Respect # hidden tag in line chart channel assignment

Apply the same fix from bar charts to line charts: skip hidden
dimensions during auto channel assignment and embedded tag walking,
so they can be used for order_by without appearing as axes or series.

Author: jswir

packages/malloy-render/src/plugins/line-chart/get-line_chart-settings.ts

@@ -220,6 +220,9 @@ export function getLineChartSettings(
     walkFields(explore, field => {
       const tag = field.tag;
       const pathTo = explore.pathTo(field);
+      // Skip hidden fields unless they have an explicit channel tag
+      const hasChannelTag = tag.has('x') || tag.has('y') || tag.has('series');
+      if (field.isHidden() && !hasChannelTag) return;
       if (tag.has('x')) {
         embeddedX.push(pathTo);
       }
@@ -247,17 +250,19 @@ export function getLineChartSettings(
     });
   }
 
+  // Exclude hidden dimensions from chart channel assignment;
+  // they remain in the data (e.g. for order_by) but aren't rendered.
   const dimensions = explore.fields.filter(
-    f => f.isBasic() && f.wasDimension()
+    f => f.isBasic() && f.wasDimension() && !f.isHidden()
   );
 
   const measures = explore.fields.filter(f => f.wasCalculation());
 
   // If still no x or y, attempt to pick the best choice
   if (xChannel.fields.length === 0) {
-    // Pick date/time field first if it exists
+    // Pick date/time field first if it exists (skip hidden)
     const dateTimeField = explore.fields.find(
-      f => f.wasDimension() && f.isTime()
+      f => f.wasDimension() && f.isTime() && !f.isHidden()
     );
     if (dateTimeField) xChannel.fields.push(explore.pathTo(dateTimeField));
     // Pick first dimension field for x

packages/malloy-render/src/stories/line_charts.stories.malloy

@@ -470,6 +470,18 @@ source: products is duckdb.table("static/data/products.parquet") extend {
       aggregate: `Sales $` is sum(`Sales $`)
       order_by: m
     }
+
+  #(story)
+  # line_chart
+  view: hidden_dimension is {
+    group_by:
+      brand
+      # hidden
+      dcId
+    aggregate: total_sales
+    order_by: dcId
+    limit: 10
+  }
 }
 
 source: missing_data is duckdb.table("static/data/missing_data.csv") extend {