Add cross-platform masked input utility with tests

src/tests/test_seed_prompt.py

@@ -0,0 +1,30 @@
+import types
+from utils import seed_prompt
+
+
+def test_masked_input_posix_backspace(monkeypatch, capsys):
+    seq = iter(["a", "b", "\x7f", "c", "\n"])
+    monkeypatch.setattr(seed_prompt.sys.stdin, "read", lambda n=1: next(seq))
+    monkeypatch.setattr(seed_prompt.sys.stdin, "fileno", lambda: 0)
+    monkeypatch.setattr(seed_prompt.termios, "tcgetattr", lambda fd: None)
+    monkeypatch.setattr(seed_prompt.termios, "tcsetattr", lambda fd, *_: None)
+    monkeypatch.setattr(seed_prompt.tty, "setraw", lambda fd: None)
+
+    result = seed_prompt.masked_input("Enter: ")
+    assert result == "ac"
+    out = capsys.readouterr().out
+    assert out.startswith("Enter: ")
+    assert out.count("*") == 3
+
+
+def test_masked_input_windows_space(monkeypatch, capsys):
+    seq = iter(["x", "y", " ", "z", "\r"])
+    fake_msvcrt = types.SimpleNamespace(getwch=lambda: next(seq))
+    monkeypatch.setattr(seed_prompt, "msvcrt", fake_msvcrt)
+    monkeypatch.setattr(seed_prompt.sys, "platform", "win32", raising=False)
+
+    result = seed_prompt.masked_input("Password: ")
+    assert result == "xy z"
+    out = capsys.readouterr().out
+    assert out.startswith("Password: ")
+    assert out.count("*") == 4