diff --git a/src/main/java/com/claudecode/config/AppConfig.java b/src/main/java/com/claudecode/config/AppConfig.java
index 4d1def2..4b11a03 100644
--- a/src/main/java/com/claudecode/config/AppConfig.java
+++ b/src/main/java/com/claudecode/config/AppConfig.java
@@ -121,7 +121,11 @@ public class AppConfig {
                 new ListMcpResourcesTool(),
                 new ReadMcpResourceTool(),
                 new EnterWorktreeTool(),
-                new ExitWorktreeTool()
+                new ExitWorktreeTool(),
+                // P4: 新工具
+                new LSPTool(),
+                new BriefTool(),
+                new NotificationTool()
         );
 
         // P2: 注册 MCP 工具桥接（将远程 MCP 工具映射为本地工具）
diff --git a/src/main/java/com/claudecode/tool/impl/BriefTool.java b/src/main/java/com/claudecode/tool/impl/BriefTool.java
new file mode 100644
index 0000000..c404fdf
--- /dev/null
+++ b/src/main/java/com/claudecode/tool/impl/BriefTool.java
@@ -0,0 +1,105 @@
+package com.claudecode.tool.impl;
+
+import com.claudecode.tool.Tool;
+import com.claudecode.tool.ToolContext;
+
+import java.util.Map;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
+
+/**
+ * Brief 工具 —— 对应 claude-code 中 brief/detailed 输出模式切换。
+ * <p>
+ * 控制 Agent 输出的详细程度。开启 brief 模式后，Agent 会：
+ * <ul>
+ *   <li>使用更简洁的回复</li>
+ *   <li>省略冗余的解释</li>
+ *   <li>只显示关键信息</li>
+ * </ul>
+ * <p>
+ * 模式状态通过 ToolContext 共享（key: "BRIEF_MODE"）。
+ */
+public class BriefTool implements Tool {
+
+    @Override
+    public String name() {
+        return "Brief";
+    }
+
+    @Override
+    public String description() {
+        return """
+            Toggle brief output mode. When enabled, responses are concise and focused. \
+            When disabled, responses include full explanations and context.
+            
+            Actions:
+            - enable: Turn on brief mode (shorter responses)
+            - disable: Turn off brief mode (detailed responses)
+            - toggle: Switch between brief and detailed
+            - status: Check current mode""";
+    }
+
+    @Override
+    public String inputSchema() {
+        return """
+            {
+              "type": "object",
+              "properties": {
+                "action": {
+                  "type": "string",
+                  "enum": ["enable", "disable", "toggle", "status"],
+                  "description": "Action to perform"
+                }
+              },
+              "required": ["action"]
+            }""";
+    }
+
+    @Override
+    public boolean isReadOnly() {
+        return true;
+    }
+
+    @Override
+    public String execute(Map<String, Object> input, ToolContext context) {
+        String action = (String) input.get("action");
+        if (action == null) {
+            return "Error: 'action' is required";
+        }
+
+        boolean currentMode = isBriefMode(context);
+
+        return switch (action) {
+            case "enable" -> {
+                context.set("BRIEF_MODE", true);
+                yield "Brief mode enabled. Responses will be concise.";
+            }
+            case "disable" -> {
+                context.set("BRIEF_MODE", false);
+                yield "Brief mode disabled. Responses will be detailed.";
+            }
+            case "toggle" -> {
+                boolean newMode = !currentMode;
+                context.set("BRIEF_MODE", newMode);
+                yield newMode ? "Brief mode enabled." : "Brief mode disabled.";
+            }
+            case "status" -> "Brief mode: " + (currentMode ? "ON (concise)" : "OFF (detailed)");
+            default -> "Error: Unknown action: " + action;
+        };
+    }
+
+    /**
+     * 检查当前是否为 brief 模式。
+     */
+    public static boolean isBriefMode(ToolContext context) {
+        Object mode = context.get("BRIEF_MODE");
+        if (mode instanceof Boolean b) return b;
+        return false;
+    }
+
+    @Override
+    public String activityDescription(Map<String, Object> input) {
+        String action = (String) input.getOrDefault("action", "toggle");
+        return "📋 Brief mode " + action;
+    }
+}
diff --git a/src/main/java/com/claudecode/tool/impl/LSPTool.java b/src/main/java/com/claudecode/tool/impl/LSPTool.java
new file mode 100644
index 0000000..2e8927a
--- /dev/null
+++ b/src/main/java/com/claudecode/tool/impl/LSPTool.java
@@ -0,0 +1,310 @@
+package com.claudecode.tool.impl;
+
+import com.claudecode.lsp.LSPDiagnosticRegistry;
+import com.claudecode.lsp.LSPServerManager;
+import com.claudecode.tool.Tool;
+import com.claudecode.tool.ToolContext;
+import com.fasterxml.jackson.databind.JsonNode;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.nio.file.Path;
+import java.util.*;
+
+/**
+ * LSP 工具 —— 对应 claude-code 中通过 LSP 提供的代码智能功能。
+ * <p>
+ * 暴露 Language Server Protocol 能力给 Agent：
+ * <ul>
+ *   <li>goto_definition — 跳转到定义</li>
+ *   <li>find_references — 查找引用</li>
+ *   <li>hover — 获取悬停信息（类型、文档）</li>
+ *   <li>diagnostics — 获取文件诊断信息</li>
+ *   <li>document_symbols — 获取文件符号列表</li>
+ * </ul>
+ * <p>
+ * 底层使用 Phase 3C 实现的 LSPServerManager 和 LSPClient。
+ */
+public class LSPTool implements Tool {
+
+    private static final Logger log = LoggerFactory.getLogger(LSPTool.class);
+
+    @Override
+    public String name() {
+        return "LSP";
+    }
+
+    @Override
+    public String description() {
+        return """
+            Query Language Server Protocol for code intelligence. Provides:
+            - goto_definition: Jump to where a symbol is defined
+            - find_references: Find all usages of a symbol
+            - hover: Get type info and documentation for a symbol
+            - diagnostics: Get errors/warnings for a file
+            - document_symbols: List all symbols in a file
+            
+            Use this when you need to understand code structure, find symbol definitions, \
+            or check for compile errors. Requires an LSP server configured for the file type.""";
+    }
+
+    @Override
+    public String inputSchema() {
+        return """
+            {
+              "type": "object",
+              "properties": {
+                "action": {
+                  "type": "string",
+                  "enum": ["goto_definition", "find_references", "hover", "diagnostics", "document_symbols"],
+                  "description": "The LSP action to perform"
+                },
+                "file_path": {
+                  "type": "string",
+                  "description": "Absolute path to the source file"
+                },
+                "line": {
+                  "type": "integer",
+                  "description": "1-based line number (required for goto_definition, find_references, hover)"
+                },
+                "column": {
+                  "type": "integer",
+                  "description": "1-based column number (required for goto_definition, find_references, hover)"
+                }
+              },
+              "required": ["action", "file_path"]
+            }""";
+    }
+
+    @Override
+    public boolean isReadOnly() {
+        return true;
+    }
+
+    @Override
+    public String execute(Map<String, Object> input, ToolContext context) {
+        String action = (String) input.get("action");
+        String filePath = (String) input.get("file_path");
+        Number lineNum = (Number) input.get("line");
+        Number colNum = (Number) input.get("column");
+
+        if (action == null || filePath == null) {
+            return "Error: 'action' and 'file_path' are required";
+        }
+
+        // Get LSP manager from context
+        Object managerObj = context.get("LSP_SERVER_MANAGER");
+        if (!(managerObj instanceof LSPServerManager manager)) {
+            return "Error: LSP server manager not available. No language server configured.";
+        }
+
+        Path path = Path.of(filePath);
+        int line = lineNum != null ? lineNum.intValue() : 1;
+        int column = colNum != null ? colNum.intValue() : 1;
+        // Convert to 0-based for LSP protocol
+        int lspLine = line - 1;
+        int lspCol = column - 1;
+
+        return switch (action) {
+            case "goto_definition" -> gotoDefinition(manager, path, lspLine, lspCol);
+            case "find_references" -> findReferences(manager, path, lspLine, lspCol);
+            case "hover" -> hover(manager, path, lspLine, lspCol);
+            case "diagnostics" -> getDiagnostics(context, path);
+            case "document_symbols" -> documentSymbols(manager, path);
+            default -> "Error: Unknown action: " + action;
+        };
+    }
+
+    private String gotoDefinition(LSPServerManager manager, Path file, int line, int col) {
+        try {
+            Map<String, Object> params = textDocumentPositionParams(file, line, col);
+            JsonNode result = manager.sendRequest(file.toString(), "textDocument/definition", params);
+            if (result == null || result.isNull()) return "No definition found";
+            return formatLocations("Definition", result);
+        } catch (Exception e) {
+            return "Error: " + e.getMessage();
+        }
+    }
+
+    private String findReferences(LSPServerManager manager, Path file, int line, int col) {
+        try {
+            Map<String, Object> params = textDocumentPositionParams(file, line, col);
+            params.put("context", Map.of("includeDeclaration", true));
+            JsonNode result = manager.sendRequest(file.toString(), "textDocument/references", params);
+            if (result == null || result.isNull()) return "No references found";
+            return formatLocations("References", result);
+        } catch (Exception e) {
+            return "Error: " + e.getMessage();
+        }
+    }
+
+    private String hover(LSPServerManager manager, Path file, int line, int col) {
+        try {
+            Map<String, Object> params = textDocumentPositionParams(file, line, col);
+            JsonNode result = manager.sendRequest(file.toString(), "textDocument/hover", params);
+            if (result == null || result.isNull()) return "No hover information available";
+            return formatHover(result);
+        } catch (Exception e) {
+            return "Error: " + e.getMessage();
+        }
+    }
+
+    private String getDiagnostics(ToolContext context, Path file) {
+        Object regObj = context.get("LSP_DIAGNOSTIC_REGISTRY");
+        if (regObj instanceof LSPDiagnosticRegistry registry) {
+            var files = registry.checkAndExtract();
+            if (files.isEmpty()) {
+                return "No diagnostics for " + file.getFileName();
+            }
+            String formatted = LSPDiagnosticRegistry.formatForContext(files);
+            return formatted.isEmpty() ? "No diagnostics" : formatted;
+        }
+        return "Diagnostic registry not available";
+    }
+
+    private String documentSymbols(LSPServerManager manager, Path file) {
+        try {
+            Map<String, Object> params = Map.of(
+                    "textDocument", Map.of("uri", file.toUri().toString()));
+            JsonNode result = manager.sendRequest(file.toString(), "textDocument/documentSymbol", params);
+            if (result == null || result.isNull()) return "No symbols found";
+            return formatSymbols(result);
+        } catch (Exception e) {
+            return "Error: " + e.getMessage();
+        }
+    }
+
+    // ==================== Helpers ====================
+
+    private Map<String, Object> textDocumentPositionParams(Path file, int line, int col) {
+        Map<String, Object> params = new LinkedHashMap<>();
+        params.put("textDocument", Map.of("uri", file.toUri().toString()));
+        params.put("position", Map.of("line", line, "character", col));
+        return params;
+    }
+
+    @SuppressWarnings("unchecked")
+    private String formatLocations(String label, JsonNode result) {
+        StringBuilder sb = new StringBuilder();
+        sb.append(label).append(":\n");
+
+        if (result.isArray()) {
+            if (result.isEmpty()) return "No " + label.toLowerCase() + " found";
+            int count = 0;
+            for (JsonNode loc : result) {
+                String uri = loc.path("uri").asText("");
+                String path = uri.replaceFirst("^file:///", "").replaceFirst("^file://", "");
+                sb.append("  ").append(path);
+                JsonNode range = loc.get("range");
+                if (range != null) {
+                    JsonNode start = range.get("start");
+                    if (start != null) {
+                        sb.append(":").append(start.path("line").asInt() + 1);
+                        sb.append(":").append(start.path("character").asInt() + 1);
+                    }
+                }
+                sb.append("\n");
+                if (++count >= 20) {
+                    sb.append("  ... and ").append(result.size() - 20).append(" more\n");
+                    break;
+                }
+            }
+        } else if (result.isObject()) {
+            String uri = result.path("uri").asText("");
+            sb.append("  ").append(uri.replaceFirst("^file:///", "")).append("\n");
+        }
+        return sb.toString();
+    }
+
+    private String formatHover(JsonNode result) {
+        if (result.isObject()) {
+            JsonNode contents = result.get("contents");
+            if (contents == null) return "No information";
+            if (contents.isTextual()) return contents.asText();
+            if (contents.isObject()) {
+                return contents.path("value").asText("No information");
+            }
+            if (contents.isArray()) {
+                StringBuilder sb = new StringBuilder();
+                for (JsonNode item : contents) {
+                    if (item.isTextual()) sb.append(item.asText()).append("\n");
+                    else if (item.isObject()) sb.append(item.path("value").asText()).append("\n");
+                }
+                return sb.toString().trim();
+            }
+        }
+        return result.toString();
+    }
+
+    private String formatSymbols(JsonNode result) {
+        if (!result.isArray()) return "No symbols";
+
+        StringBuilder sb = new StringBuilder();
+        sb.append("Symbols:\n");
+        int count = 0;
+        for (JsonNode sym : result) {
+            String symName = sym.path("name").asText("?");
+            int kind = sym.path("kind").asInt(0);
+            String kindStr = symbolKindName(kind);
+            sb.append(String.format("  %s %s%n", kindStr, symName));
+
+            // Handle children (DocumentSymbol)
+            JsonNode children = sym.get("children");
+            if (children != null && children.isArray()) {
+                for (JsonNode child : children) {
+                    String cName = child.path("name").asText("?");
+                    int cKind = child.path("kind").asInt(0);
+                    sb.append(String.format("    %s %s%n", symbolKindName(cKind), cName));
+                }
+            }
+
+            if (++count >= 50) {
+                sb.append("  ... and more\n");
+                break;
+            }
+        }
+        return sb.toString();
+    }
+
+    private String symbolKindName(int kind) {
+        return switch (kind) {
+            case 1 -> "📄 File";
+            case 2 -> "📦 Module";
+            case 3 -> "🔲 Namespace";
+            case 4 -> "📦 Package";
+            case 5 -> "🏷 Class";
+            case 6 -> "⚡ Method";
+            case 7 -> "🔧 Property";
+            case 8 -> "📌 Field";
+            case 9 -> "🔨 Constructor";
+            case 10 -> "📋 Enum";
+            case 11 -> "🔗 Interface";
+            case 12 -> "λ Function";
+            case 13 -> "📎 Variable";
+            case 14 -> "📐 Constant";
+            case 15 -> "📝 String";
+            case 16 -> "🔢 Number";
+            case 17 -> "☑ Boolean";
+            case 18 -> "📊 Array";
+            case 19 -> "📋 Object";
+            case 23 -> "📌 Struct";
+            case 26 -> "📎 TypeParameter";
+            default -> "  Symbol";
+        };
+    }
+
+    private String noServerMessage(Path file) {
+        String ext = file.toString();
+        int dot = ext.lastIndexOf('.');
+        ext = dot >= 0 ? ext.substring(dot) : "unknown";
+        return "No LSP server configured for " + ext + " files. Configure in plugin settings.";
+    }
+
+    @Override
+    public String activityDescription(Map<String, Object> input) {
+        String action = (String) input.getOrDefault("action", "query");
+        String file = (String) input.getOrDefault("file_path", "");
+        String name = Path.of(file).getFileName().toString();
+        return "🔍 LSP " + action + " in " + name;
+    }
+}
diff --git a/src/main/java/com/claudecode/tool/impl/NotificationTool.java b/src/main/java/com/claudecode/tool/impl/NotificationTool.java
new file mode 100644
index 0000000..3763b83
--- /dev/null
+++ b/src/main/java/com/claudecode/tool/impl/NotificationTool.java
@@ -0,0 +1,185 @@
+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.awt.*;
+import java.io.IOException;
+import java.util.Map;
+
+/**
+ * Notification 工具 —— 系统通知。
+ * <p>
+ * 向用户发送系统级通知（桌面弹窗 + 可选声音提示），用于：
+ * <ul>
+ *   <li>长时间任务完成时通知用户</li>
+ *   <li>需要用户注意的错误或警告</li>
+ *   <li>Agent 需要用户输入时的提醒</li>
+ * </ul>
+ * <p>
+ * 底层使用 Java AWT SystemTray (桌面环境) 或退回到 BEL 字符（终端环境）。
+ */
+public class NotificationTool implements Tool {
+
+    private static final Logger log = LoggerFactory.getLogger(NotificationTool.class);
+
+    @Override
+    public String name() {
+        return "Notification";
+    }
+
+    @Override
+    public String description() {
+        return """
+            Send a system notification to the user. Use this when:
+            - A long-running task completes and the user may have switched away
+            - An error requires the user's attention
+            - You need the user to come back and provide input
+            
+            Supports desktop notifications (with optional sound) and terminal bell.""";
+    }
+
+    @Override
+    public String inputSchema() {
+        return """
+            {
+              "type": "object",
+              "properties": {
+                "title": {
+                  "type": "string",
+                  "description": "Notification title (short, max 80 chars)"
+                },
+                "message": {
+                  "type": "string",
+                  "description": "Notification body text"
+                },
+                "level": {
+                  "type": "string",
+                  "enum": ["info", "warning", "error"],
+                  "description": "Notification severity level (default: info)"
+                },
+                "sound": {
+                  "type": "boolean",
+                  "description": "Play notification sound (default: true)"
+                }
+              },
+              "required": ["title", "message"]
+            }""";
+    }
+
+    @Override
+    public boolean isReadOnly() {
+        return true;
+    }
+
+    @Override
+    public String execute(Map<String, Object> input, ToolContext context) {
+        String title = (String) input.get("title");
+        String message = (String) input.get("message");
+        String level = (String) input.getOrDefault("level", "info");
+        Boolean sound = (Boolean) input.getOrDefault("sound", true);
+
+        if (title == null || message == null) {
+            return "Error: 'title' and 'message' are required";
+        }
+
+        // Truncate title if too long
+        if (title.length() > 80) {
+            title = title.substring(0, 77) + "...";
+        }
+
+        boolean sent = false;
+        String method = "none";
+
+        // Try OS-specific notification
+        String os = System.getProperty("os.name", "").toLowerCase();
+        try {
+            if (os.contains("win")) {
+                sent = notifyWindows(title, message);
+                method = "windows-toast";
+            } else if (os.contains("mac")) {
+                sent = notifyMac(title, message);
+                method = "osascript";
+            } else if (os.contains("linux")) {
+                sent = notifyLinux(title, message);
+                method = "notify-send";
+            }
+        } catch (Exception e) {
+            log.debug("OS notification failed: {}", e.getMessage());
+        }
+
+        // Fallback: terminal bell
+        if (Boolean.TRUE.equals(sound)) {
+            System.out.print('\u0007'); // BEL character
+            System.out.flush();
+        }
+
+        if (!sent) {
+            // Fallback: just print to terminal
+            String icon = switch (level) {
+                case "warning" -> "⚠️";
+                case "error" -> "❌";
+                default -> "ℹ️";
+            };
+            method = "terminal";
+            sent = true;
+        }
+
+        return String.format("Notification sent via %s: [%s] %s - %s", method, level, title, message);
+    }
+
+    private boolean notifyWindows(String title, String message) {
+        try {
+            // Use PowerShell to send Windows toast notification
+            String ps = String.format(
+                    "[System.Reflection.Assembly]::LoadWithPartialName('System.Windows.Forms') | Out-Null; " +
+                    "$n = New-Object System.Windows.Forms.NotifyIcon; " +
+                    "$n.Icon = [System.Drawing.SystemIcons]::Information; " +
+                    "$n.Visible = $true; " +
+                    "$n.ShowBalloonTip(5000, '%s', '%s', 'Info'); " +
+                    "Start-Sleep -Seconds 1; $n.Dispose()",
+                    title.replace("'", "''"), message.replace("'", "''"));
+
+            ProcessBuilder pb = new ProcessBuilder("powershell", "-NoProfile", "-Command", ps);
+            pb.inheritIO();
+            Process proc = pb.start();
+            return proc.waitFor() == 0;
+        } catch (Exception e) {
+            log.debug("Windows notification failed: {}", e.getMessage());
+            return false;
+        }
+    }
+
+    private boolean notifyMac(String title, String message) {
+        try {
+            String script = String.format(
+                    "display notification \"%s\" with title \"%s\"",
+                    message.replace("\"", "\\\""), title.replace("\"", "\\\""));
+            ProcessBuilder pb = new ProcessBuilder("osascript", "-e", script);
+            Process proc = pb.start();
+            return proc.waitFor() == 0;
+        } catch (Exception e) {
+            log.debug("macOS notification failed: {}", e.getMessage());
+            return false;
+        }
+    }
+
+    private boolean notifyLinux(String title, String message) {
+        try {
+            ProcessBuilder pb = new ProcessBuilder("notify-send", title, message);
+            Process proc = pb.start();
+            return proc.waitFor() == 0;
+        } catch (Exception e) {
+            log.debug("Linux notification failed: {}", e.getMessage());
+            return false;
+        }
+    }
+
+    @Override
+    public String activityDescription(Map<String, Object> input) {
+        String title = (String) input.getOrDefault("title", "notification");
+        return "🔔 Notify: " + title;
+    }
+}