feat(ai): model chip selects among connected CLI agents

The chat panel's bottom-toolbar chip was a hardcoded "Default"
label. It now shows the selected CLI agent and cycles through the
connected ones on click.

- `UiState.chat_selected_agent` — index into `AgentProvider::ALL`
  (Claude Code / Codex CLI / OpenCode / GitHub Copilot / Gemini).
- `Document::cycle_chat_agent` — advances to the next *connected*
  agent (`agent_settings.connected`); walks all 5 when none are
  connected so the user can pre-pick before connecting.
- `AIChatHit::CycleModel` — the chip's left 150 px of the input
  toolbar; `apply_click` routes it to `cycle_chat_agent`.
- The chip label now renders `AgentProvider::name()` instead of
  the static "Default".
- `chat_session::provider_for_agent` routes the selected agent to
  its `ChatProvider`: Claude Code → SDK adapter, Copilot / Gemini
  → subprocess transport. Codex / OpenCode (HTTP-server CLIs whose
  bridge isn't wired yet) fall back to Claude Code.

856 workspace tests pass (+2: cycle walks connected / wraps,
cycle with nothing connected walks all five).

crates/openpencil-desktop/src/chat_session.rs

@@ -10,10 +10,14 @@
 use std::sync::mpsc::{self, Receiver, TryRecvError};
 use std::thread;
 
-use openpencil_shell_core::chat_provider::{ChatDelta, ChatProvider, ChatRequest};
+use openpencil_shell_core::chat_provider::{
+    ChatDelta, ChatProvider, ChatRequest, CliName,
+};
 use openpencil_shell_native::WidgetHostNative;
 
 use crate::chat_claude::ClaudeCodeProvider;
+use crate::chat_copilot::CopilotProvider;
+use crate::chat_subprocess::SubprocessProvider;
 
 /// One in-flight chat turn. The worker thread owns the provider and
 /// drains `provider.send()` into the channel; [`poll`] consumes
@@ -110,7 +114,7 @@ pub fn launch_if_pending(
     let Some(user_text) = host.document_mut().chat.pending_send.take() else {
         return false;
     };
-    let provider: Box<dyn ChatProvider> = Box::new(ClaudeCodeProvider::new());
+    let provider = provider_for_agent(host.document().ui.chat_selected_agent);
     let req = ChatRequest {
         system_prompt: String::new(),
         user_message: user_text,
@@ -120,6 +124,23 @@ pub fn launch_if_pending(
     true
 }
 
+/// Build the `ChatProvider` for an agent index (into
+/// `AgentProvider::ALL`: 0 ClaudeCode, 1 CodexCli, 2 OpenCode,
+/// 3 GithubCopilot, 4 GeminiCli). Claude Code uses its dedicated
+/// SDK adapter; Copilot / Gemini use the subprocess transport.
+/// Codex + OpenCode are HTTP-server CLIs whose `ChatProvider`
+/// bridge isn't wired yet — they fall back to Claude Code so the
+/// chat still functions rather than dead-ending.
+fn provider_for_agent(agent_idx: usize) -> Box<dyn ChatProvider> {
+    match agent_idx {
+        3 => Box::new(CopilotProvider::new()),
+        4 => SubprocessProvider::for_cli(CliName::Gemini)
+            .map(|p| Box::new(p) as Box<dyn ChatProvider>)
+            .unwrap_or_else(|| Box::new(ClaudeCodeProvider::new())),
+        _ => Box::new(ClaudeCodeProvider::new()),
+    }
+}
+
 /// Pump the in-flight turn's deltas into the trailing (assistant)
 /// message. Clears `current` once the turn finishes. Returns true
 /// when the transcript changed so the caller can dirty the redraw.

crates/openpencil-shell-core/src/document.rs

@@ -335,6 +335,15 @@ pub struct UiState {
     pub locale: Locale,
     /// TopBar Globe dropdown open.
     pub locale_picker_open: bool,
+    /// AI chat model-picker dropdown open (the "Default ▴" chip in
+    /// the chat panel's bottom toolbar). Lists CLI agents that are
+    /// connected per `agent_settings.connected`.
+    pub chat_model_picker_open: bool,
+    /// Index into `AgentProvider::ALL` of the agent driving the AI
+    /// chat. Default 0 = Claude Code. The picker only *selects*
+    /// among connected agents, but the stored index is absolute so
+    /// it survives connect/disconnect churn.
+    pub chat_selected_agent: usize,
     /// File-menu dropdown anchored under folder+chevron.
     pub file_menu_open: bool,
     /// Row currently hovered while the file menu is open — drives
@@ -578,6 +587,8 @@ impl Default for UiState {
             theme_mode: ThemeMode::Dark,
             locale: Locale::ZhCn,
             locale_picker_open: false,
+            chat_model_picker_open: false,
+            chat_selected_agent: 0,
             file_menu_open: false,
             file_menu_hover: None,
             locale_picker_hover: None,

crates/openpencil-shell-core/src/document/mutators.rs

@@ -206,6 +206,24 @@ impl Document {
         self.ui.align_toolbar_hover = None;
     }
 
+    /// Advance the AI-chat agent selection to the next *connected*
+    /// CLI (`agent_settings.connected`, indexed like
+    /// `AgentProvider::ALL`). When no agent is connected the cycle
+    /// still walks all 5 entries so the user can pre-pick one and
+    /// connect it afterward in the settings modal. Wraps.
+    pub fn cycle_chat_agent(&mut self) {
+        let connected = self.ui.agent_settings.connected;
+        let any_connected = connected.iter().any(|&c| c);
+        let start = self.ui.chat_selected_agent;
+        for step in 1..=connected.len() {
+            let idx = (start + step) % connected.len();
+            if !any_connected || connected[idx] {
+                self.ui.chat_selected_agent = idx;
+                return;
+            }
+        }
+    }
+
     /// Whether `id` resolves to a node that can be mutated via
     /// selection-aware helpers (`translate_selected`,
     /// `set_selected_bounds`, etc.). Hidden + locked nodes are

crates/openpencil-shell-core/src/document/tests_mutators.rs

@@ -788,3 +788,28 @@ fn cut_selected_rolls_back_clipboard_when_delete_rejects() {
         "sentinel survives failed cut"
     );
 }
+
+#[test]
+fn cycle_chat_agent_walks_connected_then_wraps() {
+    let mut doc = Document::sample();
+    // Connect Claude Code (0) + GitHub Copilot (3) only.
+    doc.ui.agent_settings.connected = [true, false, false, true, false];
+    doc.ui.chat_selected_agent = 0;
+    // 0 → next connected is 3.
+    doc.cycle_chat_agent();
+    assert_eq!(doc.ui.chat_selected_agent, 3);
+    // 3 → wraps back to 0.
+    doc.cycle_chat_agent();
+    assert_eq!(doc.ui.chat_selected_agent, 0);
+}
+
+#[test]
+fn cycle_chat_agent_with_nothing_connected_walks_all_five() {
+    let mut doc = Document::sample();
+    doc.ui.agent_settings.connected = [false; 5];
+    doc.ui.chat_selected_agent = 0;
+    for expected in [1usize, 2, 3, 4, 0] {
+        doc.cycle_chat_agent();
+        assert_eq!(doc.ui.chat_selected_agent, expected);
+    }
+}

crates/openpencil-shell-core/src/widgets/ai_chat_panel.rs

@@ -34,6 +34,9 @@ const INPUT_AREA_HEIGHT: f32 = 56.0;
 /// Toolbar below the textarea — model picker on left, attach +
 /// send on right. Mirrors the TS panel's bottom row.
 const INPUT_TOOLBAR_HEIGHT: f32 = 40.0;
+/// Click-width of the bottom-toolbar model chip (sparkles + agent
+/// name + chevron). Fixed so hit-test needs no text measurement.
+const MODEL_CHIP_W: f32 = 150.0;
 /// Total reserved space for the input + toolbar block.
 const INPUT_HEIGHT: f32 = INPUT_AREA_HEIGHT + INPUT_TOOLBAR_HEIGHT;
 
@@ -83,6 +86,10 @@ pub enum AIChatHit {
     /// Click on the chevron at the top-left of the header — host
     /// flips the `ChatState::collapsed` flag.
     ToggleCollapse,
+    /// Click on the model chip (bottom-left of the input toolbar) —
+    /// host advances `chat_selected_agent` to the next connected
+    /// CLI agent (`Document::cycle_chat_agent`).
+    CycleModel,
 }
 
 pub struct AIChatPlaceholder<'a> {
@@ -104,9 +111,11 @@ pub struct AIChatPlaceholder<'a> {
     /// the empty-state body, between the example cards and the
     /// separator above the input.
     pub label_tip_select_elements: String,
-    /// Localised "Default" model label — appears in the bottom
-    /// toolbar's model picker.
-    pub label_default_model: String,
+    /// Name of the AI-chat agent shown in the bottom toolbar's
+    /// model chip — the connected CLI selected via `chat_selected_agent`
+    /// (`AgentProvider::label`). Falls back to "Default" only when
+    /// the stored index is somehow out of range.
+    pub model_label: String,
 }
 
 impl<'a> AIChatPlaceholder<'a> {
@@ -126,7 +135,10 @@ impl<'a> AIChatPlaceholder<'a> {
             label_start_with_ai: doc.t("ai.tryExample").to_string(),
             label_input_placeholder: doc.t("ai.designWithAgent").to_string(),
             label_tip_select_elements: doc.t("ai.tipSelectElements").to_string(),
-            label_default_model: "Default".to_string(),
+            model_label: crate::agent_settings_state::AgentProvider::ALL
+                .get(doc.ui.chat_selected_agent)
+                .map(|a| a.name().to_string())
+                .unwrap_or_else(|| "Default".to_string()),
         }
     }
 
@@ -158,6 +170,15 @@ impl<'a> AIChatPlaceholder<'a> {
             size: Point2D::new(rect.size.x - PAD * 2.0, INPUT_HEIGHT),
         };
         if rect_contains(input_rect, point) {
+            // Bottom toolbar strip = the lower `INPUT_TOOLBAR_HEIGHT`
+            // of the input box; its left `MODEL_CHIP_W` is the model
+            // chip (advances the connected-CLI selection on click).
+            let toolbar_top = input_rect.origin.y + INPUT_AREA_HEIGHT;
+            if point.y >= toolbar_top
+                && point.x <= input_rect.origin.x + MODEL_CHIP_W
+            {
+                return Some(AIChatHit::CycleModel);
+            }
             // Send chip is the rightmost ~40px of the input area.
             let send_x = input_rect.origin.x + input_rect.size.x - 40.0;
             if point.x >= send_x {
@@ -381,7 +402,7 @@ impl<'a> Widget for AIChatPlaceholder<'a> {
         );
         model_x += 20.0;
         let model_label = TextLayout::single_run(
-            &self.label_default_model,
+            &self.model_label,
             "system-ui",
             12.0,
             to_jian_color(self.theme.muted_foreground),
@@ -389,7 +410,7 @@ impl<'a> Widget for AIChatPlaceholder<'a> {
         );
         cx.backend
             .draw_text(&model_label, Point2D::new(model_x, toolbar_center_y + 4.0));
-        let model_w = cx.backend.measure_text(&self.label_default_model, 12.0);
+        let model_w = cx.backend.measure_text(&self.model_label, 12.0);
         model_x += model_w + 4.0;
         draw_icon(
             cx.backend,

crates/openpencil-shell-native/src/widget_host/keyboard.rs

@@ -413,6 +413,10 @@ impl WidgetHostNative {
                         self.document.chat.collapsed = !self.document.chat.collapsed;
                         return true;
                     }
+                    AIChatHit::CycleModel => {
+                        self.document.cycle_chat_agent();
+                        return true;
+                    }
                 }
             }
         }