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>

tests/functional/node_api.spec.ts

@@ -145,6 +145,23 @@ test.group('Node API', (group) => {
       ;(await client.post(`/api/v1/node/groups/${groupId}/release`).bearerToken(token)).assertStatus(200)
       ;(await client.post(`/api/v1/node/groups/${groupId}/heartbeat`).bearerToken(token)).assertStatus(409)
       assert.include(await db.from('ranges').where('id', r2.id).firstOrFail(), { status: 'planned', node_id: null })
+
+      // The tail lane (`?lane=tail`): the group's tail range, with a cursor and snapshot of its own.
+      const [t] = await db.table('ranges').insert({ group_id: g.id, start_id: 401, end_id: 500, next_id: 401, priority: -3 }).returning('id')
+      ;(await client.post('/api/v1/node/groups/lease?lane=sideways').bearerToken(token)).assertStatus(400)
+      const tail = await client.post('/api/v1/node/groups/lease?lane=tail').bearerToken(token)
+      tail.assertStatus(200)
+      assert.equal(tail.body().lane, 'tail')
+      assert.equal(Number(tail.body().group.id), groupId)
+      assert.deepEqual((await client.post(`/api/v1/node/groups/${groupId}/next?lane=tail`).bearerToken(token)).body().range, { id: Number(t.id), start: 401, end: 500, next: 401 })
+      ;(await client.post(`/api/v1/node/groups/${groupId}/heartbeat`).bearerToken(token)).assertStatus(409)
+      ;(await client.post(`/api/v1/node/groups/${groupId}/heartbeat?lane=tail`).bearerToken(token)).assertStatus(200)
+      ;(await putRaw(`/api/v1/node/groups/${groupId}/snapshot?next=401&lane=tail`, Buffer.from('tail at 401'))).assertStatus(200)
+      const gotTail = await client.get(`/api/v1/node/groups/${groupId}/snapshot?lane=tail`).bearerToken(token)
+      gotTail.assertStatus(200)
+      assert.equal(gotTail.header('x-snapshot-next'), '401')
+      ;(await client.post(`/api/v1/node/groups/${groupId}/release?lane=tail`).bearerToken(token)).assertStatus(200)
+      assert.include(await db.from('ranges').where('id', t.id).firstOrFail(), { status: 'planned', node_id: null })
     } finally {
       coordinatorConfig.corpus.dir = saved.corpus
       coordinatorConfig.snapshotDir = saved.snapshots