docs: add proposal for HostedSite → Store cascade delete

Deleting a HostedSite leaves the Store orphaned, blocking subdomain
reuse. Proposal: cascade delete the Store when deleting the site.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/proposals/hosting-cascade-delete.md

@@ -0,0 +1,48 @@
+# Hosting: Cascade Delete HostedSite → Store
+
+## Problem
+
+Deleting a HostedSite leaves the associated Store orphaned in the database. The Store's subdomain remains taken, so creating a new site with the same prospect/business fails with "slug already exists".
+
+## Root Cause
+
+- `hosted_site_service.delete()` does a hard delete on the HostedSite only
+- The Store (created by `hosted_site_service.create()`) is not deleted
+- `stores.subdomain` has a partial unique index (`WHERE deleted_at IS NULL`)
+- The orphaned Store is still active → subdomain collision on re-create
+
+## Recommendation
+
+When deleting a HostedSite, also delete the associated Store:
+
+```python
+def delete(self, db: Session, site_id: int) -> bool:
+    site = self.get_by_id(db, site_id)
+    store = site.store
+    db.delete(site)
+    if store:
+        # Soft-delete or hard-delete the store created for this site
+        soft_delete(store)  # or db.delete(store)
+    db.flush()
+```
+
+### Considerations
+
+- **Soft vs hard delete**: If using soft-delete, the subdomain gets freed (partial unique index filters `deleted_at IS NULL`). If hard-deleting, cascade will also remove StorePlatform, ContentPages, StoreTheme, etc.
+- **CMS content**: Deleting the Store cascades to ContentPages (created by POC builder) — this is desired since the POC content belongs to that store
+- **Merchant**: The merchant created from the prospect should NOT be deleted — it may be used by other stores or relinked later
+- **Safety**: Only delete stores that were created by the hosting module (check if store has a HostedSite backref). Don't delete stores that existed independently.
+
+## Files to modify
+
+| File | Change |
+|---|---|
+| `hosting/services/hosted_site_service.py` | Update `delete()` to also soft-delete/hard-delete the associated Store |
+| `hosting/tests/unit/test_hosted_site_service.py` | Update delete test to verify Store is also deleted |
+
+## Quick workaround (for now)
+
+Manually delete the orphaned store from the DB:
+```sql
+DELETE FROM stores WHERE subdomain = 'batirenovation-strasbourg' AND id NOT IN (SELECT store_id FROM hosted_sites);
+```