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>

tests/unit/test_script.c

@@ -0,0 +1,78 @@
+#include "naut/script.h"
+#include "test.h"
+
+#include <pthread.h>
+#include <stdatomic.h>
+#include <string.h>
+#include <unistd.h>
+
+#ifndef NAUT_PHASE7_SCRIPT
+#define NAUT_PHASE7_SCRIPT "tests/fixtures/phase7.lua"
+#endif
+
+typedef struct {
+    _Atomic unsigned calls;
+    pthread_t caller;
+    uint64_t torrent_id;
+    uint32_t file_index;
+    char destination[128];
+} move_capture;
+
+static naut_err capture_move(void *opaque, uint64_t torrent_id,
+                             uint32_t file_index, const char *destination) {
+    move_capture *capture = opaque;
+    capture->caller = pthread_self();
+    capture->torrent_id = torrent_id;
+    capture->file_index = file_index;
+    snprintf(capture->destination, sizeof capture->destination, "%s",
+             destination);
+    atomic_fetch_add(&capture->calls, 1);
+    return NAUT_OK;
+}
+
+int main(void) {
+    pthread_t owner = pthread_self();
+    move_capture capture = {0};
+    naut_event_bus *events = naut_event_bus_create();
+    naut_err error;
+    naut_script *script = naut_script_create(
+        events, NAUT_PHASE7_SCRIPT, 8, capture_move, &capture, &error);
+    CHECK(script && error == NAUT_OK);
+
+    naut_event event = {
+        .type = NAUT_EVENT_TORRENT_FINISHED,
+        .torrent_id = 42,
+    };
+    naut_event_emit(events, &event);
+    for (unsigned i = 0; i < 100 && atomic_load(&capture.calls) == 0; i++)
+        usleep(1000);
+    CHECK_EQ(atomic_load(&capture.calls), 1);
+    CHECK(!pthread_equal(owner, capture.caller));
+    CHECK_EQ(capture.torrent_id, 42);
+    CHECK_EQ(capture.file_index, 0);
+    CHECK(strcmp(capture.destination, "/tmp/naut-phase7-finished") == 0);
+
+    event = (naut_event) {
+        .type = NAUT_EVENT_FILE_COMPLETE,
+        .torrent_id = 42,
+        .index = 3,
+        .path = "/tmp/completed-file",
+    };
+    naut_event_emit(events, &event);
+    for (unsigned i = 0; i < 100 && atomic_load(&capture.calls) < 2; i++)
+        usleep(1000);
+    CHECK_EQ(atomic_load(&capture.calls), 2);
+    CHECK_EQ(capture.file_index, 3);
+    CHECK(strcmp(capture.destination, "/tmp/completed-file.moved") == 0);
+
+    naut_script_stats stats;
+    naut_script_get_stats(script, &stats);
+    CHECK_EQ(stats.queued, 2);
+    CHECK_EQ(stats.handled, 2);
+    CHECK_EQ(stats.errors, 0);
+    CHECK_EQ(stats.move_requests, 2);
+
+    naut_script_destroy(script);
+    naut_event_bus_destroy(events);
+    TEST_MAIN_END();
+}