refactor: organize agent harness courses

learn-pi-agent/s07_session_tree/code.ts

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+// s07: Session Tree — mini Pi 的第 7 版
+//
+// [U1 受控升级] AgentState.messages 从数组升级为 SessionTree：历史能分叉，一轮输入取当前路径。
+// 词汇边界：本章新增 SessionTree / SessionEntry / parentId / moveTo / currentPath / append / activeLeaf。
+// 关键：currentPath() 仍产出线性 AgentMessage[]，ProviderInput 的构造方式不变；id 计数器是实例级（不跨实例累加）。
+
+declare const process: {
+  exitCode?: number;
+};
+
+// —— 停止原因（s04 起）——
+export type StopReason = "stop" | "toolUse" | "error";
+
+// —— 消息 ——
+export type UserMessage = { role: "user"; content: string };
+export type AssistantMessage = { role: "assistant"; content: string; stopReason: StopReason };
+export type ToolResultMessage = { role: "toolResult"; toolCallId: string; content: string };
+export type AgentMessage = UserMessage | AssistantMessage | ToolResultMessage;
+
+// ============ s07 新增 [U1]：会话历史从数组变成树 ============
+
+// 一个节点 = 一条消息 + 它在树里的位置。
+export type SessionEntry = {
+  id: string;
+  parentId: string | null;
+  message: AgentMessage;
+};
+
+export class SessionTree {
+  private entries = new Map<string, SessionEntry>();
+  private activeLeafId: string | null = null;
+  private counter = 0; // 实例级：每个 SessionTree 独立计数，不跨实例累加
+
+  append(message: AgentMessage): SessionEntry {
+    const entry: SessionEntry = {
+      id: `e${++this.counter}`,
+      parentId: this.activeLeafId,
+      message,
+    };
+    this.entries.set(entry.id, entry);
+    this.activeLeafId = entry.id;
+    return entry;
+  }
+
+  // 切换当前位置到某个已有节点（分叉的起点）。不存在的 id 会抛错。
+  moveTo(entryId: string): void {
+    if (!this.entries.has(entryId)) {
+      throw new Error(`unknown entry: ${entryId}`);
+    }
+    this.activeLeafId = entryId;
+  }
+
+  // 从当前位置回溯到根，产出一条线性的消息序列。ProviderInput 就用它。
+  currentPath(): AgentMessage[] {
+    const path: AgentMessage[] = [];
+    let cursor = this.activeLeafId;
+    while (cursor) {
+      const entry = this.entries.get(cursor);
+      if (!entry) break;
+      path.push(entry.message);
+      cursor = entry.parentId;
+    }
+    return path.reverse();
+  }
+
+  allEntries(): SessionEntry[] {
+    return [...this.entries.values()];
+  }
+}
+
+// [U1] core 内部状态：messages 数组 → SessionTree；model 跨轮配置（对齐 Pi AgentState）。
+export type AgentState = {
+  session: SessionTree;
+  model: string;
+};
+
+// —— 工具契约 ——
+export type ToolSpec = { name: string; description: string; input: Record<string, string> };
+export type ToolHandler = (input: Record<string, string>) => string;
+export type ToolCall = { id: string; name: string; input: Record<string, string> };
+export type Tool = { spec: ToolSpec; handler: ToolHandler };
+
+export class ToolRegistry {
+  private tools = new Map<string, Tool>();
+  register(tool: Tool): void { this.tools.set(tool.spec.name, tool); }
+  getSpecs(): ToolSpec[] { return [...this.tools.values()].map((tool) => tool.spec); }
+  count(): number { return this.tools.size; }
+  run(call: ToolCall): string {
+    const tool = this.tools.get(call.name);
+    if (!tool) return `unknown tool: ${call.name}`;
+    return tool.handler(call.input);
+  }
+}
+
+// —— provider 对外 ——
+export type ProviderMessage =
+  | { role: "user" | "assistant"; content: string }
+  | { role: "toolResult"; toolCallId: string; content: string };
+
+// 对齐 Pi Context：messages + tools。model 在 AgentState，不进 ProviderInput。
+export type ProviderInput = {
+  messages: ProviderMessage[];
+  tools: ToolSpec[];
+};
+
+export type ProviderEvent =
+  | { type: "message_start" }
+  | { type: "text_delta"; text: string }
+  | { type: "tool_call"; call: ToolCall }
+  | { type: "message_end"; stopReason: StopReason };
+
+export interface Provider {
+  stream(input: ProviderInput): AsyncGenerator<ProviderEvent>;
+}
+
+export type Output = { log(line: string): void };
+export function createConsoleOutput(): Output { return { log: (line) => console.log(line) }; }
+
+// —— s05 起：执行插口 ——
+export type BeforeToolCallResult = { type: "allow" } | { type: "block"; reason: string };
+export type ToolHooks = {
+  beforeToolCall?: (call: ToolCall) => BeforeToolCallResult;
+  afterToolCall?: (call: ToolCall, result: string) => string;
+};
+
+export function executeToolCall(registry: ToolRegistry, hooks: ToolHooks, call: ToolCall): ToolResultMessage {
+  const before = hooks.beforeToolCall?.(call) ?? { type: "allow" };
+  if (before.type === "block") {
+    return { role: "toolResult", toolCallId: call.id, content: `blocked: ${before.reason}` };
+  }
+  let result: string;
+  try {
+    result = registry.run(call);
+  } catch (error) {
+    result = `error: ${error instanceof Error ? error.message : String(error)}`;
+  }
+  const finalResult = hooks.afterToolCall?.(call, result) ?? result;
+  return { role: "toolResult", toolCallId: call.id, content: finalResult };
+}
+
+// —— s06 起：一轮快照（对齐 Pi AgentContext：固定 messages/tools；model 在 state 不进快照）——
+export type TurnSnapshot = {
+  messages: ProviderMessage[];
+  tools: ToolSpec[];
+};
+
+function toProviderMessages(messages: AgentMessage[]): ProviderMessage[] {
+  return messages.map((message) => {
+    if (message.role === "toolResult") {
+      return { role: "toolResult", toolCallId: message.toolCallId, content: message.content };
+    }
+    return { role: message.role, content: message.content };
+  });
+}
+
+// s07：messages 从 state.session.currentPath() 取（线性投影当前路径）。
+export function createTurnSnapshot(
+  state: AgentState,
+  registry: ToolRegistry,
+): TurnSnapshot {
+  return {
+    messages: toProviderMessages(state.session.currentPath()),
+    tools: registry.getSpecs(),
+  };
+}
+
+export function buildProviderInputFromSnapshot(
+  snapshot: TurnSnapshot,
+  state: AgentState,
+): ProviderInput {
+  return {
+    messages: toProviderMessages(state.session.currentPath()),
+    tools: snapshot.tools,
+  };
+}
+
+// ============ 构造函数 ============
+export function createInitialState(model = "demo-small"): AgentState {
+  return { session: new SessionTree(), model };
+}
+
+export function createUserMessage(content: string): UserMessage {
+  return { role: "user", content };
+}
+
+// ============ 工具循环（s07：用 state.session）============
+const MAX_TURNS = 8;
+
+export async function runEventedToolLoop(
+  state: AgentState,
+  provider: Provider,
+  registry: ToolRegistry,
+  hooks: ToolHooks,
+  snapshot: TurnSnapshot,
+  output: Output,
+): Promise<AssistantMessage> {
+  let turns = 0;
+
+  while (true) {
+    turns += 1;
+    if (turns > MAX_TURNS) {
+      const stopped: AssistantMessage = {
+        role: "assistant",
+        content: "(达到最大轮次，停止)",
+        stopReason: "stop",
+      };
+      state.session.append(stopped);
+      return stopped;
+    }
+
+    const providerInput = buildProviderInputFromSnapshot(snapshot, state);
+    let content = "";
+    let stopReason: StopReason = "stop";
+    let sawToolCall = false;
+
+    for await (const event of provider.stream(providerInput)) {
+      if (event.type === "message_start") {
+        output.log("message_start");
+      } else if (event.type === "text_delta") {
+        output.log(`text_delta: ${event.text}`);
+        content += event.text;
+      } else if (event.type === "tool_call") {
+        sawToolCall = true;
+        output.log(`tool_call: ${event.call.name}`);
+        const resultMessage = executeToolCall(registry, hooks, event.call);
+        state.session.append(resultMessage);
+        output.log(`tool_result: ${resultMessage.content}`);
+      } else if (event.type === "message_end") {
+        stopReason = event.stopReason;
+        output.log(`message_end: ${stopReason}`);
+      }
+    }
+
+    if (!sawToolCall || stopReason !== "toolUse") {
+      const assistant: AssistantMessage = { role: "assistant", content, stopReason };
+      state.session.append(assistant);
+      return assistant;
+    }
+  }
+}
+
+// ============ Demo Provider（fake）============
+export class DemoProvider implements Provider {
+  public lastInput: ProviderInput | undefined;
+
+  async *stream(input: ProviderInput): AsyncGenerator<ProviderEvent> {
+    this.lastInput = input;
+    const last = input.messages[input.messages.length - 1];
+
+    yield { type: "message_start" };
+
+    if (last?.role === "toolResult") {
+      yield { type: "text_delta", text: `工具结果是：${last.content}` };
+      yield { type: "message_end", stopReason: "stop" };
+      return;
+    }
+
+    yield {
+      type: "tool_call",
+      call: { id: "call_1", name: "current_time", input: {} },
+    };
+    yield { type: "message_end", stopReason: "toolUse" };
+  }
+}
+
+// ============ 演示脚手架：演示历史分叉 ============
+
+function printPath(output: Output, title: string, path: AgentMessage[]): void {
+  output.log(title);
+  for (const message of path) {
+    output.log(`${message.role}: ${message.content}`);
+  }
+  output.log("");
+}
+
+async function main(): Promise<void> {
+  const output = createConsoleOutput();
+  const state = createInitialState();
+
+  output.log("s07: Session Tree");
+  output.log("");
+
+  // 第一条线：方案 A
+  const first = state.session.append(createUserMessage("方案 A"));
+  state.session.append({
+    role: "assistant",
+    content: "A 的回答",
+    stopReason: "stop",
+  });
+
+  printPath(output, "[路径：方案 A]", state.session.currentPath());
+
+  // 回到第一个节点，从那里分叉出方案 B
+  state.session.moveTo(first.id);
+  state.session.append({
+    role: "assistant",
+    content: "改走方案 B",
+    stopReason: "stop",
+  });
+
+  printPath(output, "[路径：方案 B]", state.session.currentPath());
+
+  // 树的全貌
+  output.log("[所有节点]");
+  for (const entry of state.session.allEntries()) {
+    output.log(
+      `${entry.id} parent=${entry.parentId ?? "null"} ${entry.message.role}: ${entry.message.content}`,
+    );
+  }
+  output.log("");
+}
+
+main().catch((error: unknown) => {
+  console.error(error);
+  process.exitCode = 1;
+});