fix: pin a source mirror on source_commit

scripts/profile_sync.py

@@ -1196,9 +1196,16 @@ def select_views(
         repo = upstream.parse_repo(url)
         if repo is None or (repo.host, repo.slug) in seen:
             continue
-        branch = branch_in_url(url) or (declared if field == "source" else None)
+        # A mirror carries the source's history, commits and branches alike:
+        # its pin is source_commit. It read `source_mirror_commit`, a field
+        # no profile carries, and fell back to profiled_date, which a bump
+        # never moves (eden judged from f6e76860 while pinned on d16735f5).
+        pin_field = "source" if field == "source_mirror" else field
+        branch = branch_in_url(url) or (
+            declared if pin_field == "source" else None
+        )
         pin, origin = resolve_pin(
-            profile, repo, cache_dir, offline, field, mode, branch
+            profile, repo, cache_dir, offline, pin_field, mode, branch
         )
         if not pin:
             continue

tests/test_profile_sync.py

@@ -250,6 +250,32 @@ class TestSourceMirror(unittest.TestCase):
             [("source_mirror", "", "https://codeberg.org/o/mirror")],
         )
 
+    def test_the_mirror_reads_the_source_pin(self):
+        """eden's mirror was judged from profiled_date while source_commit,
+        which bumps advance, named another revision."""
+        profile = {
+            "source": "https://git.eden-emu.dev/o/port",
+            "source_mirror": "https://codeberg.org/o/mirror",
+            "source_commit": "d16735f5",
+            "profiled_date": "2026-03-26",
+            "source_branch": "dev",
+        }
+        calls = []
+
+        def head(repo, cache_dir, offline, branch=None):
+            calls.append(("head", repo.host, branch))
+            return None if repo.host == "git.eden-emu.dev" else "tip"
+
+        def at(*args, **kwargs):
+            raise AssertionError("a declared pin needs no date lookup")
+
+        with mock.patch.object(profile_sync.upstream, "resolve_head", head), \
+                mock.patch.object(profile_sync.upstream, "resolve_commit_at", at):
+            views = profile_sync.select_views(profile, "unused", True)
+        self.assertEqual([(v.repo.host, v.pin) for v in views],
+                         [("codeberg.org", "d16735f5")])
+        self.assertIn(("head", "codeberg.org", "dev"), calls)
+
     def test_a_profile_without_a_mirror_is_unchanged(self):
         profile = {"source": "https://github.com/o/port"}
         self.assertEqual(