feat(autoping): autoping availability warning

## Introduced change

A new warning that notifies users when the connected XMPP server
advertises XEP-0199 (urn:xmpp:ping) support but the autoping feature
is disabled in settings. The warning can be toggled with
`/autoping warning on|off`.

The warning fires during the on-connect disco#info exchange, only for
responses from the server's own domain — responses from user JIDs or
subdomain services (e.g., conference servers) are excluded.

### Capabilities

- **On-connect detection**: Warning is emitted automatically when the
  server's disco#info response indicates `urn:xmpp:ping` support while
  autoping is disabled and the preference is enabled (default: on)
- **`/autoping warning on|off`**: Toggle the warning via the existing
  autoping command
- **Domain-scoped**: Only triggers for disco#info from the bound server
  domain; user JIDs and subdomain service JIDs are skipped
- **Case-insensitive domain matching**: Uses `g_ascii_strcasecmp` instead
  of `g_strcmp0` to handle case differences between the stanza `from`
  field and the bound domain
- **Display in settings**: Shown in both `/notify` and `/autoping`
  settings dumps, with consistent alignment and `(/autoping warning)`
  reference in each line
- **Autocomplete**: Dedicated `_autoping_autocomplete` function handles
  the `warning` subcommand with `on|off` completion

## Reasoning behind the change

Users connecting to servers that support XEP-0199 ping but have autoping
disabled may experience poorer connection stability. The warning draws
attention to this configuration mismatch without requiring users to read
documentation or dig into settings.

The warning is scoped to the server domain (not user JIDs or subdomain
services) because autoping is a connection-level feature — it only makes
sense in the context of the server's keepalive capabilities.

The warning preference defaults to `on` so users are informed by default,
but can be disabled with `/autoping warning off` if they prefer not to
see it.

## Implementation details

### Warning logic (`src/xmpp/iq.c`)

`_disco_autoping_warning_message()` is called from the on-connect
disco#info handler when the `from` field matches the bound domain. It
checks three conditions:

1. Server features contain `urn:xmpp:ping`
2. Autoping interval is 0 (disabled)
3. `PREF_AUTOPING_WARNING` is true

All three must be true for the warning to display.

### Domain matching

`g_ascii_strcasecmp(from, connection_get_domain())` is used instead of
`g_strcmp0` to handle case differences. This prevents the warning from
silently skipping if a server echoes the `from` field in a different
case than the bound domain.

### Command integration (`src/command/cmd_*.c`)

- `cmd_defs.c`: Added `/autoping warning on|off` syntax and argument
  description
- `cmd_funcs.c`: Added `warning` subcommand handler that calls
  `_cmd_set_boolean_preference` with `PREF_AUTOPING_WARNING`
- `cmd_ac.c`: Registered dedicated `_autoping_autocomplete` that handles
  the `warning` subcommand with `on|off` boolean completion

### Preference storage (`src/config/preferences.c`)

- Group: `PREF_GROUP_NOTIFICATIONS`
- Key: `autoping.warning`
- Default: `TRUE`

### Settings display (`src/ui/console.c`)

The autoping warning preference is shown in both `cons_notify_setting()`
and `cons_autoping_setting()` with consistent column alignment and a
`(/autoping warning)` reference in each line.

### Tests (`tests/functionaltests/test_autoping.c`)

Six functional tests cover all condition combinations:

| Test | Server ping | Autoping | Warning pref | Expected |
|---|---|---|---|---|
| `autoping_warning_shown_when_disabled` | yes | off | on | warning shown |
| `autoping_warning_not_shown_when_server_unsupported` | no | off | on | no warning |
| `autoping_warning_not_shown_when_autoping_enabled` | yes | on | on | no warning |
| `autoping_warning_not_shown_when_user_disabled` | yes | off | off | no warning |
| `autoping_warning_not_shown_for_user_jid` | yes (from user JID) | off | on | no warning |
| `autoping_warning_not_shown_for_subdomain_service` | yes (from subdomain) | off | on | no warning |

Co-authored-by: Jabber Developer2 <jabber.developer2@jabber.space>

src/command/cmd_ac.c

@@ -47,6 +47,7 @@ static char* _notify_autocomplete(ProfWin* window, const char* const input, gboo
 static char* _theme_autocomplete(ProfWin* window, const char* const input, gboolean previous);
 static char* _spellcheck_autocomplete(ProfWin* window, const char* const input, gboolean previous);
 static char* _autoaway_autocomplete(ProfWin* window, const char* const input, gboolean previous);
+static char* _autoping_autocomplete(ProfWin* window, const char* const input, gboolean previous);
 static char* _autoconnect_autocomplete(ProfWin* window, const char* const input, gboolean previous);
 static char* _account_autocomplete(ProfWin* window, const char* const input, gboolean previous);
 static char* _who_autocomplete(ProfWin* window, const char* const input, gboolean previous);
@@ -1056,6 +1057,7 @@ cmd_ac_init(void)
 
     autocomplete_add(autoping_ac, "set");
     autocomplete_add(autoping_ac, "timeout");
+    autocomplete_add(autoping_ac, "warning");
 
     autocomplete_add(plugins_ac, "install");
     autocomplete_add(plugins_ac, "update");
@@ -1407,6 +1409,7 @@ cmd_ac_init(void)
     g_hash_table_insert(ac_funcs, "/alias", _alias_autocomplete);
     g_hash_table_insert(ac_funcs, "/autoaway", _autoaway_autocomplete);
     g_hash_table_insert(ac_funcs, "/autoconnect", _autoconnect_autocomplete);
+    g_hash_table_insert(ac_funcs, "/autoping", _autoping_autocomplete);
     g_hash_table_insert(ac_funcs, "/avatar", _avatar_autocomplete);
     g_hash_table_insert(ac_funcs, "/ban", _ban_autocomplete);
     g_hash_table_insert(ac_funcs, "/blocked", _blocked_autocomplete);
@@ -1934,7 +1937,6 @@ _cmd_ac_complete_params(ProfWin* window, const char* const input, gboolean previ
         { "/prefs", prefs_ac },
         { "/disco", disco_ac },
         { "/room", room_ac },
-        { "/autoping", autoping_ac },
         { "/mainwin", winpos_ac },
         { "/inputwin", winpos_ac },
     };
@@ -4264,6 +4266,20 @@ _executable_autocomplete(ProfWin* window, const char* const input, gboolean prev
     return result;
 }
 
+static char*
+_autoping_autocomplete(ProfWin* window, const char* const input, gboolean previous)
+{
+    char* result = NULL;
+
+    result = autocomplete_param_with_ac(input, "/autoping", autoping_ac, TRUE, previous);
+    if (result) {
+        return result;
+    }
+
+    result = autocomplete_param_with_func(input, "/autoping warning", prefs_autocomplete_boolean_choice, previous, NULL);
+    return result;
+}
+
 static char*
 _lastactivity_autocomplete(ProfWin* window, const char* const input, gboolean previous)
 {

src/command/cmd_defs.c

@@ -1964,12 +1964,14 @@ static const struct cmd_t command_defs[] = {
               CMD_TAG_CONNECTION)
       CMD_SYN(
               "/autoping set <seconds>",
-              "/autoping timeout <seconds>")
+              "/autoping timeout <seconds>",
+              "/autoping warning on|off")
       CMD_DESC(
               "Set the interval between sending ping requests to the server to ensure the connection is kept alive.")
       CMD_ARGS(
               { "set <seconds>", "Number of seconds between sending pings, a value of 0 disables autoping." },
-              { "timeout <seconds>", "Seconds to wait for autoping responses, after which the connection is considered broken." })
+              { "timeout <seconds>", "Seconds to wait for autoping responses, after which the connection is considered broken." },
+              { "warning on|off", "Enable or disable autoping availability warning." })
     },
 
     { CMD_PREAMBLE("/ping",

src/command/cmd_funcs.c

@@ -6374,6 +6374,8 @@ cmd_autoping(ProfWin* window, const char* const command, gchar** args)
             cons_bad_cmd_usage(command);
         }
 
+    } else if (g_strcmp0(cmd, "warning") == 0) {
+        _cmd_set_boolean_preference(value, "Autoping availability warning", PREF_AUTOPING_WARNING);
     } else {
         cons_bad_cmd_usage(command);
     }

src/config/preferences.c

@@ -2290,6 +2290,7 @@ _get_group(preference_t pref)
     case PREF_TRAY:
     case PREF_TRAY_READ:
     case PREF_ADV_NOTIFY_DISCO_OR_VERSION:
+    case PREF_AUTOPING_WARNING:
         return PREF_GROUP_NOTIFICATIONS;
     case PREF_DBLOG:
     case PREF_CHLOG:
@@ -2646,6 +2647,8 @@ _get_key(preference_t pref)
         return "enabled";
     case PREF_SPELLCHECK_LANG:
         return "lang";
+    case PREF_AUTOPING_WARNING:
+        return "autoping.warning";
     default:
         return NULL;
     }
@@ -2699,6 +2702,7 @@ _get_default_boolean(preference_t pref)
     case PREF_MOOD:
     case PREF_STROPHE_SM_ENABLED:
     case PREF_STROPHE_SM_RESEND:
+    case PREF_AUTOPING_WARNING:
         return TRUE;
     case PREF_SPELLCHECK_ENABLE:
     case PREF_PGP_PUBKEY_AUTOIMPORT:

src/config/preferences.h

@@ -169,6 +169,7 @@ typedef enum {
     PREF_FORCE_ENCRYPTION_MODE,
     PREF_SPELLCHECK_ENABLE,
     PREF_SPELLCHECK_LANG,
+    PREF_AUTOPING_WARNING
 } preference_t;
 
 typedef struct prof_alias_t

src/ui/console.c

@@ -1703,6 +1703,11 @@ cons_notify_setting(void)
     else
         cons_show("Subscription requests (/notify sub) : OFF");
 
+    if (prefs_get_boolean(PREF_AUTOPING_WARNING))
+        cons_show("Autoping warning (/autoping warning): ON");
+    else
+        cons_show("Autoping warning (/autoping warning): OFF");
+
     gint remind_period = prefs_get_notify_remind();
     if (remind_period == 0) {
         cons_show("Reminder period (/notify remind)    : OFF");
@@ -2003,21 +2008,26 @@ cons_autoping_setting(void)
 {
     gint autoping_interval = prefs_get_autoping();
     if (autoping_interval == 0) {
-        cons_show("Autoping interval (/autoping)   : OFF");
+        cons_show("Autoping interval (/autoping)       : OFF");
     } else if (autoping_interval == 1) {
-        cons_show("Autoping interval (/autoping)   : 1 second");
+        cons_show("Autoping interval (/autoping)       : 1 second");
     } else {
-        cons_show("Autoping interval (/autoping)   : %d seconds", autoping_interval);
+        cons_show("Autoping interval (/autoping)       : %d seconds", autoping_interval);
     }
 
     gint autoping_timeout = prefs_get_autoping_timeout();
     if (autoping_timeout == 0) {
-        cons_show("Autoping timeout (/autoping)    : OFF");
+        cons_show("Autoping timeout (/autoping)        : OFF");
     } else if (autoping_timeout == 1) {
-        cons_show("Autoping timeout (/autoping)    : 1 second");
+        cons_show("Autoping timeout (/autoping)        : 1 second");
     } else {
-        cons_show("Autoping timeout (/autoping)    : %d seconds", autoping_timeout);
+        cons_show("Autoping timeout (/autoping)        : %d seconds", autoping_timeout);
     }
+
+    if (prefs_get_boolean(PREF_AUTOPING_WARNING))
+        cons_show("Autoping warning (/autoping warning): ON");
+    else
+        cons_show("Autoping warning (/autoping warning): OFF");
 }
 
 void

src/xmpp/iq.c

@@ -99,6 +99,7 @@ static void _disco_items_result_handler(xmpp_stanza_t* const stanza);
 static void _last_activity_get_handler(xmpp_stanza_t* const stanza);
 static void _version_get_handler(xmpp_stanza_t* const stanza);
 static void _ping_get_handler(xmpp_stanza_t* const stanza);
+static void _disco_autoping_warning_message(GHashTable* features);
 
 static int _version_result_id_handler(xmpp_stanza_t* const stanza, void* const userdata);
 static int _disco_info_response_id_handler(xmpp_stanza_t* const stanza, void* const userdata);
@@ -2429,6 +2430,11 @@ _disco_info_response_id_handler_onconnect(xmpp_stanza_t* const stanza, void* con
             }
             child = xmpp_stanza_get_next(child);
         }
+
+        // Prevent repetitions by avoiding checks of disco items (from connection_set_disco_items)
+        if (from && g_ascii_strcasecmp(from, connection_get_domain()) == 0) {
+            _disco_autoping_warning_message(features);
+        }
     }
 
     connection_features_received(from);
@@ -2436,6 +2442,21 @@ _disco_info_response_id_handler_onconnect(xmpp_stanza_t* const stanza, void* con
     return 0;
 }
 
+static void
+_disco_autoping_warning_message(GHashTable* features)
+{
+    gboolean server_supports_ping = g_hash_table_contains(features, "urn:xmpp:ping");
+    gboolean user_prefers_warning = prefs_get_boolean(PREF_AUTOPING_WARNING);
+    gboolean is_autoping_enabled = prefs_get_autoping() != 0;
+
+    if (!is_autoping_enabled && server_supports_ping && user_prefers_warning) {
+        cons_show("This server supports XEP-0199: XMPP Ping (better keepalive detection),\n"
+                  "but autoping feature is currently disabled in settings.\n"
+                  "Consider enabling it (e.g., `/autoping set 30`) for improved connection stability.\n"
+                  "Use `/autoping warning off` to disable this message.");
+    }
+}
+
 static int
 _http_upload_response_id_handler(xmpp_stanza_t* const stanza, void* const userdata)
 {