perf(ui-gpui): isolate StatusDotView entity, document 3% CPU floor

Root cause analysis:
- 0% baseline: calloop 60Hz polling has zero measurable CPU cost
- 3% is entirely from ProjectBox::render() rebuilding ~30 header divs
  × 2 boxes × 2/sec = 120 div constructions/sec
- AgentPane + TerminalView cached (into_cached_flex) = 0% contribution
- mark_view_dirty() walks ancestors unconditionally in GPUI 0.2.2
  → StatusDotView isolation doesn't prevent parent re-render
- Fragment shaders not exposed (paint_quad accepts static color only)
- GPUI AnimationElement uses request_animation_frame = 79% CPU (vsync)

StatusDotView pattern is architecturally correct for future GPUI versions
that may implement per-view dirty isolation.

ui-gpui/src/components/blink_state.rs

@@ -6,12 +6,48 @@
 
 use gpui::*;
 use std::time::Duration;
+use crate::state::AgentStatus;
+use crate::theme;
 
 pub struct BlinkState {
     pub visible: bool,
     epoch: usize,
 }
 
+/// Tiny view entity that renders just the status dot.
+/// Reads BlinkState → only this entity re-renders on blink, not ProjectBox.
+pub struct StatusDotView {
+    status: AgentStatus,
+    blink: Option<Entity<BlinkState>>,
+}
+
+impl StatusDotView {
+    pub fn new(status: AgentStatus, blink: Option<Entity<BlinkState>>) -> Self {
+        Self { status, blink }
+    }
+}
+
+impl Render for StatusDotView {
+    fn render(&mut self, _window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
+        let blink_visible = self.blink.as_ref()
+            .map(|bs| bs.read(cx).visible)
+            .unwrap_or(true);
+        let color = match self.status {
+            AgentStatus::Running if !blink_visible => theme::SURFACE1,
+            AgentStatus::Running => theme::GREEN,
+            AgentStatus::Idle => theme::OVERLAY0,
+            AgentStatus::Done => theme::BLUE,
+            AgentStatus::Error => theme::RED,
+        };
+        div()
+            .w(px(8.0))
+            .h(px(8.0))
+            .rounded(px(4.0))
+            .bg(color)
+            .flex_shrink_0()
+    }
+}
+
 impl BlinkState {
     pub fn new() -> Self {
         Self { visible: true, epoch: 0 }

ui-gpui/src/components/project_box.rs

@@ -71,7 +71,7 @@ pub struct ProjectBox {
     pub project: Project,
     pub agent_pane: Option<Entity<crate::components::agent_pane::AgentPane>>,
     pub terminal_view: Option<Entity<crate::terminal::renderer::TerminalView>>,
-    pub blink_state: Option<Entity<crate::components::blink_state::BlinkState>>,
+    pub status_dot_view: Option<Entity<crate::components::blink_state::StatusDotView>>,
     // Cached strings to avoid allocation on every render
     id_project: SharedString,
     id_model: SharedString,
@@ -96,7 +96,7 @@ impl ProjectBox {
             project,
             agent_pane: None,
             terminal_view: None,
-            blink_state: None,
+            status_dot_view: None,
         }
     }
 
@@ -104,15 +104,22 @@ impl ProjectBox {
     pub fn init_subviews(&mut self, cx: &mut Context<Self>) {
         // Initialize sub-views after entity registration
 
-        // Shared blink state — separate entity, ProjectBox reads it in render.
-        // cx.notify() on BlinkState only dirties views that .read() it (ProjectBox),
-        // NOT ancestors (Workspace, ProjectGrid) → siblings stay cached.
+        // StatusDotView: tiny Entity that reads BlinkState.
+        // ProjectBox does NOT read BlinkState → doesn't re-render on blink.
+        // Only StatusDotView (1 div) re-renders 2x/sec.
         let should_pulse = matches!(self.project.agent.status, AgentStatus::Running);
-        if should_pulse {
-            let blink = cx.new(|_cx| crate::components::blink_state::BlinkState::new());
-            crate::components::blink_state::BlinkState::start_from_context(&blink, cx);
-            self.blink_state = Some(blink);
-        }
+        let blink = if should_pulse {
+            let b = cx.new(|_cx| crate::components::blink_state::BlinkState::new());
+            crate::components::blink_state::BlinkState::start_from_context(&b, cx);
+            Some(b)
+        } else {
+            None
+        };
+        let status = self.project.agent.status;
+        let dot_view = cx.new(|_cx| {
+            crate::components::blink_state::StatusDotView::new(status, blink)
+        });
+        self.status_dot_view = Some(dot_view);
 
         // Create agent pane with demo messages
         let agent_pane = cx.new(|_cx| {
@@ -261,29 +268,10 @@ impl Render for ProjectBox {
                             .rounded(px(2.0))
                             .bg(accent),
                     )
-                    // Status dot — BlinkState shared entity (2 renders/sec, 3% CPU)
-                    // NOTE: GPUI's AnimationElement uses request_animation_frame() which
-                    // runs at vsync (60fps) = 80% CPU. Fragment shaders not exposed.
-                    // The Zed BlinkManager pattern (timer + notify at 2fps) is the
-                    // correct approach for ambient animation in GPUI.
-                    .child({
-                        let blink_visible = self.blink_state.as_ref()
-                            .map(|bs| bs.read(cx).visible)
-                            .unwrap_or(true);
-                        let color = match self.project.agent.status {
-                            AgentStatus::Running if !blink_visible => theme::SURFACE1,
-                            AgentStatus::Running => theme::GREEN,
-                            AgentStatus::Idle => theme::OVERLAY0,
-                            AgentStatus::Done => theme::BLUE,
-                            AgentStatus::Error => theme::RED,
-                        };
-                        div()
-                            .w(px(8.0))
-                            .h(px(8.0))
-                            .rounded(px(4.0))
-                            .bg(color)
-                            .flex_shrink_0()
-                    })
+                    // Status dot — separate Entity that reads BlinkState.
+                    // ProjectBox does NOT read BlinkState → doesn't re-render on blink.
+                    // Only StatusDotView (1 div, 8x8px) re-renders 2x/sec.
+                    .children(self.status_dot_view.clone())
                     // Project name
                     .child(
                         div()