fix(catalog): drill P4 VIN group nodes on live click (Ford/Nissan/Opel parent-gate gap)

getCategoryWithPartsInner had parent gates for PSA (psa::/json-vin-main-groups),
pcat (hasSubgroups), pl24 link_wid *Group* tables, Volvo (vin-group.action) and
emex — but P4 VIN/legacy group nodes whose link_wid is a positional code
("1","2","CAP1"…) and whose path is a *…group.action* drill (Ford
json-vin-sub-group, Nissan/Opel json-sub-group, etc.) matched none of them. They
fell through to the leaf parts path, fetched no parts and rendered a silent empty
panel — the dominant current '0 parça' cluster (mekanik/kaporta/Elektrikli aksam…
across many vehicles; PostHog-confirmed). Add a gate that drills any pl24
…group.action node (excluding Volvo's own vin-group.action branch) → subgroups or
retryable loadError. Lazy-heals existing flag-less rows, no reseed.

Also set has_subgroups at seed time: PSA scopes → true (always parents);
P4-legacy cats → true when linkPath is a …group.action drill. Fixes folder
signposting + lets prefetch pre-drill them instead of treating them as leaves.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/api/src/categories/categories.service.ts

@@ -120,6 +120,10 @@ export class CategoriesService {
               externalId: s.code,
               linkPath: s.linkPath || null,
               linkWid: null as string | null,
+              // PSA scopes are always parents (they hold main-groups, never direct
+              // parts) — flag them so the tree UI signposts them as folders and the
+              // prefetch worker pre-drills them instead of treating them as leaves.
+              hasSubgroups: true,
               source: "pl24" as const,
             }));
             dbCategories = await this.db
@@ -181,6 +185,10 @@ export class CategoriesService {
               externalId: c.code,
               linkPath: c.linkPath || null,
               linkWid: c.linkWid || null,
+              // Mark P4 VIN/legacy group-drill nodes (…group.action) as parents so
+              // the tree UI shows them as folders and prefetch pre-drills them. Leaf
+              // pages (image-board.action/bom) stay null (unknown→leaf downstream).
+              hasSubgroups: c.linkPath?.includes("group.action") ? true : null,
               source: "pl24" as const,
             }));
 
@@ -1123,6 +1131,39 @@ export class CategoriesService {
       // No subgroups → leaf; fall through to the parts path below.
     }
 
+    // PL24 P4 VIN / legacy group node whose link_wid is a positional code
+    // ("1","2","CAP1"…) rather than a *Group* table, so the link_wid branch above
+    // misses it, and which is neither PSA- nor Volvo-special. Its linkPath is a
+    // sub-group / main-group drill action (…group.action — never a parts leaf like
+    // image-board.action). This is the Ford / Nissan / Opel / Hyundai-Kia analog of
+    // the PSA-parent-gate gap: without it these VIN scopes ("mekanik", "kaporta",
+    // "Elektrikli aksam"…) fell through every parent branch to the leaf parts path,
+    // fetched no parts and rendered a silent empty panel — confirmed the dominant
+    // current "0 parça" cluster. Volvo's vin-group.action keeps its own branch above
+    // (it may legitimately bottom out in parts), so exclude it here. Drill on demand:
+    // subgroups → parent; an empty drill is a transient upstream failure → retryable
+    // load error (a group node is never legitimately a parts leaf).
+    if (
+      category.source === "pl24" &&
+      category.linkPath?.includes("group.action") &&
+      !category.linkPath.includes("vin-group.action") &&
+      category.vehicleId
+    ) {
+      const p4Children = await this.getChildren(categoryId);
+      const base = {
+        id: category.id,
+        name: category.name,
+        description: category.nameOriginal || null,
+        parentId: category.parentId || null,
+        parts: [],
+        schemaPics: [],
+        hotspots: [],
+      };
+      return p4Children.length > 0
+        ? { ...base, children: p4Children }
+        : { ...base, loadError: true };
+    }
+
     // EMEX Vehicle.aspx group node (linkWid="emex-group") — a parent, never a
     // parts leaf. Return its children (seeded sub-groups, or Unit leaves drilled
     // on demand by getChildren). Mirrors the pl24 group-node branch above; an