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>

edge/README.md

@@ -234,12 +234,24 @@ them:
 
 ```sh
 cargo build --release
-COORDINATOR_URL=http://coordinator:3334 NODE_TOKEN=… ./target/release/edge-node [--threads N] [--batch-articles 500000] [--ranges N] [--max-mbit M]
+COORDINATOR_URL=http://coordinator:3334 NODE_TOKEN=… ./target/release/edge-node [--threads N] [--batch-articles 500000] [--snapshot-minutes 30] [--groups N] [--max-mbit M]
 ```
 
-- **One range per thread** (default one per core): one thread reads the
-  coordinator's stream and inflates a frame ahead, another posts the
-  batches in order (one may wait), the indexer goes on meanwhile.
+- **One group per thread** (default one per core; REBUILD.md, "Voyager 3:
+  window indexing", 1 and 5): a thread leases a group (`POST
+  groups/lease`), takes its ranges in article order (`POST
+  groups/:id/next`), streams each range's chunks (`GET ranges/:id/stream`:
+  the corpus or the spool, the worker can't tell) through one carried
+  window, posts a batch at least at every range end and finishes the
+  range; one thread reads the stream and inflates a frame ahead, another
+  posts the batches in order, the indexer goes on meanwhile. The window's
+  snapshot (bincode, gzip) goes to the coordinator every
+  `--snapshot-minutes` (EDGE_SNAPSHOT_MINUTES, 30) right after a batch,
+  and when the group is given back: caught up (`next` answers 204: the
+  tail), a stop, a lost lease or a failure; the next holder restores it
+  (`GET groups/:id/snapshot`) and continues at its article. `--groups N`
+  stops after N groups; `--ranges N` is the old per-range lease
+  (`POST lease`), one range per thread without a carried window.
 - **As `commands/edge_node.ts`:** retries for network trouble and 5xx;
   409 means the lease is lost (the range stops, isn't given back); a
   batch once 500k articles or 100k files wait (a picture group's batches