fix(cli): handle empty YAML prompts

src/prompts/processors/yaml.ts

@@ -27,8 +27,9 @@ export function processYamlFile(filePath: string, prompt: Partial<Prompt>): Prom
     // Recursively resolve any file:// references in the parsed structure
     const resolved = maybeLoadConfigFromExternalFile(parsed);
 
-    // Convert back to JSON string
-    maybeParsed = JSON.stringify(resolved);
+    // Convert back to JSON while preserving the raw contents of empty YAML documents.
+    // JSON.stringify(undefined) returns undefined, but Prompt.raw must always be a string.
+    maybeParsed = JSON.stringify(resolved) ?? fileContents;
   } catch (e) {
     logger.debug(`Error parsing YAML file ${filePath}: ${e}`);
   }

test/prompts/processors/yaml.test.ts

@@ -277,9 +277,8 @@ template: "{{ variable }}   "
       const result = processYamlFile(filePath, {});
 
       expect(result).toHaveLength(1);
-      // Empty YAML parses to undefined; maybeLoadConfigFromExternalFile passes it
-      // through; JSON.stringify(undefined) is the literal string "undefined".
-      expect(result[0].raw).toBe(JSON.stringify(undefined));
+      expect(result[0].raw).toBe('');
+      expect(result[0].label).toBe(`${filePath}: `);
     });
   });
 });