fix(coding-agent): run legacy WSL bash commands via stdin

closes #5893

scripts/repro-5893-wsl-bash.mjs

@@ -0,0 +1,55 @@
+#!/usr/bin/env node
+import { existsSync } from "node:fs";
+import { createBashTool } from "../packages/coding-agent/src/core/tools/bash.ts";
+
+const shellPath = "C:\\Windows\\System32\\bash.exe";
+const nameExpansion = "$" + "{name}";
+const countExpansion = "$" + "{count}";
+const iExpansion = "$" + "{i}";
+
+function getTextOutput(result) {
+	return result.content
+		.filter((content) => content.type === "text")
+		.map((content) => content.text ?? "")
+		.join("\n");
+}
+
+async function runCase(label, command, expectedOutput) {
+	const tool = createBashTool(process.cwd(), { shellPath });
+	const result = await tool.execute(label, { command });
+	const output = getTextOutput(result).trimEnd();
+	if (output !== expectedOutput) {
+		throw new Error(
+			[
+				`${label} failed`,
+				"Expected:",
+				expectedOutput,
+				"Actual:",
+				output,
+			].join("\n"),
+		);
+	}
+	console.log(output);
+}
+
+if (process.platform !== "win32") {
+	throw new Error("This repro must run from Windows PowerShell/CMD, not macOS/Linux or inside WSL.");
+}
+
+if (!existsSync(shellPath)) {
+	throw new Error(`WSL bash launcher not found at ${shellPath}. Install/enable WSL first.`);
+}
+
+await runCase(
+	"issue-5893-simple-variable",
+	`name='World'; echo "Hello, ${nameExpansion}!"`,
+	"Hello, World!",
+);
+
+await runCase(
+	"issue-5893-loop-variable",
+	`count=3; for i in $(seq 1 ${countExpansion}); do echo "Iteration ${iExpansion} of ${countExpansion}"; done`,
+	"Iteration 1 of 3\nIteration 2 of 3\nIteration 3 of 3",
+);
+
+console.log("issue #5893 WSL bash repro passed");