fix(ui): suppress null suggestion + prevent mid-edit corruption

- Don't show value suggestions (like "null") at property key positions
- Only apply comma fix + reformat when result is valid JSON
- Prevents corruption when user is mid-edit inside a string value

Author: lan17

ui/src/core/page-components/agent-detail/modals/edit-control/json-editor-language.ts

@@ -1193,20 +1193,25 @@ function buildCompletionSuggestions(
     );
   }
 
-  const valueSchemaCursor = resolveSchemaAtJsonPath(
-    context,
-    activeEvaluator,
-    location.path
-  );
+  // Only show value suggestions when NOT at a property key position.
+  // At key positions, property suggestions are sufficient — value suggestions
+  // like "null" are confusing noise.
+  if (!propertyKeyContext) {
+    const valueSchemaCursor = resolveSchemaAtJsonPath(
+      context,
+      activeEvaluator,
+      location.path
+    );
 
-  suggestions.push(
-    ...buildSchemaValueSuggestions(
-      monaco,
-      valueRange,
-      valueSchemaCursor,
-      isStringValueContext
-    )
-  );
+    suggestions.push(
+      ...buildSchemaValueSuggestions(
+        monaco,
+        valueRange,
+        valueSchemaCursor,
+        isStringValueContext
+      )
+    );
+  }
 
   return dedupeSuggestions(suggestions);
 }

ui/src/core/page-components/agent-detail/modals/edit-control/json-editor-view.tsx

@@ -323,6 +323,8 @@ export const JsonEditorView = ({
         const current = editor.getValue();
         const commaFixed = fixJsonCommas(current);
 
+        // Only apply changes if the result is valid JSON.
+        // Don't touch broken JSON mid-edit — comma insertion can corrupt it.
         try {
           const formatted = JSON.stringify(JSON.parse(commaFixed), null, 2);
           if (formatted !== current) {
@@ -331,11 +333,7 @@ export const JsonEditorView = ({
             handleJsonChange(formatted);
           }
         } catch {
-          if (commaFixed !== current) {
-            isProgrammaticEdit = true;
-            replaceAllContent(editor, commaFixed, 'auto-comma-fix');
-            handleJsonChange(commaFixed);
-          }
+          // JSON is invalid — leave it alone, user is still editing
         }
       }, COMMA_FIX_DEBOUNCE_MS);