Merge remote-tracking branch 'origin/main' into codex/pr31-final

# Conflicts:
#	.github/workflows/ci.yml

scripts/fix-mojibake.py

@@ -17,8 +17,10 @@ PAIRS = [
     ('…', '…'),  # horizontal ellipsis
     ('•', '•'),  # bullet
     ('→', '→'),  # right arrow
-    ('↑', '←'),  # left arrow
-    ('↑', '↑'),  # up arrow (same prefix collision - rare)
+    # CP1252 leaves byte 0x90 undefined, so spell the left-arrow corruption
+    # with a Unicode escape instead of embedding an invisible control character.
+    ('\u00e2\u2020\u0090', '←'),  # left arrow
+    ('↑', '↑'),  # up arrow
     ('↓', '↓'),  # down arrow
     ('≤', '≤'),  # less-than-or-equal
     ('≥', '≥'),  # greater-than-or-equal

scripts/test-fix-mojibake.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python3
+"""Regression tests for the mojibake repair utility."""
+
+from __future__ import annotations
+
+import subprocess
+import sys
+import tempfile
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parent.parent
+SCRIPT = ROOT / "scripts" / "fix-mojibake.py"
+
+
+def main() -> int:
+    # These are the strings produced when UTF-8 arrow bytes are decoded as
+    # Windows-1252. Byte 0x90 is undefined in CP1252, hence the explicit escape.
+    source = "right →, left \u00e2\u2020\u0090, up ↑, down ↓\n"
+    expected = "right →, left ←, up ↑, down ↓\n"
+    with tempfile.TemporaryDirectory(prefix="diagram-design-mojibake-") as directory:
+        path = Path(directory) / "fixture.md"
+        path.write_text(source, encoding="utf-8")
+        result = subprocess.run(
+            [sys.executable, str(SCRIPT), str(path)],
+            capture_output=True,
+            text=True,
+            check=False,
+        )
+        if result.returncode != 0:
+            raise AssertionError(f"repair failed: {result.stdout}{result.stderr}")
+        actual = path.read_text(encoding="utf-8")
+        if actual != expected:
+            raise AssertionError(f"expected {expected!r}, got {actual!r}")
+    print("PASS: mojibake arrow sequences repair to the intended directions")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())