Support isolated live window ScreenCast streams

Render selected toplevels through a private portal-only capture protocol, preserve logical snapshot geometry, and renegotiate PipeWire video on window resizing. Bound outstanding snapshots and retry temporary contention; stop on source closure and session locking.

Validation: portal unit tests (31), capture budget unit, private-bus portal contracts, and real nested/PipeWire isolation, workspace, resize, close and paused-lock tests pass. Independent review cleared. Monitor restore integration timed out on both this build and the unchanged previous compositor under the current nested host.

scripts/tests/fixtures/window-capture.c

@@ -1,6 +1,7 @@
 /* Two overlapping clients with distinct colors for isolated capture tests. */
 #define _GNU_SOURCE
 #include <stdint.h>
+#include <poll.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -14,6 +15,9 @@ static struct wl_shm *shm;
 static struct xdg_wm_base *wm;
 static struct wl_surface *surface;
 static struct wl_buffer *buffer;
+static int width = 640, height = 480;
+static int private_capture_seen;
+static int covered;
 
 static void ping(void *data, struct xdg_wm_base *base, uint32_t serial) {
     (void)data;
@@ -24,6 +28,7 @@ static const struct xdg_wm_base_listener wm_listener = {.ping = ping};
 static void global(void *data, struct wl_registry *registry, uint32_t name,
                    const char *interface, uint32_t version) {
     (void)data; (void)version;
+    if (!strcmp(interface, "ferese_window_capture_manager_v1")) private_capture_seen = 1;
     if (!strcmp(interface, "wl_compositor"))
         compositor = wl_registry_bind(registry, name, &wl_compositor_interface, 4);
     else if (!strcmp(interface, "wl_shm"))
@@ -42,9 +47,9 @@ static const struct wl_registry_listener registry_listener = {global, removed};
 static void configure(void *data, struct xdg_surface *xdg, uint32_t serial) {
     (void)data;
     xdg_surface_ack_configure(xdg, serial);
-    xdg_surface_set_window_geometry(xdg, 0, 0, 640, 480);
+    xdg_surface_set_window_geometry(xdg, 0, 0, width, height);
     wl_surface_attach(surface, buffer, 0, 0);
-    wl_surface_damage(surface, 0, 0, 640, 480);
+    wl_surface_damage(surface, 0, 0, width, height);
     wl_surface_commit(surface);
 }
 static const struct xdg_surface_listener surface_listener = {.configure = configure};
@@ -59,25 +64,31 @@ static void close_window(void *data, struct xdg_toplevel *top) {
 }
 static const struct xdg_toplevel_listener top_listener = {.configure = size, .close = close_window};
 
+static void make_buffer(void) {
+    int fd = memfd_create("floating-size-test", MFD_CLOEXEC);
+    size_t bytes = width * height * 4;
+    if (fd < 0 || ftruncate(fd, bytes)) exit(3);
+    uint32_t *pixels = mmap(NULL, bytes, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+    if (pixels == MAP_FAILED) exit(4);
+    for (size_t i = 0; i < (size_t)width * height; i++) {
+        pixels[i] = covered ? 0xff00ff00 : (i % width < 80 ? 0x80800000 : (i / width < (size_t)height / 2 ? 0xffff0000 : 0xff0000ff));
+    }
+    struct wl_shm_pool *pool = wl_shm_create_pool(shm, fd, bytes);
+    buffer = wl_shm_pool_create_buffer(pool, 0, width, height, width * 4, WL_SHM_FORMAT_ARGB8888);
+    wl_shm_pool_destroy(pool);
+    close(fd);
+    munmap(pixels, bytes);
+}
+
 int main(int argc, char **argv) {
     struct wl_display *display = wl_display_connect(NULL);
     if (!display) return 1;
     struct wl_registry *registry = wl_display_get_registry(display);
     wl_registry_add_listener(registry, &registry_listener, NULL);
     if (wl_display_roundtrip(display) < 0 || !compositor || !shm || !wm) return 2;
-    int fd = memfd_create("floating-size-test", MFD_CLOEXEC);
-    size_t bytes = 640 * 480 * 4;
-    if (fd < 0 || ftruncate(fd, bytes)) return 3;
-    uint32_t *pixels = mmap(NULL, bytes, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
-    if (pixels == MAP_FAILED) return 4;
-    int covered = argc > 1 && !strcmp(argv[1], "cover");
-    for (size_t i = 0; i < 640 * 480; i++) {
-        pixels[i] = covered ? 0xff00ff00 : (i % 640 < 80 ? 0x80800000 : (i / 640 < 240 ? 0xffff0000 : 0xff0000ff));
-    }
-    struct wl_shm_pool *pool = wl_shm_create_pool(shm, fd, bytes);
-    buffer = wl_shm_pool_create_buffer(pool, 0, 640, 480, 640 * 4, WL_SHM_FORMAT_ARGB8888);
-    wl_shm_pool_destroy(pool);
-    close(fd);
+    if (private_capture_seen) return 9;
+    covered = argc > 1 && !strcmp(argv[1], "cover");
+    make_buffer();
     surface = wl_compositor_create_surface(compositor);
     struct xdg_surface *xdg = xdg_wm_base_get_xdg_surface(wm, surface);
     xdg_surface_add_listener(xdg, &surface_listener, NULL);
@@ -86,6 +97,28 @@ int main(int argc, char **argv) {
     xdg_toplevel_set_app_id(top, "ferese.test.window-capture");
     xdg_toplevel_set_title(top, covered ? "Occluding window" : "Capture target");
     wl_surface_commit(surface);
-    while (wl_display_dispatch(display) != -1) {}
+    if (argc > 1 && !strcmp(argv[1], "resize")) {
+        while (1) {
+            wl_display_flush(display);
+            struct pollfd fds[2] = {{wl_display_get_fd(display), POLLIN, 0}, {STDIN_FILENO, POLLIN, 0}};
+            if (poll(fds, 2, -1) < 0) break;
+            if (fds[0].revents & POLLIN && wl_display_dispatch(display) < 0) break;
+            if (fds[1].revents & POLLIN) {
+                char command;
+                if (read(STDIN_FILENO, &command, 1) != 1) break;
+                if (command == 'r') {
+                    width = 480; height = 320;
+                    wl_buffer_destroy(buffer);
+                    make_buffer();
+                    xdg_surface_set_window_geometry(xdg, 0, 0, width, height);
+                    wl_surface_attach(surface, buffer, 0, 0);
+                    wl_surface_damage(surface, 0, 0, width, height);
+                    wl_surface_commit(surface);
+                }
+            }
+        }
+    } else {
+        while (wl_display_dispatch(display) != -1) {}
+    }
     return 0;
 }