feat(chat): add /thread reply tree lookup

src/host/core/command_messages.c

@@ -1575,6 +1575,54 @@ static const session_command_message_t kSessionCommandMessages[] = {
             [SESSION_UI_LANGUAGE_PL] = "%s jest teraz zajęty; spróbuj za chwilę.",
         },
     },
+    {
+        "Usage: /thread <message-id|r#reply-id>",
+        {
+            [SESSION_UI_LANGUAGE_KO] = "사용법: /thread <메시지ID|r#답장ID>",
+            [SESSION_UI_LANGUAGE_JP] = "使い方: /thread <メッセージID|r#返信ID>",
+            [SESSION_UI_LANGUAGE_ZH] = "用法：/thread <消息ID|r#回复ID>",
+            [SESSION_UI_LANGUAGE_RU] = "Использование: /thread <id сообщения|r#id ответа>",
+            [SESSION_UI_LANGUAGE_DE] = "Verwendung: /thread <Nachrichten-ID|r#Antwort-ID>",
+            [SESSION_UI_LANGUAGE_FR] = "Utilisation : /thread <id-message|r#id-réponse>",
+            [SESSION_UI_LANGUAGE_PL] = "Użycie: /thread <id-wiadomości|r#id-odpowiedzi>",
+        },
+    },
+    {
+        "Reply r#%s was not found.",
+        {
+            [SESSION_UI_LANGUAGE_KO] = "답장 r#%s을(를) 찾을 수 없습니다.",
+            [SESSION_UI_LANGUAGE_JP] = "返信 r#%s が見つかりません。",
+            [SESSION_UI_LANGUAGE_ZH] = "未找到回复 r#%s。",
+            [SESSION_UI_LANGUAGE_RU] = "Ответ r#%s не найден.",
+            [SESSION_UI_LANGUAGE_DE] = "Antwort r#%s wurde nicht gefunden.",
+            [SESSION_UI_LANGUAGE_FR] = "Réponse r#%s introuvable.",
+            [SESSION_UI_LANGUAGE_PL] = "Nie znaleziono odpowiedzi r#%s.",
+        },
+    },
+    {
+        "Message #%s was not found.",
+        {
+            [SESSION_UI_LANGUAGE_KO] = "메시지 #%s을(를) 찾을 수 없습니다.",
+            [SESSION_UI_LANGUAGE_JP] = "メッセージ #%s が見つかりません。",
+            [SESSION_UI_LANGUAGE_ZH] = "未找到消息 #%s。",
+            [SESSION_UI_LANGUAGE_RU] = "Сообщение #%s не найдено.",
+            [SESSION_UI_LANGUAGE_DE] = "Nachricht #%s wurde nicht gefunden.",
+            [SESSION_UI_LANGUAGE_FR] = "Message #%s introuvable.",
+            [SESSION_UI_LANGUAGE_PL] = "Nie znaleziono wiadomości #%s.",
+        },
+    },
+    {
+        "Thread for #%s:",
+        {
+            [SESSION_UI_LANGUAGE_KO] = "메시지 #%s의 스레드:",
+            [SESSION_UI_LANGUAGE_JP] = "メッセージ #%s のスレッド:",
+            [SESSION_UI_LANGUAGE_ZH] = "消息 #%s 的线程：",
+            [SESSION_UI_LANGUAGE_RU] = "Тред сообщения #%s:",
+            [SESSION_UI_LANGUAGE_DE] = "Thread zu Nachricht #%s:",
+            [SESSION_UI_LANGUAGE_FR] = "Fil du message #%s :",
+            [SESSION_UI_LANGUAGE_PL] = "Wątek wiadomości #%s:",
+        },
+    },
 };
 
 // Returns the message in the session's UI language, or the English text when

src/host/core/help_entries.c

@@ -615,6 +615,29 @@ static const session_help_entry_t kSessionHelpEssential[] = {
                     "ответ <id сообщения|r<id ответа>> <текст>",
             },
     },
+    {
+        .kind = SESSION_HELP_ENTRY_COMMAND,
+        .label = "thread <message-id|r#reply-id>",
+        .description =
+            {
+                "Show a message and its complete reply thread.",
+                "메시지와 전체 답장 스레드를 보여줍니다.",
+                "メッセージと返信スレッド全体を表示します。",
+                "显示消息及其完整回复线程。",
+                "Показать сообщение и всю цепочку ответов.",
+                "Eine Nachricht und ihren vollständigen Antwort-Thread anzeigen.",
+                "Afficher un message et tout son fil de réponses.",
+                "Pokaż wiadomość i cały wątek odpowiedzi.",
+            },
+        .label_translations =
+            {
+                [SESSION_UI_LANGUAGE_KO] = "스레드 <메시지ID|r#답장ID>",
+                [SESSION_UI_LANGUAGE_JP] = "スレッド <メッセージID|r#返信ID>",
+                [SESSION_UI_LANGUAGE_ZH] = "线程 <消息ID|r#回复ID>",
+                [SESSION_UI_LANGUAGE_RU] =
+                    "тред <id сообщения|r#id ответа>",
+            },
+    },
     {
         .kind = SESSION_HELP_ENTRY_COMMAND,
         .label = "pm <username>|<message>",

src/host/core/locales.c

@@ -653,6 +653,16 @@ static const session_command_alias_t kSessionCommandAliases[] = {
                 [SESSION_UI_LANGUAGE_RU] = "/ответ",
             },
     },
+    {
+        .canonical = "/thread",
+        .localized =
+            {
+                [SESSION_UI_LANGUAGE_KO] = "/스레드",
+                [SESSION_UI_LANGUAGE_JP] = "/スレッド",
+                [SESSION_UI_LANGUAGE_ZH] = "/线程",
+                [SESSION_UI_LANGUAGE_RU] = "/тред",
+            },
+    },
     {
         .canonical = "/nick",
         .localized =

src/host/output/moderation.c

@@ -1333,3 +1333,97 @@ static void session_handle_chat_lookup(session_ctx_t *ctx,
     session_send_history_entry(ctx, &entry);
     session_send_reply_tree(ctx, entry.message_id, 0U, 1U);
 }
+
+static void session_handle_thread(session_ctx_t *ctx, const char *arguments)
+{
+    if (ctx == nullptr || ctx->owner == nullptr) {
+        return;
+    }
+
+    static const char *kUsage = "Usage: /thread <message-id|r#reply-id>";
+    char usage[SSH_CHATTER_MESSAGE_LIMIT];
+    session_command_format_usage(ctx, "/thread",
+                                 session_command_localize(ctx, kUsage), usage,
+                                 sizeof(usage));
+
+    if (arguments == nullptr) {
+        session_send_system_line(ctx, usage);
+        return;
+    }
+
+    char working[64];
+    snprintf(working, sizeof(working), "%s", arguments);
+    trim_whitespace_inplace(working);
+    if (working[0] == '\0') {
+        session_send_system_line(ctx, usage);
+        return;
+    }
+
+    char *saveptr = nullptr;
+    char *target = strtok_r(working, " \t", &saveptr);
+    if (target == nullptr || strtok_r(nullptr, " \t", &saveptr) != nullptr) {
+        session_send_system_line(ctx, usage);
+        return;
+    }
+
+    bool targeting_reply = false;
+    if (*target == 'r' || *target == 'R') {
+        targeting_reply = true;
+        ++target;
+    }
+    if (*target == '#') {
+        ++target;
+    }
+    if (*target == '\0') {
+        session_send_system_line(ctx, usage);
+        return;
+    }
+
+    uint64_t identifier = 0U;
+    if (!host_compact_id_decode(target, &identifier) || identifier == 0U) {
+        session_send_system_line(ctx, usage);
+        return;
+    }
+
+    uint64_t message_id = identifier;
+    if (targeting_reply) {
+        chat_reply_entry_t reply = {0};
+        if (!host_replies_find_entry_by_id(ctx->owner, identifier, &reply)) {
+            char message[SSH_CHATTER_MESSAGE_LIMIT];
+            char label[32];
+            if (!host_compact_id_encode(identifier, label, sizeof(label))) {
+                snprintf(label, sizeof(label), "%" PRIu64, identifier);
+            }
+            session_command_snprintf(ctx, message, sizeof(message),
+                                     "Reply r#%s was not found.", label);
+            session_send_system_line(ctx, message);
+            return;
+        }
+        message_id = reply.parent_message_id;
+    }
+
+    chat_history_entry_t entry = {0};
+    if (message_id == 0U ||
+        !host_history_find_entry_by_id(ctx->owner, message_id, &entry)) {
+        char message[SSH_CHATTER_MESSAGE_LIMIT];
+        char label[32];
+        if (!host_compact_id_encode(message_id, label, sizeof(label))) {
+            snprintf(label, sizeof(label), "%" PRIu64, message_id);
+        }
+        session_command_snprintf(ctx, message, sizeof(message),
+                                 "Message #%s was not found.", label);
+        session_send_system_line(ctx, message);
+        return;
+    }
+
+    char header[SSH_CHATTER_MESSAGE_LIMIT];
+    char label[32];
+    if (!host_compact_id_encode(message_id, label, sizeof(label))) {
+        snprintf(label, sizeof(label), "%" PRIu64, message_id);
+    }
+    session_command_snprintf(ctx, header, sizeof(header), "Thread for #%s:",
+                             label);
+    session_send_system_line(ctx, header);
+    session_send_history_entry(ctx, &entry);
+    session_send_reply_tree(ctx, entry.message_id, 0U, 1U);
+}

src/host/runtime/dispatch.c

@@ -281,6 +281,11 @@ static void session_dispatch_command(session_ctx_t *ctx, const char *line)
         return;
     }
 
+    else if (session_parse_command_any(ctx, "/thread", effective_line, &args)) {
+        session_handle_thread(ctx, args);
+        return;
+    }
+
     else if (session_parse_command_any(ctx, "/image", effective_line, &args)) {
         session_handle_image(ctx, args);
         return;

tests/unit/test_ddial_hub.c

@@ -278,6 +278,172 @@ TEST(rebuild_is_idempotent)
     CHECK_EQ(reply_count_for(parent.message_id), 1);
 }
 
+static bool command_output(const char *command, char *output, size_t output_cap)
+{
+    if (command == NULL || output == NULL || output_cap == 0U) {
+        return false;
+    }
+    output[0] = '\0';
+
+    int pipefd[2];
+    if (socketpair(AF_UNIX, SOCK_STREAM, 0, pipefd) != 0) {
+        return false;
+    }
+
+    session_ctx_t ctx = {0};
+    ctx.transport_kind = SESSION_TRANSPORT_TELNET;
+    ctx.telnet_fd = pipefd[1];
+    ctx.owner = g_host;
+    ctx.terminal_width = 80;
+    ctx.terminal_height = 24;
+    session_dispatch_command(&ctx, command);
+    close(pipefd[1]);
+
+    size_t used = 0U;
+    while (used + 1U < output_cap) {
+        ssize_t n = read(pipefd[0], output + used, output_cap - used - 1U);
+        if (n > 0) {
+            used += (size_t)n;
+            continue;
+        }
+        if (n < 0 && errno == EINTR) {
+            continue;
+        }
+        break;
+    }
+    close(pipefd[0]);
+    output[used] = '\0';
+    return true;
+}
+
+TEST(thread_command_shows_mixed_nested_tree_from_message_or_reply)
+{
+    chat_history_entry_t root =
+        commit_user("ThreadRoot", "thread root marker");
+    chat_history_entry_t ddial = commit_system(
+        "71#8[T1:Dialer) ddial child marker^ >>RE:ThreadRoot: thread root "
+        "marker");
+    uint64_t ddial_reply_id = 0U;
+    CHECK(host_ddial_reply_link_get(ddial.message_id, &ddial_reply_id, NULL,
+                                    0U));
+
+    chat_reply_entry_t nested = {0};
+    nested.parent_message_id = root.message_id;
+    nested.parent_reply_id = ddial_reply_id;
+    snprintf(nested.username, sizeof(nested.username), "%s", "NestedUser");
+    snprintf(nested.message, sizeof(nested.message), "%s",
+             "nested child marker");
+    chat_reply_entry_t nested_stored = {0};
+    CHECK(host_replies_commit_entry(g_host, &nested, &nested_stored));
+
+    chat_reply_entry_t direct = {0};
+    direct.parent_message_id = root.message_id;
+    snprintf(direct.username, sizeof(direct.username), "%s", "DirectUser");
+    snprintf(direct.message, sizeof(direct.message), "%s",
+             "direct child marker");
+    chat_reply_entry_t direct_stored = {0};
+    CHECK(host_replies_commit_entry(g_host, &direct, &direct_stored));
+
+    char root_label[32];
+    char ddial_label[32];
+    char nested_label[32];
+    char direct_label[32];
+    CHECK(host_compact_id_encode(root.message_id, root_label,
+                                 sizeof(root_label)));
+    CHECK(host_compact_id_encode(ddial_reply_id, ddial_label,
+                                 sizeof(ddial_label)));
+    CHECK(host_compact_id_encode(nested_stored.reply_id, nested_label,
+                                 sizeof(nested_label)));
+    CHECK(host_compact_id_encode(direct_stored.reply_id, direct_label,
+                                 sizeof(direct_label)));
+
+    char command[128];
+    snprintf(command, sizeof(command), "/thread %s", root_label);
+    char output[32768];
+    CHECK(command_output(command, output, sizeof(output)));
+
+    char expected[256];
+    snprintf(expected, sizeof(expected), "Thread for #%s:", root_label);
+    CHECK(strstr(output, expected) != NULL);
+    CHECK(strstr(output, "thread root marker") != NULL);
+    snprintf(expected, sizeof(expected), "    (r#%s) ddial child marker",
+             ddial_label);
+    char *ddial_pos = strstr(output, expected);
+    CHECK(ddial_pos != NULL);
+    snprintf(expected, sizeof(expected), "        (r#%s) nested child marker",
+             nested_label);
+    char *nested_pos = strstr(output, expected);
+    CHECK(nested_pos != NULL);
+    snprintf(expected, sizeof(expected), "    (r#%s) direct child marker",
+             direct_label);
+    char *direct_pos = strstr(output, expected);
+    CHECK(direct_pos != NULL);
+    CHECK(ddial_pos < nested_pos && nested_pos < direct_pos);
+
+    snprintf(command, sizeof(command), "/thread r#%s", nested_label);
+    CHECK(command_output(command, output, sizeof(output)));
+    snprintf(expected, sizeof(expected), "Thread for #%s:", root_label);
+    CHECK(strstr(output, expected) != NULL);
+    CHECK(strstr(output, "thread root marker") != NULL);
+    CHECK(strstr(output, "ddial child marker") != NULL);
+    CHECK(strstr(output, "nested child marker") != NULL);
+    CHECK(strstr(output, "direct child marker") != NULL);
+}
+
+TEST(thread_command_accepts_ddial_root_id)
+{
+    chat_history_entry_t root =
+        commit_system("71#9[T1:DialRoot) ddial root marker");
+    chat_history_entry_t reply = commit_system(
+        "71#8[T1:Dialer) ddial root reply marker^ >>RE:[9] DialRoot: ddial "
+        "root marker");
+    uint64_t reply_id = 0U;
+    CHECK(host_ddial_reply_link_get(reply.message_id, &reply_id, NULL, 0U));
+
+    char root_label[32];
+    char reply_label[32];
+    CHECK(host_compact_id_encode(root.message_id, root_label,
+                                 sizeof(root_label)));
+    CHECK(host_compact_id_encode(reply_id, reply_label, sizeof(reply_label)));
+    char command[128];
+    snprintf(command, sizeof(command), "/thread d%s", root_label);
+    char output[16384];
+    CHECK(command_output(command, output, sizeof(output)));
+    CHECK(strstr(output, "ddial root marker") != NULL);
+    char expected[256];
+    snprintf(expected, sizeof(expected), "    (r#%s) ddial root reply marker",
+             reply_label);
+    CHECK(strstr(output, expected) != NULL);
+}
+
+TEST(thread_command_rejects_bad_targets_without_mutation)
+{
+    size_t history_before = host_history_total(g_host);
+    ttak_mutex_lock(&g_host->lock);
+    size_t replies_before = g_host->reply_count;
+    ttak_mutex_unlock(&g_host->lock);
+
+    const char *usage_commands[] = {
+        "/thread", "/thread nonsense", "/thread 1 extra", "/thread r#",
+    };
+    char output[16384];
+    for (size_t idx = 0U;
+         idx < sizeof(usage_commands) / sizeof(usage_commands[0]); ++idx) {
+        CHECK(command_output(usage_commands[idx], output, sizeof(output)));
+        CHECK(strstr(output, "Usage: /thread <message-id|r#reply-id>") != NULL);
+    }
+
+    CHECK(command_output("/thread 9999", output, sizeof(output)));
+    CHECK(strstr(output, "Message #9999 was not found.") != NULL);
+    CHECK(command_output("/thread r#9999", output, sizeof(output)));
+    CHECK(strstr(output, "Reply r#9999 was not found.") != NULL);
+    CHECK_EQ(host_history_total(g_host), history_before);
+    ttak_mutex_lock(&g_host->lock);
+    size_t replies_after = g_host->reply_count;
+    ttak_mutex_unlock(&g_host->lock);
+    CHECK_EQ(replies_after, replies_before);
+}
+
 TEST(full_reply_table_drops_the_oldest)
 {
     ttak_mutex_lock(&g_host->lock);
@@ -698,6 +864,9 @@ int main(void)
     RUN_TEST(ddial_reply_to_chatter_message_and_chatter_reply);
     RUN_TEST(unmatched_ddial_reply_stays_a_plain_line);
     RUN_TEST(rebuild_is_idempotent);
+    RUN_TEST(thread_command_shows_mixed_nested_tree_from_message_or_reply);
+    RUN_TEST(thread_command_accepts_ddial_root_id);
+    RUN_TEST(thread_command_rejects_bad_targets_without_mutation);
     RUN_TEST(full_reply_table_drops_the_oldest);
     RUN_TEST(station_key_create_match_revoke);
     RUN_TEST(failed_logins_block_an_address);