18 files changed, 653 insertions, 2 deletions

diff --git a/src/common/backend.h b/src/common/backend.h
index f0fae03..fd60418 100644
--- a/src/common/backend.h
+++ b/src/common/backend.h
@@ -15,6 +15,8 @@ struct yasl_display {
     struct yasl_display_cbs callbacks;
     struct yasl_loop *loop;
     void *app_runner;
+    /* Backend's copy of yasl_display_spec.app_id, or NULL; for desktop services. */
+    const char *app_id;
 };
 
 struct yasl_surface {
@@ -89,6 +91,8 @@ struct yasl_backend_ops {
     bool (*surface_show_window_menu)(struct yasl_surface *s, struct yasl_vector2i pos);
     bool (*surface_drag_carry)(struct yasl_surface *s, struct yasl_vector2i offset);
     bool (*surface_place_under_pointer)(struct yasl_surface *s, struct yasl_vector2i at);
+    /* Optional; NULL means the bell is unsupported. */
+    bool (*surface_bell)(struct yasl_surface *s);
     void *(*display_get_native_handle)(struct yasl_display *d);
     void *(*surface_get_native_handle)(struct yasl_surface *s);
     bool (*surface_get_native_frame)(struct yasl_surface *s,
diff --git a/src/common/desktop.c b/src/common/desktop.c
new file mode 100644
index 0000000..23c62d7
--- /dev/null
+++ b/src/common/desktop.c
@@ -0,0 +1,81 @@
+#include "yasl/desktop.h"
+#include "common/backend.h"
+#include "common/desktop.h"
+
+#include <string.h>
+
+/* Large enough for any path the platform APIs return. */
+#define DESKTOP_STR_MAX 4096
+
+/* An RFC 3986 scheme, then ':', and no control characters anywhere. */
+static bool uri_valid(const char *uri)
+{
+    unsigned char c = (unsigned char)uri[0];
+    if ((unsigned)((c | 32) - 'a') >= 26) return false;
+    const char *p = uri + 1;
+    for (; *p != ':'; p++) {
+        c = (unsigned char)*p;
+        bool alpha = (unsigned)((c | 32) - 'a') < 26;
+        bool digit = (unsigned)(c - '0') < 10;
+        if (!alpha && !digit && c != '+' && c != '-' && c != '.') return false;
+    }
+    for (; *p; p++) {
+        c = (unsigned char)*p;
+        if (c < 0x20 || c == 0x7f) return false;
+    }
+    return true;
+}
+
+/* Copy len bytes and a NUL when they fit, and report the full length. */
+static size_t copy_out(char *out, size_t cap, const char *s, size_t len)
+{
+    if (len && len < cap) {
+        memcpy(out, s, len);
+        out[len] = '\0';
+    }
+    return len;
+}
+
+bool yasl_display_open_uri(struct yasl_display *d, const char *uri)
+{
+    if (!d || !uri || !uri_valid(uri)) return false;
+    return desktop_open_uri(uri);
+}
+
+bool yasl_display_notify(struct yasl_display *d, const char *title, const char *body)
+{
+    if (!d || !title) return false;
+    return desktop_notify(d->app_id, title, body ? body : "");
+}
+
+uint32_t yasl_display_appearance(struct yasl_display *d)
+{
+    return d ? desktop_appearance() : 0;
+}
+
+bool yasl_surface_bell(struct yasl_surface *s)
+{
+    if (!s || !s->display->ops->surface_bell) return false;
+    return s->display->ops->surface_bell(s);
+}
+
+size_t yasl_executable_path(char *out, size_t cap)
+{
+    if (!out && cap) return 0;
+    char buf[DESKTOP_STR_MAX];
+    return copy_out(out, cap, buf, desktop_executable_path(buf, sizeof(buf)));
+}
+
+size_t yasl_resource_dir(char *out, size_t cap)
+{
+    if (!out && cap) return 0;
+    char buf[DESKTOP_STR_MAX];
+    return copy_out(out, cap, buf, desktop_resource_dir(buf, sizeof(buf)));
+}
+
+size_t yasl_default_locale(char *out, size_t cap)
+{
+    if (!out && cap) return 0;
+    char buf[DESKTOP_STR_MAX];
+    return copy_out(out, cap, buf, desktop_default_locale(buf, sizeof(buf)));
+}
diff --git a/src/common/desktop.h b/src/common/desktop.h
new file mode 100644
index 0000000..9af5952
--- /dev/null
+++ b/src/common/desktop.h
@@ -0,0 +1,19 @@
+#ifndef YASL_COMMON_DESKTOP_H
+#define YASL_COMMON_DESKTOP_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+/* Operating-system desktop services behind yasl/desktop.h. Common code
+ * validates arguments first. Path and locale functions write a NUL-terminated
+ * string to buf and return its length, or zero on failure or when it does not
+ * fit in cap. */
+bool desktop_open_uri(const char *uri);
+bool desktop_notify(const char *app_id, const char *title, const char *body);
+uint32_t desktop_appearance(void);
+size_t desktop_executable_path(char *buf, size_t cap);
+size_t desktop_resource_dir(char *buf, size_t cap);
+size_t desktop_default_locale(char *buf, size_t cap);
+
+#endif
diff --git a/src/common/meson.build b/src/common/meson.build
index 015c61c..26565ee 100644
--- a/src/common/meson.build
+++ b/src/common/meson.build
@@ -1 +1 @@
-sources += files('app.c', 'backend.c', 'input.c', 'native.c', 'timing.c', 'utf8.c')
+sources += files('app.c', 'backend.c', 'desktop.c', 'input.c', 'native.c', 'timing.c', 'utf8.c')
diff --git a/src/platform/cocoa/desktop.m b/src/platform/cocoa/desktop.m
new file mode 100644
index 0000000..526cbb9
--- /dev/null
+++ b/src/platform/cocoa/desktop.m
@@ -0,0 +1,145 @@
+#import <AppKit/AppKit.h>
+#import <UserNotifications/UserNotifications.h>
+
+#include "common/desktop.h"
+#include "yasl/desktop.h"
+
+#include <CoreFoundation/CoreFoundation.h>
+#include <limits.h>
+#include <mach-o/dyld.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static size_t copy_str(char *buf, size_t cap, const char *s)
+{
+    size_t len = s ? strlen(s) : 0;
+    if (!len || len >= cap) return 0;
+    memcpy(buf, s, len + 1);
+    return len;
+}
+
+bool desktop_open_uri(const char *uri)
+{
+    @autoreleasepool {
+        NSString *str = [NSString stringWithUTF8String:uri];
+        NSURL *url = str ? [NSURL URLWithString:str] : nil;
+        return url && [[NSWorkspace sharedWorkspace] openURL:url];
+    }
+}
+
+/* Show banners while the application is in front, too. */
+@interface YaslNotificationDelegate : NSObject <UNUserNotificationCenterDelegate>
+@end
+
+@implementation YaslNotificationDelegate
+- (void)userNotificationCenter:(UNUserNotificationCenter *)center
+       willPresentNotification:(UNNotification *)notification
+         withCompletionHandler:(void (^)(UNNotificationPresentationOptions))completionHandler
+{
+    (void)center;
+    (void)notification;
+    completionHandler(UNNotificationPresentationOptionBanner);
+}
+@end
+
+static YaslNotificationDelegate *notification_delegate;
+static bool authorization_requested;
+
+/* UNUserNotificationCenter raises an exception outside an app bundle. */
+static bool notifications_available(void)
+{
+    NSBundle *bundle = [NSBundle mainBundle];
+    return bundle.bundleIdentifier && [bundle.bundlePath.pathExtension isEqualToString:@"app"];
+}
+
+bool desktop_notify(const char *app_id, const char *title, const char *body)
+{
+    (void)app_id;
+    if (!notifications_available()) return false;
+    @autoreleasepool {
+        NSString *heading = [NSString stringWithUTF8String:title];
+        NSString *message = [NSString stringWithUTF8String:body];
+        if (!heading || !message) return false;
+        UNUserNotificationCenter *center = [UNUserNotificationCenter currentNotificationCenter];
+        if (!notification_delegate) {
+            notification_delegate = [[YaslNotificationDelegate alloc] init];
+            center.delegate = notification_delegate;
+        }
+        if (!authorization_requested) {
+            authorization_requested = true;
+            [center requestAuthorizationWithOptions:UNAuthorizationOptionAlert
+                                  completionHandler:^(BOOL granted, NSError *error) {
+                (void)granted;
+                (void)error;
+            }];
+        }
+        UNMutableNotificationContent *content = [[UNMutableNotificationContent alloc] init];
+        content.title = heading;
+        content.body = message;
+        UNNotificationRequest *request =
+            [UNNotificationRequest requestWithIdentifier:[[NSUUID UUID] UUIDString]
+                                                 content:content
+                                                 trigger:nil];
+        [content release];
+        [center addNotificationRequest:request withCompletionHandler:nil];
+        return true;
+    }
+}
+
+uint32_t desktop_appearance(void)
+{
+    @autoreleasepool {
+        uint32_t flags = 0;
+        NSAppearanceName name = [NSApp.effectiveAppearance
+            bestMatchFromAppearancesWithNames:@[NSAppearanceNameAqua, NSAppearanceNameDarkAqua]];
+        if ([name isEqualToString:NSAppearanceNameDarkAqua])
+            flags |= YASL_APPEARANCE_DARK;
+        else if (name)
+            flags |= YASL_APPEARANCE_LIGHT;
+        if ([NSWorkspace sharedWorkspace].accessibilityDisplayShouldIncreaseContrast)
+            flags |= YASL_APPEARANCE_HIGH_CONTRAST;
+        return flags;
+    }
+}
+
+size_t desktop_executable_path(char *buf, size_t cap)
+{
+    char raw[PATH_MAX];
+    uint32_t size = sizeof(raw);
+    char resolved[PATH_MAX];
+    if (_NSGetExecutablePath(raw, &size) != 0 || !realpath(raw, resolved)) return 0;
+    return copy_str(buf, cap, resolved);
+}
+
+size_t desktop_resource_dir(char *buf, size_t cap)
+{
+    @autoreleasepool {
+        NSBundle *bundle = [NSBundle mainBundle];
+        if (!bundle.bundleIdentifier || ![bundle.bundlePath.pathExtension isEqualToString:@"app"])
+            return 0;
+        NSString *path = bundle.resourcePath;
+        return path ? copy_str(buf, cap, path.fileSystemRepresentation) : 0;
+    }
+}
+
+size_t desktop_default_locale(char *buf, size_t cap)
+{
+    /* Identifiers such as "zh-Hans_CN" are not POSIX names, so build the name
+     * from the language and region codes alone. */
+    char name[64] = "en_US.UTF-8";
+    CFLocaleRef locale = CFLocaleCopyCurrent();
+    if (locale) {
+        CFStringRef language = CFLocaleGetValue(locale, kCFLocaleLanguageCode);
+        CFStringRef region = CFLocaleGetValue(locale, kCFLocaleCountryCode);
+        char lang[16], reg[16];
+        if (language && CFStringGetCString(language, lang, sizeof(lang), kCFStringEncodingUTF8) && lang[0]) {
+            if (region && CFStringGetCString(region, reg, sizeof(reg), kCFStringEncodingUTF8) && reg[0])
+                snprintf(name, sizeof(name), "%s_%s.UTF-8", lang, reg);
+            else
+                snprintf(name, sizeof(name), "%s.UTF-8", lang);
+        }
+        CFRelease(locale);
+    }
+    return copy_str(buf, cap, name);
+}
diff --git a/src/platform/cocoa/meson.build b/src/platform/cocoa/meson.build
index 8230376..5fc5f5e 100644
--- a/src/platform/cocoa/meson.build
+++ b/src/platform/cocoa/meson.build
@@ -1 +1 @@
-sources += files('window.m', 'keymap.c')
+sources += files('window.m', 'desktop.m', 'keymap.c')
diff --git a/src/platform/cocoa/window.m b/src/platform/cocoa/window.m
index 811a7c6..75dce54 100644
--- a/src/platform/cocoa/window.m
+++ b/src/platform/cocoa/window.m
@@ -1366,6 +1366,7 @@ struct cocoa_display *cocoa_display_open(struct yasl_loop *loop, const struct ya
         darwin_ctx.cbs = &darwin_ctx.base.callbacks;
         darwin_ctx.ud = spec->ud;
         if (spec->app_id) darwin_ctx.app_id = strdup(spec->app_id);
+        darwin_ctx.base.app_id = darwin_ctx.app_id;
     }
     return &darwin_ctx;
 }
@@ -2191,6 +2192,14 @@ static bool impl_surface_place_under_pointer(struct yasl_surface *s, struct yasl
     return cocoa_surface_place_under_pointer((struct cocoa_surface *)s, at);
 }
 
+static bool impl_surface_bell(struct yasl_surface *s)
+{
+    assert([NSThread isMainThread]);
+    (void)s;
+    NSBeep();
+    return true;
+}
+
 static void *impl_display_get_native_handle(struct yasl_display *d)
 {
     return d ? (void *)NSApp : NULL;
@@ -2249,6 +2258,7 @@ const struct yasl_backend_ops yasl_cocoa_backend = {
     .surface_show_window_menu = impl_surface_show_window_menu,
     .surface_drag_carry = impl_surface_drag_carry,
     .surface_place_under_pointer = impl_surface_place_under_pointer,
+    .surface_bell = impl_surface_bell,
     .display_get_native_handle = impl_display_get_native_handle,
     .surface_get_native_handle = impl_surface_get_native_handle,
     .surface_get_native_frame = impl_surface_get_native_frame,
diff --git a/src/platform/freedesktop/dbus.c b/src/platform/freedesktop/dbus.c
new file mode 100644
index 0000000..abca900
--- /dev/null
+++ b/src/platform/freedesktop/dbus.c
@@ -0,0 +1,187 @@
+#define _GNU_SOURCE
+#include "platform/freedesktop/dbus.h"
+
+#if YASL_HAS_DBUS
+
+#include <dbus/dbus.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+
+/* The portal may need activation on first use; bound how long a query blocks. */
+#define PORTAL_TIMEOUT_MS 1000
+
+static DBusConnection *bus;
+
+/* The session bus address, without libdbus's X11 autolaunch fallback. */
+static char *session_address(void)
+{
+    const char *env = getenv("DBUS_SESSION_BUS_ADDRESS");
+    if (env && *env) return strdup(env);
+    const char *run = getenv("XDG_RUNTIME_DIR");
+    if (!run || !*run) return NULL;
+    char path[4096];
+    struct stat st;
+    if (snprintf(path, sizeof(path), "%s/bus", run) >= (int)sizeof(path) ||
+        stat(path, &st) != 0 || !S_ISSOCK(st.st_mode))
+        return NULL;
+    char *escaped = dbus_address_escape_value(path);
+    if (!escaped) return NULL;
+    char *address = NULL;
+    if (asprintf(&address, "unix:path=%s", escaped) < 0) address = NULL;
+    dbus_free(escaped);
+    return address;
+}
+
+static DBusConnection *session_bus(void)
+{
+    if (bus && dbus_connection_get_is_connected(bus)) return bus;
+    if (bus) {
+        dbus_connection_close(bus);
+        dbus_connection_unref(bus);
+        bus = NULL;
+    }
+    char *address = session_address();
+    if (!address) return NULL;
+    DBusError err;
+    dbus_error_init(&err);
+    DBusConnection *c = dbus_connection_open_private(address, &err);
+    free(address);
+    if (!c) {
+        dbus_error_free(&err);
+        return NULL;
+    }
+    dbus_connection_set_exit_on_disconnect(c, FALSE);
+    if (!dbus_bus_register(c, &err)) {
+        dbus_error_free(&err);
+        dbus_connection_close(c);
+        dbus_connection_unref(c);
+        return NULL;
+    }
+    bus = c;
+    return bus;
+}
+
+bool bus_notify(const char *app, const char *title, const char *body)
+{
+    DBusConnection *c = session_bus();
+    if (!c) return false;
+    DBusMessage *msg = dbus_message_new_method_call("org.freedesktop.Notifications",
+            "/org/freedesktop/Notifications", "org.freedesktop.Notifications", "Notify");
+    if (!msg) return false;
+
+    const char *icon = "";
+    dbus_uint32_t replaces = 0;
+    dbus_int32_t expire = -1;
+    DBusMessageIter it, sub, entry, value;
+    dbus_message_iter_init_append(msg, &it);
+    bool ok = dbus_message_iter_append_basic(&it, DBUS_TYPE_STRING, &app) &&
+        dbus_message_iter_append_basic(&it, DBUS_TYPE_UINT32, &replaces) &&
+        dbus_message_iter_append_basic(&it, DBUS_TYPE_STRING, &icon) &&
+        dbus_message_iter_append_basic(&it, DBUS_TYPE_STRING, &title) &&
+        dbus_message_iter_append_basic(&it, DBUS_TYPE_STRING, &body);
+    /* No actions. */
+    ok = ok && dbus_message_iter_open_container(&it, DBUS_TYPE_ARRAY, "s", &sub) &&
+        dbus_message_iter_close_container(&it, &sub);
+    /* Hints: desktop-entry names the application's .desktop file. */
+    const char *hint = "desktop-entry";
+    ok = ok && dbus_message_iter_open_container(&it, DBUS_TYPE_ARRAY, "{sv}", &sub) &&
+        dbus_message_iter_open_container(&sub, DBUS_TYPE_DICT_ENTRY, NULL, &entry) &&
+        dbus_message_iter_append_basic(&entry, DBUS_TYPE_STRING, &hint) &&
+        dbus_message_iter_open_container(&entry, DBUS_TYPE_VARIANT, "s", &value) &&
+        dbus_message_iter_append_basic(&value, DBUS_TYPE_STRING, &app) &&
+        dbus_message_iter_close_container(&entry, &value) &&
+        dbus_message_iter_close_container(&sub, &entry) &&
+        dbus_message_iter_close_container(&it, &sub);
+    ok = ok && dbus_message_iter_append_basic(&it, DBUS_TYPE_INT32, &expire);
+
+    if (ok) {
+        dbus_message_set_no_reply(msg, TRUE);
+        ok = dbus_connection_send(c, msg, NULL);
+        if (ok) dbus_connection_flush(c);
+    }
+    dbus_message_unref(msg);
+    return ok;
+}
+
+/* Read an integer from it, unwrapping variants: Settings.Read nests one more. */
+static bool iter_int(DBusMessageIter *it, int64_t *out)
+{
+    DBusMessageIter inner[4];
+    int depth = 0;
+    while (dbus_message_iter_get_arg_type(it) == DBUS_TYPE_VARIANT && depth < 4) {
+        dbus_message_iter_recurse(it, &inner[depth]);
+        it = &inner[depth++];
+    }
+    DBusBasicValue v;
+    switch (dbus_message_iter_get_arg_type(it)) {
+    case DBUS_TYPE_BYTE: dbus_message_iter_get_basic(it, &v); *out = v.byt; return true;
+    case DBUS_TYPE_BOOLEAN: dbus_message_iter_get_basic(it, &v); *out = v.bool_val; return true;
+    case DBUS_TYPE_INT16: dbus_message_iter_get_basic(it, &v); *out = v.i16; return true;
+    case DBUS_TYPE_UINT16: dbus_message_iter_get_basic(it, &v); *out = v.u16; return true;
+    case DBUS_TYPE_INT32: dbus_message_iter_get_basic(it, &v); *out = v.i32; return true;
+    case DBUS_TYPE_UINT32: dbus_message_iter_get_basic(it, &v); *out = v.u32; return true;
+    case DBUS_TYPE_INT64: dbus_message_iter_get_basic(it, &v); *out = v.i64; return true;
+    case DBUS_TYPE_UINT64:
+        dbus_message_iter_get_basic(it, &v);
+        if (v.u64 > INT64_MAX) return false;
+        *out = (int64_t)v.u64;
+        return true;
+    default: return false;
+    }
+}
+
+bool portal_read_int(const char *ns, const char *key, int64_t *out)
+{
+    DBusConnection *c = session_bus();
+    if (!c) return false;
+    /* ReadOne is portal version 2; older portals only have Read. */
+    static const char *const methods[] = {"ReadOne", "Read"};
+    for (int i = 0; i < 2; i++) {
+        DBusMessage *msg = dbus_message_new_method_call("org.freedesktop.portal.Desktop",
+                "/org/freedesktop/portal/desktop", "org.freedesktop.portal.Settings", methods[i]);
+        if (!msg) return false;
+        if (!dbus_message_append_args(msg, DBUS_TYPE_STRING, &ns, DBUS_TYPE_STRING, &key,
+                                      DBUS_TYPE_INVALID)) {
+            dbus_message_unref(msg);
+            return false;
+        }
+        DBusError err;
+        dbus_error_init(&err);
+        DBusMessage *reply = dbus_connection_send_with_reply_and_block(c, msg,
+                PORTAL_TIMEOUT_MS, &err);
+        dbus_message_unref(msg);
+        if (!reply) {
+            bool retry = dbus_error_has_name(&err, DBUS_ERROR_UNKNOWN_METHOD);
+            dbus_error_free(&err);
+            if (retry) continue;
+            return false;
+        }
+        DBusMessageIter it;
+        bool ok = dbus_message_iter_init(reply, &it) && iter_int(&it, out);
+        dbus_message_unref(reply);
+        return ok;
+    }
+    return false;
+}
+
+#else
+
+bool bus_notify(const char *app, const char *title, const char *body)
+{
+    (void)app;
+    (void)title;
+    (void)body;
+    return false;
+}
+
+bool portal_read_int(const char *ns, const char *key, int64_t *out)
+{
+    (void)ns;
+    (void)key;
+    (void)out;
+    return false;
+}
+
+#endif
diff --git a/src/platform/freedesktop/dbus.h b/src/platform/freedesktop/dbus.h
new file mode 100644
index 0000000..3b1662b
--- /dev/null
+++ b/src/platform/freedesktop/dbus.h
@@ -0,0 +1,16 @@
+#ifndef YASL_FREEDESKTOP_DBUS_H
+#define YASL_FREEDESKTOP_DBUS_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+/* Session-bus helpers. The first call opens a private connection that later
+ * calls reuse. Each returns false when YASL is built without libdbus-1 or no
+ * session bus is reachable. Call from one thread at a time. */
+
+/* Send org.freedesktop.Notifications.Notify without waiting for a reply. */
+bool bus_notify(const char *app, const char *title, const char *body);
+/* Read an integer setting through the XDG Settings portal, waiting briefly. */
+bool portal_read_int(const char *ns, const char *key, int64_t *out);
+
+#endif
diff --git a/src/platform/freedesktop/desktop.c b/src/platform/freedesktop/desktop.c
new file mode 100644
index 0000000..a8b9bc7
--- /dev/null
+++ b/src/platform/freedesktop/desktop.c
@@ -0,0 +1,150 @@
+#define _GNU_SOURCE
+#include "common/desktop.h"
+#include "platform/freedesktop/dbus.h"
+#include "yasl/desktop.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/syscall.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+extern char **environ;
+
+static size_t copy_str(char *buf, size_t cap, const char *s)
+{
+    size_t len = strlen(s);
+    if (!len || len >= cap) return 0;
+    memcpy(buf, s, len + 1);
+    return len;
+}
+
+/* Find an executable in PATH, like execvp but before forking. */
+static bool find_program(const char *name, char *out, size_t cap)
+{
+    const char *path = getenv("PATH");
+    if (!path || !*path) path = "/usr/local/bin:/usr/bin:/bin";
+    size_t name_len = strlen(name);
+    while (*path) {
+        const char *end = strchr(path, ':');
+        size_t dir_len = end ? (size_t)(end - path) : strlen(path);
+        if (dir_len && dir_len + 1 + name_len < cap) {
+            memcpy(out, path, dir_len);
+            out[dir_len] = '/';
+            memcpy(out + dir_len + 1, name, name_len + 1);
+            if (access(out, X_OK) == 0) return true;
+        }
+        if (!end) break;
+        path = end + 1;
+    }
+    return false;
+}
+
+bool desktop_open_uri(const char *uri)
+{
+    char program[4096];
+    if (!find_program("xdg-open", program, sizeof(program))) return false;
+    char *argv[] = {"xdg-open", (char *)uri, NULL};
+
+    /* Prepare everything before fork: the children of a threaded process may
+     * only make async-signal-safe calls. */
+    struct sigaction dfl = {.sa_handler = SIG_DFL};
+    sigemptyset(&dfl.sa_mask);
+    sigset_t none;
+    sigemptyset(&none);
+    long max_fd = sysconf(_SC_OPEN_MAX);
+    if (max_fd < 0 || max_fd > 65536) max_fd = 65536;
+
+    /* The middle child exits at once, so the opener is reparented away from
+     * the application and never needs reaping here. */
+    pid_t pid = fork();
+    if (pid < 0) return false;
+    if (pid == 0) {
+        setsid();
+        pid_t opener = fork();
+        if (opener != 0) _exit(opener < 0 ? 1 : 0);
+        for (int sig = 1; sig < NSIG; sig++)
+            if (sig != SIGKILL && sig != SIGSTOP) sigaction(sig, &dfl, NULL);
+        sigprocmask(SIG_SETMASK, &none, NULL);
+        int null = open("/dev/null", O_RDONLY);
+        if (null > 0) {
+            dup2(null, STDIN_FILENO);
+            close(null);
+        }
+        /* Keep application descriptors, such as pty masters, out of the opener. */
+#ifdef SYS_close_range
+        if (syscall(SYS_close_range, 3u, ~0u, 0u) != 0)
+#endif
+            for (int fd = 3; fd < max_fd; fd++) close(fd);
+        execve(program, argv, environ);
+        _exit(127);
+    }
+
+    int status;
+    pid_t done;
+    do {
+        done = waitpid(pid, &status, 0);
+    } while (done < 0 && errno == EINTR);
+    /* An application reaper can collect the middle child first. */
+    if (done < 0) return errno == ECHILD;
+    return WIFEXITED(status) && WEXITSTATUS(status) == 0;
+}
+
+bool desktop_notify(const char *app_id, const char *title, const char *body)
+{
+    return bus_notify(app_id ? app_id : "yasl", title, body);
+}
+
+uint32_t desktop_appearance(void)
+{
+    uint32_t flags = 0;
+    bool portal = false;
+    int64_t value;
+    if (portal_read_int("org.freedesktop.appearance", "color-scheme", &value)) {
+        portal = true;
+        if (value == 1) flags |= YASL_APPEARANCE_DARK;
+        else if (value == 2) flags |= YASL_APPEARANCE_LIGHT;
+    }
+    if (portal_read_int("org.freedesktop.appearance", "contrast", &value)) {
+        portal = true;
+        if (value == 1) flags |= YASL_APPEARANCE_HIGH_CONTRAST;
+    }
+    if (portal) return flags;
+
+    /* GTK_THEME is "Name" or "Name:variant", as in "Adwaita:dark". */
+    const char *theme = getenv("GTK_THEME");
+    if (!theme) return 0;
+    if (strstr(theme, "HighContrast")) flags |= YASL_APPEARANCE_HIGH_CONTRAST;
+    if (strstr(theme, ":dark") || strstr(theme, "HighContrastInverse"))
+        flags |= YASL_APPEARANCE_DARK;
+    return flags;
+}
+
+size_t desktop_executable_path(char *buf, size_t cap)
+{
+    /* readlink truncates silently, so a full buffer may hold a cut path. */
+    ssize_t len = readlink("/proc/self/exe", buf, cap);
+    if (len <= 0 || (size_t)len >= cap) return 0;
+    buf[len] = '\0';
+    return (size_t)len;
+}
+
+size_t desktop_resource_dir(char *buf, size_t cap)
+{
+    (void)buf;
+    (void)cap;
+    return 0;
+}
+
+size_t desktop_default_locale(char *buf, size_t cap)
+{
+    static const char *const vars[] = {"LC_ALL", "LC_CTYPE", "LANG"};
+    for (size_t i = 0; i < sizeof(vars) / sizeof(vars[0]); i++) {
+        const char *v = getenv(vars[i]);
+        if (v && *v) return copy_str(buf, cap, v);
+    }
+    return copy_str(buf, cap, "C.UTF-8");
+}
diff --git a/src/platform/freedesktop/meson.build b/src/platform/freedesktop/meson.build
new file mode 100644
index 0000000..6f43895
--- /dev/null
+++ b/src/platform/freedesktop/meson.build
@@ -0,0 +1 @@
+sources += files('desktop.c', 'dbus.c')
diff --git a/src/platform/meson.build b/src/platform/meson.build
index 892969f..593353c 100644
--- a/src/platform/meson.build
+++ b/src/platform/meson.build
@@ -3,6 +3,10 @@
 if system == 'linux' or system == 'darwin'
     subdir('posix')
 endif
+# Desktop services shared by the Linux backends.
+if system == 'linux'
+    subdir('freedesktop')
+endif
 
 if has_wayland
     subdir('wayland')
diff --git a/src/platform/wayland/api.h b/src/platform/wayland/api.h
index e5e933e..6c3154c 100644
--- a/src/platform/wayland/api.h
+++ b/src/platform/wayland/api.h
@@ -38,5 +38,6 @@ bool wayland_surface_start_interactive_resize(struct wayland_surface *s, enum ya
 bool wayland_surface_show_window_menu(struct wayland_surface *s, struct yasl_vector2i pos);
 bool wayland_surface_drag_carry(struct wayland_surface *s, struct yasl_vector2i offset);
 bool wayland_surface_place_under_pointer(struct wayland_surface *s, struct yasl_vector2i at);
+bool wayland_surface_bell(struct wayland_surface *s);
 
 #endif
diff --git a/src/platform/wayland/backend.c b/src/platform/wayland/backend.c
index c3c7bed..c6272ce 100644
--- a/src/platform/wayland/backend.c
+++ b/src/platform/wayland/backend.c
@@ -177,6 +177,11 @@ static bool impl_surface_place_under_pointer(struct yasl_surface *s, struct yasl
     return wayland_surface_place_under_pointer((struct wayland_surface *)s, at);
 }
 
+static bool impl_surface_bell(struct yasl_surface *s)
+{
+    return wayland_surface_bell((struct wayland_surface *)s);
+}
+
 static void *impl_display_get_native_handle(struct yasl_display *d)
 {
     struct wayland_display *w = (struct wayland_display *)d;
@@ -225,6 +230,7 @@ const struct yasl_backend_ops yasl_wayland_backend = {
     .surface_show_window_menu = impl_surface_show_window_menu,
     .surface_drag_carry = impl_surface_drag_carry,
     .surface_place_under_pointer = impl_surface_place_under_pointer,
+    .surface_bell = impl_surface_bell,
     .display_get_native_handle = impl_display_get_native_handle,
     .surface_get_native_handle = impl_surface_get_native_handle,
 };
diff --git a/src/platform/wayland/internal.h b/src/platform/wayland/internal.h
index c35db7f..84a603d 100644
--- a/src/platform/wayland/internal.h
+++ b/src/platform/wayland/internal.h
@@ -25,6 +25,7 @@
 #include "protocols/primary-selection-unstable-v1-client-protocol.h"
 #include "protocols/relative-pointer-unstable-v1-client-protocol.h"
 #include "protocols/pointer-constraints-unstable-v1-client-protocol.h"
+#include "protocols/xdg-system-bell-v1-client-protocol.h"
 
 #include <fcntl.h>
 #include <limits.h>
@@ -217,6 +218,7 @@ struct wayland_display {
     struct wp_cursor_shape_manager_v1 *cursor_shape_mgr;
     struct zwp_relative_pointer_manager_v1 *relative_pointer_mgr;
     struct zwp_pointer_constraints_v1 *pointer_constraints;
+    struct xdg_system_bell_v1 *system_bell;
     struct wl_cursor_theme *cursor_theme;
     const char *cursor_theme_name;
     struct zwp_tablet_manager_v2 *tablet_mgr;
diff --git a/src/platform/wayland/shell.c b/src/platform/wayland/shell.c
index a12bd4d..8795989 100644
--- a/src/platform/wayland/shell.c
+++ b/src/platform/wayland/shell.c
@@ -214,6 +214,8 @@ static void registry_global(void *data, struct wl_registry *registry,
     } else if (strcmp(interface, zwp_pointer_constraints_v1_interface.name) == 0) {
         c->pointer_constraints = wl_registry_bind(registry, name,
                 &zwp_pointer_constraints_v1_interface, 1);
+    } else if (strcmp(interface, xdg_system_bell_v1_interface.name) == 0) {
+        c->system_bell = wl_registry_bind(registry, name, &xdg_system_bell_v1_interface, 1);
     } else if (strcmp(interface, wp_fractional_scale_manager_v1_interface.name) == 0) {
         c->scale_mgr = wl_registry_bind(registry, name,
                 &wp_fractional_scale_manager_v1_interface, 1);
@@ -403,3 +405,10 @@ int surface_init_shell(struct wayland_surface *w, const char *title)
     }
     return 0;
 }
+
+bool wayland_surface_bell(struct wayland_surface *w)
+{
+    if (!w || w->closed || !w->conn || !w->conn->system_bell || !w->surface) return false;
+    xdg_system_bell_v1_ring(w->conn->system_bell, w->surface);
+    return true;
+}
diff --git a/src/platform/wayland/surface.c b/src/platform/wayland/surface.c
index 0f6d7d7..cf1877d 100644
--- a/src/platform/wayland/surface.c
+++ b/src/platform/wayland/surface.c
@@ -202,6 +202,7 @@ static void display_free(struct wayland_display *c)
     if (c->cursor_shape_mgr) wp_cursor_shape_manager_v1_destroy(c->cursor_shape_mgr);
     if (c->relative_pointer_mgr) zwp_relative_pointer_manager_v1_destroy(c->relative_pointer_mgr);
     if (c->pointer_constraints) zwp_pointer_constraints_v1_destroy(c->pointer_constraints);
+    if (c->system_bell) xdg_system_bell_v1_destroy(c->system_bell);
     if (c->cursor_theme) wl_cursor_theme_destroy(c->cursor_theme);
     if (c->tablet_mgr) zwp_tablet_manager_v2_destroy(c->tablet_mgr);
     if (c->text_input_mgr) zwp_text_input_manager_v3_destroy(c->text_input_mgr);
@@ -246,6 +247,7 @@ struct wayland_display *wayland_display_open(struct yasl_loop *loop, const struc
         c->cbs = &c->base.callbacks;
         c->ud = spec->ud;
         if (spec->app_id) c->app_id = strdup(spec->app_id);
+        c->base.app_id = c->app_id;
     }
     c->xkb_ctx = xkb_context_new(XKB_CONTEXT_NO_FLAGS);
     c->wl = c->xkb_ctx ? wl_display_connect(NULL) : NULL;
diff --git a/src/platform/x11/window.c b/src/platform/x11/window.c
index f60a878..be1ff32 100644
--- a/src/platform/x11/window.c
+++ b/src/platform/x11/window.c
@@ -1601,6 +1601,7 @@ static struct yasl_display *display_open(struct yasl_loop *loop,
     }
     d->base.loop = d->loop;
     d->app_id = strdup(spec && spec->app_id ? spec->app_id : "YASL");
+    d->base.app_id = d->app_id;
     if (!d->loop || !d->app_id) {
         if (d->owns_loop) yasl_loop_destroy(d->loop);
         free(d->app_id);
@@ -1803,6 +1804,18 @@ static bool place(struct yasl_surface *base, struct yasl_vector2i at)
     return true;
 }
 
+static bool bell(struct yasl_surface *base)
+{
+    struct x11_surface *s = (struct x11_surface *)base;
+    struct x11_display *d = (struct x11_display *)base->display;
+    if (s->destroyed || !d->native) return false;
+    /* The XKB bell names the window, so the window manager can flash it. */
+    if (!XkbBell(d->native, s->window, 0, None))
+        XBell(d->native, 0);
+    XFlush(d->native);
+    return true;
+}
+
 static void drag_end(struct x11_display *d, enum yasl_drag_end how)
 {
     if (!d || !d->drag.active) return;
@@ -2045,6 +2058,7 @@ const struct yasl_backend_ops yasl_x11_backend = {
     .surface_set_cursor = cursor,
     .surface_drag_carry = drag_carry,
     .surface_place_under_pointer = place,
+    .surface_bell = bell,
     .surface_start_interactive_move = interactive_move,
     .surface_start_interactive_resize = interactive_resize,
     .surface_show_window_menu = show_window_menu,