correct: classify malformed HRPs as usage

Author: codex

src/codex32/cli.py

@@ -544,7 +544,10 @@ def _correct(
     separator = normalized.lower().rfind("1")
     if separator <= 0:
         raise _UsageError("Enter a complete application prefix followed by the separator 1.")
-    hrp = normalized[:separator].lower()
+    raw_hrp = normalized[:separator]
+    if len(raw_hrp) > 83 or any(not 33 <= ord(character) <= 126 for character in raw_hrp):
+        raise _UsageError("The application prefix must be at most 83 printable ASCII characters.")
+    hrp = raw_hrp.lower()
     if context.master_seed and hrp != Profile.MS.value:
         raise _UsageError("This command accepts only Bitcoin master-seed input beginning with ms1.")
     try:

tests/test_cli.py

@@ -1728,6 +1728,15 @@ def test_cli_rejects_sixteen_consecutive_erasures_as_outside_regular_bound() ->
     assert "No valid correction found" in result.stderr
 
 
+def test_correct_rejects_malformed_immutable_hrp_as_usage() -> None:
+    damaged = "é" + VECTOR_1["secret_s"][1:]
+
+    result = _invoke(["correct"], damaged)
+
+    assert result.exit_code == 2
+    assert "application prefix" in result.stderr
+
+
 @pytest.mark.parametrize(
     ("byte_length", "options"),
     ((16, []), (64, []), (20, ["--bytes", "20"]), (24, ["--bytes", "?"])),