diff --git a/src/core/assembler.ts b/src/core/assembler.ts
index 2d3fbab..6a5647b 100644
--- a/src/core/assembler.ts
+++ b/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);
diff --git a/tests/core/assembler.test.ts b/tests/core/assembler.test.ts
index 77fda23..45d5604 100644
--- a/tests/core/assembler.test.ts
+++ b/tests/core/assembler.test.ts
@@ -184,10 +184,15 @@ describe("assembleBuildPrompt", () => {
     expect(prompt).toContain("归档");
   });
 
-  it("task.md 不存在时抛出错误", async () => {
-    await expect(
-      assembleBuildPrompt(defaultConfig, TMP_DIR, "nonexistent"),
-    ).rejects.toThrow("task.md not found");
+  it("task.md 不存在时抛出 CommandError 并附带提示", async () => {
+    try {
+      await assembleBuildPrompt(defaultConfig, TMP_DIR, "nonexistent");
+      expect.unreachable();
+    } catch (e: any) {
+      expect(e.message).toContain("尚未完成规划");
+      expect(e.message).toContain("nonexistent");
+      expect(e.hint).toContain("rune plan");
+    }
   });
 });