Quote GeoJson identifier properties that aren't valid JS identifiers

[adarshsm]

Closes #1782.

The bug

If the features in a GeoJson have no unique id, find_identifier() looks for a property with a unique value per feature. It then writes it into the styler/highlighter switch with dot notation: feature.properties.<key>. If the key isn't a valid JavaScript identifier, the generated code is wrong:

property key	generated	what JavaScript does
Time (UTC) (the issue's data)	switch(feature.properties.Time (UTC))	calls feature.properties.Time(UTC) → ReferenceError: UTC is not defined
property-key	switch(feature.properties.property-key)	evaluates feature.properties.property - key → ReferenceError
osm.id	n/a	get_feature_id splits on . and raises KeyError: 'osm' in Python during render()

In the browser the styler throws when Leaflet styles the first feature, so the layer isn't drawn. That's why the reporter's features disappear only when style_function is passed: without a style or highlight function no identifier is needed.

I reproduced it with the demo.json attached to the issue on current main. All 35 features are LineStrings without id, and the first property with unique values is "Time (UTC)". I ran the generated _styler function in node against every feature:

• before: ReferenceError: UTC is not defined
• after: styled 35 of 35

The fix

• find_identifier() keeps feature.properties.<key> when key.isidentifier(), so output for ordinary keys is unchanged. Other keys use bracket notation with the key encoded by the existing HTML-safe _to_escaped_json, e.g. feature.properties["Time (UTC)"].
• GeoJsonStyleMapper.get_feature_id() reads that bracket form back with json.loads instead of splitting the expression on ..

Tests

• test_geojson_find_identifier: the two property-key cases asserted the broken dot form. They now expect feature.properties["property-key"]. I added an identifier key (property_key) to cover the dot-notation branch.
• New test_geojson_style_identifier_with_special_characters, parametrized over Time (UTC), @id and osm.id. It renders a styled map, checks the switch(...) expression, and checks the resulting style map.
• All new or changed cases fail on main and pass with this change.
• pytest tests (without selenium/playwright/snapshots): 380 passed. 5 failed, and those same 5 also fail on unmodified main in my environment: three PNG-export tests (ImportError), test_timedynamic_geo_json (geodatasets not installed) and test_icon_invalid_marker_colors (no warning emitted). black --check and ruff check pass on the touched files.

🤖 Generated with Claude Code

[hansthen]

Good catch. I see no problems.