fix: build 命令在 plan 未完成时给出友好提示而非未预期错误

src/core/assembler.ts

@@ -2,6 +2,7 @@ import { existsSync } from "node:fs";
 import { readFile } from "node:fs/promises";
 import { join } from "node:path";
 import type { RuneConfig } from "../types.ts";
+import { CommandError } from "../cli/errors.ts";
 import { getChangeDir } from "./config.ts";
 import { parseTasks } from "./task-parser.ts";
 
@@ -69,7 +70,11 @@ export async function assembleBuildPrompt(
   changeName: string,
 ): Promise<string> {
   const build = config.stages.build;
-  if (!build) throw new Error("build 阶段未配置");
+  if (!build) {
+    throw new CommandError("构建阶段未配置", {
+      hint: "请在 .rune/config.yaml 中配置 stages.build",
+    });
+  }
 
   const changeDir = getChangeDir(projectRoot, changeName);
   const taskPath = join(changeDir, "task.md");
@@ -78,7 +83,9 @@ export async function assembleBuildPrompt(
   try {
     taskContent = await readFile(taskPath, "utf-8");
   } catch {
-    throw new Error(`task.md not found in ${changeDir}`);
+    throw new CommandError(`变更 "${changeName}" 尚未完成规划，task.md 不存在`, {
+      hint: `请先完成规划阶段：rune plan ${changeName} 生成所有规划文档`,
+    });
   }
 
   const tasks = parseTasks(taskContent);