[FIX] website_sale_aplicoop: three defects in the group order slug

- create(): slugs were only checked against the database, so records created
  in the same batch (duplicating several orders from the list view, importing
  rows sharing a name) collided on group_order_slug_uniq. _generate_unique_slug
  now also skips the slugs already handed out in the batch.
- _redirect_to_slug_url(): `post` is passed as a dict instead of splatted, so a
  query parameter named `suffix` no longer binds to the keyword argument of the
  same name (HTTP 500 on /eskaera/<id>/checkout?suffix=x, and a corrupted path
  on the shop route).
- post-migrate: the backfill runs with tracking_disable, `slug` is tracked and
  the upgrade posted a chatter message on every pre-existing order.

Tests for the two reachable cases: batch create and query parameters kept
across the legacy redirect.

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

website_sale_aplicoop/models/group_order.py

@@ -398,14 +398,18 @@ class GroupOrder(models.Model):
             domain.append(("id", "not in", self.ids))
         return bool(self.sudo().search_count(domain, limit=1))
 
-    def _generate_unique_slug(self, name):
-        """Build a free slug out of `name`, adding a counter when needed."""
+    def _generate_unique_slug(self, name, taken=()):
+        """Build a free slug out of `name`, adding a counter when needed.
+
+        `taken` holds the slugs already handed out in the same batch, which are
+        not in the database yet and so are invisible to `_is_slug_taken`.
+        """
         base = self._normalize_slug(name)
         if not base or base.isdigit() or base in RESERVED_SLUGS:
             base = f"{base}-{DEFAULT_SLUG_BASE}" if base else DEFAULT_SLUG_BASE
         candidate = base
         counter = 2
-        while self._is_slug_taken(candidate):
+        while candidate in taken or self._is_slug_taken(candidate):
             candidate = f"{base}-{counter}"
             counter += 1
         return candidate
@@ -413,17 +417,15 @@ class GroupOrder(models.Model):
     @api.model_create_multi
     def create(self, vals_list):
         """Give every consumer group order a slug for its public URL."""
-        vals_list = [
-            dict(
-                vals,
-                slug=(
-                    self._normalize_slug(vals.get("slug"))
-                    or self._generate_unique_slug(vals.get("name"))
-                ),
+        taken = set()
+        new_vals_list = []
+        for vals in vals_list:
+            slug = self._normalize_slug(vals.get("slug")) or self._generate_unique_slug(
+                vals.get("name"), taken=taken
             )
-            for vals in vals_list
-        ]
-        return super().create(vals_list)
+            taken.add(slug)
+            new_vals_list.append(dict(vals, slug=slug))
+        return super().create(new_vals_list)
 
     def write(self, vals):
         """Normalize the slug, regenerating it from the name when emptied."""