fix(references): persist chat.history mutations in aiChatHydrated.onAction

The hydrate-mode task uses `hydrateMessages` to read the full message
chain from Postgres on every turn, so any `chat.history.*` mutation
inside `onAction` (undo / rollback / remove / replace) was lost the
moment the next turn started — the in-memory accumulator was
overwritten by a fresh DB read.

Write the mutated chain through with `prisma.chat.update` at the end
of `onAction` so next turn's hydrate sees the pruned/edited state.

Author: ericallam

references/ai-chat/src/trigger/chat.ts

@@ -890,7 +890,7 @@ export const aiChatHydrated = chat
       }),
     ]),
 
-    onAction: async ({ action }) => {
+    onAction: async ({ action, chatId }) => {
       switch (action.type) {
         case "undo":
           // Remove the last user message + assistant response
@@ -912,6 +912,18 @@ export const aiChatHydrated = chat
           });
           break;
       }
+      // Hydrate-mode task: `chat.history.*` mutations live in the
+      // in-memory accumulator for this turn only. The NEXT turn's
+      // `hydrateMessages` reads from Postgres, so any action that
+      // mutates history must also be persisted back to the DB or it'll
+      // be overwritten on the next message. Write the mutated chain
+      // through here.
+      await prisma.chat.update({
+        where: { id: chatId },
+        data: {
+          messages: chat.history.all() as unknown as ChatMessagesForWrite,
+        },
+      });
     },
 
     onChatStart: async ({ chatId, runId, chatAccessToken, clientData, preloaded }) => {