Lease lanes for the tail, a mixed lease order, coordinator:status, the edge end to end

A group now has two lease lanes (migration 6600): `history` works the ranges the bounds hand out, `tail` the tail
planner's, each with its own holder, window, snapshot and takeover redo, so a thread on the tail never wades
through a group's history and a held group's tail isn't stuck behind it. The edge puts `--tail-threads`
(EDGE_TAIL_THREADS, 1 of 2+ by default) of its threads on the tail lane; the group routes take `?lane=`. The
lease order within a lane alternates the group with the most planned articles and the longest unheld one. The
takeover redo puts back only the lane's ranges the window did after the snapshot, and a group whose last range
is held by a holder gone quiet can be taken over.

`coordinator:status` prints the catalog's room, the ranges by band, the last hour's rates, the held groups with
their snapshots and the phase-2 backlogs. `tests/e2e` runs the real edge-node binary against the node API: the
corpus-fill race, a failed stream and the restart that restores the snapshot, a restart without the snapshot
file, a takeover (STREAM_CHUNK_WAIT_MINUTES is a setting now). CI builds the binary before the tests.

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

lib/edge/index.ts

@@ -1,7 +1,7 @@
 export { RangeIndexer, postedSpan, chunkOf, candidatesOf, releaseKeyOf, uploadsOf, UPLOAD_GAP_MS, type EdgeBatch, type ReleaseChunk, type DroppedChunk, type ProbeCandidate, type CandidateKind, type RuleCount, type Fragment, type RangeIndexerOptions } from './range_indexer.js'
 export { encodeFrame, decodeFrames, isKeepalive, KEEPALIVE, type Frame } from './stream.js'
 export { toWire, fromWire, type WireBatch } from './wire.js'
-export type { Lease, GroupLease, NextRange } from './lease.js'
+export type { Lease, GroupLease, Lane, NextRange } from './lease.js'
 export type { EdgeSegment, FileMeta } from './scan.js'
 export { throttle } from './throttle.js'
 export { filterOverviews, undelta, type ChunkDrops } from './corpus_filter.js'

lib/edge/lease.ts

@@ -7,11 +7,20 @@ export interface Lease {
 }
 
 /**
- * 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).
+ * A group's two cursors (REBUILD.md, "Voyager 3: window indexing", 1): `history` works the ranges the lease bounds
+ * hand out (the windows, the history), `tail` the tail planner's ranges. Each lane has its own holder, window and
+ * snapshot; the group routes take `?lane=` (history by default).
+ */
+export type Lane = 'history' | 'tail'
+
+/**
+ * A group lease (REBUILD.md, "Voyager 3: window indexing", 1): the group a worker thread holds, the lane, the rules,
+ * and the snapshot of the lane'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 }
+  lane: Lane
   rules: Rules
   snapshot: { next: number } | null
 }