refactor(agent-loop): simplify message machine

packages/ui/acp/src/index.ts

@@ -1088,7 +1088,7 @@ export function apply(ctx: Context, config: AcpConfig): void {
         // produces an error stop reason).
         const stopReason = await new Promise<StopReason>((resolve, reject) => {
           rec.inflight = { resolve, reject, turn: undefined }
-          rec.agent.send(preparedContent, { contexts: preparedContexts })
+          rec.agent.send(preparedContent, { source: { kind: 'user' }, contexts: preparedContexts })
         })
         return { stopReason }
       },

packages/ui/tui/src/index.ts

@@ -2522,9 +2522,9 @@ export function createTuiChat(
     if (agent.status === 'disposed') {
       appendNotice(`Agent "${agent.id}" is disposed.`, 'error')
     } else if (agent.status === 'running') {
-      agent.steer(content, { contexts })
+      agent.steer(content, { source: { kind: 'user' }, contexts })
     } else {
-      agent.send(content, { contexts })
+      agent.send(content, { source: { kind: 'user' }, contexts })
     }
   }