kernel: load ui surfaces from RML asset files + dev hot-reload

Externalize UI documents so RML/RCSS design changes need no C++ recompile — and,
in dev, no restart.

- UiSurfaceSpec::rml_path now actually loads the document from a file (path wins
  over rml_inline, as documented). Resolution: absolute path as-is; relative path
  against $UNBOX_ASSET_DIR, else the compile-time UNBOX_ASSET_DIR_DEFAULT (the
  install data dir), else cwd. The document URL is set so its <link> RCSS / asset
  refs resolve relative to the doc's own dir. Missing/unreadable file -> nullptr
  (degrade, never throw).
- Dev hot-reload (gated by $UNBOX_DEV): an inotify watcher integrated into the
  wl_event_loop (never blocks) watches the asset DIRS (dir-watch for IN_CLOSE_WRITE
  / IN_MOVED_TO, since editors save via temp+rename), coalesces events, and on a
  change to a surface's backing .rml/.rcss reloads the document IN PLACE:
  ClearStyleSheetCache + UnloadDocument + reload, preserving the surface's RmlUi
  context, data model and the extension's registered bind_*/bind_list* getters
  (the extension does NOT re-register), and its geometry/visibility; preview
  textures are kept. A malformed file on reload is ERROR-ISOLATED — the previous
  good document keeps rendering, one warning is logged, and a later good save
  recovers; the session never dies.
- Test seam Server::ui_reload_surface() drives reload deterministically.

ui.hpp documents rml_path + the dev hot-reload behavior. kernel 54 cases/232
assertions green on build + build-asan (incl. the UNBOX_DEV inotify path), no new
suppressions. Edits confined to packages/kernel/.

1 files changed, 8 insertions, 1 deletions

diff --git a/packages/kernel/src/server.cpp b/packages/kernel/src/server.cpp
index d97104e..5d78b70 100644
--- a/packages/kernel/src/server.cpp
+++ b/packages/kernel/src/server.cpp
@@ -105,6 +105,10 @@ auto Server::ui_click_element(const char* tag, int index) -> bool {
     return impl_->substrate != nullptr && impl_->substrate->click_element(tag, index);
 }
 
+auto Server::ui_reload_surface() -> bool {
+    return impl_->substrate != nullptr && impl_->substrate->reload_first_surface();
+}
+
 void Server::ui_set_touch_override(UiTouchOverride ov) {
     if (impl_->substrate == nullptr) {
         return;
@@ -371,8 +375,11 @@ void Server::Impl::start_substrate() {
         wlr_log(WLR_INFO, "ui-substrate: renderer is not gles2; substrate unavailable");
     }
     // A data-event/getter throw disables the owning extension via the same
-    // isolation path the bus uses (Server::Impl is the DisableSink).
+    // isolation path the bus uses (Server::Impl is the DisableSink). The
+    // wl_event_loop lets the substrate poll the dev hot-reload inotify fd
+    // (UNBOX_DEV-gated) without ever blocking the loop.
     substrate = Substrate::create(display_egl, allocator, renderer,
+                                  wl_display_get_event_loop(display),
                                   [this](ExtensionId who) { disable(who); });
 }