fix: Retry sends message with retry flag to avoid duplicate storage

Added retry:true flag to sendChatMessage input. Server skips storing
the user message when retry is set. Frontend uses a dedicated
retryLastMessage function that skips the optimistic message add.

apps/server/trpc/routers/chat-session.ts

@@ -26,6 +26,7 @@ export function chatSessionProcedures(publicProcedure: ProcedureBuilder) {
         targetId: z.string().min(1),
         initiativeId: z.string().min(1),
         message: z.string().min(1),
+        retry: z.boolean().optional(),
         provider: z.string().optional(),
       }))
       .mutation(async ({ ctx, input }) => {
@@ -49,18 +50,20 @@ export function chatSessionProcedures(publicProcedure: ProcedureBuilder) {
           });
         }
 
-        // Store user message
-        await chatRepo.createMessage({
-          chatSessionId: session.id,
-          role: 'user',
-          content: input.message,
-        });
+        // Store user message (skip on retry — message already exists)
+        if (!input.retry) {
+          await chatRepo.createMessage({
+            chatSessionId: session.id,
+            role: 'user',
+            content: input.message,
+          });
 
-        ctx.eventBus.emit({
-          type: 'chat:message_created' as const,
-          timestamp: new Date(),
-          payload: { chatSessionId: session.id, role: 'user' as const },
-        });
+          ctx.eventBus.emit({
+            type: 'chat:message_created' as const,
+            timestamp: new Date(),
+            payload: { chatSessionId: session.id, role: 'user' as const },
+          });
+        }
 
         // Check if agent exists and is waiting for input
         if (session.agentId) {