diff --git a/src/core/terminal.ts b/src/core/terminal.ts
index 11870961..5e99a143 100644
--- a/src/core/terminal.ts
+++ b/src/core/terminal.ts
@@ -29,13 +29,26 @@ export interface ControllingTerminal {
   close: () => void;
 }
 
+/** Minimal terminal construction hooks so tests can cover `/dev/tty` attach behavior. */
+export interface ControllingTerminalDeps {
+  openSync: typeof fs.openSync;
+  createReadStream: (fd: number) => tty.ReadStream;
+  createWriteStream: (fd: number) => tty.WriteStream;
+}
+
 /** Open the controlling terminal so the UI can stay interactive while stdin carries patch data. */
-export function openControllingTerminal(): ControllingTerminal | null {
+export function openControllingTerminal(
+  deps: ControllingTerminalDeps = {
+    openSync: fs.openSync,
+    createReadStream: (fd) => new tty.ReadStream(fd),
+    createWriteStream: (fd) => new tty.WriteStream(fd),
+  },
+): ControllingTerminal | null {
   try {
-    const stdinFd = fs.openSync("/dev/tty", "r");
-    const stdoutFd = fs.openSync("/dev/tty", "w");
-    const stdin = new tty.ReadStream(stdinFd);
-    const stdout = new tty.WriteStream(stdoutFd);
+    const stdinFd = deps.openSync("/dev/tty", "r");
+    const stdoutFd = deps.openSync("/dev/tty", "w");
+    const stdin = deps.createReadStream(stdinFd);
+    const stdout = deps.createWriteStream(stdoutFd);
 
     return {
       stdin,
diff --git a/test/terminal.test.ts b/test/terminal.test.ts
index 11169a4a..eceb3e91 100644
--- a/test/terminal.test.ts
+++ b/test/terminal.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, test } from "bun:test";
 import type { CliInput } from "../src/core/types";
-import { resolveRuntimeCliInput, shouldUsePagerMode, usesPipedPatchInput } from "../src/core/terminal";
+import { openControllingTerminal, resolveRuntimeCliInput, shouldUsePagerMode, usesPipedPatchInput } from "../src/core/terminal";
 
 function createPatchInput(file?: string, pager = false): CliInput {
   return {
@@ -35,3 +35,65 @@ describe("terminal runtime defaults", () => {
     expect(resolveRuntimeCliInput(input, true).options.pager).toBe(true);
   });
 });
+
+describe("controlling terminal attachment", () => {
+  test("opens /dev/tty for read and write and closes both streams", () => {
+    const calls: Array<[string, string]> = [];
+    let stdinDestroyed = false;
+    let stdoutDestroyed = false;
+
+    const stdin = {
+      destroy() {
+        stdinDestroyed = true;
+      },
+    } as never;
+    const stdout = {
+      destroy() {
+        stdoutDestroyed = true;
+      },
+    } as never;
+
+    const controllingTerminal = openControllingTerminal({
+      openSync(path, flags) {
+        calls.push([String(path), String(flags)]);
+        return flags === "r" ? 11 : 12;
+      },
+      createReadStream(fd) {
+        expect(fd).toBe(11);
+        return stdin;
+      },
+      createWriteStream(fd) {
+        expect(fd).toBe(12);
+        return stdout;
+      },
+    });
+
+    expect(controllingTerminal).not.toBeNull();
+    expect(calls).toEqual([
+      ["/dev/tty", "r"],
+      ["/dev/tty", "w"],
+    ]);
+    expect(controllingTerminal?.stdin).toBe(stdin);
+    expect(controllingTerminal?.stdout).toBe(stdout);
+
+    controllingTerminal?.close();
+    expect(stdinDestroyed).toBe(true);
+    expect(stdoutDestroyed).toBe(true);
+  });
+
+  test("returns null when the controlling terminal cannot be opened", () => {
+    const controllingTerminal = openControllingTerminal({
+      openSync() {
+        throw new Error("no tty");
+      },
+      createReadStream() {
+        throw new Error("unreachable");
+      },
+      createWriteStream() {
+        throw new Error("unreachable");
+      },
+    });
+
+    expect(controllingTerminal).toBeNull();
+  });
+});