fix: window list flicker and icons missing from the icon theme

The Windows tab rebuilt every row once a second, and each rebuild walked
every window icon through its fallback names again, so the rows blinked.
It now re-renders only when the state changed.

Icon lookup only searched the configured theme, so an app the theme
lacks (pcmanfm-qt under candy-icons) lost its icon and showed its label.
It now falls back to hicolor, as the icon theme spec does, in hicolor's
size/category layout.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

3 files changed, 24 insertions, 6 deletions

diff --git a/deckit/server.py b/deckit/server.py
index e392041..6bea422 100644
--- a/deckit/server.py
+++ b/deckit/server.py
@@ -84,12 +84,15 @@ def icon_path(name: str, theme: str | None = None, bases=ICON_BASES):
     """An app icon from the installed icon theme, so launchers follow the theme."""
     if not ICON.fullmatch(name):
         return None
-    theme = theme or icon_theme()
-    for base in bases:
-        for sub in ("apps/scalable", "apps/64", "apps/48", "apps/32"):
-            path = Path(base) / theme / sub / f"{name}.svg"
-            if path.is_file():
-                return path
+    # hicolor last: the spec's fallback every theme inherits, where apps
+    # install their own icon when the theme has none for them.
+    for th in (theme or icon_theme(), "hicolor"):
+        for base in bases:
+            # Themes lay out category/size (candy-icons) or size/category (hicolor).
+            for sub in ("apps/scalable", "apps/64", "apps/48", "apps/32", "scalable/apps"):
+                path = Path(base) / th / sub / f"{name}.svg"
+                if path.is_file():
+                    return path
     return None
 
 
diff --git a/static/modules/windows.js b/static/modules/windows.js
index d3e882e..7404f03 100644
--- a/static/modules/windows.js
+++ b/static/modules/windows.js
@@ -110,6 +110,11 @@ export default {
   },
 
   update(st, el) {
+    // Polled every second: rebuilding unchanged rows reloads every icon
+    // through its fallbacks, which flickers, so only a change re-renders.
+    const key = JSON.stringify(st);
+    if (key === el._last) return;
+    el._last = key;
     const ws = el.querySelector(".ws");
     ws.textContent = "";
     for (const id of st.workspaces ?? []) {
diff --git a/tests/test_server.py b/tests/test_server.py
index a8fdf0d..7f2ee1c 100644
--- a/tests/test_server.py
+++ b/tests/test_server.py
@@ -128,6 +128,16 @@ class Server(unittest.TestCase):
         self.assertIsNone(srv.icon_path("../x", "candy-icons", [base]))
         self.assertIsNone(srv.icon_path("nope", "candy-icons", [base]))
 
+    def test_icon_path_falls_back_to_hicolor(self):
+        import tempfile
+        from pathlib import Path
+        base = Path(tempfile.mkdtemp())
+        (base / "candy-icons" / "apps" / "scalable").mkdir(parents=True)
+        d = base / "hicolor" / "scalable" / "apps"
+        d.mkdir(parents=True)
+        (d / "pcmanfm-qt.svg").write_text("<svg/>")
+        self.assertEqual(srv.icon_path("pcmanfm-qt", "candy-icons", [base]), d / "pcmanfm-qt.svg")
+
     def test_art_route(self):
         from unittest import mock
         with mock.patch.object(srv, "art", return_value=(b"PNGDATA", "image/png")):