fix: journal copies constructors at replay time, not record time

canvas enriches its cmd dict AFTER appendcmd; a record-time copy ships a bare canvas and glow renders its dim default stage. Store the live reference; copy at read. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01G7y9rTA1r8r8EhEnPSQenR
sspickle · Aug 16, 2026 · Aug 16, 2026 · Aug 16, 2026 · Aug 16, 2026 · Aug 16, 2026
commit 48b25c45685491cf7ca57647c9c9f6717bd32a2c
diff --git a/vpython/_scene_journal.py b/vpython/_scene_journal.py
@@ -31,17 +31,20 @@ def record_cmd(self, cmd):
         if cmd.get('cmd') is None:
             # Follow-up on an existing object (title/caption/...): same idx
             # as its constructor — must NOT clobber it.
-            self._extras.append(dict(cmd))
+            self._extras.append(cmd)
             return
         if idx not in self._cmds:
             self._order.append(idx)
-        self._cmds[idx] = dict(cmd)
+        # Store the LIVE reference, copy at replay time: constructors are
+        # enriched after appendcmd (canvas adds its attrs afterwards), and a
+        # record-time copy ships a bare canvas (observed: dim default scene).
+        self._cmds[idx] = cmd
 
     def record_attr(self, idx, attr):
         self._dirty.add((idx, attr))
 
     def constructors(self):
-        return [self._cmds[i] for i in self._order]
+        return [dict(self._cmds[i]) for i in self._order]
 
     def dirty_attrs(self):
         return set(self._dirty)

diff --git a/vpython/test/test_scene_journal.py b/vpython/test/test_scene_journal.py
@@ -18,12 +18,17 @@ def test_records_constructors_in_creation_order():
     assert [c['cmd'] for c in cmds] == ['canvas', 'sphere', 'box']
 
 
-def test_constructor_copies_are_isolated_from_caller_mutation():
+def test_late_enriched_constructor_keys_are_included_at_replay():
+    # canvas builds its cmd incrementally AFTER appendcmd; the journal must
+    # reflect the enriched dict, not a bare record-time snapshot.
     j = SceneJournal()
-    cmd = {'cmd': 'sphere', 'idx': 2}
+    cmd = {'cmd': 'canvas', 'idx': 1}
     j.record_cmd(cmd)
-    cmd['radius'] = 99
-    assert 'radius' not in j.constructors()[0]
+    cmd['ambient'] = [0.2, 0.2, 0.2]
+    assert j.constructors()[0]['ambient'] == [0.2, 0.2, 0.2]
+    # but the returned list is still a copy: mutating it is inert
+    j.constructors()[0]['hacked'] = True
+    assert 'hacked' not in j.constructors()[0]
 
 
 def test_delete_removes_object_and_its_dirty_attrs():