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/db/oath_ledger_test.go

@@ -0,0 +1,54 @@
+package db
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestOathLedgerRoundTrip(t *testing.T) {
+	d, err := New(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer d.Close()
+
+	why := map[string]string{"tier": "dns_txt", "lane": "spread"}
+	hash := HashWhyJSON(why)
+	entry, err := d.InsertOathLedger(
+		"operator", OathSpreadTierEscalation, "agent-1", "#aabbcc", hash, OathOutcomeSuccess,
+		map[string]string{"command_type": "reorder_tiers"},
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if entry == nil || entry.ID == 0 {
+		t.Fatalf("expected inserted entry, got %+v", entry)
+	}
+	if entry.WhyHash != hash {
+		t.Fatalf("why_hash = %q want %q", entry.WhyHash, hash)
+	}
+
+	rows, err := d.ListOathLedger(10)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(rows) != 1 {
+		t.Fatalf("rows = %+v", rows)
+	}
+	if rows[0].ActionType != OathSpreadTierEscalation || rows[0].Actor != "operator" {
+		t.Fatalf("unexpected row: %+v", rows[0])
+	}
+}
+
+func TestHashWhyJSONStable(t *testing.T) {
+	src := map[string]interface{}{"verdict": "retry spread", "clearance": 4}
+	h1 := HashWhyJSON(src)
+	h2 := HashWhyJSON(src)
+	if h1 == "" || h1 != h2 {
+		t.Fatalf("hash unstable: %q %q", h1, h2)
+	}
+	if len(h1) != 64 {
+		t.Fatalf("expected sha256 hex length 64, got %d", len(h1))
+	}
+	_, _ = json.Marshal(src)
+}