feat(links): log CONTENT_EDIT on text changes (no content persisted)

Previously, editing a custom link's text content created a spurious
URL_CHANGE row (fixed last commit) but no audit entry at all for the
actual content change. The product requirement: a change-log row SHOULD
be created so auditors see content was edited, but should NOT persist
the content itself.

LinkUpdateView now:

- Captures self.original_text in get_initial() alongside
  self.original_url.
- After super().form_valid() writes the new text, compares old vs new
  text. If different, creates a LinkChangeLog with
  change_type=CONTENT_EDIT and metadata={'changed': True} — no content
  payload. Applies to both LINK and CUSTOM link types.
- URL-change logging behaviour is unchanged.

Tests in TestCustomLinkEditUrlChangeLog now cover:
  - custom link text edit creates CONTENT_EDIT, no URL_CHANGE
  - custom link text unchanged creates no log
  - regular link text change creates CONTENT_EDIT
  - regular link URL change still logs URL_CHANGE

links/views.py

@@ -171,6 +171,10 @@ class LinkUpdateView(UpdateView):
     def get_initial(self):
         initial = super().get_initial()
         self.original_url = self.object.original_url
+        # Capture the existing content so form_valid can detect text edits
+        # and log them as a CONTENT_EDIT change (without persisting the
+        # content itself).
+        self.original_text = self.object.text
         return initial
 
     def get_context_data(self, **kwargs):
@@ -216,6 +220,21 @@ class LinkUpdateView(UpdateView):
         else:
             logger.info("URL did not change")
 
+        # Log a CONTENT_EDIT entry when the link's text changed, regardless of
+        # link type. We deliberately don't persist the actual content — only a
+        # marker that it changed (per product requirement).
+        new_text = form.cleaned_data.get('text') or ''
+        if (self.original_text or '') != new_text:
+            try:
+                LinkChangeLog.objects.create(
+                    link=self.object,
+                    change_type=LinkChangeLog.ChangeType.CONTENT_EDIT,
+                    metadata={'changed': True},
+                )
+                logger.info(f"Created CONTENT_EDIT LinkChangeLog for link {self.object.pk}")
+            except Exception as e:
+                logger.error(f"Error creating CONTENT_EDIT LinkChangeLog for link {self.object.pk}: {str(e)}")
+
         return response
 
     def form_invalid(self, form):

tests/test_links_api.py

@@ -242,7 +242,11 @@ class TestCustomLinkEditUrlChangeLog:
     "URL changed" entry, because custom-link URLs are derived from the
     alias and the original_url form field is hidden for custom links.
     Regression test for the bug where every edit of a custom link
-    produced a LinkChangeLog row."""
+    produced a LinkChangeLog row.
+
+    A CONTENT_EDIT entry, however, SHOULD be created whenever the text
+    changes (for either custom or regular links). The actual content is
+    NOT persisted in the log — only a marker that it changed."""
 
     def _update(self, client, link, **payload):
         data = {
@@ -264,7 +268,12 @@ class TestCustomLinkEditUrlChangeLog:
             original_url="/custom/mynote",
             text="old body text",
         )
-        before = LinkChangeLog.objects.filter(link=link).count()
+        before_url_logs = LinkChangeLog.objects.filter(
+            link=link, change_type=LinkChangeLog.ChangeType.URL_CHANGE
+        ).count()
+        before_content_logs = LinkChangeLog.objects.filter(
+            link=link, change_type=LinkChangeLog.ChangeType.CONTENT_EDIT
+        ).count()
 
         response = self._update(client, link, text="new body text")
         assert response.status_code == 200
@@ -272,7 +281,18 @@ class TestCustomLinkEditUrlChangeLog:
         link.refresh_from_db()
         assert link.text == "new body text"
         assert link.original_url == "/custom/mynote"
-        assert LinkChangeLog.objects.filter(link=link).count() == before
+        # No spurious URL-change log
+        assert LinkChangeLog.objects.filter(
+            link=link, change_type=LinkChangeLog.ChangeType.URL_CHANGE
+        ).count() == before_url_logs
+        # A content-edit log IS created, without persisting the content
+        content_logs = LinkChangeLog.objects.filter(
+            link=link, change_type=LinkChangeLog.ChangeType.CONTENT_EDIT
+        ).order_by("-changed_at")
+        assert content_logs.count() == before_content_logs + 1
+        assert content_logs.first().metadata == {"changed": True}
+        assert "new body text" not in str(content_logs.first().metadata)
+        assert "old body text" not in str(content_logs.first().metadata)
 
     def test_regular_link_text_unchanged_creates_no_url_change_log(self, client):
         link = Link.objects.create(
@@ -296,6 +316,49 @@ class TestCustomLinkEditUrlChangeLog:
         assert response.status_code == 200
         assert LinkChangeLog.objects.filter(link=link).count() == before
 
+    def test_custom_link_text_unchanged_creates_no_content_log(self, client):
+        link = Link.objects.create(
+            alias="mynote",
+            link_type=Link.LinkType.CUSTOM,
+            original_url="/custom/mynote",
+            text="same body text",
+        )
+        before = LinkChangeLog.objects.filter(link=link).count()
+
+        response = self._update(client, link, text="same body text")
+        assert response.status_code == 200
+        assert LinkChangeLog.objects.filter(link=link).count() == before
+
+    def test_regular_link_text_change_creates_content_log(self, client):
+        """Regular (LINK-type) links can also carry text content; editing that
+        text should produce a CONTENT_EDIT entry too."""
+        link = Link.objects.create(
+            alias="gh",
+            link_type=Link.LinkType.LINK,
+            original_url="https://github.com",
+            text="original notes",
+        )
+        before = LinkChangeLog.objects.filter(link=link).count()
+
+        response = client.post(
+            f"/link/{link.pk}/edit/",
+            {
+                "alias": "gh",
+                "original_url": "https://github.com",
+                "link_type": Link.LinkType.LINK,
+                "description": "",
+                "text": "edited notes",
+            },
+            follow=True,
+        )
+        assert response.status_code == 200
+        content_logs = LinkChangeLog.objects.filter(
+            link=link, change_type=LinkChangeLog.ChangeType.CONTENT_EDIT
+        ).order_by("-changed_at")
+        assert content_logs.count() == before + 1
+        assert content_logs.first().metadata == {"changed": True}
+        assert "edited notes" not in str(content_logs.first().metadata)
+
     def test_regular_link_url_change_logs_change(self, client):
         link = Link.objects.create(
             alias="gh",