fix: correct custom_properties lifecycle in github_repository

- include custom_properties in create request body to satisfy org-required
  property enforcement at creation time
- read custom_properties via dedicated GetAllCustomPropertyValues endpoint
  instead of repo.CustomProperties (which GET /repos never populates)
- handle partial and full removal in update via CreateOrUpdateCustomProperties
  with null values; removing the block entirely leaves existing values intact
  (Optional+Computed behavior)

Author: faradayfan

github/resource_github_repository.go

@@ -925,8 +925,15 @@ func resourceGithubRepositoryRead(ctx context.Context, d *schema.ResourceData, m
 		}
 	}
 
-	if len(repo.CustomProperties) > 0 {
-		if err := d.Set("custom_properties", repo.CustomProperties); err != nil {
+	customPropertyValues, _, err := client.Repositories.GetAllCustomPropertyValues(ctx, owner, repoName)
+	if err == nil {
+		customProps := make(map[string]string, len(customPropertyValues))
+		for _, v := range customPropertyValues {
+			if strVal, ok := v.Value.(string); ok {
+				customProps[v.PropertyName] = strVal
+			}
+		}
+		if err := d.Set("custom_properties", customProps); err != nil {
 			return diag.Errorf("error setting custom_properties: %s", err.Error())
 		}
 	}
@@ -979,6 +986,30 @@ func resourceGithubRepositoryUpdate(ctx context.Context, d *schema.ResourceData,
 	}
 	d.SetId(repo.GetName()) // It's possible that `repo.GetName()` is different from `repoName` if the repository is renamed
 
+	if d.HasChange("custom_properties") {
+		newProps := d.Get("custom_properties").(map[string]interface{})
+		if len(newProps) > 0 {
+			if err := setRepositoryCustomProperties(ctx, client, owner, repoName, newProps); err != nil {
+				return diag.FromErr(err)
+			}
+		} else {
+			// custom_properties was removed from config — clear any previously set values
+			oldRaw, _ := d.GetChange("custom_properties")
+			if oldProps, ok := oldRaw.(map[string]interface{}); ok && len(oldProps) > 0 {
+				clearValues := make([]*github.CustomPropertyValue, 0, len(oldProps))
+				for k := range oldProps {
+					clearValues = append(clearValues, &github.CustomPropertyValue{
+						PropertyName: k,
+						Value:        nil,
+					})
+				}
+				if _, err := client.Repositories.CreateOrUpdateCustomProperties(ctx, owner, repoName, clearValues); err != nil {
+					return diag.FromErr(err)
+				}
+			}
+		}
+	}
+
 	if d.HasChange("pages") && !d.IsNewResource() {
 		opts := expandPagesUpdate(d.Get("pages").([]any))
 		if opts != nil {
@@ -1139,6 +1170,18 @@ func expandPagesUpdate(input []any) *github.PagesUpdate {
 	return update
 }
 
+func setRepositoryCustomProperties(ctx context.Context, client *github.Client, owner, repoName string, props map[string]any) error {
+	customPropertyValues := make([]*github.CustomPropertyValue, 0, len(props))
+	for k, v := range props {
+		customPropertyValues = append(customPropertyValues, &github.CustomPropertyValue{
+			PropertyName: k,
+			Value:        v,
+		})
+	}
+	_, err := client.Repositories.CreateOrUpdateCustomProperties(ctx, owner, repoName, customPropertyValues)
+	return err
+}
+
 func flattenPages(pages *github.Pages) []any {
 	if pages == nil {
 		return []any{}