Add cross-platform masked input utility with tests

src/utils/seed_prompt.py

@@ -0,0 +1,73 @@
+import os
+import sys
+
+try:
+    import msvcrt  # type: ignore
+except ImportError:  # pragma: no cover - Windows only
+    msvcrt = None  # type: ignore
+
+try:
+    import termios
+    import tty
+except ImportError:  # pragma: no cover - POSIX only
+    termios = None  # type: ignore
+    tty = None  # type: ignore
+
+
+def _masked_input_windows(prompt: str) -> str:
+    """Windows implementation using ``msvcrt``."""
+    if msvcrt is None:  # pragma: no cover - should not happen
+        return input(prompt)
+
+    sys.stdout.write(prompt)
+    sys.stdout.flush()
+    buffer: list[str] = []
+    while True:
+        ch = msvcrt.getwch()
+        if ch in ("\r", "\n"):
+            sys.stdout.write("\n")
+            return "".join(buffer)
+        if ch in ("\b", "\x7f"):
+            if buffer:
+                buffer.pop()
+                sys.stdout.write("\b \b")
+        else:
+            buffer.append(ch)
+            sys.stdout.write("*")
+        sys.stdout.flush()
+
+
+def _masked_input_posix(prompt: str) -> str:
+    """POSIX implementation using ``termios`` and ``tty``."""
+    if termios is None or tty is None:  # pragma: no cover - should not happen
+        return input(prompt)
+
+    fd = sys.stdin.fileno()
+    old_settings = termios.tcgetattr(fd)
+    sys.stdout.write(prompt)
+    sys.stdout.flush()
+    buffer: list[str] = []
+    try:
+        tty.setraw(fd)
+        while True:
+            ch = sys.stdin.read(1)
+            if ch in ("\r", "\n"):
+                sys.stdout.write("\n")
+                return "".join(buffer)
+            if ch in ("\x7f", "\b"):
+                if buffer:
+                    buffer.pop()
+                    sys.stdout.write("\b \b")
+            else:
+                buffer.append(ch)
+                sys.stdout.write("*")
+            sys.stdout.flush()
+    finally:
+        termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
+
+
+def masked_input(prompt: str) -> str:
+    """Return input from the user while masking typed characters."""
+    if sys.platform == "win32":
+        return _masked_input_windows(prompt)
+    return _masked_input_posix(prompt)