feat: add optional messageID to ShellInput (#20657)

packages/opencode/src/session/prompt.ts

@@ -756,7 +756,7 @@ NOTE: At any point in time through this workflow you should feel free to ask the
         }
         const model = input.model ?? agent.model ?? (yield* lastModel(input.sessionID))
         const userMsg: MessageV2.User = {
-          id: MessageID.ascending(),
+          id: input.messageID ?? MessageID.ascending(),
           sessionID: input.sessionID,
           time: { created: Date.now() },
           role: "user",
@@ -1827,6 +1827,7 @@ NOTE: At any point in time through this workflow you should feel free to ask the
 
   export const ShellInput = z.object({
     sessionID: SessionID.zod,
+    messageID: MessageID.zod.optional(),
     agent: z.string(),
     model: z
       .object({