Receive data on all sessions simultaneously via multi-socket select

interactive_loop now watches every connected session's socket in one
select() call. Background session data is stored in that session's scroll
buffers without touching the screen (suppress_draw flag). When the user
switches to that session, refresh_all() replays everything from the buffer.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

termtcp.c

@@ -149,6 +149,9 @@ static void on_sigint(int signum)
     sigint_pending = 1;
 }
 
+/* set while receiving data for a background session — suppresses live screen writes */
+static int suppress_draw = 0;
+
 /* ── BPQ / monitor state (shared across all sessions) ─────── */
 int mon_visible  = 1;
 int mon_tx       = 1;
@@ -954,11 +957,12 @@ void append_mon(const char *text, int len, int attr)
 
     const char *p   = text;
     const char *end = text + len;
+    int live = (mon_win != NULL && !suppress_draw);
 
     S->mon_part_cur = attr;
     if (S->mon_part_len == 0) S->mon_part_base = attr;
 
-    if (mon_win && S->mon_scroll == 0)
+    if (live && S->mon_scroll == 0)
         wattron(mon_win, S->mon_part_cur);
 
     while (p < end) {
@@ -969,7 +973,7 @@ void append_mon(const char *text, int len, int attr)
                 S->mon_part[S->mon_part_len++] = (char)0x1B;
                 S->mon_part[S->mon_part_len++] = p[1];
             }
-            if (mon_win && S->mon_scroll == 0) {
+            if (live && S->mon_scroll == 0) {
                 wattroff(mon_win, S->mon_part_cur);
                 wattron(mon_win, na);
             }
@@ -984,19 +988,19 @@ void append_mon(const char *text, int len, int attr)
             if (S->mon_sbuf_count < SCRL_MAX) S->mon_sbuf_count++;
             S->mon_part_len   = 0;
             S->mon_part_base  = S->mon_part_cur;
-            if (mon_win && S->mon_scroll == 0)
+            if (live && S->mon_scroll == 0)
                 waddch(mon_win, '\n');
             p++;
         } else if (c >= 32 && c < 127) {
             if (S->mon_part_len < SCRL_W - 1)
                 S->mon_part[S->mon_part_len++] = (char)c;
-            if (mon_win && S->mon_scroll == 0)
+            if (live && S->mon_scroll == 0)
                 waddch(mon_win, c);
             p++;
         } else { p++; }
     }
 
-    if (mon_win && S->mon_scroll == 0) {
+    if (live && S->mon_scroll == 0) {
         wattroff(mon_win, S->mon_part_cur);
         wrefresh(mon_win);
         if (input_win) wrefresh(input_win);
@@ -1009,11 +1013,12 @@ void append_out(const char *text, int len, int attr)
 
     const char *p   = text;
     const char *end = text + len;
+    int live = (out_win != NULL && !suppress_draw);
 
     S->out_part_cur = attr;
     if (S->out_part_len == 0) S->out_part_base = attr;
 
-    if (out_win && S->out_scroll == 0)
+    if (live && S->out_scroll == 0)
         wattron(out_win, S->out_part_cur);
 
     while (p < end) {
@@ -1024,7 +1029,7 @@ void append_out(const char *text, int len, int attr)
                 S->out_part[S->out_part_len++] = (char)0x1B;
                 S->out_part[S->out_part_len++] = p[1];
             }
-            if (out_win && S->out_scroll == 0) {
+            if (live && S->out_scroll == 0) {
                 wattroff(out_win, S->out_part_cur);
                 wattron(out_win, na);
             }
@@ -1039,19 +1044,19 @@ void append_out(const char *text, int len, int attr)
             if (S->out_sbuf_count < SCRL_MAX) S->out_sbuf_count++;
             S->out_part_len   = 0;
             S->out_part_base  = S->out_part_cur;
-            if (out_win && S->out_scroll == 0)
+            if (live && S->out_scroll == 0)
                 waddch(out_win, '\n');
             p++;
         } else if (c >= 32 && c < 127) {
             if (S->out_part_len < SCRL_W - 1)
                 S->out_part[S->out_part_len++] = (char)c;
-            if (out_win && S->out_scroll == 0)
+            if (live && S->out_scroll == 0)
                 waddch(out_win, c);
             p++;
         } else { p++; }
     }
 
-    if (out_win && S->out_scroll == 0) {
+    if (live && S->out_scroll == 0) {
         wattroff(out_win, S->out_part_cur);
         wrefresh(out_win);
         if (input_win) wrefresh(input_win);
@@ -3165,27 +3170,46 @@ void interactive_loop(void)
 
         draw_status();
 
+        /* Watch stdin + every connected session's socket */
         FD_ZERO(&readfds);
         FD_SET(STDIN_FILENO, &readfds);
-        if (S->connected && S->sock >= 0) FD_SET(S->sock, &readfds);
+        int maxfd = STDIN_FILENO;
+        for (int i = 0; i < MAX_SESSIONS; i++) {
+            if (sessions[i].active && sessions[i].connected && sessions[i].sock >= 0) {
+                FD_SET(sessions[i].sock, &readfds);
+                if (sessions[i].sock > maxfd) maxfd = sessions[i].sock;
+            }
+        }
 
         tv.tv_sec  = 1;
         tv.tv_usec = 0;
-        int maxfd = (S->connected && S->sock > STDIN_FILENO) ? S->sock : STDIN_FILENO;
         int ready = select(maxfd + 1, &readfds, NULL, NULL, &tv);
         if (ready < 0) continue;
 
-        /* Network data */
+        /* Network data — process all active sessions */
-        if (S->connected && S->sock >= 0 && FD_ISSET(S->sock, &readfds)) {
+        Session *active = S;
+        for (int i = 0; i < MAX_SESSIONS; i++) {
+            if (!sessions[i].active || !sessions[i].connected || sessions[i].sock < 0)
+                continue;
+            if (!FD_ISSET(sessions[i].sock, &readfds))
+                continue;
+
+            int is_bg = (&sessions[i] != active);
+            S = &sessions[i];
+            if (is_bg) suppress_draw = 1;
+
             int n = recv(S->sock, recv_buf, sizeof(recv_buf)-1, 0);
             if (n > 0) {
                 bpq_process(recv_buf, n);
-                draw_input();
+                if (!is_bg) draw_input();
             } else if (n == 0 || (n < 0 && errno != EAGAIN)) {
                 append_out("\n*** Server closed connection ***\n", 33,
                            COLOR_PAIR(CP_RED));
                 tcp_disconnect();
             }
+
+            suppress_draw = 0;
+            S = active;
         }
 
         /* Keyboard */