feat: P3 — WebKit container process pinned to dashboard

Dashward now actually renders content on the dashboard workspace. The
container is a separate gjs subprocess (so a WebKit crash can't take
down gnome-shell), and the extension pins its window to the dashboard
slot via the WindowGuard whitelist.

container/src/main.ts: tiny GJS bootstrap that creates a borderless
fullscreen Gtk.Window with a WebKit2 WebView and loads dashboard.html
from a runtime directory passed in via argv. `GLib.set_prgname` happens
before any GTK init so Wayland's xdg-shell app_id matches
`top.hangmanlab.dashward.container` -- that's the wm_class fingerprint
the extension matches against.

extension/src/container-supervisor.ts: spawn the container via
Gio.Subprocess; pump its stdout/stderr into journal under `[container
stdout|stderr]` tags so we can diagnose WebKit crashes without
attaching; watch display::window-created for the app_id match; on
arrival, whitelist with WindowGuard before moving to dashboard (so the
move's window-added doesn't bounce); make_fullscreen; clear the cached
ref on the window's `unmanaged` signal. Dispose SIGTERMs the
subprocess. P3 explicitly skips auto-restart / exponential backoff and
DBus signaling -- those land in P4.

container/runtime/runtime.ts + styles.css: a "Dashward" placeholder
card on the 12-column grid so the dashboard workspace is visually
distinct from a regular workspace; widget mounting / edit mode is P5+.

Verified on the ubuntu2504-test VM: extension enables cleanly, dashboard
shows the placeholder, switching to/from dashboard works, ding's window
is still ignored. MESA/EGL stderr lines are VM-only software-rendering
fallback noise (no virgl).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

container/runtime/runtime.ts

@@ -1,6 +1,7 @@
-// Stub: page-side runtime (design §11).
-// Loads layout.json, instantiates widgets in iframes on the 12-column grid,
-// handles edit mode, persists changes via the shell bridge.
+// Page-side runtime (design §11). For P3 the grid is just decoration —
+// it renders a "no widgets yet" placeholder so the dashboard workspace
+// has visible content. Real widget loading / edit mode / layout
+// persistence come in P5+.
 
 declare global {
   interface Window {
@@ -10,6 +11,18 @@ declare global {
   }
 }
 
-console.info('[dashward-runtime] P0 stub loaded');
+const grid = document.getElementById('grid');
+if (grid) {
+  const placeholder = document.createElement('section');
+  placeholder.className = 'placeholder';
+  placeholder.innerHTML = `
+    <h1>Dashward</h1>
+    <p class="hint">P3 — empty dashboard.</p>
+    <p class="meta">No widgets installed yet. Widget SDK + edit mode arrive in P5.</p>
+  `;
+  grid.appendChild(placeholder);
+}
+
+console.info('[dashward-runtime] P3 placeholder mounted');
 
 export {};

container/runtime/styles.css

@@ -1,16 +1,28 @@
 :root {
   --bg: #f5f5f7;
   --fg: #1c1c1e;
+  --fg-muted: rgba(28, 28, 30, 0.55);
   --grid-gap: 16px;
 }
 
 [data-theme="dark"] {
   --bg: #0f0f12;
   --fg: #f0f0f5;
+  --fg-muted: rgba(240, 240, 245, 0.55);
 }
 
-html, body { margin: 0; padding: 0; height: 100%; background: var(--bg); color: var(--fg); }
-body { font-family: ui-sans-serif, system-ui, -apple-system, sans-serif; }
+html, body {
+  margin: 0;
+  padding: 0;
+  height: 100%;
+  background: var(--bg);
+  color: var(--fg);
+}
+
+body {
+  font-family: ui-sans-serif, system-ui, -apple-system, 'Inter', sans-serif;
+  -webkit-font-smoothing: antialiased;
+}
 
 #grid {
   display: grid;
@@ -20,3 +32,32 @@ body { font-family: ui-sans-serif, system-ui, -apple-system, sans-serif; }
   min-height: 100%;
   box-sizing: border-box;
 }
+
+.placeholder {
+  grid-column: 1 / -1;
+  display: grid;
+  place-items: center;
+  align-content: center;
+  gap: 12px;
+  min-height: 80vh;
+  text-align: center;
+}
+
+.placeholder h1 {
+  font-size: clamp(3rem, 8vw, 6rem);
+  font-weight: 200;
+  letter-spacing: -0.02em;
+  margin: 0;
+}
+
+.placeholder .hint {
+  font-size: 1.25rem;
+  margin: 0;
+  opacity: 0.7;
+}
+
+.placeholder .meta {
+  font-size: 0.9rem;
+  margin: 0;
+  color: var(--fg-muted);
+}

container/src/main.ts

@@ -1,10 +1,51 @@
-// Stub: see design §7 — WebKit kiosk bootstrap.
-// Creates a GtkWindow, attaches a WebKitWebView, loads dashboard.html,
-// connects to the Shell DBus service.
+// Dashward web container — GJS bootstrap.
+// Spawned by the extension's ContainerSupervisor as a separate process so
+// a crash here cannot bring down gnome-shell.
+//
+// argv[0] (after the script): the runtime directory containing
+// dashboard.html, runtime.js, styles.css. The directory is passed by the
+// extension so we don't have to guess our install path.
 
 import GLib from 'gi://GLib';
+import Gtk from 'gi://Gtk?version=3.0';
+import WebKit2 from 'gi://WebKit2?version=4.1';
+import System from 'system';
 
-GLib.set_prgname('dashward-container');
-log('[dashward-container] P0 stub started');
+// Wayland's xdg-shell app_id is derived from prgname for plain GTK
+// windows (i.e. not a GApplication). Set this BEFORE any GTK init so
+// the compositor labels our top-level correctly -- the extension uses
+// this app_id to identify and pin our window to the dashboard workspace.
+const APP_ID = 'top.hangmanlab.dashward.container';
+GLib.set_prgname(APP_ID);
+GLib.set_application_name('Dashward');
 
-declare function log(msg: string): void;
+const args = System.programArgs;
+const runtimeDir = args[0];
+if (!runtimeDir) {
+  printerr('dashward-container: missing runtime dir argument');
+  System.exit(2);
+}
+
+Gtk.init(null);
+
+const window = new Gtk.Window({
+  type: Gtk.WindowType.TOPLEVEL,
+  title: 'Dashward',
+  decorated: false,
+});
+// X11 fallback for app_id; harmless on Wayland.
+window.set_wmclass(APP_ID, APP_ID);
+window.set_default_size(800, 600);
+
+const webview = new WebKit2.WebView();
+window.add(webview);
+
+const indexUri = `file://${runtimeDir}/dashboard.html`;
+webview.load_uri(indexUri);
+print(`dashward-container: loading ${indexUri}`);
+
+window.connect('destroy', () => Gtk.main_quit());
+window.show_all();
+window.fullscreen();
+
+Gtk.main();