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.

PROBLEMS.md

@@ -68,7 +68,7 @@ Automatable gaps are closed; remaining items below are by-design limits, archite
 
 | Item | Notes |
 |------|-------|
-| **Erasure-coded multi-lane propagation** | **Partial foundation** — server `internal/erasure/` RS 4+2 + shard API; deploy plans attach `erasure_plan` when Calibrate `server.erasure_lanes_enabled`; agent `deploy/erasure_staging.go` reassembles from parallel lane URLs as fallback when primary staging fails. **Not shipped:** live parallel lane orchestration, seeder-side shard fan-out, or erasure-first (non-fallback) spread E2E. |
+| **Erasure-coded multi-lane propagation** | **Partial foundation** — server `internal/erasure/` RS 4+2 + shard API; deploy plans attach `erasure_plan` when Calibrate `server.erasure_lanes_enabled`; agent `deploy/erasure_staging.go` reassembles from parallel lane URLs as fallback when primary staging fails. **Fleet Torrent (partial):** `fleet_torrent_enabled` adds shard DHT gossip, primary seeder election, BGP swarm magnets, and C2 torrent manifest — **not shipped:** live peer HTTP shard serving on agents, UDP/magnet tracker, or erasure-first spread E2E. |
 | **P2 remaining (manual only)** | Live Docker/Podman container start on operator host; real WinRM/GPO/systemd/crontab on remote owned hosts; live BITS/curl against non-mock C2; live multi-hop discover→spread without Playwright stub; live TLS/mesh beacon; full `wg_setup` on real Windows hosts. |
 
 ## Do not commit