Initial commit: Naut-Torrent — from-scratch 10 GbE BitTorrent client

A maintainable, extensible BitTorrent client (C11, Linux/io_uring) targeting
10 GbE saturation. All torrent functionality is built from scratch; liburing
is the only linked third-party dependency on the data path.

Implements Phases 1-7 of the roadmap:
- core: page-aligned buffer pool, MPMC/Treiber queues, bitfields, worker pool
- crypto: SHA-1/256 (SHA-NI + scalar), Merkle (BEP-52), RC4 (MSE)
- bencode/metainfo: zero-copy parser, v1/v2/hybrid .torrent + magnet
- peer: sans-IO wire codec, MSE/PE handshake state machine, BEP-10, ut_metadata, PEX
- piece/storage: block-level multi-peer engine, rarest-first + endgame,
  per-file completion events + single-file relocate (move-as-you-finish)
- tracker/dht: HTTP + UDP (BEP-15) trackers, BEP-5 KRPC iterative lookup
- platform: io_uring reactor (SQPOLL, registered buffers, SEND_ZC)
- surface: versioned RPC, native plugin ABI, sandboxed Lua scripting, nautd/nautctl

Verified against libtorrent (single/multi/hybrid, MSE, magnet-via-DHT, swarm);
unit + interop tests green; ASan/UBSan/TSan clean. Scripting reference in
docs/scripting.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

include/naut/pipeline.h

@@ -0,0 +1,29 @@
+/* pipeline.h - adaptive request window based on observed bandwidth-delay product. */
+#ifndef NAUT_PIPELINE_H
+#define NAUT_PIPELINE_H
+
+#include "naut/common.h"
+
+typedef struct {
+    double rtt_seconds;
+    double bytes_per_second;
+    double last_sample_at;
+    uint32_t depth;
+    uint32_t min_depth;
+    uint32_t max_depth;
+    uint32_t block_size;
+} naut_pipeline;
+
+void naut_pipeline_init(naut_pipeline *p, uint32_t block_size,
+                        uint32_t min_depth, uint32_t max_depth,
+                        uint32_t initial_depth);
+
+/* Record one completed request. sent_at and received_at are monotonic seconds.
+ * The controller smooths RTT and delivery rate, then targets 2x BDP to absorb
+ * scheduling jitter without allowing an unbounded request window. */
+void naut_pipeline_on_block(naut_pipeline *p, uint32_t bytes,
+                            double sent_at, double received_at);
+
+uint32_t naut_pipeline_depth(const naut_pipeline *p);
+
+#endif /* NAUT_PIPELINE_H */