fix(web): the style editor takes over its own blocks -- and gets to at all

Two defects, both found by rendering the real partial in a browser rather than
by reading the code.

It was losing a race to its own fields. The hand-off guard asked "do any
fallback controls differ from their server-rendered defaults?" as a proxy for
"is someone editing this?". But the fallback holds this block's own font
fields, and the font-selector widget populates them on the same 50ms timer --
so a plain page load, with nobody touching anything, raced into "dirty" and the
editor removed itself, leaving the 701-line accordion form it exists to
replace. Measured: seven customization.*.font selects dirty ~60ms after
injection, clean again by 400ms. The question is whether a *person* typed, and
event.isTrusted answers exactly that; the listeners now go on synchronously,
because the edit worth protecting can happen before initWidget runs.

It took over too much. Taking over removed the whole fallback section, but a
customization block can hold more than styling -- football keeps
favorite_result_colors there -- so that removed the only UI those fields had,
and the editor also rendered them as an element, giving every row an "enabled"
and three colour columns. Core now marks the blocks it recognises as styling
(the compact declaration already did; hand-written adoption did not), the
widget renders only those, and the template drops only the children the widget
reports owning.

Verified on football's real schema: 28 rows across four mode tabs, columns
Element/Font/Size/Colour/X/Y, favorite_result_colors still editable with its
ten inputs, no duplicated field names, no console errors.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

test/web_interface/test_style_editor_takeover.py

@@ -0,0 +1,127 @@
+"""When the style editor takes over a customization block, it takes over
+exactly its own part of it -- and it actually gets to take over at all.
+
+Two defects this pins, both found by rendering the real partial in a browser
+rather than by reading the code:
+
+1. The hand-off guard asked "do any fallback controls differ from their
+   server-rendered defaults?" as a proxy for "is someone editing this?". The
+   fallback contains this block's own font fields, and the font-selector
+   widget populates them on the same 50ms timer -- so a plain page load with
+   nobody touching anything raced into "dirty" (seven customization.*.font
+   selects, measured ~60ms after injection) and the style editor removed
+   itself, leaving the accordion form it exists to replace. The question is
+   whether a *person* typed, and isTrusted answers exactly that.
+
+2. Taking over used to remove the whole fallback section. A customization
+   block can hold more than styling -- football keeps favorite_result_colors
+   there -- so that removed the only UI those fields had.
+
+These assert on the template source because the behaviour lives in an inline
+script that no Python test executes; the browser check that found both is not
+something CI runs.
+"""
+
+import re
+import sys
+from pathlib import Path
+
+import pytest
+
+PROJECT_ROOT = Path(__file__).parent.parent.parent
+sys.path.insert(0, str(PROJECT_ROOT))
+
+TEMPLATE = (PROJECT_ROOT / "web_interface" / "templates" / "v3" / "partials"
+            / "plugin_config.html")
+
+
+@pytest.fixture(scope="module")
+def source():
+    return TEMPLATE.read_text(encoding="utf-8")
+
+
+class TestTheHandOffGuard:
+    def test_it_asks_whether_a_person_typed(self, source):
+        assert "isTrusted" in source, (
+            "a programmatic change by a sibling widget must not read as a "
+            "user edit -- that is what removed the editor on a plain load")
+        assert "userEdited" in source
+
+    def test_it_no_longer_diffs_values_against_defaults(self, source):
+        assert "fallbackIsDirty" not in source, (
+            "value-diffing cannot distinguish a user's edit from another "
+            "widget populating this block's own fields")
+        assert "defaultSelected" not in source
+
+    def test_the_listeners_are_attached_synchronously(self, source):
+        """The edit worth protecting can happen before initWidget runs, so
+        the listeners cannot wait for it.
+
+        Scoped to this branch: the template defines an initWidget for every
+        widget it can render, and the first one in the file belongs to a
+        different branch entirely.
+        """
+        start = source.index("obj_widget == 'style-editor'")
+        branch = source[start:source.index("{% elif prop.properties %}", start)]
+        assert "watchForRealEdits" in branch
+        assert branch.index("watchForRealEdits") < branch.index("function initWidget"), (
+            "the watcher must be installed above this branch's initWidget, "
+            "and invoked immediately rather than from inside it")
+
+    def test_the_guard_still_backs_off_for_a_real_edit(self, source):
+        assert re.search(r"if \(userEdited\) \{ container\.remove\(\); return; \}",
+                         source), "a genuine in-progress edit must still win"
+
+
+class TestItTakesOverOnlyItsOwnBlocks:
+    def test_children_are_individually_addressable(self, source):
+        assert 'data-child-key="{{ nested_key }}"' in source, (
+            "without a handle per child the only options are removing the "
+            "whole section or none of it")
+
+    def test_removal_is_driven_by_what_the_widget_reported(self, source):
+        assert "ownedKeys" in source
+        assert "fallback.querySelector(" in source
+
+    def test_an_unowned_child_survives(self, source):
+        """The empty-section case still removes the lot, so a block that is
+        entirely styling looks exactly as it did before."""
+        assert "!fallback.querySelector('[data-child-key]')" in source
+
+
+class TestTheSchemaSaysWhichBlocksAreStyling:
+    def test_adopted_blocks_are_marked_and_others_are_not(self):
+        from src.element_style import expand_style_elements
+
+        schema = {
+            "type": "object",
+            "properties": {
+                "customization": {
+                    "type": "object",
+                    "properties": {
+                        "score_text": {
+                            "type": "object",
+                            "properties": {
+                                "font": {"type": "string",
+                                         "default": "PressStart2P-Regular.ttf"},
+                                "font_size": {"type": "integer", "default": 10},
+                                "text_color": {"type": "array",
+                                               "default": [255, 255, 255]},
+                            },
+                        },
+                        # Not styling: a feature that happens to live here.
+                        "favorite_result_colors": {
+                            "type": "object",
+                            "properties": {
+                                "enabled": {"type": "boolean", "default": False},
+                                "win_color": {"type": "array",
+                                              "default": [0, 255, 0]},
+                            },
+                        },
+                    },
+                },
+            },
+        }
+        props = expand_style_elements(schema)["properties"]["customization"]["properties"]
+        assert props["score_text"]["x-style-managed"] is True
+        assert "x-style-managed" not in props["favorite_result_colors"]