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>

apps/nautctl/main.c

@@ -0,0 +1,93 @@
+#include "naut/rpc.h"
+
+#include <jansson.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define DEFAULT_SOCKET "/tmp/nautd.sock"
+
+static void usage(const char *program) {
+    fprintf(stderr,
+        "usage: %s [--socket PATH] METHOD [PARAMS_JSON]\n"
+        "       %s [--socket PATH] events\n", program, program);
+}
+
+static json_t *parse_params(const char *text) {
+    if (!text) return json_object();
+    json_error_t error;
+    return json_loads(text, JSON_REJECT_DUPLICATES | JSON_DECODE_ANY, &error);
+}
+
+static int print_json(json_t *json) {
+    if (!json) return 1;
+    if (json_dumpf(json, stdout, JSON_INDENT(2) | JSON_SORT_KEYS) != 0)
+        return 1;
+    putchar('\n');
+    return 0;
+}
+
+static int stream_events(const char *socket_path) {
+    int fd = naut_rpc_connect_unix(socket_path);
+    if (fd < 0) return 1;
+    json_t *request = json_pack("{s:s,s:o}", "method", "subscribe",
+                                "params", json_object());
+    if (!request ||
+        naut_rpc_send_json(fd, NAUT_RPC_REQUEST, request) != NAUT_OK) {
+        json_decref(request);
+        close(fd);
+        return 1;
+    }
+    json_decref(request);
+    for (;;) {
+        naut_rpc_frame_type type;
+        json_t *payload = NULL;
+        if (naut_rpc_recv_json(fd, &type, &payload) != NAUT_OK) {
+            close(fd);
+            return 1;
+        }
+        print_json(payload);
+        fflush(stdout);
+        json_decref(payload);
+    }
+}
+
+int main(int argc, char **argv) {
+    const char *socket_path = getenv("NAUT_SOCKET");
+    if (!socket_path || !*socket_path) socket_path = DEFAULT_SOCKET;
+    int arg = 1;
+    if (arg < argc && strcmp(argv[arg], "--socket") == 0) {
+        if (arg + 1 >= argc) {
+            usage(argv[0]);
+            return 2;
+        }
+        socket_path = argv[arg + 1];
+        arg += 2;
+    }
+    if (arg >= argc || arg + 2 < argc) {
+        usage(argv[0]);
+        return 2;
+    }
+    signal(SIGPIPE, SIG_IGN);
+    const char *method = argv[arg++];
+    if (strcmp(method, "events") == 0)
+        return stream_events(socket_path);
+    json_t *params = parse_params(arg < argc ? argv[arg] : NULL);
+    if (!params) {
+        fprintf(stderr, "nautctl: invalid JSON parameters\n");
+        return 2;
+    }
+    json_t *reply = NULL;
+    naut_err error = naut_rpc_call(socket_path, method, params, &reply);
+    json_decref(params);
+    if (error != NAUT_OK) {
+        fprintf(stderr, "nautctl: RPC failed: %s\n", naut_strerror(error));
+        return 1;
+    }
+    int result = print_json(reply);
+    bool ok = json_is_true(json_object_get(reply, "ok"));
+    json_decref(reply);
+    return result || !ok;
+}