Improve MCP safeStringify, OIDC error messages, and catalog model reference config

Signed-off-by: benjdlambert <ben@blam.sh>

plugins/mcp-actions-backend/src/services/McpService.test.ts

@@ -219,7 +219,7 @@ describe('McpService', () => {
         text: JSON.stringify({ output: 'test' }),
       },
     ]);
-    expect((result as any).structuredContent).toEqual({ output: 'test' });
+    expect(result).toHaveProperty('structuredContent', { output: 'test' });
 
     const histogram = mockMetrics.createHistogram.mock.results[0]?.value;
     expect(histogram.record).toHaveBeenCalledTimes(1);

plugins/mcp-actions-backend/src/services/McpService.ts

@@ -37,7 +37,7 @@ import { FilterRule, McpServerConfig } from '../config';
 
 function safeStringify(value: unknown): string {
   try {
-    return JSON.stringify(value);
+    return JSON.stringify(value) ?? String(value);
   } catch {
     return String(value);
   }
@@ -245,7 +245,7 @@ export class McpService {
                 content: [
                   {
                     type: 'text',
-                    text: JSON.stringify(output),
+                    text: safeStringify(output),
                   },
                 ],
                 structuredContent: output,