dedup folder labels to prevent each_key_duplicate crash (#9565)

Folder labels are exposed verbatim as `inherited_labels` (via the
`folder_labels` SQL function) and rendered in keyed `{#each}` blocks that
throw Svelte's `each_key_duplicate` on a repeated key, crashing the list
views. The UI dedups labels on entry, but API / CLI / git-sync writes do
not, so a folder.yaml with `labels: [foo, foo]` persists duplicates.

- Dedup on write in create_folder and update_folder (order-preserving).
- Make folder_labels() dedup on read so it is resilient regardless of how a
  row was populated, plus a one-time cleanup of already-persisted duplicates
  so direct folder.labels reads (folder list, editor) are safe too.

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

backend/migrations/20260614075900_dedup_folder_labels.down.sql

@@ -0,0 +1,6 @@
+-- Restore the original passthrough definition (the one-time data cleanup is not reverted).
+CREATE OR REPLACE FUNCTION folder_labels(w_id text, item_path text) RETURNS text[]
+LANGUAGE sql STABLE SECURITY DEFINER SET search_path = public AS $$
+    SELECT labels FROM folder
+    WHERE workspace_id = w_id AND item_path LIKE 'f/%' AND name = split_part(item_path, '/', 2)
+$$;

backend/migrations/20260614075900_dedup_folder_labels.up.sql

@@ -0,0 +1,33 @@
+-- Folder labels are exposed verbatim as `inherited_labels` (via folder_labels) and
+-- rendered in keyed `{#each}` blocks in the UI, which throw `each_key_duplicate` on a
+-- repeated key. The write paths now dedup, but make the read resilient regardless of
+-- how a row was populated, and clean up any duplicates already persisted.
+
+-- Dedup while preserving first-seen order.
+CREATE OR REPLACE FUNCTION folder_labels(w_id text, item_path text) RETURNS text[]
+LANGUAGE sql STABLE SECURITY DEFINER SET search_path = public AS $$
+    SELECT (
+        SELECT array_agg(l ORDER BY first_ord)
+        FROM (
+            SELECT u.l, min(u.ord) AS first_ord
+            FROM unnest(f.labels) WITH ORDINALITY AS u(l, ord)
+            GROUP BY u.l
+        ) deduped
+    )
+    FROM folder f
+    WHERE f.workspace_id = w_id AND item_path LIKE 'f/%' AND f.name = split_part(item_path, '/', 2)
+$$;
+
+-- One-time cleanup of rows that already contain duplicate labels, so direct reads of
+-- folder.labels (folder list, editor) are also safe.
+UPDATE folder
+SET labels = (
+    SELECT array_agg(l ORDER BY first_ord)
+    FROM (
+        SELECT u.l, min(u.ord) AS first_ord
+        FROM unnest(labels) WITH ORDINALITY AS u(l, ord)
+        GROUP BY u.l
+    ) deduped
+)
+WHERE labels IS NOT NULL
+  AND cardinality(labels) <> (SELECT count(DISTINCT x) FROM unnest(labels) AS x);

backend/windmill-api-groups/src/folders.rs

@@ -86,6 +86,14 @@ pub struct UpdateFolder {
     pub labels: Option<Vec<String>>,
 }
 
+// Folder labels are surfaced verbatim as `inherited_labels` and rendered in keyed
+// `{#each}` blocks; a repeated label is a duplicate key that crashes the list views.
+// The UI dedups on entry but API/CLI/git-sync writes do not, so normalize on write.
+fn dedup_labels(labels: &mut Vec<String>) {
+    let mut seen = std::collections::HashSet::new();
+    labels.retain(|l| seen.insert(l.clone()));
+}
+
 #[derive(Deserialize)]
 pub struct Owner {
     pub owner: String,
@@ -226,8 +234,11 @@ async fn create_folder(
     Extension(webhook): Extension<WebhookShared>,
     Extension(cache): Extension<Arc<AuthCache>>,
     Path(w_id): Path<String>,
-    Json(ng): Json<NewFolder>,
+    Json(mut ng): Json<NewFolder>,
 ) -> Result<String> {
+    if let Some(labels) = ng.labels.as_mut() {
+        dedup_labels(labels);
+    }
     if let RuleCheckResult::Blocked(msg) = check_deploy_rules(
         &w_id,
         AuditAuthorable::username(&authed),
@@ -471,7 +482,8 @@ async fn update_folder(
         );
     }
 
-    if let Some(labels) = ng.labels.as_ref() {
+    if let Some(labels) = ng.labels.as_mut() {
+        dedup_labels(labels);
         if labels.is_empty() {
             // normalize cleared labels to NULL so the field stays out of API/tarball output
             sqlb.set("labels", "NULL");