Fix double-wrapped compiler errors emitting spurious file:1:1: prefix (#24316)

Author: Copilot

pkg/parser/import_error.go

@@ -84,6 +84,13 @@ type FormattedParserError struct {
 func (e *FormattedParserError) Error() string { return e.formatted }
 func (e *FormattedParserError) Unwrap() error { return e.cause }
 
+// NewFormattedParserError creates a FormattedParserError with the given pre-formatted
+// message string. Use this in external packages (e.g. pkg/workflow) to return an error
+// that isFormattedCompilerError can detect without double-wrapping.
+func NewFormattedParserError(formatted string) *FormattedParserError {
+	return &FormattedParserError{formatted: formatted}
+}
+
 // FormatImportError formats an import error as a compilation error with source location
 func FormatImportError(err *ImportError, yamlContent string) error {
 	importErrorLog.Printf("Formatting import error: path=%s, file=%s, line=%d", err.ImportPath, err.FilePath, err.Line)

pkg/parser/schema_compiler.go

@@ -354,7 +354,7 @@ func validateWithSchemaAndLocation(frontmatter map[string]any, schemaJSON, conte
 
 				// Format and return the error
 				formattedErr := console.FormatError(compilerErr)
-				return errors.New(formattedErr)
+				return &FormattedParserError{formatted: formattedErr}
 			}
 		}
 
@@ -382,7 +382,7 @@ func validateWithSchemaAndLocation(frontmatter map[string]any, schemaJSON, conte
 
 		// Format and return the error
 		formattedErr := console.FormatError(compilerErr)
-		return errors.New(formattedErr)
+		return &FormattedParserError{formatted: formattedErr}
 	}
 
 	// Fallback to the original error if we can't format it nicely

pkg/workflow/compiler_error_formatter_test.go

@@ -45,6 +45,11 @@ func TestIsFormattedCompilerError(t *testing.T) {
 			}, "imports:\n  - missing.md"),
 			expected: true,
 		},
+		{
+			name:     "error from parser.NewFormattedParserError is detected as formatted",
+			err:      parser.NewFormattedParserError("workflow.md:5:3: error: bad value"),
+			expected: true,
+		},
 		{
 			name:     "plain error is not formatted",
 			err:      errors.New("plain error"),

pkg/workflow/frontmatter_error.go

@@ -73,11 +73,11 @@ func (c *Compiler) createFrontmatterError(filePath, content string, err error, f
 				context := errorStr[loc[0]+1:] // +1 to skip the leading newline
 				// Return VSCode-compatible format on first line, followed by source context only
 				frontmatterErrorLog.Print("Formatting error for VSCode compatibility")
-				return fmt.Errorf("%s\n%s", vscodeFormat, context)
+				return parser.NewFormattedParserError(fmt.Sprintf("%s\n%s", vscodeFormat, context))
 			}
 
 			// If we can't extract source context, return just the VSCode format
-			return fmt.Errorf("%s", vscodeFormat)
+			return parser.NewFormattedParserError(vscodeFormat)
 		}
 
 		// Fallback if we can't parse the line/col