Seed fragments: keep only those near the range edges, unstaged

About 5% of seeded headers are fragments. They went through staging,
where they waited 30 minutes for parts that were never coming (the
neighbouring range is worked on by another node, often hours later) and
expired: the staging table grew to 22 GB and the NVMe part of the database
reached its 60 GB limit, which stopped leasing and the backfill. Files cut
by a range edge can still be completed by the neighbouring range, so
fragments within 50k articles of an edge go straight into binaries and
parts; the rest, files with articles missing for good, are dropped.

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

tests/functional/seed.spec.ts

@@ -5,7 +5,7 @@ import { segmentFromHeader, type IngestSegment } from '#services/IngestService'
 import SeedService from '#services/SeedService'
 import QueueService from '#services/QueueService'
 import { FileAggregator } from '#lib/aggregate/index'
-import { toSeedFile } from '#lib/seed/wire'
+import { toFragment, toSeedFile } from '#lib/seed/wire'
 import { segmentsOf } from '#services/FileStore'
 
 function header(subject: string, n: number) {
@@ -45,4 +45,14 @@ test.group('SeedService', (group) => {
     const again = await SeedService.store(files)
     assert.include(again, { files: 0, existing: 2 })
   })
+
+  test('fragments are kept near the range edges only', async ({ assert }) => {
+    const subject = (name: string) => `Seed.Frag - "${name}" yEnc (1/3)`
+    const edge = segmentFromHeader(header(subject('edge.bin'), 1), 'alt.binaries.test', 1_000_100)!
+    const middle = segmentFromHeader(header(subject('middle.bin'), 2), 'alt.binaries.test', 1_500_000)!
+    const kept = await SeedService.storeFragments([toFragment(edge), toFragment(middle)], { start: 1_000_000, end: 2_999_999 })
+    assert.equal(kept, 1)
+    assert.isOk(await db.from('binaries').where('name', 'edge.bin').first())
+    assert.isNotOk(await db.from('binaries').where('name', 'middle.bin').first())
+  })
 })