从Claude Code的源码中学到了什么——详细拆解＂动态提示词组装＂机制

// 伪代码示意interface PromptFragment {  id: string;           // 唯一标识  content: string;      // 提示内容  condition: ContextCondition;  // 触发条件  priority: number;     // 优先级  tokens: number;       // token数（用于预算管理）}// 条件判断示例const conditions = {  mode: 'plan' | 'coordinator' | 'default',  toolsAvailable: string[],  userType: 'ant' | 'external',  // 内部员工vs外部用户  featureFlags: Record<string, boolean>}

// 每次调用API前执行：function assemblePrompt(context: Context): string {  const fragments: string[] = [];  // 1. 筛选符合条件的提示碎片  const activeFragments = allFragments.filter(f =>     evaluateCondition(f.condition, context)  );  // 2. 按优先级排序  activeFragments.sort((a, b) => b.priority - a.priority);  // 3. 构建token预算（防止超窗）  let tokenBudget = MAX_CONTEXT_TOKENS;  for (const fragment of activeFragments) {    if (fragment.tokens <= tokenBudget) {      fragments.push(fragment.content);      tokenBudget -= fragment.tokens;    } else {      // 超出预算，用指针替代完整内容      fragments.push(createPointer(fragment));    }  }  // 4. 注入CLAUDE.md（最高优先级，用户自定义覆盖）  fragments.push(context.claudeMdContent);  // 5. 最终拼接  return fragments.join('\n\n');}

// 概念示意图：Transformer的KV Cache机制interface KVCache {  // 每个token处理时产生的三个向量  keys: Float32Array[];    // Key: "我包含什么信息？"  values: Float32Array[];  // Value: "我携带什么信息？"  queries: Float32Array[]; // Query: "我在找什么？"}// 缓存的本质：存储已处理token的Key和Value向量// 这样新token只需要计算Query，然后与缓存的Keys匹配

// 基于源码分析的缓存断点设计interface CacheBreakpoint {  id: number;  name: string;  content: string;  position: 'prefix' | 'dynamic' | 'suffix';  sticky: boolean;  // 粘性锁存器}// 14个断点的具体分布const CACHE_BREAKPOINTS: CacheBreakpoint[] = [  // ===== 前缀层（全局共享，所有用户共用）=====  { id: 1, name: "identity", content: "You are Claude Code...", position: 'prefix', sticky: true },  { id: 2, name: "core_capabilities", content: "You are an interactive CLI tool...", position: 'prefix', sticky: true },  { id: 3, name: "security_rules", content: "Security guidelines...", position: 'prefix', sticky: true },  { id: 4, name: "task_rules", content: "Task execution rules...", position: 'prefix', sticky: true },  // ===== 工具定义层（相对静态）=====  { id: 5, name: "tool_read", content: "Read tool schema...", position: 'prefix', sticky: true },  { id: 6, name: "tool_edit", content: "Edit tool schema...", position: 'prefix', sticky: true },  { id: 7, name: "tool_bash", content: "Bash tool schema...", position: 'prefix', sticky: true },  { id: 8, name: "tool_grep", content: "Grep tool schema...", position: 'prefix', sticky: true },  { id: 9, name: "other_tools", content: "40+ tool schemas...", position: 'prefix', sticky: true },  // ===== 动态内容层（会话相关）=====  { id: 10, name: "claude_md", content: "Project CLAUDE.md", position: 'dynamic', sticky: false },  { id: 11, name: "memory_md", content: "MEMORY.md content", position: 'dynamic', sticky: false },  { id: 12, name: "mcp_tools", content: "MCP server tools", position: 'dynamic', sticky: false },  // ===== 对话历史层（持续变化）=====  { id: 13, name: "conversation", content: "Previous messages", position: 'dynamic', sticky: false },  { id: 14, name: "current_input", content: "User's current message", position: 'suffix', sticky: false },];

// 核心问题：模式切换会导致缓存失效吗？// 答案：Claude Code用"粘性锁存器"防止这个问题interface StickyLatch {  // 即使模式切换，这部分内容保持不变  lockedContent: string;  // 允许在lockedContent之后动态添加  appendOnly: boolean;}// 实际应用示例const SYSTEM_PROMPT_DYNAMIC_BOUNDARY: StickyLatch = {  // 核心身份和能力声明（永远不变）  lockedContent: `    You are Claude Code, Anthropic's official CLI for coding.    You are an interactive CLI tool...    [安全守则 5,677 tokens]    [工具定义 ~15,000 tokens]  `,  // 以下内容可以追加，但不能破坏lockedContent  appendOnly: true};// 模式切换时（如进入Plan Mode）function switchMode(newMode: 'plan' | 'default' | 'coordinator'): void {  // 不替换整个提示词，而是在lockedContent后追加模式指令  const modeInstruction = getModeInstruction(newMode);  // 缓存前缀（lockedContent）保持warm  // 只有模式指令和对话是新token  return `${SYSTEM_PROMPT_DYNAMIC_BOUNDARY.lockedContent}  ${modeInstruction}  [对话历史]`;}

// 成本计算（基于Anthropic定价）const PRICING = {  input: 3.00,           // $/million tokens  cacheWrite: 3.75,      // $/million tokens (1.25x)  cacheRead: 0.30,       // $/million tokens (0.1x)};// 典型会话场景（30K tokens系统提示 + 对话）function calculateCost(turns: number): void {  const systemTokens = 27000;  // 系统提示 + 工具定义  const conversationTokens = 3000;  // 每轮对话  // 无缓存：每轮都重新处理全部token  const noCacheCost = turns * (systemTokens + conversationTokens) * PRICING.input / 1e6;  // 有缓存：只付一次写入费，后续读缓存  const cacheWriteCost = systemTokens * PRICING.cacheWrite / 1e6;  const cacheReadCost = (turns - 1) * systemTokens * PRICING.cacheRead / 1e6;  const dynamicCost = turns * conversationTokens * PRICING.input / 1e6;  const withCacheCost = cacheWriteCost + cacheReadCost + dynamicCost;  // 10轮对话示例  // 无缓存: 10 * 30000 * 3 / 1e6 = $0.90  // 有缓存: (27000 * 3.75 + 9 * 27000 * 0.3 + 10 * 3000 * 3) / 1e6 = $0.24  // 节省: 73%}

// 简化版数据结构（基于源码分析）interface PromptFragment {  id: string;                    // 唯一标识，如 "tool-usage-bash"  content: string;               // 提示内容  condition?: ContextCondition;  // 触发条件  priority: number;              // 优先级（0-100）  estimatedTokens: number;       // 预估token数  cacheable: boolean;           // 是否可缓存  category: 'identity' | 'rules' | 'tools' | 'memory' | 'context';}// 上下文条件判断interface ContextCondition {  mode?: 'plan' | 'coordinator' | 'default';  tools?: string[];              // 需要启用的工具  userType?: 'ant' | 'external'; // 内部员工 vs 外部用户  featureFlags?: Record<string, boolean>;  projectConfig?: boolean;       // 是否有项目级配置}

// 示例1：工具使用 - Bash（75 tokens）const TOOL_USAGE_BASH: PromptFragment = {  id: "tool-usage-bash",  content: `Reserve the Bash tool exclusively for system commands and terminal operations.Examples of appropriate Bash usage:- Package management: npm install, pip install, cargo add- Build commands: make, npm run build, cargo build- Git operations: git status, git log --oneline -20- System queries: ps aux, df -h, curl -I https://api.example.comExamples that should use other tools:- Reading files → use Read tool instead of cat- Editing files → use Edit tool instead of sed/awk- Searching content → use Grep tool instead of grep/rg- File discovery → use Glob tool instead of find/ls`,  condition: { tools: ['Bash'] },  priority: 70,  estimatedTokens: 75,  cacheable: true,  category: 'tools'};// 示例2：安全守则 - 文件操作（~600 tokens）const FILE_OPERATION_RULES: PromptFragment = {  id: "file-operation-rules",  content: `## Task Execution Rules1. **Read before modifying**: NEVER propose changes to code you haven't read.    Read the relevant code first, understand its context and dependencies.2. **Don't over-engineer**: Only make changes that are directly requested    or are obviously necessary (e.g., syntax errors, type mismatches).    Do not refactor unrelated code or add unnecessary abstractions.3. **Don't create unnecessary files**: Prefer editing existing files over    creating new ones. Use the most appropriate file type for the task at hand.4. **No unnecessary error handling**: Don't add error handling for scenarios    that can't happen, and don't add try/catch blocks unless the code path    can actually fail in expected operation.5. **Security vigilance**: Be careful not to introduce security vulnerabilities    such as SQL injection, XSS, or path traversal.`,  condition: { mode: 'default' },  priority: 90,  // 高优先级，用户规则之前  estimatedTokens: 540,  cacheable: true,  category: 'rules'};// 示例3：Plan Mode 专用提示（~200 tokens）const PLAN_MODE_INSTRUCTIONS: PromptFragment = {  id: "plan-mode-instructions",  content: `You are in Plan Mode. Your task is to explore the codebase, understand its structure, and propose a detailed implementation plan.**Constraints:**- Use ONLY read-only tools (Read, Glob, Grep)- Do NOT write files, edit code, or execute commands- Present a clear, step-by-step plan before any modifications**Output format:**1. Current state analysis2. Proposed changes with file paths3. Potential risks and mitigations4. Testing strategy`,  condition: { mode: 'plan' },  priority: 85,  estimatedTokens: 150,  cacheable: true,  category: 'rules'};

// 源码中发现的提示碎片注册方式// 所有碎片存储在统一注册表中const PROMPT_FRAGMENTS_REGISTRY: Map<string, PromptFragment> = new Map();// 注册函数function registerPromptFragment(fragment: PromptFragment): void {  PROMPT_FRAGMENTS_REGISTRY.set(fragment.id, fragment);}// 批量注册BUILT_IN_FRAGMENTS.forEach(registerPromptFragment);// 用户自定义碎片（通过 CLAUDE.md 注入）function registerUserFragment(content: string, priority: number = 100): void {  registerPromptFragment({    id: `user-${Date.now()}`,    content,    priority,  // 用户碎片最高优先级    cacheable: false,  // 动态内容不缓存    category: 'context'  });}