diff --git a/static/js/skills.js b/static/js/skills.js
index 8eac3954c..0bea897b2 100644
--- a/static/js/skills.js
+++ b/static/js/skills.js
@@ -514,6 +514,8 @@ function _buildBuiltinCards() {
 
     card.addEventListener('click', (e) => {
       if (e.target.closest('button, input, textarea')) return;
+      // Editing in progress → don't collapse on an outside-the-textarea click.
+      if (card.querySelector('.skill-md-editor')) return;
       _expandBuiltinCard(card, b.name);
     });
     return card;
@@ -786,6 +788,10 @@ function renderSkillsList() {
     card.addEventListener('click', (e) => {
       if (card._suppressNextClick) { card._suppressNextClick = false; return; }
       if (e.target.closest('button, input, textarea')) return;
+      // While editing, a click on the card body (outside the textarea) must
+      // NOT collapse the card — that silently discards unsaved edits. Only
+      // Save/Cancel exit edit mode.
+      if (card.querySelector('.skill-md-editor')) return;
       if (_selectMode) {
         const cb = card.querySelector('.skill-select-cb');
         if (cb) { cb.checked = !cb.checked; cb.dispatchEvent(new Event('change')); }
diff --git a/tests/test_skill_edit_no_collapse_on_outside_click_js.py b/tests/test_skill_edit_no_collapse_on_outside_click_js.py
new file mode 100644
index 000000000..1a25c5325
--- /dev/null
+++ b/tests/test_skill_edit_no_collapse_on_outside_click_js.py
@@ -0,0 +1,56 @@
+"""Regression guard for issue #4002 — clicking the card body outside the
+edit textarea collapsed the skill card and silently discarded unsaved edits.
+
+In Brain > Skills, the card's click handler toggles expand/collapse. The
+edit <textarea> stops propagation only for clicks landing ON the textarea,
+so a click on the surrounding card padding bubbled up to the card handler
+and collapsed the card mid-edit — losing the user's changes. The fix bails
+out of the card click handler while a `.skill-md-editor` is present, so the
+card only leaves edit mode via Save (or the Cancel button added in #3580).
+
+skills.js pulls in browser globals (DOM), so it can't be imported under
+node; this guards the fix at the source level so it can't be silently
+dropped. Both the user-skill card (`_expandSkillCard`) and the built-in
+capability card (`_expandBuiltinCard`) share the same bug and the same
+guard, so both are covered here.
+"""
+import re
+from pathlib import Path
+
+SRC = Path(__file__).resolve().parent.parent / "static/js/skills.js"
+
+# The guard the fix introduces inside the card click handler.
+GUARD = re.compile(r"querySelector\(\s*['\"]\.skill-md-editor['\"]\s*\)\s*\)\s*return")
+
+
+def _handler_body(text: str, anchor: str, call: str) -> str:
+    """Return the card click-handler body: the slice from `anchor` (a string
+    unique to the handler we care about) up to its collapse trigger `call`.
+    `_expandSkillCard` is called from several places, so we must anchor on the
+    handler itself rather than the first textual match of the call."""
+    start = text.index(anchor)
+    end = text.index(call, start)
+    return text[start:end]
+
+
+def test_user_skill_card_does_not_collapse_while_editing():
+    text = SRC.read_text(encoding="utf-8")
+    body = _handler_body(
+        text, "// Click to expand/collapse", "_expandSkillCard(card, name)"
+    )
+    assert GUARD.search(body), (
+        "user-skill card click handler must skip collapse while a "
+        ".skill-md-editor is present (issue #4002)"
+    )
+
+
+def test_builtin_card_does_not_collapse_while_editing():
+    text = SRC.read_text(encoding="utf-8")
+    # The built-in capability card has a single handler ending in
+    # _expandBuiltinCard; take the click handler that immediately precedes it.
+    before = text[: text.index("_expandBuiltinCard(card, b.name)")]
+    body = before[before.rindex("card.addEventListener('click'"):]
+    assert GUARD.search(body), (
+        "built-in capability card click handler must skip collapse while a "
+        ".skill-md-editor is present (issue #4002)"
+    )