test(tools): add unit tests for error handling functions

* Implement tests for error functions like errRequiredField, errInvalidField, and errEntityNotFound.
* Ensure proper metadata is returned for various error scenarios.
* Validate error handling in CRM, Files, and other tools.
* Introduce tests for parsing stored file IDs and UUIDs.
* Enhance coverage for helper functions related to project resolution and session management.

internal/tools/files_test.go

@@ -1,6 +1,10 @@
 package tools
 
-import "testing"
+import (
+	"testing"
+
+	"github.com/google/uuid"
+)
 
 func TestDecodeBase64AcceptsWhitespaceAndMultipleVariants(t *testing.T) {
 	tests := []struct {
@@ -27,3 +31,45 @@ func TestDecodeBase64AcceptsWhitespaceAndMultipleVariants(t *testing.T) {
 		})
 	}
 }
+
+func TestParseStoredFileIDAcceptsUUIDAndURI(t *testing.T) {
+	id := uuid.New()
+
+	tests := []struct {
+		name  string
+		input string
+		want  uuid.UUID
+	}{
+		{name: "bare uuid", input: id.String(), want: id},
+		{name: "resource uri", input: fileURIPrefix + id.String(), want: id},
+		{name: "resource uri with surrounding whitespace", input: "  " + fileURIPrefix + id.String() + "  ", want: id},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := parseStoredFileID(tc.input)
+			if err != nil {
+				t.Fatalf("parseStoredFileID(%q) error = %v", tc.input, err)
+			}
+			if got != tc.want {
+				t.Fatalf("parseStoredFileID(%q) = %v, want %v", tc.input, got, tc.want)
+			}
+		})
+	}
+}
+
+func TestParseStoredFileIDRejectsInvalidValues(t *testing.T) {
+	tests := []string{
+		"",
+		"not-a-uuid",
+		fileURIPrefix + "not-a-uuid",
+	}
+
+	for _, input := range tests {
+		t.Run(input, func(t *testing.T) {
+			if _, err := parseStoredFileID(input); err == nil {
+				t.Fatalf("parseStoredFileID(%q) = nil error, want error", input)
+			}
+		})
+	}
+}