Add disc count validation before apply

Check audio file count vs JSON track count per disc before processing.
Aborts with a clear error showing which discs have discrepancies and
whether tracks are missing from the JSON or audio files are missing
from the directory.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/musiksammlung/cli.py

@@ -13,7 +13,7 @@ from musiksammlung.cover import copy_covers
 from musiksammlung.llm_parser import parse_tracklist
 from musiksammlung.models import Album
 from musiksammlung.ocr import ocr_images
-from musiksammlung.organizer import apply_mapping, build_mapping
+from musiksammlung.organizer import apply_mapping, build_mapping, check_disc_counts
 from musiksammlung.playlist import generate_playlist
 from musiksammlung.ripper import RipperConfig, interactive_rip
 from musiksammlung.tagger import tag_album
@@ -146,6 +146,36 @@ def apply(
     raw = json.loads(album_json.read_text(encoding="utf-8"))
     album = Album.model_validate(raw)
 
+    # Prüfe Track-Anzahl pro Disc
+    checks = check_disc_counts(album, input_dir)
+    problems = [c for c in checks if not c.ok]
+    if problems:
+        typer.echo(
+            "\nFEHLER: Track-Diskrepanz zwischen gerippten Dateien und album.json:\n",
+            err=True,
+        )
+        for c in checks:
+            status = "OK" if c.ok else "!!"
+            typer.echo(
+                f"  [{status}] Disc {c.disc_number}: "
+                f"{c.audio_file_count} Datei(en), {c.json_track_count} JSON-Track(s)",
+                err=True,
+            )
+            if c.surplus_files:
+                typer.echo(
+                    f"       → {c.surplus_files} Track(s) fehlen im JSON "
+                    f"(Tracks {c.json_track_count + 1}–{c.audio_file_count} eintragen)",
+                    err=True,
+                )
+            elif c.surplus_json:
+                typer.echo(
+                    f"       → {c.surplus_json} JSON-Eintrag/Einträge ohne Audiodatei "
+                    f"(Tracks {c.audio_file_count + 1}–{c.json_track_count} prüfen)",
+                    err=True,
+                )
+        typer.echo(f"\nBitte {album_json} korrigieren und erneut aufrufen.", err=True)
+        raise typer.Exit(1)
+
     mapping = build_mapping(album, input_dir, output_dir)
     typer.echo(f"Mapping: {len(mapping)} Dateien")
     for src, dst in mapping.items():

src/musiksammlung/organizer.py

@@ -5,6 +5,7 @@ from __future__ import annotations
 import logging
 import re
 import shutil
+from dataclasses import dataclass
 from pathlib import Path
 
 from musiksammlung.config import AUDIO_EXTENSIONS
@@ -13,6 +14,29 @@ from musiksammlung.models import Album
 logger = logging.getLogger(__name__)
 
 
+@dataclass
+class DiscCheck:
+    """Ergebnis der Track-Zählung für eine einzelne Disc."""
+
+    disc_number: int
+    audio_file_count: int
+    json_track_count: int
+
+    @property
+    def ok(self) -> bool:
+        return self.audio_file_count == self.json_track_count
+
+    @property
+    def surplus_files(self) -> int:
+        """Dateien ohne JSON-Eintrag (Tracks fehlen im JSON)."""
+        return max(0, self.audio_file_count - self.json_track_count)
+
+    @property
+    def surplus_json(self) -> int:
+        """JSON-Einträge ohne Datei (Dateien fehlen im Verzeichnis)."""
+        return max(0, self.json_track_count - self.audio_file_count)
+
+
 def _sanitize_filename(name: str) -> str:
     """Entfernt problematische Zeichen aus Dateinamen."""
     return re.sub(r'[<>:"/\\|?*]', "_", name).strip()
@@ -28,6 +52,31 @@ def discover_audio_files(directory: Path) -> list[Path]:
     return sorted(files, key=extract_number)
 
 
+def check_disc_counts(album: Album, input_dir: Path) -> list[DiscCheck]:
+    """Vergleicht Dateianzahl und JSON-Track-Anzahl pro Disc.
+
+    Args:
+        album: Validiertes Album-Modell
+        input_dir: Verzeichnis mit gerippten Dateien (enthält CD1/, CD2/, ... bei Multi-Disc)
+
+    Returns:
+        Liste von DiscCheck-Objekten — auch für korrekte Discs (ok=True).
+    """
+    multi_disc = len(album.discs) > 1
+    results: list[DiscCheck] = []
+
+    for disc in album.discs:
+        source_dir = input_dir / f"CD{disc.disc_number}" if multi_disc else input_dir
+        file_count = len(discover_audio_files(source_dir)) if source_dir.exists() else 0
+        results.append(DiscCheck(
+            disc_number=disc.disc_number,
+            audio_file_count=file_count,
+            json_track_count=len(disc.tracks),
+        ))
+
+    return results
+
+
 def build_mapping(
     album: Album,
     input_dir: Path,