fix: 修复滚动限制 + 自动检测Shell类型

滚动修复：
- scroll() 使用实际渲染行数而非消息数计算 maxOffset
- 解决 /help 等多行输出无法滚动到顶部的问题

Shell 检测：
- Windows 自动检测 PowerShell 7+ > Windows PowerShell > cmd.exe
- 动态调整 BashTool 描述，告知AI使用正确的命令语法
- 系统提示词包含详细的 Shell 使用指南（PowerShell cmdlets）
- header 显示检测到的 Shell 类型
- Unix 优先 bash，回退 sh

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/main/java/com/claudecode/context/SystemPromptBuilder.java

@@ -1,5 +1,7 @@
 package com.claudecode.context;
 
+import com.claudecode.tool.impl.BashTool;
+
 /**
  * 系统提示词构建器 —— 对应 claude-code/src/prompts.ts。
  * <p>
@@ -66,8 +68,8 @@ public class SystemPromptBuilder {
         sb.append("- Working directory: ").append(workDir).append("\n");
         sb.append("- OS: ").append(osName).append("\n");
         sb.append("- User: ").append(userName).append("\n");
-        sb.append("- Shell: ").append(System.getenv().getOrDefault("SHELL",
-                System.getenv().getOrDefault("COMSPEC", "unknown"))).append("\n");
+        // 使用 BashTool 检测到的 shell 信息（比 COMSPEC/SHELL 环境变量更准确）
+        sb.append(BashTool.getShellHint());
         sb.append("\n");
 
         // 行为准则

src/main/java/com/claudecode/tool/impl/BashTool.java

@@ -2,6 +2,8 @@ package com.claudecode.tool.impl;
 
 import com.claudecode.tool.Tool;
 import com.claudecode.tool.ToolContext;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.io.BufferedReader;
 import java.io.InputStreamReader;
@@ -10,15 +12,47 @@ import java.util.Map;
 import java.util.concurrent.TimeUnit;
 
 /**
- * Bash 工具 —— 对应 claude-code/src/tools/bash/BashTool.ts。
+ * Shell 工具 —— 对应 claude-code/src/tools/bash/BashTool.ts。
  * <p>
  * 在指定工作目录中执行 shell 命令，返回 stdout/stderr 输出。
+ * 自动检测最佳可用 shell：
+ * <ul>
+ *   <li>Windows: PowerShell &gt; cmd.exe</li>
+ *   <li>Unix/Linux/macOS: bash（或 SHELL 环境变量）</li>
+ * </ul>
  */
 public class BashTool implements Tool {
 
+    private static final Logger log = LoggerFactory.getLogger(BashTool.class);
+
     /** 默认超时（秒） */
     private static final int DEFAULT_TIMEOUT = 120;
 
+    /** 检测到的 shell 类型 */
+    public enum ShellType {
+        POWERSHELL("PowerShell", "pwsh", "-NoProfile", "-Command"),
+        POWERSHELL_WINDOWS("PowerShell", "powershell.exe", "-NoProfile", "-Command"),
+        CMD("cmd.exe", "cmd.exe", "/c", null),
+        BASH("Bash", "bash", "-c", null),
+        SH("sh", "sh", "-c", null);
+
+        final String displayName;
+        final String executable;
+        final String flag1;
+        final String flag2; // 可选的额外 flag
+
+        ShellType(String displayName, String executable, String flag1, String flag2) {
+            this.displayName = displayName;
+            this.executable = executable;
+            this.flag1 = flag1;
+            this.flag2 = flag2;
+        }
+    }
+
+    private static final boolean IS_WINDOWS = System.getProperty("os.name", "").toLowerCase().contains("win");
+    private static final ShellType DETECTED_SHELL = detectShell();
+    private static final String SHELL_HINT = buildShellHint();
+
     @Override
     public String name() {
         return "Bash";
@@ -26,6 +60,19 @@ public class BashTool implements Tool {
 
     @Override
     public String description() {
+        if (IS_WINDOWS && DETECTED_SHELL.displayName.equals("PowerShell")) {
+            return """
+                Execute a command in the working directory using PowerShell. \
+                Use PowerShell syntax (Get-ChildItem, Select-String, Get-Content, etc). \
+                Common equivalents: ls→Get-ChildItem, grep→Select-String, cat→Get-Content, \
+                rm→Remove-Item, cp→Copy-Item, mv→Move-Item, find→Get-ChildItem -Recurse. \
+                Commands run in a subprocess with timeout protection.""";
+        } else if (IS_WINDOWS) {
+            return """
+                Execute a command in the working directory using cmd.exe. \
+                Use Windows cmd syntax (dir, type, find, etc). \
+                Commands run in a subprocess with timeout protection.""";
+        }
         return """
             Execute a bash command in the working directory. \
             Use this for file operations, running scripts, installing packages, \
@@ -60,15 +107,7 @@ public class BashTool implements Tool {
         Path workDir = context.getWorkDir();
 
         try {
-            // 根据操作系统选择 shell
-            boolean isWindows = System.getProperty("os.name").toLowerCase().contains("win");
-            ProcessBuilder pb;
-            if (isWindows) {
-                pb = new ProcessBuilder("cmd", "/c", command);
-            } else {
-                pb = new ProcessBuilder("bash", "-c", command);
-            }
-
+            ProcessBuilder pb = buildProcess(command);
             pb.directory(workDir.toFile());
             pb.redirectErrorStream(true);
 
@@ -104,10 +143,101 @@ public class BashTool implements Tool {
     @Override
     public String activityDescription(Map<String, Object> input) {
         String cmd = (String) input.getOrDefault("command", "");
-        // 截断过长的命令
         if (cmd.length() > 60) {
             cmd = cmd.substring(0, 57) + "...";
         }
         return "⚡ " + cmd;
     }
+
+    /** 构建 ProcessBuilder，根据检测到的 shell 类型 */
+    private ProcessBuilder buildProcess(String command) {
+        return switch (DETECTED_SHELL) {
+            case POWERSHELL -> new ProcessBuilder("pwsh", "-NoProfile", "-Command", command);
+            case POWERSHELL_WINDOWS -> new ProcessBuilder("powershell.exe", "-NoProfile", "-Command", command);
+            case CMD -> new ProcessBuilder("cmd.exe", "/c", command);
+            case BASH -> new ProcessBuilder("bash", "-c", command);
+            case SH -> new ProcessBuilder("sh", "-c", command);
+        };
+    }
+
+    /** 检测最佳可用 shell */
+    private static ShellType detectShell() {
+        if (IS_WINDOWS) {
+            // 优先 pwsh (PowerShell 7+)
+            if (isCommandAvailable("pwsh", "--version")) {
+                log.info("Detected shell: PowerShell 7+ (pwsh)");
+                return ShellType.POWERSHELL;
+            }
+            // 回退到 Windows PowerShell 5.x
+            if (isCommandAvailable("powershell.exe", "-NoProfile", "-Command", "echo ok")) {
+                log.info("Detected shell: Windows PowerShell (powershell.exe)");
+                return ShellType.POWERSHELL_WINDOWS;
+            }
+            // 最终回退到 cmd
+            log.info("Detected shell: cmd.exe (fallback)");
+            return ShellType.CMD;
+        }
+
+        // Unix: 优先 bash
+        String shellEnv = System.getenv("SHELL");
+        if (shellEnv != null && shellEnv.contains("bash")) {
+            return ShellType.BASH;
+        }
+        if (isCommandAvailable("bash", "--version")) {
+            return ShellType.BASH;
+        }
+        return ShellType.SH;
+    }
+
+    /** 检查命令是否可用 */
+    private static boolean isCommandAvailable(String... cmd) {
+        try {
+            Process p = new ProcessBuilder(cmd)
+                    .redirectErrorStream(true)
+                    .start();
+            p.getInputStream().readAllBytes();
+            return p.waitFor(5, TimeUnit.SECONDS) && p.exitValue() == 0;
+        } catch (Exception e) {
+            return false;
+        }
+    }
+
+    /** 获取 shell 提示信息（供系统提示词使用） */
+    public static String getShellHint() {
+        return SHELL_HINT;
+    }
+
+    /** 获取检测到的 shell 显示名 */
+    public static String getDetectedShellName() {
+        return DETECTED_SHELL.displayName;
+    }
+
+    private static String buildShellHint() {
+        if (IS_WINDOWS && DETECTED_SHELL.displayName.equals("PowerShell")) {
+            return """
+                - Shell: %s (detected on Windows)
+                - IMPORTANT: The Bash tool executes commands via PowerShell, NOT bash or cmd.exe.
+                - Use PowerShell native cmdlets and syntax:
+                  - List files: Get-ChildItem (or ls/dir aliases)
+                  - Search text: Select-String -Pattern "xxx" -Path *.java
+                  - Read file: Get-Content file.txt
+                  - Delete: Remove-Item path
+                  - Copy: Copy-Item src dst
+                  - Move: Move-Item src dst
+                  - Find files: Get-ChildItem -Recurse -Filter "*.java"
+                  - Current dir: Get-Location (or pwd)
+                  - Environment vars: $env:PATH
+                  - Pipe: cmd1 | cmd2
+                  - String comparison: -eq, -ne, -like, -match
+                - Standard tools (git, mvn, npm, java, python) work normally.
+                """.formatted(DETECTED_SHELL.displayName);
+        } else if (IS_WINDOWS) {
+            return """
+                - Shell: cmd.exe (Windows)
+                - Use Windows cmd syntax: dir, type, find, etc.
+                - Standard tools (git, mvn, npm) work normally.
+                """;
+        }
+        return "- Shell: " + DETECTED_SHELL.displayName + "\n";
+    }
 }

src/main/java/com/claudecode/tui/ClaudeCodeComponent.java

@@ -6,6 +6,7 @@ import com.claudecode.console.BannerPrinter;
 import com.claudecode.core.AgentLoop;
 import com.claudecode.core.TokenTracker;
 import com.claudecode.tool.ToolRegistry;
+import com.claudecode.tool.impl.BashTool;
 import com.claudecode.tui.UIMessage.*;
 import io.mybatis.jink.component.*;
 import io.mybatis.jink.input.Key;
@@ -92,6 +93,9 @@ public class ClaudeCodeComponent extends Component<ClaudeCodeComponent.TuiState>
     private volatile boolean askInputMode = false;  // 是否在自由输入模式（选择"其他"后）
     private volatile String askQuestion;            // 当前问题文本
 
+    /** 最近一次渲染的总行数（用于滚动限制） */
+    private volatile int lastRenderedItemCount = 0;
+
     /** 首次用户输入回调（用于 conversation summary） */
     private Consumer<String> onFirstUserInput;
 
@@ -226,8 +230,8 @@ public class ClaudeCodeComponent extends Component<ClaudeCodeComponent.TuiState>
                 Text.of(
                         Text.of("Tools: ").dimmed(),
                         Text.of(String.valueOf(toolCount)).color(Color.BRIGHT_CYAN),
-                        Text.of(" │ Commands: ").dimmed(),
-                        Text.of(String.valueOf(cmdCount)).color(Color.BRIGHT_CYAN)
+                        Text.of(" │ Shell: ").dimmed(),
+                        Text.of(BashTool.getDetectedShellName()).color(Color.BRIGHT_CYAN)
                 )
         };
 
@@ -283,6 +287,9 @@ public class ClaudeCodeComponent extends Component<ClaudeCodeComponent.TuiState>
             ));
         }
 
+        // 记录总行数（供 scroll() 使用）
+        lastRenderedItemCount = allItems.size();
+
         // 虚拟滚动
         List<Renderable> visibleItems;
         if (maxLines > 0 && allItems.size() > maxLines) {
@@ -984,8 +991,8 @@ public class ClaudeCodeComponent extends Component<ClaudeCodeComponent.TuiState>
     // ==================== 滚动 ====================
 
     private void scroll(TuiState s, int delta) {
-        int totalMessages = s.messages.size() + 1; // +1 for initial system msg
-        int maxOffset = Math.max(0, totalMessages - 1);
+        int totalItems = lastRenderedItemCount;
+        int maxOffset = Math.max(0, totalItems - 1);
         int newOffset = Math.max(0, Math.min(s.scrollOffset + delta, maxOffset));
         setState(new TuiState(s.inputText, s.messages, newOffset, s.thinking, s.thinkingText));
     }