fix(web-chat): normalize chat copy to plain text (#1114)

* fix(web-chat): force plain-text clipboard copy from chat messages

* test(e2e): make chat copy test target deterministic message

src/channels/web/static/app.js

@@ -600,6 +600,22 @@ document.getElementById('chat-input').addEventListener('paste', (e) => {
   }
 });
 
+const chatMessagesEl = document.getElementById('chat-messages');
+chatMessagesEl.addEventListener('copy', (e) => {
+  const selection = window.getSelection();
+  if (!selection || selection.isCollapsed) return;
+  const anchorNode = selection.anchorNode;
+  const focusNode = selection.focusNode;
+  if (!anchorNode || !focusNode) return;
+  if (!chatMessagesEl.contains(anchorNode) || !chatMessagesEl.contains(focusNode)) return;
+  const text = selection.toString();
+  if (!text || !e.clipboardData) return;
+  // Force plain-text clipboard output so dark-theme styling never leaks on paste.
+  e.preventDefault();
+  e.clipboardData.clearData();
+  e.clipboardData.setData('text/plain', text);
+});
+
 function addGeneratedImage(dataUrl, path) {
   const container = document.getElementById('chat-messages');
   const card = document.createElement('div');

tests/e2e/scenarios/test_chat.py

@@ -74,3 +74,44 @@ async def test_empty_message_not_sent(page):
     await page.wait_for_timeout(2000)
     final_count = await page.locator(f"{SEL['message_user']}, {SEL['message_assistant']}").count()
     assert final_count == initial_count, "Empty message should not create new messages"
+
+
+async def test_copy_from_chat_forces_plain_text(page):
+    """Copying selected chat text should populate plain text clipboard data only."""
+    await page.evaluate("addMessage('assistant', 'Copy me into Sheets')")
+
+    copied = await page.evaluate(
+        """
+        () => {
+          const content = Array.from(document.querySelectorAll('#chat-messages .message.assistant .message-content'))
+            .find((el) => (el.textContent || '').includes('Copy me into Sheets'));
+          if (!content) return {ok: false, reason: 'no content'};
+          const range = document.createRange();
+          range.selectNodeContents(content);
+          const sel = window.getSelection();
+          sel.removeAllRanges();
+          sel.addRange(range);
+
+          const store = {};
+          const evt = new Event('copy', { bubbles: true, cancelable: true });
+          evt.clipboardData = {
+            clearData: () => { Object.keys(store).forEach((k) => delete store[k]); },
+            setData: (t, v) => { store[t] = v; },
+            getData: (t) => store[t] || '',
+          };
+
+          content.dispatchEvent(evt);
+          return {
+            ok: true,
+            defaultPrevented: evt.defaultPrevented,
+            text: store['text/plain'] || '',
+            html: store['text/html'] || '',
+          };
+        }
+        """
+    )
+
+    assert copied["ok"], copied.get("reason", "copy setup failed")
+    assert copied["defaultPrevented"] is True
+    assert "Copy me into Sheets" in copied["text"]
+    assert copied["html"] == ""