Rebuild: coordinator (planner, NNTP pool, spool, prefetcher, leases, rule sets), node API and the edge:node worker

- groups:add / ranges:plan / nodes:create / coordinator:run commands
- the node API: lease, the range's chunks as one framed stream from the
  spool, batches, heartbeat, finish, release (node guard, token per node)
- edge:node: needs COORDINATOR_URL and NODE_TOKEN only (placeholders for
  the rest), posts a batch every 10 chunks, gives its range back on SIGTERM
- releases are gathered per batch: 1.04 chunk rows per release at 10
  chunks per batch (1.35 when built per XOVER chunk)
- partitions are checked per batch instead of remembered

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

lib/edge/stream.ts

@@ -0,0 +1,35 @@
+/**
+ * A range's chunks on the wire (REBUILD.md, prefetch): one streaming
+ * response, a frame per chunk: from (8 bytes), to (8 bytes), length
+ * (4 bytes), then the chunk as the news server sent it (compressed XOVER).
+ */
+export interface Frame {
+  from: number
+  to: number
+  data: Buffer
+}
+
+const HEADER = 20
+
+export function encodeFrame(frame: Frame): Buffer {
+  const head = Buffer.alloc(HEADER)
+  head.writeBigUInt64BE(BigInt(frame.from), 0)
+  head.writeBigUInt64BE(BigInt(frame.to), 8)
+  head.writeUInt32BE(frame.data.length, 16)
+  return Buffer.concat([head, frame.data])
+}
+
+/** The frames of a byte stream, as they complete. */
+export async function* decodeFrames(stream: AsyncIterable<Uint8Array> | Iterable<Uint8Array>): AsyncGenerator<Frame> {
+  let buffer = Buffer.alloc(0)
+  for await (const piece of stream) {
+    buffer = buffer.length === 0 ? Buffer.from(piece) : Buffer.concat([buffer, piece])
+    while (buffer.length >= HEADER) {
+      const length = buffer.readUInt32BE(16)
+      if (buffer.length < HEADER + length) break
+      yield { from: Number(buffer.readBigUInt64BE(0)), to: Number(buffer.readBigUInt64BE(8)), data: buffer.subarray(HEADER, HEADER + length) }
+      buffer = buffer.subarray(HEADER + length)
+    }
+  }
+  if (buffer.length > 0) throw new Error(`Stream ended inside a frame (${buffer.length} bytes left)`)
+}