fix: preserve fork parent linkage on workspace id change (#9716)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/windmill-api-workspaces/src/workspaces_extra.rs

@@ -65,13 +65,22 @@ pub(crate) async fn change_workspace_id(
         old_id, rw.new_id
     );
 
-    // Create new workspace with new id and name
+    // Create new workspace with new id and name. A fork that keeps a wm-fork-
+    // id must carry its parent_workspace_id over, otherwise it becomes a
+    // parentless "fork of nothing" with no source to compare or merge against.
+    // A non-fork target id means the workspace is being promoted out of a fork,
+    // so the parent pointer is intentionally cleared.
     info!("Creating new workspace row");
+    let new_is_fork = rw.new_id.starts_with(WM_FORK_PREFIX);
     sqlx::query!(
-        "INSERT INTO workspace SELECT $1, $2, owner, false, premium FROM workspace WHERE id = $3",
+        "INSERT INTO workspace (id, name, owner, deleted, premium, parent_workspace_id)
+         SELECT $1, $2, owner, false, premium,
+                CASE WHEN $4 THEN parent_workspace_id ELSE NULL END
+         FROM workspace WHERE id = $3",
         &rw.new_id,
         &rw.new_name,
-        &old_id
+        &old_id,
+        new_is_fork
     )
     .execute(&mut *tx)
     .await?;
@@ -347,6 +356,18 @@ pub(crate) async fn change_workspace_id(
     .execute(&mut *tx)
     .await?;
 
+    // Re-parent child forks: any fork whose parent_workspace_id was the old id
+    // must follow the renamed parent to the new id, otherwise it is left
+    // pointing at the soft-deleted old shell (whose data has moved here).
+    info!("Re-parenting child forks to the new workspace id");
+    sqlx::query!(
+        "UPDATE workspace SET parent_workspace_id = $1 WHERE parent_workspace_id = $2",
+        &rw.new_id,
+        &old_id
+    )
+    .execute(&mut *tx)
+    .await?;
+
     info!("Updating workspace_protection_rule table");
     sqlx::query!(
         "UPDATE workspace_protection_rule SET workspace_id = $1 WHERE workspace_id = $2",