add sheet music OCR CLI tool using Audiveris

Adds a Typer CLI (sheet-music-ocr) that converts scanned sheet music
(PDF, PNG, JPG, TIFF) to MusicXML via Audiveris, preserving lyrics and
text annotations. Includes Audiveris in the nix dev shell.

https://claude.ai/code/session_017GqUbuRDT58toRaxMtfRmf

python/sheet_music_ocr/audiveris.py

@@ -0,0 +1,62 @@
+"""Audiveris subprocess wrapper for optical music recognition."""
+
+from __future__ import annotations
+
+import shutil
+import subprocess
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from pathlib import Path
+
+
+class AudiverisError(Exception):
+    """Raised when Audiveris processing fails."""
+
+
+def find_audiveris() -> str:
+    """Find the Audiveris executable on PATH.
+
+    Returns:
+        Path to the audiveris executable.
+
+    Raises:
+        AudiverisError: If Audiveris is not found.
+    """
+    path = shutil.which("audiveris")
+    if not path:
+        msg = "Audiveris not found on PATH. Install it via 'nix develop' or add it to your environment."
+        raise AudiverisError(msg)
+    return path
+
+
+def run_audiveris(input_path: Path, output_dir: Path) -> Path:
+    """Run Audiveris on an input file and return the path to the generated .mxl.
+
+    Args:
+        input_path: Path to the input sheet music file (PDF, PNG, JPG, TIFF).
+        output_dir: Directory where Audiveris will write its output.
+
+    Returns:
+        Path to the generated .mxl file.
+
+    Raises:
+        AudiverisError: If Audiveris fails or produces no output.
+    """
+    audiveris = find_audiveris()
+    result = subprocess.run(
+        [audiveris, "-batch", "-export", "-output", str(output_dir), str(input_path)],
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+    if result.returncode != 0:
+        msg = f"Audiveris failed (exit {result.returncode}):\n{result.stderr}"
+        raise AudiverisError(msg)
+
+    mxl_files = list(output_dir.rglob("*.mxl"))
+    if not mxl_files:
+        msg = f"Audiveris produced no .mxl output in {output_dir}"
+        raise AudiverisError(msg)
+
+    return mxl_files[0]