diff --git a/packages/coding-agent/src/mcp/transports/stdio.ts b/packages/coding-agent/src/mcp/transports/stdio.ts
index d6e6ebe60..d3d0e2212 100644
--- a/packages/coding-agent/src/mcp/transports/stdio.ts
+++ b/packages/coding-agent/src/mcp/transports/stdio.ts
@@ -110,23 +110,17 @@ async function resolveWindowsCommandPath(
 function quoteCmdArg(value: string): string {
 	if (value.length === 0) return '""';
 	let result = '"';
-	let backslashes = 0;
 	for (const char of value) {
-		if (char === "\\") {
-			backslashes++;
-			continue;
-		}
 		if (char === '"') {
-			result += "\\".repeat(backslashes * 2 + 1);
-			result += '"';
-			backslashes = 0;
-			continue;
+			result += '^"';
+		} else if (char === "^") {
+			result += "^^";
+		} else if (char === "%") {
+			result += "^%";
+		} else {
+			result += char;
 		}
-		result += "\\".repeat(backslashes);
-		backslashes = 0;
-		result += char === "%" ? "^%" : char;
 	}
-	result += "\\".repeat(backslashes * 2);
 	return `${result}"`;
 }
 
diff --git a/packages/coding-agent/test/mcp-stdio-transport.test.ts b/packages/coding-agent/test/mcp-stdio-transport.test.ts
index ffb2159c1..5f3396c74 100644
--- a/packages/coding-agent/test/mcp-stdio-transport.test.ts
+++ b/packages/coding-agent/test/mcp-stdio-transport.test.ts
@@ -62,6 +62,37 @@ describe("resolveStdioSpawnCommand", () => {
 		}
 	});
 
+	it("escapes quoted JSON args before routing .cmd shims through cmd.exe", async () => {
+		const tempDir = await fs.mkdtemp(path.join(os.tmpdir(), "omp-mcp-quotes-"));
+		try {
+			const shim = path.join(tempDir, "codegraph.cmd");
+			await Bun.write(shim, "@echo off\r\n");
+
+			const result = await resolveStdioSpawnCommand(
+				{ type: "stdio", command: "codegraph", args: ["--config", '{"a":"b&c|d"}'] },
+				{
+					cwd: tempDir,
+					env: {
+						COMSPEC: "C:\\Windows\\System32\\cmd.exe",
+						PATH: tempDir,
+						PATHEXT: ".cmd",
+					},
+					platform: "win32",
+				},
+			);
+
+			expect(result.cmd).toEqual([
+				"C:\\Windows\\System32\\cmd.exe",
+				"/d",
+				"/s",
+				"/c",
+				`"${shim}" "--config" "{^"a^":^"b&c|d^"}"`,
+			]);
+		} finally {
+			await fs.rm(tempDir, { recursive: true, force: true });
+		}
+	});
+
 	it("resolves extension-less absolute Windows paths to the sibling .cmd shim", async () => {
 		// Mirrors npm's Windows shim layout: bare `codegraph` (shebang script),
 		// `codegraph.cmd` (cmd.exe wrapper), and `codegraph.ps1` siblings under