The window worker: group leases, the stream serving the corpus, the snapshot through the API (design 1 and 5)

A worker thread leases a group and takes its ranges in article order through
one carried window; the coordinator keeps one cursor a group (group_leases,
migration 6500) and hands out the next range, the rules and nothing about
where the chunks are: the range stream serves a stored range's chunks from the
corpus file and a live one's from the spool. The window's snapshot (bincode:
the frontier, the open files, releases and albums, the upload numbers, the
batch-counter table) goes to the coordinator every EDGE_SNAPSHOT_MINUTES and
when the group is given back, and the next holder restores it; a takeover
after LEASE_TTL_SECONDS plans the ranges from the snapshot's article again.
The prefetcher runs ahead of held groups' cursors and skips chunks the corpus
has. LEASE_MIN_PRIORITY..LEASE_MAX_PRIORITY bound what is leased. edge-node
holds groups by default; --ranges keeps the old per-range path.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

lib/edge/lease.ts

@@ -5,3 +5,18 @@ export interface Lease {
   range: { id: number; group: string; start: number; end: number; next: number }
   rules: Rules
 }
+
+/**
+ * A group lease (REBUILD.md, "Voyager 3: window indexing", 1): the group a worker thread holds, the rules, and the
+ * snapshot of the group's window when there is one (its next article; the body comes from GET groups/:id/snapshot).
+ */
+export interface GroupLease {
+  group: { id: number; name: string; priority: number }
+  rules: Rules
+  snapshot: { next: number } | null
+}
+
+/** The group's next range in article order, leased to the holder (POST groups/:id/next; 204 when caught up). */
+export interface NextRange {
+  range: { id: number; start: number; end: number; next: number }
+}