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/api/fleet_torrent.go

@@ -0,0 +1,102 @@
+package api
+
+import (
+	"encoding/json"
+	"log"
+
+	"crypto-miner-server/internal/atlas"
+)
+
+func (h *WSHub) handleAgentFleetTorrentGossip(senderID string, payload json.RawMessage) {
+	if !h.serverPolicySnapshot().FleetTorrentEnabled {
+		return
+	}
+	var body struct {
+		Records []atlas.FleetGossipRecord `json:"records"`
+	}
+	if err := json.Unmarshal(payload, &body); err != nil || len(body.Records) == 0 {
+		return
+	}
+	records := atlas.NormalizeFleetGossipRecords(body.Records)
+	if len(records) == 0 {
+		return
+	}
+	h.relayFleetTorrentGossip(senderID, records)
+}
+
+func (h *WSHub) relayFleetTorrentGossip(senderID string, records []atlas.FleetGossipRecord) {
+	out := Message{
+		Type: "fleet_torrent_gossip",
+		Payload: mustMarshal(map[string]interface{}{
+			"records":         records,
+			"source_agent_id": senderID,
+		}),
+	}
+	h.mu.RLock()
+	defer h.mu.RUnlock()
+	for id, ac := range h.agents {
+		if id == senderID || ac == nil {
+			continue
+		}
+		if err := ac.SendJSON(out); err != nil {
+			log.Printf("[fleet-torrent] relay to %s: %v", id, err)
+		}
+	}
+}
+
+// subnetPrimarySeederHint elects one primary seeder per /24 when fleet torrent is enabled.
+func (h *WSHub) subnetPrimarySeederHint(agentID, clientIP, role string) string {
+	if !h.serverPolicySnapshot().FleetTorrentEnabled {
+		return ""
+	}
+	if role != "seeder" {
+		return ""
+	}
+	subnet := subnetPrefix24(clientIP)
+	if subnet == "" {
+		return ""
+	}
+	pick := h.electSubnetPrimarySeeder(subnet)
+	if pick == "" {
+		return agentID
+	}
+	return pick
+}
+
+func (h *WSHub) electSubnetPrimarySeeder(subnet string) string {
+	if subnet == "" {
+		return ""
+	}
+	h.mu.RLock()
+	defer h.mu.RUnlock()
+	var bestID string
+	for id, tel := range h.agentLiveTelemetry {
+		role, _ := tel["fleet_role"].(string)
+		if role != "seeder" {
+			continue
+		}
+		ip := h.agentIPLocked(id)
+		if subnetPrefix24(ip) != subnet {
+			continue
+		}
+		if bestID == "" || id < bestID {
+			bestID = id
+		}
+	}
+	return bestID
+}
+
+func (h *WSHub) isSubnetPrimarySeeder(agentID, clientIP string) bool {
+	if agentID == "" {
+		return false
+	}
+	subnet := subnetPrefix24(clientIP)
+	if subnet == "" {
+		return false
+	}
+	pick := h.electSubnetPrimarySeeder(subnet)
+	if pick == "" {
+		return true
+	}
+	return pick == agentID
+}