Add SPA session validation and buglist, update migration docs

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

docs/CLAUDE.dist.md

@@ -893,7 +893,7 @@ Details: `php artisan rsx:man model_fetch`
 
 ### Migrations
 
-**Forward-only, no rollbacks.**
+**Forward-only, no rollbacks. Deterministic transformations against known state.**
 
 ```bash
 php artisan make:migration:safe create_users_table
@@ -902,6 +902,19 @@ php artisan migrate
 php artisan migrate:commit
 ```
 
+**NO defensive coding in migrations:**
+```php
+// ❌ WRONG - conditional logic
+$fk_exists = DB::select("SELECT ... FROM information_schema...");
+if (!empty($fk_exists)) { DB::statement("ALTER TABLE foo DROP FOREIGN KEY bar"); }
+
+// ✅ CORRECT - direct statements
+DB::statement("ALTER TABLE foo DROP FOREIGN KEY bar");
+DB::statement("ALTER TABLE foo DROP COLUMN baz");
+```
+
+No `IF EXISTS`, no `information_schema` queries, no fallbacks. Know current state, write exact transformation. Failures fail loud - snapshot rollback exists for recovery.
+
 ---
 
 ## FILE ATTACHMENTS