Feat: 新增 DropdownMenu 组件

src/session.ts

@@ -121,6 +121,12 @@ export type MessageMeta = {
   resultMd?: string;
   asThinking?: boolean;
   isSummary?: boolean;
+  isModelChange?: boolean;
+  modelConfig?: {
+    model: string;
+    thinkingEnabled: boolean;
+    reasoningEffort?: string;
+  };
   skill?: SkillInfo;
 };
 
@@ -598,7 +604,7 @@ The candidate skills are as follows:\n\n`;
       if (!fs.existsSync(root)) {
         return [];
       }
-      let entries: fs.Dirent[] = [];
+      let entries: fs.Dirent[];
       try {
         entries = fs.readdirSync(root, { withFileTypes: true });
       } catch {
@@ -1326,6 +1332,25 @@ ${skillMd}
     return messages;
   }
 
+  addSessionSystemMessage(sessionId: string, content: string, meta?: MessageMeta): void {
+    const now = new Date().toISOString();
+    const message: SessionMessage = {
+      id: crypto.randomUUID(),
+      sessionId,
+      role: "system",
+      content,
+      contentParams: null,
+      messageParams: null,
+      compacted: false,
+      visible: true,
+      createTime: now,
+      updateTime: now,
+      meta,
+    };
+    this.appendSessionMessage(sessionId, message);
+    this.onAssistantMessage(message, false);
+  }
+
   private normalizeSessionMessage(message: SessionMessage): SessionMessage {
     if (message.role !== "tool") {
       return message;

src/tests/dropdownMenu.test.ts

@@ -0,0 +1,148 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { calculateVisibleStart } from "../ui/DropdownMenu";
+
+test("calculateVisibleStart centers active item when possible", () => {
+  // 10 items, max 5 visible, active index 4 (middle)
+  // Should show items 2-6 (start at 2)
+  const start = calculateVisibleStart(4, 10, 5);
+  assert.equal(start, 2);
+});
+
+test("calculateVisibleStart handles active item at the beginning", () => {
+  // 10 items, max 5 visible, active index 0
+  // Should show items 0-4 (start at 0)
+  const start = calculateVisibleStart(0, 10, 5);
+  assert.equal(start, 0);
+});
+
+test("calculateVisibleStart handles active item at the end", () => {
+  // 10 items, max 5 visible, active index 9 (last)
+  // Should show items 5-9 (start at 5)
+  const start = calculateVisibleStart(9, 10, 5);
+  assert.equal(start, 5);
+});
+
+test("calculateVisibleStart handles fewer items than maxVisible", () => {
+  // 3 items, max 5 visible, active index 1
+  // Should show all items (start at 0)
+  const start = calculateVisibleStart(1, 3, 5);
+  assert.equal(start, 0);
+});
+
+test("calculateVisibleStart handles single item", () => {
+  // 1 item, max 5 visible, active index 0
+  // Should start at 0
+  const start = calculateVisibleStart(0, 1, 5);
+  assert.equal(start, 0);
+});
+
+test("calculateVisibleStart handles empty list", () => {
+  // 0 items, max 5 visible, active index 0
+  // Should start at 0
+  const start = calculateVisibleStart(0, 0, 5);
+  assert.equal(start, 0);
+});
+
+test("calculateVisibleStart handles activeIndex near start with odd maxVisible", () => {
+  // 10 items, max 7 visible (odd), active index 2
+  // floor((7-1)/2) = 3, so 2-3 = -1, clamped to 0
+  const start = calculateVisibleStart(2, 10, 7);
+  assert.equal(start, 0);
+});
+
+test("calculateVisibleStart handles activeIndex near start with even maxVisible", () => {
+  // 10 items, max 6 visible (even), active index 2
+  // floor((6-1)/2) = 2, so 2-2 = 0
+  const start = calculateVisibleStart(2, 10, 6);
+  assert.equal(start, 0);
+});
+
+test("calculateVisibleStart keeps active item centered in middle range", () => {
+  // 20 items, max 5 visible, active index 10
+  // floor((5-1)/2) = 2, so 10-2 = 8
+  const start = calculateVisibleStart(10, 20, 5);
+  assert.equal(start, 8);
+});
+
+test("calculateVisibleStart handles activeIndex at exact boundary", () => {
+  // 10 items, max 5 visible, active index 2 (boundary where centering starts)
+  // floor((5-1)/2) = 2, so 2-2 = 0
+  const start = calculateVisibleStart(2, 10, 5);
+  assert.equal(start, 0);
+});
+
+test("calculateVisibleStart handles activeIndex just after boundary", () => {
+  // 10 items, max 5 visible, active index 3
+  // floor((5-1)/2) = 2, so 3-2 = 1
+  const start = calculateVisibleStart(3, 10, 5);
+  assert.equal(start, 1);
+});
+
+test("calculateVisibleStart handles large maxVisible", () => {
+  // 10 items, max 100 visible, active index 5
+  // Should show all items (start at 0)
+  const start = calculateVisibleStart(5, 10, 100);
+  assert.equal(start, 0);
+});
+
+test("calculateVisibleStart handles activeIndex equal to totalItems", () => {
+  // 10 items, max 5 visible, active index 10 (out of bounds)
+  // floor((5-1)/2) = 2, so 10-2 = 8, clamped to 5 (10-5)
+  const start = calculateVisibleStart(10, 10, 5);
+  assert.equal(start, 5);
+});
+
+test("calculateVisibleStart with maxVisible of 1", () => {
+  // 5 items, max 1 visible, active index 2
+  // floor((1-1)/2) = 0, so 2-0 = 2, clamped to 4 (5-1)
+  const start = calculateVisibleStart(2, 5, 1);
+  assert.equal(start, 2);
+});
+
+test("calculateVisibleStart with maxVisible of 1 at end", () => {
+  // 5 items, max 1 visible, active index 4 (last)
+  // floor((1-1)/2) = 0, so 4-0 = 4, clamped to 4 (5-1)
+  const start = calculateVisibleStart(4, 5, 1);
+  assert.equal(start, 4);
+});
+
+test("calculateVisibleStart scrolling behavior - moving down", () => {
+  // Simulate scrolling through a list
+  // 10 items, max 5 visible
+
+  // Start at index 0
+  assert.equal(calculateVisibleStart(0, 10, 5), 0);
+
+  // Move to index 2 (still centered)
+  assert.equal(calculateVisibleStart(2, 10, 5), 0);
+
+  // Move to index 5 (window should scroll)
+  assert.equal(calculateVisibleStart(5, 10, 5), 3);
+
+  // Move to index 8 (near end)
+  assert.equal(calculateVisibleStart(8, 10, 5), 5);
+
+  // Move to index 9 (at end)
+  assert.equal(calculateVisibleStart(9, 10, 5), 5);
+});
+
+test("calculateVisibleStart scrolling behavior - moving up", () => {
+  // Simulate scrolling up through a list
+  // 10 items, max 5 visible
+
+  // Start at index 9 (end)
+  assert.equal(calculateVisibleStart(9, 10, 5), 5);
+
+  // Move to index 6
+  assert.equal(calculateVisibleStart(6, 10, 5), 4);
+
+  // Move to index 4 (window should scroll up)
+  assert.equal(calculateVisibleStart(4, 10, 5), 2);
+
+  // Move to index 1 (near start)
+  assert.equal(calculateVisibleStart(1, 10, 5), 0);
+
+  // Move to index 0 (at start)
+  assert.equal(calculateVisibleStart(0, 10, 5), 0);
+});

src/ui/App.tsx

@@ -8,6 +8,7 @@ import OpenAI from "openai";
 import {
   SessionManager,
   type LlmStreamProgress,
+  type MessageMeta,
   type SessionEntry,
   type SessionMessage,
   type SessionStatus,
@@ -268,12 +269,47 @@ export function App({ projectRoot, version = "", onRestart }: AppProps): React.R
       const { changed } = writeModelConfigSelection(selection, current, projectRoot);
       const next = resolveCurrentSettings(projectRoot);
       setResolvedSettings(next);
+
       if (!changed) {
         return "Model settings unchanged";
       }
+
+      const activeSessionId = sessionManager.getActiveSessionId();
+      const meta: MessageMeta = {
+        isModelChange: true,
+        modelConfig: {
+          model: selection.model,
+          thinkingEnabled: selection.thinkingEnabled,
+          reasoningEffort: selection.reasoningEffort,
+        },
+      };
+      const content = `/model\n⎿ Set model to ${selection.model}`;
+
+      if (activeSessionId) {
+        sessionManager.addSessionSystemMessage(activeSessionId, content, meta);
+      } else {
+        const now = new Date().toISOString();
+        setMessages((prev) => [
+          ...prev,
+          {
+            id: crypto.randomUUID(),
+            sessionId: "local",
+            role: "system" as const,
+            content,
+            contentParams: null,
+            messageParams: null,
+            compacted: false,
+            visible: true,
+            createTime: now,
+            updateTime: now,
+            meta,
+          },
+        ]);
+      }
+
       return `Model settings updated: ${formatModelConfig(current)} → ${formatModelConfig(next)}`;
     },
-    [projectRoot]
+    [projectRoot, sessionManager]
   );
 
   const handleSubmit = useCallback(