fix(terminal): preserve Pi reading position across synchronized redraws (#234)

Reanchor only uniquely matched content after complete synchronized Pi redraws. Preserve standard clearing and cancel stale anchors on user actions or interrupted updates.

Related to #159.

nebula_app/src/gpui_shell/terminal/view/activity_tests.rs

@@ -14,6 +14,46 @@ fn hook(session: &str, name: &str, sequence: u64) -> AiHookEvent {
     crate::ai_hook::parse_remote_envelope(wire.as_bytes(), Some(42)).unwrap()
 }
 
+#[gpui::test]
+fn pi_redraw_anchor_follows_accepted_hook_and_command_lifecycle(cx: &mut TestAppContext) {
+    use nebula_terminal::term::test::TermSize;
+    use nebula_terminal::vte::ansi::Processor;
+
+    let (view, window, _) = open(cx);
+    view.update(window, |view, cx| {
+        let event = |kind: &str, seq: u64| {
+            crate::ai_hook::parse_remote_envelope(
+                format!("nebula-hook/1 source=pi pane=42\n{{\"kind\":\"{kind}\",\"session_id\":\"redraw-policy\",\"bridge_sequence\":{seq}}}").as_bytes(),
+                Some(42),
+            ).unwrap()
+        };
+        let check = |view: &mut TerminalView, expected: usize| {
+            let mut term = view.session.as_ref().unwrap().term.lock();
+            term.resize(TermSize::new(60, 5));
+            let mut stream = Processor::<nebula_terminal::vte::ansi::StdSyncHandler>::default();
+            let text = (0..12).map(|n| format!("ROW_{n:03}")).collect::<Vec<_>>().join("\r\n");
+            let frame = format!("\x1b[?2026h\x1b[2J\x1b[H\x1b[3J{text}\x1b[?2026l");
+            term.scroll_display(Scroll::Bottom);
+            stream.advance(&mut *term, frame.as_bytes());
+            term.scroll_display(Scroll::Top);
+            term.scroll_display(Scroll::Delta(-2));
+            stream.advance(&mut *term, frame.as_bytes());
+            assert_eq!(term.grid().display_offset(), expected);
+        };
+        check(view, 0);
+        assert!(view.handle_ai_hook(&event("session-start", 1), cx));
+        check(view, 5);
+        assert!(view.handle_ai_hook(&event("done", 2), cx));
+        check(view, 5); // 回合结束不是 Pi 进程退出。
+        assert!(view.handle_ai_hook(&event("session-end", 3), cx));
+        check(view, 0);
+        assert!(view.handle_ai_hook(&event("session-start", 4), cx));
+        check(view, 5);
+        view.finish_foreground_command(Some(0), cx);
+        check(view, 0);
+    });
+}
+
 fn screen(view: &mut TerminalView, text: &str) {
     feed(view, format!("\x1b[2J\x1b[H{}", text.replace('\n', "\r\n")).as_bytes());
 }

nebula_app/src/gpui_shell/terminal/view/agent_activity.rs

@@ -67,6 +67,11 @@ impl TerminalView {
                         | crate::ai_hook::AiTurnOutcome::Incomplete
                 );
         }
+        if let Some(session) = &self.session {
+            session.term.lock().set_redraw_anchor_enabled(
+                event.source == "pi" && event.kind != AiHookKind::SessionEnd,
+            );
+        }
         if let Some(target) = target {
             let previous = self.recovery.target.clone();
             self.recovery.confirm(target);

nebula_app/src/gpui_shell/terminal/view/pointer.rs

@@ -853,6 +853,9 @@ impl TerminalView {
         _window: &mut Window,
         cx: &mut Context<Self>,
     ) {
+        if let Some(session) = &self.session {
+            session.term.lock().cancel_redraw_anchor();
+        }
         let delta_y = event.delta.pixel_delta(self.line_height).y.as_f32();
         // 旧壳 `mouse_wheel_input`：Ctrl+滚轮先于一切滚动消费者，一步 1
         // 逻辑像素，钳在 4–64。设置页步进会写盘；这里同样写 `font_size=`，

nebula_app/src/gpui_shell/terminal/view/runtime.rs

@@ -127,6 +127,9 @@ impl TerminalView {
     /// the primary edge; the cached-prompt path calls the same reset so the two
     /// lifecycle routes cannot drift apart.
     pub(super) fn clear_foreground_agent_state(&mut self, cx: &mut Context<Self>) -> bool {
+        if let Some(session) = &self.session {
+            session.term.lock().set_redraw_anchor_enabled(false);
+        }
         self.confirmation.observe_waiting(false);
         self.recovery.command_ended();
         self.answers.close();