fix: drain stdout before resolving when a child holds the pipe past exit (#5753)

packages/coding-agent/test/suite/regressions/5208-late-bash-output.test.ts

@@ -0,0 +1,29 @@
+import { describe, expect, it } from "vitest";
+import { type BashOperations, createBashTool } from "../../../src/core/tools/bash.ts";
+
+function getTextOutput(result: { content?: Array<{ type: string; text?: string }> }): string {
+	return (
+		result.content
+			?.filter((block) => block.type === "text")
+			.map((block) => block.text ?? "")
+			.join("\n") ?? ""
+	);
+}
+
+describe("regression #5208: late bash output callbacks", () => {
+	it("ignores output callbacks after bash operations resolve", async () => {
+		const operations: BashOperations = {
+			exec: async (_command, _cwd, { onData }) => {
+				onData(Buffer.from("before\n", "utf-8"));
+				setTimeout(() => onData(Buffer.from("late\n", "utf-8")), 0);
+				return { exitCode: 0 };
+			},
+		};
+		const bash = createBashTool(process.cwd(), { operations });
+
+		const result = await bash.execute("test-call-late-output", { command: "late-output" });
+		await new Promise((resolve) => setTimeout(resolve, 20));
+
+		expect(getTextOutput(result).trim()).toBe("before");
+	});
+});