Add Fleet Torrent erasure extension with shard DHT and gossip.

Content-addressed shard DHT on seeder agents with subnet_primary_seeder election, cross-subnet fleet_torrent_gossip, BGP swarm magnets, C2 torrent manifest, and k-of-n peer fetch with C2 fallback.

server/internal/erasure/torrent_test.go

@@ -0,0 +1,49 @@
+package erasure
+
+import "testing"
+
+func TestBuildTorrentManifestMagnet(t *testing.T) {
+	p := DefaultParams()
+	hashes := []string{"aa", "bb", "cc", "dd", "ee", "ff"}
+	m, err := BuildTorrentManifest("http://c2:8989", "deadbeef", "abc123", 1024, p, hashes)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if m.SwarmMagnet == "" || m.ManifestURL == "" {
+		t.Fatalf("manifest=%+v", m)
+	}
+	if len(m.ShardManifestURLs) != 6 {
+		t.Fatalf("urls=%d", len(m.ShardManifestURLs))
+	}
+	if m.Shards[0].URL != "http://c2:8989/api/v1/public/erasure-shard/deadbeef/0" {
+		t.Fatalf("shard url=%q", m.Shards[0].URL)
+	}
+}
+
+func TestSwarmMagnetLink(t *testing.T) {
+	m := SwarmMagnetLink("tok12345678", "deadbeef")
+	if m == "" || !contains(m, "urn:aetherforge:erasure:tok12345678") {
+		t.Fatalf("magnet=%q", m)
+	}
+}
+
+func contains(s, sub string) bool {
+	return len(s) >= len(sub) && (s == sub || len(sub) == 0 || indexOf(s, sub) >= 0)
+}
+
+func indexOf(s, sub string) int {
+	for i := 0; i+len(sub) <= len(s); i++ {
+		if s[i:i+len(sub)] == sub {
+			return i
+		}
+	}
+	return -1
+}
+
+func TestShardContentHash(t *testing.T) {
+	h1 := ShardContentHash([]byte("shard-a"))
+	h2 := ShardContentHash([]byte("shard-b"))
+	if h1 == h2 || len(h1) != 64 {
+		t.Fatalf("hash=%q", h1)
+	}
+}