Prevent selecting message action buttons

Mark message action button chrome as non-selectable so copy/paste captures message text without toolbar icon labels.

Add a static regression for the shared action-buttons stylesheet.

tests/test_message_action_buttons_static.py

@@ -0,0 +1,17 @@
+from pathlib import Path
+
+
+PROJECT_ROOT = Path(__file__).resolve().parents[1]
+
+
+def test_message_action_buttons_are_not_text_selectable() -> None:
+    css = PROJECT_ROOT.joinpath(
+        "webui",
+        "components",
+        "messages",
+        "action-buttons",
+        "simple-action-buttons.css",
+    ).read_text(encoding="utf-8")
+
+    block = css[css.index(".step-action-buttons {"):css.index("}", css.index(".step-action-buttons {"))]
+    assert "user-select: none;" in block

webui/components/messages/AGENTS.md

@@ -15,6 +15,7 @@
 - Keep message DOM helpers compatible with extension points that modify rendered messages.
 - Sanitize or safely render model/user-provided content through shared rendering paths.
 - Avoid layout shifts that break long-running message streaming.
+- Keep message action chrome out of text selection so copy/paste captures message content without button labels or icons.
 
 ## Work Guidance
 

webui/components/messages/action-buttons/simple-action-buttons.css

@@ -12,6 +12,7 @@
   opacity: 0;
   transition: opacity 0.2s ease-in-out;
   pointer-events: none;
+  user-select: none;
 }
 
 .step-action-buttons .expand-btn {