config-loader,cli: better presentation of config schema validation errors

packages/config-loader/src/lib/schema/compile.ts

@@ -104,10 +104,14 @@ export function compileConfigSchemas(
 
     const valid = validate(config);
     if (!valid) {
-      // TODO(Rugvip): better messages here, with more context such as which file the error occurred in
-      const errors = ajv.errorsText(validate.errors);
+      const errors = validate.errors ?? [];
       return {
-        errors: [errors],
+        errors: errors.map(({ dataPath, message, params }) => {
+          const paramStr = Object.entries(params)
+            .map(([name, value]) => `${name}=${value}`)
+            .join(' ');
+          return `Config ${message || ''} { ${paramStr} } at ${dataPath}`;
+        }),
         visibilityByPath: new Map(),
       };
     }

packages/config-loader/src/lib/schema/load.ts

@@ -61,9 +61,11 @@ export async function loadConfigSchema(
     ): AppConfig[] {
       const result = validate(configs);
       if (result.errors) {
-        throw new Error(
+        const error = new Error(
           `Config validation failed, ${result.errors.join('; ')}`,
         );
+        (error as any).messages = result.errors;
+        throw error;
       }
 
       let processedConfigs = configs;