kernel: fix asset hot-reload regression (watch the whole asset dir, not the .rml basename)

The watch_file refactor (35e5d32) moved the substrate's UI-asset hot-reload onto
the shared FileWatcher but armed a BASENAME watch on the document's .rml file only.
The dock's styling lives in a separately-<link>ed dock.rcss, so editing it (the
common case) never matched the watch — asset hot-reload silently stopped working on
the real seat (no "dev hot-reload ON" line, no reload on save), while config
watching kept working. The ui_reload_surface() seam test passed because it bypassed
the real inotify->reload path.

Fix: FileWatcher::add_dir watches the document's whole DIRECTORY (so any .rml/.rcss
in it triggers the surface reload); the substrate uses it and restores the
"dev hot-reload ON (inotify watching asset dir '...')" log. Added an END-TO-END
test mirroring the dock (a doc that <link>s a separate .rcss, real inotify event,
wl_event_loop pumped, assert the document actually reloaded) — fails on the buggy
code, passes now; no more relying on the seam.

Real-seat verified: editing dock.rcss now reloads the live dock (border-radius +
background-color changes apply on save). kernel 59 cases/260 assertions green on
build + build-asan, no new suppressions. Edits confined to packages/kernel/.

1 files changed, 17 insertions, 6 deletions

diff --git a/packages/kernel/src/ui_substrate.cpp b/packages/kernel/src/ui_substrate.cpp
index 8b7440e..1f289bd 100644
--- a/packages/kernel/src/ui_substrate.cpp
+++ b/packages/kernel/src/ui_substrate.cpp
@@ -809,14 +809,22 @@ Rml::ElementDocument* Substrate::Impl::load_document_first(Surface& s) {
             return nullptr;
         }
         // Dev-only: register an asset hot-reload watch on the kernel's SHARED
-        // file watcher (the same machinery Host::watch_file uses). The callback
-        // flags this surface for reload, applied (coalesced) at the next
-        // tick_all on the GL context. Only this DECISION is UNBOX_DEV-gated; the
-        // watcher infra itself is always available.
+        // file watcher (the same machinery Host::watch_file uses). We watch the
+        // document's whole DIRECTORY (add_dir), NOT just the .rml basename:
+        // RmlUi resolves `<link href="x.rcss">` and image srcs relative to the
+        // document dir, and the dock keeps its dock.rcss BESIDE dock.rml — so a
+        // change to ANY file in that dir (the .rml OR a linked .rcss/asset) must
+        // reload. (Watching only the .rml basename was the regression: editing
+        // dock.rcss fired no reload.) The callback flags this surface for reload,
+        // applied (coalesced) at the next tick_all on the GL context. Only this
+        // DECISION is UNBOX_DEV-gated; the watcher infra itself is always
+        // available (Host::watch_file is ungated).
         if (hot_reload_enabled() && watcher != nullptr) {
             Surface* sp = &s;
-            s.asset_watch = watcher->add(
-                s.resolved_path,
+            const std::string dir =
+                std::filesystem::path(s.resolved_path).parent_path().string();
+            s.asset_watch = watcher->add_dir(
+                dir,
                 [this, sp] {
                     if (std::find(pending_reloads.begin(), pending_reloads.end(), sp) ==
                         pending_reloads.end()) {
@@ -824,6 +832,9 @@ Rml::ElementDocument* Substrate::Impl::load_document_first(Surface& s) {
                     }
                 },
                 s.who);
+            wlr_log(WLR_INFO,
+                    "ui-substrate: dev hot-reload ON (inotify watching asset dir '%s')",
+                    dir.c_str());
         }
     } else {
         doc = s.context->LoadDocumentFromMemory(s.rml_inline);