feat(presenter): M103 AI 助手栏视图模型与事件投影

- 新增 crates/presenter/src/agent.rs（Presenter 门面：agent_rail / agent_submit /
  agent_mark_read / agent_confirm + AgentTransport 端口 + 裁决审计镜像）
- 新增 agent/rail.rs：AgentRail（messages / unread / busy / draft / confirm / streaming /
  yolo / endpoint_label / error），四类 AgentEvent 的投影与唯一脱敏闸门
- 新增 agent/mock.rs：脚本化后端（正常问答 / 流式中途出错 / 需确认的写操作）
- dto/agent.rs：ConfirmRequest / Sensitivity + AgentEvent::{Failed, ConfirmRequested,
  ConfirmResolved}；AgentEvent 去掉 Eq（details 含 serde_json::Value）
- state.rs：AiSession 迁成 AgentRail，apply_agent 走 rail.ingest + 未读规则（可见性 =
  独立页或栏展开）；navigate/toggle_ai 展开时清未读
- 测试：agent/tests.rs 14 条（四条路径 + JWT 红线 + YOLO 语义 + 提交前置条件），
  state_tests.rs 补 4 条（Failed / ConfirmRequested / 未读可见性 / 用户消息不计未读）
- 两行声明补进 lib.rs（pub mod agent）与 dto/mod.rs（重导出 ConfirmRequest/Sensitivity）

crates/presenter/src/state_tests.rs

@@ -1,6 +1,7 @@
 //! state.rs 的单元测试（拆文件保持单文件 ≤400 行）。
 
-use super::{grid_positions, AiSession, AppState};
+use super::{grid_positions, AppState};
+use crate::agent::AgentRail;
 use crate::dialogs::{DialogKind, DialogRequest, DialogSource};
 use crate::dto::{
     AgentEvent, AppEvent, ChatMessage, ChatRole, CoreEvent, Diagnosis, DiagnosisReport,
@@ -159,12 +160,13 @@ fn ai_stream_deltas_accumulate_and_finish() {
 
 #[test]
 fn ai_session_finish_stream_clears_every_flag() {
-    let mut session = AiSession::new();
+    let mut session = AgentRail::new();
     session.messages.push(ChatMessage::user("hi"));
     session.messages.push(ChatMessage::assistant_stream());
     session.finish_stream();
     assert!(session.messages.iter().all(|message| !message.streaming));
     assert!(!session.streaming);
+    assert!(!session.busy);
 }
 
 #[test]
@@ -239,6 +241,107 @@ fn toggling_ai_from_the_page_form_docks_it_again() {
     assert!(state.prefs.ai_collapsed);
 }
 
+#[test]
+fn failed_event_settles_streaming_and_keeps_the_evidence() {
+    let mut state = AppState::new();
+    state.apply(AppEvent::Agent(AgentEvent::MessageAppended(
+        ChatMessage::assistant_stream(),
+    )));
+    state.apply(AppEvent::Agent(AgentEvent::MessageDelta {
+        index: 0,
+        delta: "我先读一下".to_string(),
+    }));
+    state.apply(AppEvent::Agent(AgentEvent::Failed {
+        message: "provider 断流：read timeout".to_string(),
+    }));
+
+    // 抓得住：已到的增量不丢、流式标记收敛、错误进横幅也进会话历史
+    assert_eq!(state.ai.messages[0].text, "我先读一下");
+    assert!(!state.ai.messages[0].streaming);
+    assert!(!state.ai.streaming);
+    assert!(!state.ai.busy);
+    assert_eq!(
+        state.ai.error.as_deref(),
+        Some("provider 断流：read timeout")
+    );
+    assert_eq!(state.ai.messages[1].role, ChatRole::System);
+    // 抓不住：这里不判断错误归因（那是 core::diagnose 的事）
+}
+
+#[test]
+fn confirm_request_keeps_the_shell_busy_until_it_resolves() {
+    let mut state = AppState::new();
+    state.apply(AppEvent::Agent(AgentEvent::ConfirmRequested {
+        request: confirm_request("req-1"),
+    }));
+    assert!(state.ai.busy, "有待确认时 UI 必须禁用输入");
+    assert_eq!(
+        state.ai.confirm.as_ref().map(|request| request.id.as_str()),
+        Some("req-1")
+    );
+
+    // 别处已裁决（重放/超时）：僵尸弹窗必须收掉
+    state.apply(AppEvent::Agent(AgentEvent::ConfirmResolved {
+        id: "req-1".to_string(),
+    }));
+    assert!(!state.ai.busy);
+    assert!(state.ai.confirm.is_none());
+}
+
+#[test]
+fn unread_counts_only_while_the_rail_is_out_of_sight() {
+    let mut state = AppState::new();
+    // 展开的常驻栏在任何页面都挂着：到达即已读
+    assert!(state.agent_rail_visible());
+    state.apply(AppEvent::Agent(AgentEvent::MessageAppended(
+        ChatMessage::assistant_stream(),
+    )));
+    assert_eq!(state.ai.unread, 0);
+
+    // 收成 icon 轨 = 用户看不见
+    state.prefs.ai_collapsed = true;
+    assert!(!state.agent_rail_visible());
+    state.apply(AppEvent::Agent(AgentEvent::MessageDelta {
+        index: 0,
+        delta: "长回复".to_string(),
+    }));
+    assert_eq!(state.ai.unread, 0, "增量属于同一条消息，不重复计数");
+    state.apply(AppEvent::Agent(AgentEvent::ToolCallStarted {
+        name: "read_game_log".to_string(),
+        summary: "读取日志".to_string(),
+    }));
+    assert_eq!(state.ai.unread, 1);
+
+    // 展开栏 = 用户在看它，未读立刻归零
+    state.toggle_ai();
+    assert_eq!(state.ai.unread, 0);
+
+    // 独立页形态永远算可见
+    state.navigate(Route::Agent);
+    assert!(state.agent_rail_visible());
+}
+
+#[test]
+fn user_messages_never_count_as_unread() {
+    let mut state = AppState::new();
+    state.prefs.ai_collapsed = true;
+    state.apply(AppEvent::Agent(AgentEvent::MessageAppended(
+        ChatMessage::user("我自己说的话"),
+    )));
+    assert_eq!(state.ai.unread, 0);
+}
+
+/// 待确认请求样例（High 级写操作）。
+fn confirm_request(id: &str) -> crate::dto::ConfirmRequest {
+    crate::dto::ConfirmRequest {
+        id: id.to_string(),
+        tool: "set_config".to_string(),
+        summary: "把下载并发 64 → 16".to_string(),
+        details: serde_json::json!({ "path": "download.concurrency" }),
+        sensitivity: crate::dto::Sensitivity::High,
+    }
+}
+
 #[test]
 fn toggle_nav_flips_the_pref() {
     let mut state = AppState::new();