log.warn({ err, fileId: part.fileId }, "ranged 7z listing failed");
+    return null;
+  }
+}