fix(bot): roll back inserted bot row when adapter fails to load (#2497)

create_bot inserts the Bot row first and only then instantiates the
adapter via platform_mgr.load_bot. When the adapter constructor raises
(e.g. KeyError on a missing credential key), the insert is already
committed and nothing removes the row: the HTTP layer returns 500 but
a permanently disabled orphan bot stays in the DB. Callers never
receive the bot uuid, so they cannot compensate by deleting it, and
load_bots_from_db skips enable=False bots, so the orphan is never
loaded or surfaced anywhere.

Wrap load_bot in try/except and delete the inserted row before
re-raising. Add a regression test asserting the DELETE is issued when
the adapter constructor fails.

src/langbot/pkg/api/http/service/bot.py

@@ -137,7 +137,16 @@ class BotService:
 
         bot = await self.get_bot(context, bot_data['uuid'], include_secret=True)
 
-        await self.ap.platform_mgr.load_bot(context, bot)
+        try:
+            await self.ap.platform_mgr.load_bot(context, bot)
+        except Exception:
+            # The bot row was already inserted above; without this rollback a
+            # failing adapter constructor (e.g. a missing optional credential
+            # key) would leave a permanently disabled orphan bot in the DB.
+            await self.ap.persistence_mgr.execute_async(
+                sqlalchemy.delete(persistence_bot.Bot).where(persistence_bot.Bot.uuid == bot_data['uuid'])
+            )
+            raise
 
         return bot_data['uuid']