fix(links): custom link edits spuriously logged URL changes

When editing a CUSTOM link's text content, the ViewUpdateView's
URL-change check was comparing the captured original_url (e.g.
'/custom/mynote') against form.cleaned_data['original_url'], which
for custom links is blank because the original_url input is hidden in
link_form.html and not submitted. They never matched, so every edit
produced a spurious LinkChangeLog 'URL changed' row.

Use the recomputed /custom/{alias} value (already set on
form.instance.original_url) for custom links, and only the submitted
form value for regular links. So the log now fires only when:

- a regular link's URL actually changes, or
- a custom link's alias changes (which derives a new /custom/{alias}).

Add TestCustomLinkEditUrlChangeLog covering:
  - custom link text-edit produces no URL-change log
  - regular link edit leaving URL unchanged produces no log
  - regular link URL change logs once with old/new URL
  - custom link alias change logs once with old/new derived URL

links/views.py

@@ -198,8 +198,15 @@ class LinkUpdateView(UpdateView):
         # Invalidate the alias cache so the redirect hot-path sees the updated link
         cache.delete(f"link:alias:{form.instance.alias.lower()}")
 
-        new_url = form.cleaned_data['original_url']
-        if self.original_url != new_url:
+        # Compare against the URL that will actually be persisted. For custom
+        # links the original_url form field is hidden (it's derived from the
+        # alias), so use the recomputed value instead of the blank submitted
+        # one — otherwise every edit logs a spurious "URL changed".
+        if form.cleaned_data.get('link_type') == Link.LinkType.CUSTOM:
+            new_url = f'/custom/{alias}'
+        else:
+            new_url = form.cleaned_data.get('original_url')
+        if new_url is not None and self.original_url != new_url:
             logger.info(f"URL changed from {self.original_url} to {new_url}")
             try:
                 self.object.log_url_change(self.original_url)

tests/test_links_api.py

@@ -5,7 +5,7 @@ Links are managed via Django template views, tested through the Django test clie
 
 import pytest
 
-from links.models import Link, Tag
+from links.models import Link, LinkChangeLog, Tag
 
 
 @pytest.mark.django_db
@@ -234,3 +234,112 @@ class TestLinkTagAutoCreate:
         assert tag.name == "spaced out"
         assert tag.slug == "spaced-out"
         assert Tag.objects.count() == before + 1
+
+
+@pytest.mark.django_db
+class TestCustomLinkEditUrlChangeLog:
+    """Editing a CUSTOM link's content (text) must NOT log a spurious
+    "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."""
+
+    def _update(self, client, link, **payload):
+        data = {
+            "alias": link.alias,
+            # The original_url input is hidden for custom links and not
+            # submitted by the browser, so keep it blank in this helper.
+            "original_url": "",
+            "link_type": Link.LinkType.CUSTOM,
+            "description": "",
+            "text": "",
+        }
+        data.update(payload)
+        return client.post(f"/link/{link.pk}/edit/", data, follow=True)
+
+    def test_custom_link_text_edit_creates_no_url_change_log(self, client):
+        link = Link.objects.create(
+            alias="mynote",
+            link_type=Link.LinkType.CUSTOM,
+            original_url="/custom/mynote",
+            text="old body text",
+        )
+        before = LinkChangeLog.objects.filter(link=link).count()
+
+        response = self._update(client, link, text="new body text")
+        assert response.status_code == 200
+
+        link.refresh_from_db()
+        assert link.text == "new body text"
+        assert link.original_url == "/custom/mynote"
+        assert LinkChangeLog.objects.filter(link=link).count() == before
+
+    def test_regular_link_text_unchanged_creates_no_url_change_log(self, client):
+        link = Link.objects.create(
+            alias="gh",
+            link_type=Link.LinkType.LINK,
+            original_url="https://github.com",
+        )
+        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": "an edit that keeps the URL",
+                "text": "",
+            },
+            follow=True,
+        )
+        assert response.status_code == 200
+        assert LinkChangeLog.objects.filter(link=link).count() == before
+
+    def test_regular_link_url_change_logs_change(self, client):
+        link = Link.objects.create(
+            alias="gh",
+            link_type=Link.LinkType.LINK,
+            original_url="https://github.com",
+        )
+        before = LinkChangeLog.objects.filter(link=link).count()
+
+        response = client.post(
+            f"/link/{link.pk}/edit/",
+            {
+                "alias": "gh",
+                "original_url": "https://github.com/junv",
+                "link_type": Link.LinkType.LINK,
+                "description": "",
+                "text": "",
+            },
+            follow=True,
+        )
+        assert response.status_code == 200
+        logs = LinkChangeLog.objects.filter(link=link).order_by("-changed_at")
+        assert logs.count() == before + 1
+        assert logs.first().old_url == "https://github.com"
+        assert logs.first().new_url == "https://github.com/junv"
+
+    def test_custom_link_alias_change_logs_url_change(self, client):
+        """When the alias of a custom link changes, the derived URL changes
+        too, and that should be logged once."""
+        link = Link.objects.create(
+            alias="mynote",
+            link_type=Link.LinkType.CUSTOM,
+            original_url="/custom/mynote",
+            text="body text",
+        )
+        before = LinkChangeLog.objects.filter(link=link).count()
+
+        # Helper defaults text to "" (custom links require non-empty text)
+        response = self._update(client, link, alias="newnote", text="body text")
+        assert response.status_code == 200
+
+        link.refresh_from_db()
+        assert link.alias == "newnote"
+        assert link.original_url == "/custom/newnote"
+        logs = LinkChangeLog.objects.filter(link=link).order_by("-changed_at")
+        assert logs.count() == before + 1
+        assert logs.first().old_url == "/custom/mynote"
+        assert logs.first().new_url == "/custom/newnote"