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>

plugins/example/example.c

@@ -0,0 +1,93 @@
+#include "naut/naut_plugin.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+typedef struct {
+    uint8_t *data;
+    size_t capacity;
+} memory_storage;
+
+static unsigned finished_events;
+
+static void *memory_open(const char *root, naut_err *error) {
+    (void)root;
+    memory_storage *storage = calloc(1, sizeof(*storage));
+    if (!storage) {
+        *error = NAUT_ERR_NOMEM;
+        return NULL;
+    }
+    storage->capacity = 1u << 20;
+    storage->data = calloc(1, storage->capacity);
+    if (!storage->data) {
+        free(storage);
+        *error = NAUT_ERR_NOMEM;
+        return NULL;
+    }
+    *error = NAUT_OK;
+    return storage;
+}
+
+static void memory_close(void *opaque) {
+    memory_storage *storage = opaque;
+    free(storage->data);
+    free(storage);
+}
+
+static naut_err memory_read(void *opaque, int64_t offset,
+                            void *buffer, size_t length) {
+    memory_storage *storage = opaque;
+    if (offset < 0 || (uint64_t)offset + length > storage->capacity)
+        return NAUT_ERR_RANGE;
+    memcpy(buffer, storage->data + offset, length);
+    return NAUT_OK;
+}
+
+static naut_err memory_write(void *opaque, int64_t offset,
+                             const void *buffer, size_t length) {
+    memory_storage *storage = opaque;
+    if (offset < 0 || (uint64_t)offset + length > storage->capacity)
+        return NAUT_ERR_RANGE;
+    memcpy(storage->data + offset, buffer, length);
+    return NAUT_OK;
+}
+
+static naut_err example_events(void *context, const char *request,
+                               char **response) {
+    (void)context;
+    (void)request;
+    char buffer[64];
+    snprintf(buffer, sizeof buffer, "{\"finished\":%u}", finished_events);
+    *response = strdup(buffer);
+    return *response ? NAUT_OK : NAUT_ERR_NOMEM;
+}
+
+static void on_event(void *context, const naut_event *event) {
+    (void)context;
+    if (event->type == NAUT_EVENT_TORRENT_FINISHED) finished_events++;
+}
+
+naut_err naut_plugin_register(const naut_host_api *host) {
+    if (!host || host->abi_version != NAUT_PLUGIN_ABI_VERSION ||
+        host->struct_size < sizeof(*host))
+        return NAUT_ERR_INVAL;
+    static const naut_storage_backend_v1 storage = {
+        .abi_version = NAUT_PLUGIN_ABI_VERSION,
+        .struct_size = sizeof(storage),
+        .name = "memory",
+        .open = memory_open,
+        .close = memory_close,
+        .read = memory_read,
+        .write = memory_write,
+    };
+    naut_err error = host->set_plugin_name(host->host_context, "example");
+    if (error == NAUT_OK)
+        error = host->register_storage_backend(host->host_context, &storage);
+    if (error == NAUT_OK)
+        error = host->register_rpc(host->host_context, "example.events",
+                                   example_events, NULL);
+    if (error == NAUT_OK)
+        error = host->subscribe_event(host->host_context, on_event, NULL);
+    return error;
+}