fix auto_socket: handle_nl_link silently skipped on if_indextoname failure for deleted interfaces

When ip link del removes an interface, the kernel sends RTM_DELLINK after the interface is unregistered from the name table.
if_indextoname fails and handle_nl_link silently returned without calling remove_iface_sockets,
causing old ETCP sockets to accumulate indefinitely.

Fix: fall through to remove_iface_sockets(ifindex) even when if_indextoname fails.

Test: added diagnostics (diag_dump_state, per-category debug levels to file) to verify socket/links cleanup.

tests/test_auto_socket_dynamic.c

@@ -183,6 +183,51 @@ static void start_traffic(void) {
     timeout_handle = uasync_set_timeout(ctx.ua, TRAF_MON_TB,  NULL, traffic_monitor_timer, "traf_mon");
 }
 
+/* ── diagnostics ── */
+static void diag_dump_state(const char* label) {
+    fprintf(stderr, "--- DIAG [%s] r=%d s=%d ---\n", label, ctx.round, ctx.step);
+    struct ll_entry* e = ctx.client->connections->head;
+    int conn_n = 0;
+    while (e) { conn_n++; e = e->next; }
+    fprintf(stderr, "  connections=%d\n", conn_n);
+    fprintf(stderr, "  current_iface=%s prev_iface=%s\n", ctx.cur_iface, ctx.prev_iface[0] ? ctx.prev_iface : "(none)");
+
+    /* list sockets */
+    fprintf(stderr, "  sockets:\n");
+    struct ETCP_SOCKET* s = ctx.client->etcp_sockets;
+    while (s) {
+        char ifname[IFNAMSIZ] = "?";
+        if (s->netif_index) if_indextoname(s->netif_index, ifname);
+        fprintf(stderr, "    %-30s fd=%d if=%s(%u) fam=%d tcp=%d\n",
+                s->name, (int)s->fd, ifname, s->netif_index,
+                s->local_addr.ss_family, s->is_tcp);
+        s = s->next;
+    }
+
+    /* list links for the server connection */
+    fprintf(stderr, "  links to srv 0x%016llx:\n", (unsigned long long)ctx.srv_node_id);
+    e = ctx.client->connections->head;
+    while (e) {
+        struct conn_queue_entry* ce = (struct conn_queue_entry*)e->data;
+        if (ce->conn->peer_node_id == ctx.srv_node_id) {
+            int nlink = 0; for (struct ETCP_LINK* tl = ce->conn->links; tl; tl = tl->next) nlink++;
+            fprintf(stderr, "    conn=%s state=%d links=%d\n",
+                    ce->conn->log_name, ce->conn->state, nlink);
+            struct ETCP_LINK* l = ce->conn->links;
+            while (l) {
+                char ifname[IFNAMSIZ] = "?";
+                if (l->conn->netif_index) if_indextoname(l->conn->netif_index, ifname);
+                fprintf(stderr, "      link=%d init=%d status=%d is_tcp=%d sock=%s if=%s\n",
+                        l->local_link_id, l->initialized, l->link_status, l->is_tcp,
+                        l->conn ? l->conn->name : "?", ifname);
+                l = l->next;
+            }
+        }
+        e = e->next;
+    }
+    fflush(stderr);
+}
+
 /* ── ip addr add/del via system ── */
 static int ip_addr_add(const char* ifname, const char* cidr) {
     char cmd[256]; snprintf(cmd, sizeof(cmd), "ip addr add %s dev %s 2>/dev/null", cidr, ifname);
@@ -229,6 +274,7 @@ static void phase_del_last(void* arg) {
     (void)arg;
     if (ctx.result) return;
     ctx.step = 11;
+    diag_dump_state("before del_last");
     ip_link_del(rounds[N_ROUNDS-1].ifname);
     uasync_set_timeout(ctx.ua, STEP_TB, NULL, phase_check_del_last, "chk_del_last");
 }
@@ -256,15 +302,19 @@ static void phase_check_del_last(void* arg) {
 static void phase_check_ip(void* arg) {
     (void)arg; if (ctx.result) return;
     static uint64_t wait_start = 0;
+    static int diag_cnt = 0;
     ctx.step = 6;
     if (count_links_to_srv(ctx.cur_iface) == 0 || ctx.total_recv <= ctx.recv_at_ip_change) {
+        if (++diag_cnt <= 3) diag_dump_state("wait chk_ip");
         if (!wait_start) wait_start = get_time_tb();
         if (get_time_tb() - wait_start < (uint64_t)STEP_TB * 10) {
             uasync_set_timeout(ctx.ua, STEP_TB/3, NULL, phase_check_ip, "chk_ip"); return;
         }
+        diag_dump_state("timeout chk_ip");
         fail("traffic not recovered after IP change");
         return;
     }
+    diag_cnt = 0;
     wait_start = 0;
     do_check(); if (ctx.result) return;
 
@@ -422,7 +472,13 @@ static void setup(void) {
 static void cleanup(void) { test_unlink(scf); test_unlink(ccf); test_rmdir(tdir); }
 
 int main(void) {
-    debug_config_init(); debug_set_level(DEBUG_LEVEL_WARN);
+    debug_config_init();
+    debug_enable_file_output("/tmp/as_dyn_diag.log", 1);
+    debug_set_level(DEBUG_LEVEL_WARN);
+    debug_set_category_level(DEBUG_CATEGORY_SOCKET, DEBUG_LEVEL_INFO);
+    debug_set_category_level(DEBUG_CATEGORY_CONNECTION, DEBUG_LEVEL_INFO);
+    debug_set_category_level(DEBUG_CATEGORY_ETCP, DEBUG_LEVEL_INFO);
+    debug_set_category_level(DEBUG_CATEGORY_DEBUG, DEBUG_LEVEL_INFO);
     utun_instance_set_tun_init_enabled(0);
     setup();