feat: add :last, :search, :mute-joins commands and MOTD support

- :last [N]: show last N messages from log (max 50, default 10)
- :search <keyword>: case-insensitive full-text search across log history
- :mute-joins: per-client toggle to silence join/leave system messages,
  indicated by [静音] in the title bar
- MOTD: display motd.txt from state directory on connect before entering chat
- Add message_search() to message.c/h for log file scanning
- Update :help and tui help screen (EN/ZH) with new commands

include/message.h

@@ -22,4 +22,8 @@ int message_save(const message_t *msg);
 /* Format a message for display */
 void message_format(const message_t *msg, char *buffer, size_t buf_size, int width);
 
+/* Search log file for messages matching query (case-insensitive, username or content).
+ * Returns the last max_results matches in chronological order; caller must free *results. */
+int message_search(const char *query, message_t **results, int max_results);
+
 #endif /* MESSAGE_H */

include/ssh_server.h

@@ -30,6 +30,7 @@ typedef struct client {
     time_t connect_time;
     time_t last_active;
     atomic_bool redraw_pending;
+    bool mute_joins;
     pthread_t thread;
     atomic_bool connected;
     int ref_count;                   /* Reference count for safe cleanup */

src/message.c

@@ -244,6 +244,78 @@ int message_save(const message_t *msg) {
     return rc;
 }
 
+/* Search log file for messages whose username or content contains query.
+ * Case-insensitive. Returns the last max_results matches (most recent); caller frees *results. */
+int message_search(const char *query, message_t **results, int max_results) {
+    char log_path[PATH_MAX];
+
+    message_t *res = calloc(max_results, sizeof(message_t));
+    if (!res) return 0;
+
+    if (!query || query[0] == '\0' ||
+        tnt_state_path(log_path, sizeof(log_path), LOG_FILE) < 0) {
+        *results = res;
+        return 0;
+    }
+
+    pthread_mutex_lock(&g_message_file_lock);
+    FILE *fp = fopen(log_path, "r");
+    if (!fp) {
+        pthread_mutex_unlock(&g_message_file_lock);
+        *results = res;
+        return 0;
+    }
+
+    char line[2048];
+    int count = 0;
+
+    while (fgets(line, sizeof(line), fp)) {
+        size_t line_len = strlen(line);
+        if (line_len >= sizeof(line) - 1) {
+            int c;
+            while ((c = fgetc(fp)) != '\n' && c != EOF);
+            continue;
+        }
+
+        char line_copy[2048];
+        strncpy(line_copy, line, sizeof(line_copy) - 1);
+        line_copy[sizeof(line_copy) - 1] = '\0';
+
+        char *timestamp_str = strtok(line_copy, "|");
+        char *username = strtok(NULL, "|");
+        char *content = strtok(NULL, "\n");
+
+        if (!timestamp_str || !username || !content || username[0] == '\0') continue;
+        if (strlen(username) >= MAX_USERNAME_LEN || strlen(content) >= MAX_MESSAGE_LEN) continue;
+        if (!utf8_is_valid_string(username) || !utf8_is_valid_string(content)) continue;
+
+        if (strcasestr(username, query) == NULL && strcasestr(content, query) == NULL) continue;
+
+        time_t msg_time = parse_rfc3339_utc(timestamp_str);
+        if (msg_time == (time_t)-1) continue;
+
+        message_t m;
+        m.timestamp = msg_time;
+        strncpy(m.username, username, MAX_USERNAME_LEN - 1);
+        m.username[MAX_USERNAME_LEN - 1] = '\0';
+        strncpy(m.content, content, MAX_MESSAGE_LEN - 1);
+        m.content[MAX_MESSAGE_LEN - 1] = '\0';
+
+        if (count < max_results) {
+            res[count++] = m;
+        } else {
+            memmove(&res[0], &res[1], (max_results - 1) * sizeof(message_t));
+            res[max_results - 1] = m;
+            /* count stays at max_results */
+        }
+    }
+
+    fclose(fp);
+    pthread_mutex_unlock(&g_message_file_lock);
+    *results = res;
+    return (count < max_results) ? count : max_results;
+}
+
 /* Format a message for display */
 void message_format(const message_t *msg, char *buffer, size_t buf_size, int width) {
     struct tm tm_info;

src/ssh_server.c

@@ -1198,6 +1198,9 @@ static void execute_command(client_t *client) {
                        "list, users, who    - Show online users\n"
                        "nick/name <name>    - Change nickname\n"
                        "msg/w <user> <text> - Whisper to user\n"
+                       "last [N]            - Show last N messages\n"
+                       "search <keyword>    - Search message history\n"
+                       "mute-joins          - Toggle join/leave notices\n"
                        "help, commands      - Show this help\n"
                        "clear, cls          - Clear command output\n"
                        "q, quit, exit       - Disconnect\n"
@@ -1289,6 +1292,63 @@ static void execute_command(client_t *client) {
                            "Nickname changed: %s -> %s\n", old_name, client->username);
         }
 
+    } else if (strncmp(cmd, "last", 4) == 0 && (cmd[4] == ' ' || cmd[4] == '\0')) {
+        char *arg = cmd + 4;
+        while (*arg == ' ') arg++;
+        int n = 10;
+        if (*arg != '\0') {
+            char *endp;
+            long val = strtol(arg, &endp, 10);
+            if (*endp != '\0' || val < 1 || val > 50) {
+                buffer_appendf(output, sizeof(output), &pos,
+                               "Usage: last [N]  (N: 1-50, default 10)\n");
+                goto cmd_done;
+            }
+            n = (int)val;
+        }
+
+        message_t *last_msgs = NULL;
+        int last_count = message_load(&last_msgs, n);
+        buffer_appendf(output, sizeof(output), &pos,
+                       "--- Last %d message(s) ---\n", last_count);
+        for (int i = 0; i < last_count; i++) {
+            char ts[20];
+            struct tm tmi;
+            localtime_r(&last_msgs[i].timestamp, &tmi);
+            strftime(ts, sizeof(ts), "%m-%d %H:%M", &tmi);
+            buffer_appendf(output, sizeof(output), &pos,
+                           "[%s] %s: %s\n", ts, last_msgs[i].username, last_msgs[i].content);
+        }
+        free(last_msgs);
+
+    } else if (strncmp(cmd, "search ", 7) == 0) {
+        char *query = cmd + 7;
+        while (*query == ' ') query++;
+        if (*query == '\0') {
+            buffer_appendf(output, sizeof(output), &pos,
+                           "Usage: search <keyword>\n");
+        } else {
+            message_t *found = NULL;
+            int found_count = message_search(query, &found, 15);
+            buffer_appendf(output, sizeof(output), &pos,
+                           "--- Search: \"%s\" (%d match(es)) ---\n", query, found_count);
+            for (int i = 0; i < found_count; i++) {
+                char ts[20];
+                struct tm tmi;
+                localtime_r(&found[i].timestamp, &tmi);
+                strftime(ts, sizeof(ts), "%m-%d %H:%M", &tmi);
+                buffer_appendf(output, sizeof(output), &pos,
+                               "[%s] %s: %s\n", ts, found[i].username, found[i].content);
+            }
+            free(found);
+        }
+
+    } else if (strcmp(cmd, "mute-joins") == 0 || strcmp(cmd, "mute") == 0) {
+        client->mute_joins = !client->mute_joins;
+        buffer_appendf(output, sizeof(output), &pos,
+                       "Join/leave notifications: %s\n",
+                       client->mute_joins ? "muted" : "unmuted");
+
     } else if (strcmp(cmd, "q") == 0 || strcmp(cmd, "quit") == 0 ||
                strcmp(cmd, "exit") == 0) {
         client->connected = false;
@@ -1310,6 +1370,7 @@ static void execute_command(client_t *client) {
                        "Type 'help' for available commands\n", cmd);
     }
 
+cmd_done:
     buffer_appendf(output, sizeof(output), &pos,
                    "\nPress any key to continue...");
 
@@ -1607,10 +1668,33 @@ void* client_handle_session(void *arg) {
     room_broadcast(g_room, &join_msg);
     message_save(&join_msg);
 
+    /* Show MOTD if motd.txt exists in state directory */
+    {
+        char motd_path[PATH_MAX];
+        if (tnt_state_path(motd_path, sizeof(motd_path), "motd.txt") == 0) {
+            FILE *motd_fp = fopen(motd_path, "r");
+            if (motd_fp) {
+                char motd_buf[sizeof(client->command_output) - 64];
+                size_t motd_len = fread(motd_buf, 1, sizeof(motd_buf) - 1, motd_fp);
+                fclose(motd_fp);
+                if (motd_len > 0) {
+                    motd_buf[motd_len] = '\0';
+                    snprintf(client->command_output, sizeof(client->command_output),
+                             "=== 公告 / MOTD ===\n%s", motd_buf);
+                    tui_render_command_output(client);
+                    seen_update_seq = room_get_update_seq(g_room);
+                    goto main_loop;
+                }
+            }
+        }
+    }
+
     /* Render initial screen */
     tui_render_screen(client);
     seen_update_seq = room_get_update_seq(g_room);
 
+main_loop:
+
     /* Main input loop */
     while (client->connected && ssh_channel_is_open(client->channel)) {
         int ready = ssh_channel_poll_timeout(client->channel, 1000, 0);

src/tui.c

@@ -5,6 +5,12 @@
 #include <stdarg.h>
 #include <unistd.h>
 
+static bool is_join_leave_msg(const message_t *msg) {
+    if (strcmp(msg->username, "系统") != 0) return false;
+    return strstr(msg->content, "加入了聊天室") != NULL ||
+           strstr(msg->content, "离开了聊天室") != NULL;
+}
+
 static const char *username_color(const char *name) {
     static const char *colors[] = {
         "\033[31m", "\033[32m", "\033[33m",
@@ -222,6 +228,17 @@ void tui_render_screen(client_t *client) {
 
     /* Now render using snapshot (no lock held) */
 
+    /* If mute_joins is set, remove join/leave messages from snapshot in place */
+    if (client->mute_joins && msg_snapshot) {
+        int filtered = 0;
+        for (int i = 0; i < snapshot_count; i++) {
+            if (!is_join_leave_msg(&msg_snapshot[i])) {
+                msg_snapshot[filtered++] = msg_snapshot[i];
+            }
+        }
+        snapshot_count = filtered;
+    }
+
     /* Move to top (Home) - Do NOT clear screen to prevent flicker */
     buffer_appendf(buffer, buf_size, &pos, ANSI_HOME);
 
@@ -232,8 +249,9 @@ void tui_render_screen(client_t *client) {
 
     char title[256];
     snprintf(title, sizeof(title),
-             " %s | 在线: %d | 模式: %s | ? 帮助 ",
+             " %s | 在线: %d | 模式: %s%s | ? 帮助 ",
-             client->username, online, mode_str);
+             client->username, online, mode_str,
+             client->mute_joins ? " [静音]" : "");
 
     int title_width = utf8_string_width(title);
     int padding = render_width - title_width;
@@ -419,6 +437,9 @@ const char* tui_get_help_text(help_lang_t lang) {
                "  :nick <name>         - Change nickname\n"
                "  :msg <user> <text>   - Whisper to user\n"
                "  :w <user> <text>     - Short alias for :msg\n"
+               "  :last [N]            - Show last N messages (max 50)\n"
+               "  :search <keyword>    - Search message history\n"
+               "  :mute-joins          - Toggle join/leave notices\n"
                "  :help                - Show available commands\n"
                "  :clear               - Clear command output\n"
                "  :q, :quit, :exit     - Disconnect\n"
@@ -463,6 +484,9 @@ const char* tui_get_help_text(help_lang_t lang) {
                "  :nick <名字>         - 更改昵称\n"
                "  :msg <用户> <文本>   - 私聊\n"
                "  :w <用户> <文本>     - :msg 的简写\n"
+               "  :last [N]            - 显示最后 N 条消息(最多50)\n"
+               "  :search <关键词>     - 搜索消息历史\n"
+               "  :mute-joins          - 切换加入/离开提示\n"
                "  :help                - 显示可用命令\n"
                "  :clear               - 清空命令输出\n"
                "  :q, :quit, :exit     - 断开连接\n"