Show detailed batch repair preview

ROADMAP.md

@@ -28,12 +28,12 @@
 
 ## v0.3 — Safe Repair
 
-- [ ] Dry-run repair plan
-- [ ] Backup before repair
-- [ ] Compatibility symlink creation
+- [x] Dry-run repair plan
+- [x] Backup before repair
+- [x] Compatibility symlink creation
 - [ ] Compatibility copy creation
 - [ ] Rename repair
-- [ ] Rollback log
+- [x] Rollback log and recovery center
 
 ## v0.4 — Migration Wizard
 

docs/design/audio-comparison.md

@@ -0,0 +1,32 @@
+# Audio comparison for duplicate review
+
+## Problem
+
+Filenames alone are weak evidence. DJs need to hear each candidate and locate it
+on disk before deciding which copy is authoritative.
+
+## Design
+
+Exact-duplicate and cloud-conflict groups expose a shared audio player with a
+preview action for each file. Switching files reuses the same player, making
+back-to-back comparison quick. A separate action reveals the selected file in
+macOS Finder.
+
+The browser never receives unrestricted filesystem access. Each analyzed audio
+path gets a short, process-local HMAC token. Preview and Finder endpoints reject
+altered, expired, missing, non-audio, or otherwise unsigned paths. Audio serving
+supports HTTP byte ranges so playback can seek without loading an entire track.
+
+## Edge cases
+
+- A file moved after analysis is rejected.
+- Forged or stale tokens cannot select another local file.
+- Preview controls remain useful if autoplay is blocked because native audio
+  controls stay visible.
+- Finder failures are reported beside the button without affecting analysis.
+
+## Tests
+
+- Valid signed audio resolves to the analyzed file.
+- A modified token is rejected.
+- Duplicate detail payloads include preview and Finder controls for every file.

docs/design/backup-recovery-center.md

@@ -0,0 +1,30 @@
+# Backup recovery center
+
+## Problem
+
+An immediate undo button is not enough. A DJ may restart Serato Doctor, notice
+an issue later, or need to understand how much disk space safety snapshots use.
+
+## Architecture
+
+The recovery center reads the existing JSON manifests beneath
+`_Serato_/.serato-doctor-backups/`. It reports creation time, selected keeper,
+affected paths, restore status, and snapshot size. Invalid or incomplete backup
+folders are ignored rather than presented as restorable.
+
+Restore remains conservative: it only replaces a symbolic-link alias and
+refuses to overwrite a real file. A successful restore records its timestamp in
+the manifest so the UI cannot accidentally offer the same rollback twice.
+
+## Edge cases
+
+- No backup directory is treated as an empty history.
+- Malformed manifests do not prevent valid backups from loading.
+- Restored snapshots remain visible for audit purposes and disk accounting.
+- Backups can only be restored through the Serato library that owns them.
+
+## Tests
+
+- Backup history reports size and ready status.
+- Restore changes the persistent status to restored.
+- Static recovery assets are included in the package.

docs/design/batch-duplicate-review.md

@@ -0,0 +1,37 @@
+# Batch duplicate review
+
+## Problem
+
+Opening a diagnostic, opening each group again, scrolling to a separate repair
+form, and applying one change at a time creates unnecessary friction and many
+small backups.
+
+## Design
+
+Duplicate and cloud-conflict diagnostics now open as a sequential review queue.
+Each group presents its candidates together with audio preview and Finder
+controls. Choosing a keeper records the decision and advances immediately.
+Uncertain groups can be skipped without changing them.
+
+All approved decisions are submitted as one dry-run plan. Apply creates one
+backup containing every affected audio file plus the Serato metadata snapshot,
+then installs all compatibility shortcuts as one rollback unit. Any validation
+or filesystem failure prevents or rolls back the batch.
+
+The dry-run opens in a closable modal that names every selected keeper and every
+path that will become a compatibility shortcut. Closing the modal preserves the
+queue position and all decisions so the DJ can continue reviewing before apply.
+
+## Edge cases
+
+- The same group cannot be submitted twice.
+- A file cannot be both a keeper and a disposable file across choices.
+- Every group is rescanned and revalidated before preview and apply.
+- Skipped and unreviewed groups remain untouched.
+- Revisiting a group preserves and visibly marks its selected keeper.
+
+## Tests
+
+- Two groups produce one backup and one restorable receipt.
+- Batch preview reports combined changes without modifying files.
+- Existing single-group repair remains a wrapper around the batch engine.

docs/design/duplicate-repair.md

@@ -0,0 +1,39 @@
+# Duplicate repair
+
+## Problem
+
+Duplicate and cloud-conflict files waste space, but deleting either path can
+unmap tracks in crates or Serato's database. DJs need to choose the authoritative
+copy and understand every change before it happens.
+
+## Design
+
+The web interface requires an analysis, an explicit keeper selection, and a
+dry-run preview. Applying the plan first creates a timestamped backup beneath
+`_Serato_/.serato-doctor-backups/`. The snapshot contains every replaced audio
+file, loaded crate/smart-crate metadata, database V2, and a JSON restore manifest.
+
+The non-kept audio path is then replaced with a symbolic link to the keeper.
+This removes the extra audio payload while preserving every existing saved path.
+Crate files and database V2 are never rewritten. The UI exposes immediate
+restore using the manifest.
+
+Users may retain all backups or set a positive rotation limit. Rotation occurs
+only after a repair succeeds.
+
+## Edge cases
+
+- The duplicate group is rescanned and validated immediately before preview and
+  apply.
+- Existing symlinks cannot be selected as disposable duplicate files.
+- A partial failure restores already-changed files before reporting the error.
+- Restore refuses to overwrite a real file.
+- Healthy symlink aliases are excluded from future duplicate counts.
+
+## Tests
+
+- Backup creation includes audio and Serato metadata.
+- The old path resolves to the selected keeper after repair.
+- Restore returns the original file contents.
+- Invalid keeper choices are rejected.
+- Limited and unlimited retention behave deterministically.

serato_doctor/duplicates.py

@@ -11,7 +11,9 @@ def find_duplicate_groups(
 ) -> Tuple[DuplicateGroup, ...]:
     """Find exact-name duplicates and suspected numeric conflict copies."""
 
-    track_tuple = tuple(tracks)
+    # Healthy symlinks preserve legacy Serato paths without consuming another
+    # copy of the audio, so they are aliases rather than duplicate files.
+    track_tuple = tuple(track for track in tracks if not track.path.is_symlink())
     by_name: DefaultDict[str, List[DiskTrack]] = defaultdict(list)
     by_conflict_name: DefaultDict[str, List[DiskTrack]] = defaultdict(list)
 

serato_doctor/repair.py

@@ -0,0 +1,242 @@
+"""Backup-first duplicate consolidation.
+
+Serato's binary metadata is deliberately not rewritten.  Removed duplicate files
+are replaced with symbolic links, so every existing path continues to resolve.
+"""
+
+import json
+import shutil
+from dataclasses import dataclass
+from datetime import datetime, timezone
+from pathlib import Path
+from typing import Iterable, Optional, Tuple
+from uuid import uuid4
+
+
+BACKUP_FOLDER = ".serato-doctor-backups"
+
+
+@dataclass(frozen=True)
+class DuplicateRepairPlan:
+    keeper: Path
+    replaced: Tuple[Path, ...]
+    metadata_files: Tuple[Path, ...]
+
+    @property
+    def changes(self) -> int:
+        return len(self.replaced)
+
+
+@dataclass(frozen=True)
+class RepairReceipt:
+    backup: Path
+    keeper: Path
+    replaced: Tuple[Path, ...]
+
+
+@dataclass(frozen=True)
+class BackupSummary:
+    path: Path
+    created_at: str
+    keeper: Path
+    replaced: Tuple[Path, ...]
+    size_bytes: int
+    restored_at: Optional[str]
+
+    @property
+    def status(self) -> str:
+        return "restored" if self.restored_at else "ready"
+
+
+def plan_duplicate_repair(
+    keeper: Path, duplicates: Iterable[Path], serato_root: Path
+) -> DuplicateRepairPlan:
+    keeper = keeper.expanduser().resolve()
+    candidates = tuple(path.expanduser().resolve() for path in duplicates)
+    if keeper not in candidates:
+        raise ValueError("The file to keep must belong to this duplicate group")
+    if not keeper.is_file():
+        raise ValueError(f"The file to keep no longer exists: {keeper}")
+    replaced = tuple(path for path in candidates if path != keeper)
+    if not replaced:
+        raise ValueError("Choose a duplicate group containing at least two files")
+    if any(not path.is_file() or path.is_symlink() for path in replaced):
+        raise ValueError("A duplicate changed since the analysis; analyze again")
+    metadata = tuple(
+        sorted(
+            path
+            for path in serato_root.expanduser().resolve().rglob("*")
+            if path.is_file()
+            and BACKUP_FOLDER not in path.parts
+            and (
+                path.name == "database V2"
+                or path.suffix.casefold() in {".crate", ".scrate"}
+            )
+        )
+    )
+    return DuplicateRepairPlan(keeper, replaced, metadata)
+
+
+def apply_duplicate_repair(
+    plan: DuplicateRepairPlan,
+    serato_root: Path,
+    backup_limit: Optional[int] = 10,
+) -> RepairReceipt:
+    """Create a complete rollback snapshot, then replace extras with symlinks."""
+    return apply_duplicate_repair_batch((plan,), serato_root, backup_limit)
+
+
+def apply_duplicate_repair_batch(
+    plans: Iterable[DuplicateRepairPlan],
+    serato_root: Path,
+    backup_limit: Optional[int] = 10,
+) -> RepairReceipt:
+    """Apply several approved duplicate choices as one atomic backup."""
+    plans = tuple(plans)
+    if not plans:
+        raise ValueError("Choose at least one duplicate group")
+    if backup_limit is not None and backup_limit < 1:
+        raise ValueError("Backup limit must be at least 1, or unlimited")
+    replaced_paths = tuple(
+        path for plan in plans for path in plan.replaced
+    )
+    if len(set(replaced_paths)) != len(replaced_paths):
+        raise ValueError("The same file appears in more than one repair choice")
+    keepers = {plan.keeper for plan in plans}
+    if keepers.intersection(replaced_paths):
+        raise ValueError("A selected keeper cannot be removed by another choice")
+    backup_root = serato_root.expanduser().resolve() / BACKUP_FOLDER
+    backup = backup_root / _backup_name()
+    files_root = backup / "files"
+    metadata_root = backup / "serato-metadata"
+    backup.mkdir(parents=True)
+
+    entries = []
+    try:
+        for plan in plans:
+            for path in plan.replaced:
+                destination = files_root / _safe_backup_path(path)
+                destination.parent.mkdir(parents=True, exist_ok=True)
+                shutil.copy2(path, destination)
+                entries.append(
+                    {
+                        "original": str(path),
+                        "backup": str(destination),
+                        "keeper": str(plan.keeper),
+                    }
+                )
+        for path in plans[0].metadata_files:
+            relative = path.relative_to(serato_root.expanduser().resolve())
+            destination = metadata_root / relative
+            destination.parent.mkdir(parents=True, exist_ok=True)
+            shutil.copy2(path, destination)
+        manifest = {
+            "created_at": datetime.now(timezone.utc).isoformat(),
+            "keeper": str(plans[0].keeper),
+            "keepers": [str(plan.keeper) for plan in plans],
+            "choice_count": len(plans),
+            "replaced": entries,
+            "strategy": "symlink",
+        }
+        (backup / "manifest.json").write_text(
+            json.dumps(manifest, indent=2), encoding="utf-8"
+        )
+        for entry in entries:
+            path = Path(entry["original"])
+            path.unlink()
+            path.symlink_to(Path(entry["keeper"]))
+    except Exception:
+        _rollback_entries(entries)
+        shutil.rmtree(backup, ignore_errors=True)
+        raise
+
+    rotate_backups(backup_root, backup_limit)
+    return RepairReceipt(backup, plans[0].keeper, replaced_paths)
+
+
+def restore_backup(backup: Path) -> Tuple[Path, ...]:
+    manifest_path = backup.expanduser().resolve() / "manifest.json"
+    manifest = json.loads(manifest_path.read_text(encoding="utf-8"))
+    restored = []
+    for entry in manifest["replaced"]:
+        original = Path(entry["original"])
+        saved = Path(entry["backup"])
+        if original.exists() and not original.is_symlink():
+            raise ValueError(f"Restore would overwrite a real file: {original}")
+        if original.is_symlink():
+            original.unlink()
+        original.parent.mkdir(parents=True, exist_ok=True)
+        shutil.copy2(saved, original)
+        restored.append(original)
+    manifest["restored_at"] = datetime.now(timezone.utc).isoformat()
+    manifest_path.write_text(json.dumps(manifest, indent=2), encoding="utf-8")
+    return tuple(restored)
+
+
+def list_backups(serato_root: Path) -> Tuple[BackupSummary, ...]:
+    backup_root = serato_root.expanduser().resolve() / BACKUP_FOLDER
+    if not backup_root.is_dir():
+        return ()
+    summaries = []
+    for backup in backup_root.iterdir():
+        manifest_path = backup / "manifest.json"
+        if not manifest_path.is_file():
+            continue
+        try:
+            manifest = json.loads(manifest_path.read_text(encoding="utf-8"))
+            replaced = tuple(
+                Path(entry["original"]) for entry in manifest["replaced"]
+            )
+            size = sum(
+                path.stat().st_size
+                for path in backup.rglob("*")
+                if path.is_file()
+            )
+            summaries.append(
+                BackupSummary(
+                    path=backup.resolve(),
+                    created_at=manifest["created_at"],
+                    keeper=Path(manifest["keeper"]),
+                    replaced=replaced,
+                    size_bytes=size,
+                    restored_at=manifest.get("restored_at"),
+                )
+            )
+        except (KeyError, OSError, TypeError, json.JSONDecodeError):
+            continue
+    return tuple(
+        sorted(summaries, key=lambda item: item.created_at, reverse=True)
+    )
+
+
+def rotate_backups(backup_root: Path, limit: Optional[int]) -> None:
+    if limit is None or not backup_root.is_dir():
+        return
+    backups = sorted(
+        (path for path in backup_root.iterdir() if (path / "manifest.json").is_file()),
+        key=lambda path: path.name,
+        reverse=True,
+    )
+    for expired in backups[limit:]:
+        shutil.rmtree(expired)
+
+
+def _backup_name() -> str:
+    stamp = datetime.now(timezone.utc).strftime("%Y%m%dT%H%M%SZ")
+    return f"{stamp}-{uuid4().hex[:8]}"
+
+
+def _safe_backup_path(path: Path) -> Path:
+    anchorless = path.as_posix().lstrip("/").replace(":", "_")
+    return Path(anchorless)
+
+
+def _rollback_entries(entries: Iterable[dict]) -> None:
+    for entry in entries:
+        original = Path(entry["original"])
+        saved = Path(entry["backup"])
+        if original.is_symlink():
+            original.unlink()
+        if not original.exists() and saved.is_file():
+            original.parent.mkdir(parents=True, exist_ok=True)
+            shutil.copy2(saved, original)

serato_doctor/web.py

@@ -1,11 +1,18 @@
 import argparse
+import base64
+import binascii
+import hmac
 import json
+import mimetypes
+import secrets
+import subprocess
 from collections import Counter
 from dataclasses import asdict
 from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
 from importlib import resources
 from pathlib import Path
-from typing import Iterable
+from typing import Iterable, Optional
+from urllib.parse import parse_qs, quote, urlsplit
 
 from serato_doctor.crate_parser import load_library_crates
 from serato_doctor.database_parser import parse_database
@@ -16,13 +23,24 @@ from serato_doctor.models.crate import CrateKind
 from serato_doctor.models.duplicate import DuplicateKind
 from serato_doctor.models.library import Library
 from serato_doctor.scanner import scan_filesystem
+from serato_doctor.repair import (
+    BACKUP_FOLDER,
+    apply_duplicate_repair,
+    apply_duplicate_repair_batch,
+    list_backups,
+    plan_duplicate_repair,
+    restore_backup,
+)
 
 
 MAX_REQUEST_BYTES = 64 * 1024
 DETAIL_LIMIT = 50
+FILE_TOKEN_SECRET = secrets.token_bytes(32)
 STATIC_FILES = {
     "/": ("index.html", "text/html; charset=utf-8"),
     "/app.css": ("app.css", "text/css; charset=utf-8"),
+    "/recovery.css": ("recovery.css", "text/css; charset=utf-8"),
+    "/layout-fixes.css": ("layout-fixes.css", "text/css; charset=utf-8"),
     "/app.js": ("app.js", "text/javascript; charset=utf-8"),
 }
 
@@ -31,6 +49,44 @@ def _display_path(path: Path) -> str:
     return str(path)
 
 
+def _file_token(path: Path) -> str:
+    encoded = base64.urlsafe_b64encode(str(path.resolve()).encode()).decode()
+    signature = hmac.digest(FILE_TOKEN_SECRET, encoded.encode(), "sha256").hex()
+    return f"{encoded}.{signature}"
+
+
+def _verified_audio(token: str) -> Path:
+    try:
+        encoded, signature = token.rsplit(".", 1)
+        expected = hmac.digest(
+            FILE_TOKEN_SECRET, encoded.encode(), "sha256"
+        ).hex()
+        if not hmac.compare_digest(signature, expected):
+            raise ValueError
+        path = Path(base64.urlsafe_b64decode(encoded.encode()).decode())
+    except (binascii.Error, ValueError, UnicodeDecodeError):
+        raise ValueError("Invalid or expired file preview")
+    if not path.is_file() or path.suffix.casefold() not in {
+        ".mp3",
+        ".m4a",
+        ".wav",
+        ".aif",
+        ".aiff",
+        ".flac",
+    }:
+        raise ValueError("Audio file is no longer available")
+    return path
+
+
+def _file_preview(path: Path) -> dict:
+    token = _file_token(path)
+    return {
+        "path": _display_path(path),
+        "audio_url": f"/api/audio?token={quote(token)}",
+        "reveal_token": token,
+    }
+
+
 def _first_reason(match) -> str:
     for item in match.evidence:
         if item.matched:
@@ -149,6 +205,9 @@ def diagnostic_details(library: Library, limit: int = DETAIL_LIMIT) -> dict:
                 {
                     "filename": group.display_name,
                     "files": [_display_path(track.path) for track in group.tracks],
+                    "file_previews": [
+                        _file_preview(track.path) for track in group.tracks
+                    ],
                 }
                 for group in exact_duplicates[:limit]
             ],
@@ -164,6 +223,9 @@ def diagnostic_details(library: Library, limit: int = DETAIL_LIMIT) -> dict:
                 {
                     "filename": group.display_name,
                     "files": [_display_path(track.path) for track in group.tracks],
+                    "file_previews": [
+                        _file_preview(track.path) for track in group.tracks
+                    ],
                 }
                 for group in cloud_conflicts[:limit]
             ],
@@ -225,9 +287,134 @@ def analyze_paths(
     return result
 
 
+def duplicate_repair(
+    serato: Path,
+    music: Path,
+    keeper: Path,
+    group_files: Iterable[Path],
+    backup_limit: Optional[int],
+    apply: bool = False,
+) -> dict:
+    """Validate a current duplicate group and preview or apply consolidation."""
+    serato = serato.expanduser().resolve()
+    music = music.expanduser().resolve()
+    keeper = keeper.expanduser().resolve()
+    requested = tuple(path.expanduser().resolve() for path in group_files)
+    if not serato.is_dir() or not music.is_dir():
+        raise ValueError("Analyze the library again before repairing duplicates")
+    tracks = scan_filesystem(music).tracks
+    groups = find_duplicate_groups(tracks)
+    valid_groups = [
+        {track.path.resolve() for track in group.tracks} for group in groups
+    ]
+    if set(requested) not in valid_groups:
+        raise ValueError("This duplicate group changed; analyze the library again")
+    plan = plan_duplicate_repair(keeper, requested, serato)
+    result = {
+        "keeper": str(plan.keeper),
+        "replaced": [str(path) for path in plan.replaced],
+        "metadata_backups": len(plan.metadata_files),
+        "strategy": "shortcut",
+        "database_v2_modified": False,
+    }
+    if apply:
+        receipt = apply_duplicate_repair(plan, serato, backup_limit)
+        result.update({"applied": True, "backup": str(receipt.backup)})
+    else:
+        result["applied"] = False
+    return result
+
+
+def duplicate_repair_batch(
+    serato: Path,
+    music: Path,
+    choices: Iterable[dict],
+    backup_limit: Optional[int],
+    apply: bool = False,
+) -> dict:
+    """Validate and preview or apply several keeper choices together."""
+    serato = serato.expanduser().resolve()
+    music = music.expanduser().resolve()
+    if not serato.is_dir() or not music.is_dir():
+        raise ValueError("Analyze the library again before repairing duplicates")
+    groups = find_duplicate_groups(scan_filesystem(music).tracks)
+    valid_groups = [
+        {track.path.resolve() for track in group.tracks} for group in groups
+    ]
+    plans = []
+    selected_groups = set()
+    for choice in choices:
+        requested = tuple(Path(value).expanduser().resolve() for value in choice["group_files"])
+        group_key = frozenset(requested)
+        if set(requested) not in valid_groups:
+            raise ValueError("A duplicate group changed; analyze the library again")
+        if group_key in selected_groups:
+            raise ValueError("A duplicate group was selected more than once")
+        selected_groups.add(group_key)
+        plans.append(
+            plan_duplicate_repair(Path(choice["keeper"]), requested, serato)
+        )
+    if not plans:
+        raise ValueError("Choose at least one duplicate group")
+    replaced = [str(path) for plan in plans for path in plan.replaced]
+    result = {
+        "choice_count": len(plans),
+        "replaced": replaced,
+        "decisions": [
+            {
+                "keeper": str(plan.keeper),
+                "replaced": [str(path) for path in plan.replaced],
+            }
+            for plan in plans
+        ],
+        "metadata_backups": len(plans[0].metadata_files),
+        "strategy": "shortcut",
+        "database_v2_modified": False,
+    }
+    if apply:
+        receipt = apply_duplicate_repair_batch(plans, serato, backup_limit)
+        result.update({"applied": True, "backup": str(receipt.backup)})
+    else:
+        result["applied"] = False
+    return result
+
+
+def backup_history(serato: Path) -> dict:
+    serato = serato.expanduser().resolve()
+    if not serato.is_dir():
+        raise ValueError(f"Serato folder does not exist: {serato}")
+    backups = list_backups(serato)
+    return {
+        "total": len(backups),
+        "size_bytes": sum(backup.size_bytes for backup in backups),
+        "items": [
+            {
+                "path": str(backup.path),
+                "created_at": backup.created_at,
+                "keeper": str(backup.keeper),
+                "replaced": [str(path) for path in backup.replaced],
+                "size_bytes": backup.size_bytes,
+                "status": backup.status,
+                "restored_at": backup.restored_at,
+            }
+            for backup in backups
+        ],
+    }
+
+
 class SeratoDoctorHandler(BaseHTTPRequestHandler):
     def do_GET(self) -> None:
-        asset = STATIC_FILES.get(self.path)
+        request = urlsplit(self.path)
+        if request.path == "/api/audio":
+            try:
+                token = parse_qs(request.query)["token"][0]
+                self._audio_response(_verified_audio(token))
+            except (BrokenPipeError, ConnectionResetError):
+                return
+            except (KeyError, IndexError, OSError, ValueError) as error:
+                self._json_response(404, {"error": str(error)})
+            return
+        asset = STATIC_FILES.get(request.path)
         if asset is None:
             self._json_response(404, {"error": "Not found"})
             return
@@ -239,12 +426,23 @@ class SeratoDoctorHandler(BaseHTTPRequestHandler):
         )
         self.send_response(200)
         self.send_header("Content-Type", content_type)
+        self.send_header("Cache-Control", "no-store")
         self.send_header("Content-Length", str(len(content)))
         self.end_headers()
         self.wfile.write(content)
 
     def do_POST(self) -> None:
-        if self.path != "/api/analyze":
+        allowed = {
+            "/api/analyze",
+            "/api/duplicates/preview",
+            "/api/duplicates/apply",
+            "/api/duplicates/batch/preview",
+            "/api/duplicates/batch/apply",
+            "/api/backups/restore",
+            "/api/backups",
+            "/api/reveal",
+        }
+        if self.path not in allowed:
             self._json_response(404, {"error": "Not found"})
             return
         try:
@@ -254,15 +452,89 @@ class SeratoDoctorHandler(BaseHTTPRequestHandler):
             payload = json.loads(self.rfile.read(length))
             if not isinstance(payload, dict):
                 raise ValueError("Request body must be a JSON object")
+            if self.path == "/api/analyze":
                 roots = [Path(value) for value in payload.get("reference_roots", [])]
                 result = analyze_paths(
                     Path(payload["serato"]), Path(payload["music"]), roots
                 )
-        except (KeyError, TypeError, json.JSONDecodeError, ValueError) as error:
+            elif self.path == "/api/reveal":
+                path = _verified_audio(payload["token"])
+                subprocess.run(["open", "-R", str(path)], check=True)
+                result = {"revealed": str(path)}
+            elif self.path == "/api/backups":
+                result = backup_history(Path(payload["serato"]))
+            elif self.path == "/api/backups/restore":
+                serato = Path(payload["serato"]).expanduser().resolve()
+                backup = Path(payload["backup"]).expanduser().resolve()
+                backup_root = (serato / BACKUP_FOLDER).resolve()
+                if backup.parent != backup_root:
+                    raise ValueError("That backup does not belong to this library")
+                restored = restore_backup(backup)
+                result = {"restored": [str(path) for path in restored]}
+            elif self.path.startswith("/api/duplicates/batch/"):
+                raw_limit = payload.get("backup_limit", 10)
+                backup_limit = None if raw_limit is None else int(raw_limit)
+                result = duplicate_repair_batch(
+                    Path(payload["serato"]),
+                    Path(payload["music"]),
+                    payload["choices"],
+                    backup_limit,
+                    apply=self.path.endswith("/apply"),
+                )
+            else:
+                raw_limit = payload.get("backup_limit", 10)
+                backup_limit = None if raw_limit is None else int(raw_limit)
+                result = duplicate_repair(
+                    Path(payload["serato"]),
+                    Path(payload["music"]),
+                    Path(payload["keeper"]),
+                    (Path(value) for value in payload["group_files"]),
+                    backup_limit,
+                    apply=self.path.endswith("/apply"),
+                )
+        except (
+            KeyError,
+            TypeError,
+            OSError,
+            json.JSONDecodeError,
+            ValueError,
+        ) as error:
             self._json_response(400, {"error": str(error)})
             return
         self._json_response(200, result)
 
+    def _audio_response(self, path: Path) -> None:
+        size = path.stat().st_size
+        start, end = 0, size - 1
+        status = 200
+        range_header = self.headers.get("Range")
+        if range_header and range_header.startswith("bytes="):
+            raw_start, _, raw_end = range_header[6:].partition("-")
+            start = int(raw_start or 0)
+            end = min(int(raw_end) if raw_end else end, end)
+            if start < 0 or start > end:
+                raise ValueError("Invalid audio range")
+            status = 206
+        length = end - start + 1
+        self.send_response(status)
+        self.send_header(
+            "Content-Type", mimetypes.guess_type(path.name)[0] or "audio/mpeg"
+        )
+        self.send_header("Accept-Ranges", "bytes")
+        self.send_header("Content-Length", str(length))
+        if status == 206:
+            self.send_header("Content-Range", f"bytes {start}-{end}/{size}")
+        self.end_headers()
+        with path.open("rb") as audio:
+            audio.seek(start)
+            remaining = length
+            while remaining:
+                chunk = audio.read(min(64 * 1024, remaining))
+                if not chunk:
+                    break
+                self.wfile.write(chunk)
+                remaining -= len(chunk)
+
     def _json_response(self, status: int, payload: dict) -> None:
         content = json.dumps(payload).encode("utf-8")
         self.send_response(status)

serato_doctor/webui/app.js

@@ -8,7 +8,32 @@ const drilldownTitle = document.querySelector('#drilldown-title');
 const drilldownCount = document.querySelector('#drilldown-count');
 const drilldownSummary = document.querySelector('#drilldown-summary');
 const drilldownList = document.querySelector('#drilldown-list');
+const repairPanel = document.querySelector('#duplicate-repair');
+const repairChoice = document.querySelector('#repair-choice');
+const repairPreview = document.querySelector('#repair-preview');
+const repairMessage = document.querySelector('#repair-message');
+const previewRepairButton = document.querySelector('#preview-repair');
+const applyRepairButton = document.querySelector('#apply-repair');
+const restoreRepairButton = document.querySelector('#restore-repair');
+const loadBackupsButton = document.querySelector('#load-backups');
+const backupSummary = document.querySelector('#backup-summary');
+const backupList = document.querySelector('#backup-list');
+const audioPreview = document.querySelector('#audio-preview');
+const audioPreviewName = document.querySelector('#audio-preview-name');
+const audioPlayer = document.querySelector('#audio-player');
+const closeAudioPreview = document.querySelector('#close-audio-preview');
+const batchPreviewModal = document.querySelector('#batch-preview-modal');
+const batchPreviewSummary = document.querySelector('#batch-preview-summary');
+const batchPreviewList = document.querySelector('#batch-preview-list');
+const batchPreviewSafety = document.querySelector('#batch-preview-safety');
+const closeBatchPreview = document.querySelector('#close-batch-preview');
+const continueReviewing = document.querySelector('#continue-reviewing');
+const acceptPreview = document.querySelector('#accept-preview');
 let latestAnalysis = null;
+let selectedDuplicateGroup = null;
+let previewedRepair = null;
+let latestBackup = null;
+let reviewState = null;
 
 function expandHome(path) {
   return path.trim();
@@ -24,9 +49,55 @@ function escapeHtml(value) {
   }[character]));
 }
 
+function formatBytes(bytes) {
+  if (!bytes) return '0 B';
+  const units = ['B', 'KB', 'MB', 'GB', 'TB'];
+  const unit = Math.min(Math.floor(Math.log(bytes) / Math.log(1024)), units.length - 1);
+  return `${(bytes / (1024 ** unit)).toFixed(unit ? 1 : 0)} ${units[unit]}`;
+}
+
+function formatDate(value) {
+  const date = new Date(value);
+  return Number.isNaN(date.valueOf()) ? value : date.toLocaleString([], {dateStyle: 'medium', timeStyle: 'short'});
+}
+
+async function loadBackups() {
+  loadBackupsButton.disabled = true;
+  backupSummary.textContent = 'Looking for recovery snapshots…';
+  try {
+    const response = await fetch('/api/backups', {method: 'POST', headers: {'Content-Type': 'application/json'}, body: JSON.stringify({serato: expandHome(document.querySelector('#serato-path').value)})});
+    const data = await response.json();
+    if (!response.ok) throw new Error(data.error || 'Could not load backups');
+    backupSummary.textContent = `${data.total} backup${data.total === 1 ? '' : 's'} · ${formatBytes(data.size_bytes)} on disk`;
+    backupList.innerHTML = data.items.length ? data.items.map((backup) => `
+      <article class="backup-item">
+        <div><span class="backup-status ${backup.status}">${backup.status === 'restored' ? 'Restored' : 'Ready to restore'}</span><strong>${formatDate(backup.created_at)}</strong><small>Kept: ${escapeHtml(backup.keeper)}</small><small>${backup.replaced.length} original file${backup.replaced.length === 1 ? '' : 's'} · ${formatBytes(backup.size_bytes)}</small></div>
+        <button type="button" data-restore-backup="${escapeHtml(backup.path)}" ${backup.status === 'restored' ? 'disabled' : ''}>${backup.status === 'restored' ? 'Already restored' : 'Restore'}</button>
+      </article>
+    `).join('') : '<div class="empty-detail">No repair backups found for this library yet.</div>';
+  } catch (error) {
+    backupSummary.textContent = error.message;
+    backupList.innerHTML = '';
+  } finally { loadBackupsButton.disabled = false; }
+}
+
+loadBackupsButton.addEventListener('click', loadBackups);
+backupList.addEventListener('click', async (event) => {
+  const button = event.target.closest('[data-restore-backup]');
+  if (!button || button.disabled) return;
+  if (!window.confirm('Restore the original duplicate files from this backup? Existing real files will never be overwritten.')) return;
+  button.disabled = true; button.textContent = 'Restoring…';
+  try {
+    const response = await fetch('/api/backups/restore', {method: 'POST', headers: {'Content-Type': 'application/json'}, body: JSON.stringify({serato: expandHome(document.querySelector('#serato-path').value), backup: button.dataset.restoreBackup})});
+    const result = await response.json();
+    if (!response.ok) throw new Error(result.error || 'Restore failed');
+    await loadBackups();
+  } catch (error) { backupSummary.textContent = error.message; button.disabled = false; button.textContent = 'Restore'; }
+});
+
 function detailLines(item) {
-  if (item.files) {
-    return item.files.map((file) => `<li>${escapeHtml(file)}</li>`).join('');
+  if (item.file_previews) {
+    return item.file_previews.map((file) => `<li class="file-compare-row"><span>${escapeHtml(file.path)}</span><div><button type="button" data-audio-url="${escapeHtml(file.audio_url)}" data-audio-name="${escapeHtml(file.path)}">▶ Play preview</button><button type="button" data-reveal-token="${escapeHtml(file.reveal_token)}">Show in Finder</button></div></li>`).join('');
   }
   const lines = [];
   if (item.artist || item.title) lines.push(`${item.artist || 'Unknown artist'} — ${item.title || item.filename}`);
@@ -51,12 +122,24 @@ function renderDetail(key) {
   drilldownCount.textContent = `${detail.total ?? 0} found`;
   drilldownSummary.textContent = detail.summary;
 
+  repairPanel.hidden = true;
+  selectedDuplicateGroup = null;
+  previewedRepair = null;
+  latestBackup = null;
+  restoreRepairButton.hidden = true;
   if (!detail.items?.length) {
     drilldownList.innerHTML = '<div class="empty-detail">Nothing to review here. Tiny victory parade, very tasteful.</div>';
     return;
   }
 
-  drilldownList.innerHTML = detail.items.map((item) => `
+  if (detail.items[0].file_previews) {
+    reviewState = {key, index: 0, choices: new Map()};
+    repairPanel.hidden = false;
+    renderReviewGroup();
+    return;
+  }
+
+  drilldownList.innerHTML = detail.items.map((item, index) => `
     <article class="detail-item">
       <strong>${escapeHtml(item.filename || item.path || 'Untitled item')}</strong>
       <ul>${detailLines(item)}</ul>
@@ -64,6 +147,149 @@ function renderDetail(key) {
   `).join('');
 }
 
+function renderReviewGroup() {
+  const groups = latestAnalysis.details[reviewState.key].items;
+  const group = groups[reviewState.index];
+  const chosen = reviewState.choices.get(reviewState.index);
+  drilldownCount.textContent = `${reviewState.index + 1} of ${groups.length} · ${reviewState.choices.size} approved`;
+  drilldownSummary.textContent = 'Listen to each candidate, choose the keeper, and we’ll move to the next group. Skip anything uncertain.';
+  drilldownList.innerHTML = `
+    <article class="review-workspace">
+      <div class="review-heading"><div><span>Comparing now</span><strong>${escapeHtml(group.filename)}</strong></div><span>${reviewState.choices.size} selected</span></div>
+      <div class="review-candidates">${group.file_previews.map((file, index) => `
+        <section class="review-candidate ${chosen === file.path ? 'winner' : ''}">
+          <span class="candidate-number">Option ${index + 1}</span>
+          <strong>${escapeHtml(file.path.split('/').pop())}</strong>
+          <small>${escapeHtml(file.path)}</small>
+          <div class="file-actions"><button type="button" data-audio-url="${escapeHtml(file.audio_url)}" data-audio-name="${escapeHtml(file.path)}">▶ Play preview</button><button type="button" data-reveal-token="${escapeHtml(file.reveal_token)}">Show in Finder</button></div>
+          <button class="choose-winner" type="button" data-choose-winner="${index}">${chosen === file.path ? '✓ Selected keeper' : 'Keep this one →'}</button>
+        </section>
+      `).join('')}</div>
+      <div class="review-navigation"><button type="button" data-review-previous ${reviewState.index === 0 ? 'disabled' : ''}>← Previous</button><button type="button" data-review-skip>Skip for now</button></div>
+    </article>`;
+  updateBatchSummary();
+}
+
+function updateBatchSummary() {
+  if (!reviewState) return;
+  const groups = latestAnalysis.details[reviewState.key].items;
+  repairChoice.innerHTML = `<div class="batch-summary"><strong>${reviewState.choices.size} group${reviewState.choices.size === 1 ? '' : 's'} approved</strong><span>${groups.length - reviewState.choices.size} skipped or still awaiting a decision</span></div>`;
+  previewRepairButton.disabled = reviewState.choices.size === 0;
+  previewedRepair = null;
+  applyRepairButton.disabled = true;
+  repairPreview.hidden = true;
+}
+
+function repairPayload() {
+  if (!reviewState?.choices.size) throw new Error('Choose at least one keeper');
+  const groups = latestAnalysis.details[reviewState.key].items;
+  const choices = Array.from(reviewState.choices, ([index, keeper]) => ({keeper, group_files: groups[index].files}));
+  return {serato: expandHome(document.querySelector('#serato-path').value), music: expandHome(document.querySelector('#music-path').value), choices, backup_limit: document.querySelector('#keep-all-backups').checked ? null : Number(document.querySelector('#backup-limit').value)};
+}
+
+async function requestRepair(endpoint) {
+  const response = await fetch(endpoint, {method: 'POST', headers: {'Content-Type': 'application/json'}, body: JSON.stringify(repairPayload())});
+  const data = await response.json();
+  if (!response.ok) throw new Error(data.error || 'Duplicate cleanup failed');
+  return data;
+}
+
+previewRepairButton.addEventListener('click', async () => {
+  repairMessage.textContent = 'Checking the plan…'; applyRepairButton.disabled = true;
+  try {
+    previewedRepair = await requestRepair('/api/duplicates/batch/preview');
+    batchPreviewSummary.textContent = `${previewedRepair.choice_count} keeper decision(s) · ${previewedRepair.replaced.length} duplicate file(s) consolidated`;
+    batchPreviewList.innerHTML = previewedRepair.decisions.map((decision, index) => `
+      <article class="preview-decision"><span>Decision ${index + 1}</span><div class="winner-path"><b>Keep</b><strong>${escapeHtml(decision.keeper.split('/').pop())}</strong><small>${escapeHtml(decision.keeper)}</small></div><div class="replaced-paths"><b>Replace with a shortcut</b>${decision.replaced.map((path) => `<small>${escapeHtml(path)}</small>`).join('')}</div></article>
+    `).join('');
+    batchPreviewSafety.textContent = `${previewedRepair.metadata_backups} Serato metadata file(s) and every replaced audio file will be backed up. Database V2 will not be modified.`;
+    repairPreview.innerHTML = `<strong>Preview approved</strong><p>${previewedRepair.choice_count} keeper decision(s) are ready for one backed-up apply.</p>`;
+    repairPreview.hidden = false; applyRepairButton.disabled = false;
+    repairMessage.textContent = 'Preview complete. Nothing has changed yet.';
+    batchPreviewModal.showModal();
+  } catch (error) { repairMessage.textContent = error.message; }
+});
+
+function dismissBatchPreview() { batchPreviewModal.close(); }
+closeBatchPreview.addEventListener('click', dismissBatchPreview);
+continueReviewing.addEventListener('click', dismissBatchPreview);
+acceptPreview.addEventListener('click', dismissBatchPreview);
+
+applyRepairButton.addEventListener('click', async () => {
+  if (!previewedRepair) return;
+  applyRepairButton.disabled = true; repairMessage.textContent = 'Creating the backup before making changes…';
+  try {
+    const result = await requestRepair('/api/duplicates/batch/apply');
+    latestBackup = result.backup;
+    repairMessage.textContent = `Cleanup complete. Restore backup: ${result.backup}`;
+    previewRepairButton.disabled = true;
+    restoreRepairButton.hidden = false;
+    await loadBackups();
+  } catch (error) { repairMessage.textContent = error.message; applyRepairButton.disabled = false; }
+});
+
+restoreRepairButton.addEventListener('click', async () => {
+  if (!latestBackup) return;
+  restoreRepairButton.disabled = true; repairMessage.textContent = 'Restoring the duplicate files…';
+  try {
+    const response = await fetch('/api/backups/restore', {method: 'POST', headers: {'Content-Type': 'application/json'}, body: JSON.stringify({serato: expandHome(document.querySelector('#serato-path').value), backup: latestBackup})});
+    const result = await response.json();
+    if (!response.ok) throw new Error(result.error || 'Restore failed');
+    repairMessage.textContent = `Restore complete. ${result.restored.length} original file(s) returned.`;
+    restoreRepairButton.hidden = true;
+    await loadBackups();
+  } catch (error) { repairMessage.textContent = error.message; restoreRepairButton.disabled = false; }
+});
+
+async function handleFileAction(event) {
+  const previewButton = event.target.closest('[data-audio-url]');
+  const revealButton = event.target.closest('[data-reveal-token]');
+  if (!previewButton && !revealButton) return false;
+  event.preventDefault(); event.stopPropagation();
+  if (previewButton) {
+    audioPlayer.src = previewButton.dataset.audioUrl;
+    audioPreviewName.textContent = previewButton.dataset.audioName.split('/').pop();
+    audioPreview.hidden = false;
+    try { await audioPlayer.play(); } catch (_) { /* Native controls remain available. */ }
+  } else {
+    const original = revealButton.textContent;
+    revealButton.disabled = true; revealButton.textContent = 'Opening…';
+    try {
+      const response = await fetch('/api/reveal', {method: 'POST', headers: {'Content-Type': 'application/json'}, body: JSON.stringify({token: revealButton.dataset.revealToken})});
+      const result = await response.json();
+      if (!response.ok) throw new Error(result.error || 'Could not open Finder');
+      revealButton.textContent = 'Shown in Finder';
+    } catch (error) { revealButton.textContent = error.message; }
+    setTimeout(() => { revealButton.disabled = false; revealButton.textContent = original; }, 1800);
+  }
+  return true;
+}
+
+closeAudioPreview.addEventListener('click', () => { audioPlayer.pause(); audioPlayer.removeAttribute('src'); audioPlayer.load(); audioPreview.hidden = true; });
+repairChoice.addEventListener('click', handleFileAction);
+drilldownList.addEventListener('click', async (event) => {
+  if (await handleFileAction(event) || !reviewState) return;
+  const groups = latestAnalysis.details[reviewState.key].items;
+  const winner = event.target.closest('[data-choose-winner]');
+  if (winner) {
+    const fileIndex = Number(winner.dataset.chooseWinner);
+    reviewState.choices.set(reviewState.index, groups[reviewState.index].files[fileIndex]);
+    if (reviewState.index < groups.length - 1) reviewState.index += 1;
+    renderReviewGroup();
+    return;
+  }
+  if (event.target.closest('[data-review-skip]')) {
+    reviewState.choices.delete(reviewState.index);
+    if (reviewState.index < groups.length - 1) reviewState.index += 1;
+    renderReviewGroup();
+    return;
+  }
+  if (event.target.closest('[data-review-previous]') && reviewState.index > 0) {
+    reviewState.index -= 1;
+    renderReviewGroup();
+  }
+});
+
 function render(data) {
   latestAnalysis = data;
   document.querySelectorAll('[data-field]').forEach((element) => {

serato_doctor/webui/index.html

@@ -5,7 +5,9 @@
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <meta name="color-scheme" content="dark">
   <title>Serato Doctor</title>
-  <link rel="stylesheet" href="/app.css">
+  <link rel="stylesheet" href="/app.css?v=3">
+  <link rel="stylesheet" href="/recovery.css?v=3">
+  <link rel="stylesheet" href="/layout-fixes.css?v=3">
 </head>
 <body>
   <div class="ambient ambient-one"></div>
@@ -20,10 +22,11 @@
         <a class="nav-item active" href="#dashboard"><span>⌁</span> Dashboard</a>
         <a class="nav-item" href="#scan"><span>◎</span> New analysis</a>
         <a class="nav-item" href="#diagnostics"><span>◇</span> Diagnostics</a>
+        <a class="nav-item" href="#recovery"><span>↶</span> Recovery</a>
       </nav>
       <div class="safety-card">
         <span class="safety-icon">✓</span>
-        <div><strong>Read-only mode</strong><p>Your library will not be modified.</p></div>
+        <div><strong>Protected mode</strong><p>Analysis is read-only. Repairs require a preview and backup.</p></div>
       </div>
       <div class="sidebar-foot">Local interface · v0.1</div>
     </aside>
@@ -88,9 +91,45 @@
           <p id="drilldown-summary">Click a metric above to see example files and saved paths behind that number.</p>
           <div id="drilldown-list" class="detail-list"></div>
         </div>
+
+        <div id="duplicate-repair" class="repair-panel panel" hidden>
+          <div class="section-heading"><div><p class="eyebrow">Batch cleanup</p><h2>Review all selected changes</h2></div><span class="repair-tag">One backup · one apply</span></div>
+          <p>Approved choices are combined into one plan. Skipped groups remain untouched, and Serato’s database V2 is never edited.</p>
+          <div id="repair-choice" class="repair-choice"></div>
+          <div class="backup-options">
+            <label>Backups to keep <input id="backup-limit" type="number" min="1" value="10"></label>
+            <label class="check-label"><input id="keep-all-backups" type="checkbox"> Keep every backup</label>
+          </div>
+          <div id="repair-preview" class="repair-preview" hidden></div>
+          <div class="repair-actions">
+            <button id="preview-repair" type="button">Preview all selected changes</button>
+            <button id="apply-repair" class="danger-action" type="button" disabled>Apply all selected changes</button>
+            <button id="restore-repair" type="button" hidden>Restore this backup</button>
+          </div>
+          <div id="repair-message" class="repair-message" role="status"></div>
+        </div>
       </section>
+
+      <section id="recovery" class="recovery-panel panel">
+        <div class="section-heading"><div><p class="eyebrow">Safety net</p><h2>Backup recovery</h2></div><button id="load-backups" type="button">Check backups</button></div>
+        <p>Repair backups appear here automatically before any duplicate is consolidated. Review saved snapshots, disk usage, and restore history.</p>
+        <div id="backup-summary" class="backup-summary">Analyze your library, then choose a duplicate to preview its automatic backup.</div>
+        <div id="backup-list" class="backup-list"></div>
+      </section>
+      <div id="audio-preview" class="audio-preview" hidden>
+        <div><span>Now previewing</span><strong id="audio-preview-name"></strong></div>
+        <audio id="audio-player" controls preload="metadata"></audio>
+        <button id="close-audio-preview" type="button" aria-label="Close audio preview">×</button>
+      </div>
+      <dialog id="batch-preview-modal" class="batch-preview-modal">
+        <div class="modal-heading"><div><p class="eyebrow">Final dry-run</p><h2>Here’s exactly what will happen</h2></div><button id="close-batch-preview" type="button" aria-label="Close preview">×</button></div>
+        <p id="batch-preview-summary"></p>
+        <div id="batch-preview-list" class="batch-preview-list"></div>
+        <div class="modal-safety"><span>✓</span><p><strong>Backup happens first</strong><small id="batch-preview-safety"></small></p></div>
+        <div class="modal-actions"><button id="continue-reviewing" type="button">Close and continue reviewing</button><button id="accept-preview" type="button">Looks right</button></div>
+      </dialog>
     </main>
   </div>
-  <script src="/app.js" defer></script>
+  <script src="/app.js?v=6" defer></script>
 </body>
 </html>

serato_doctor/webui/layout-fixes.css

@@ -0,0 +1,407 @@
+.recovery-panel {
+  margin-top: 42px;
+}
+
+@media (max-width: 680px) {
+  .recovery-panel {
+    margin-top: 28px;
+  }
+}
+
+.review-workspace {
+  padding: clamp(16px, 3vw, 24px);
+  border: 1px solid rgba(155, 135, 245, .18);
+  border-radius: 16px;
+  background: rgba(255, 255, 255, .02);
+}
+
+.review-heading,
+.review-navigation {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 16px;
+}
+
+.review-heading span,
+.batch-summary span {
+  color: var(--muted);
+  font-size: 10px;
+}
+
+.review-heading strong {
+  display: block;
+  margin-top: 5px;
+  font-size: 14px;
+}
+
+.review-candidates {
+  display: grid;
+  grid-template-columns: repeat(2, minmax(0, 1fr));
+  gap: 12px;
+  margin: 18px 0;
+}
+
+.review-candidate {
+  display: flex;
+  flex-direction: column;
+  gap: 9px;
+  min-width: 0;
+  padding: 16px;
+  border: 1px solid var(--line);
+  border-radius: 14px;
+  background: rgba(6, 8, 12, .28);
+}
+
+.review-candidate.winner {
+  border-color: rgba(84, 212, 154, .52);
+  background: rgba(84, 212, 154, .06);
+}
+
+.candidate-number {
+  color: var(--violet);
+  font-size: 9px;
+  font-weight: 750;
+  text-transform: uppercase;
+  letter-spacing: .1em;
+}
+
+.review-candidate > strong,
+.review-candidate > small {
+  overflow-wrap: anywhere;
+}
+
+.review-candidate > strong {
+  font-size: 12px;
+}
+
+.review-candidate > small {
+  flex: 1;
+  color: var(--muted);
+  font-size: 9px;
+  line-height: 1.5;
+}
+
+.choose-winner {
+  margin-top: 4px;
+  border: 0;
+  border-radius: 10px;
+  padding: 10px 12px;
+  background: linear-gradient(135deg, #907be9, #6e59cf);
+  color: white;
+  font: 750 11px/1 inherit;
+  cursor: pointer;
+}
+
+.winner .choose-winner {
+  background: rgba(84, 212, 154, .18);
+  color: #8ce4b8;
+}
+
+.review-navigation button {
+  border: 1px solid var(--line);
+  border-radius: 9px;
+  padding: 8px 11px;
+  background: rgba(255, 255, 255, .04);
+  color: var(--muted);
+  font: 700 10px/1 inherit;
+  cursor: pointer;
+}
+
+.review-navigation button:disabled {
+  opacity: .35;
+}
+
+.batch-summary {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 12px;
+  padding: 14px;
+  border: 1px solid rgba(102, 217, 232, .2);
+  border-radius: 12px;
+  background: rgba(102, 217, 232, .05);
+}
+
+.batch-summary strong {
+  font-size: 12px;
+}
+
+@media (max-width: 760px) {
+  .review-candidates {
+    grid-template-columns: 1fr;
+  }
+
+  .review-heading,
+  .batch-summary {
+    align-items: flex-start;
+    flex-direction: column;
+  }
+}
+
+.batch-preview-modal {
+  width: min(820px, calc(100vw - 32px));
+  max-height: min(82vh, 760px);
+  padding: 24px;
+  overflow: auto;
+  border: 1px solid rgba(155, 135, 245, .3);
+  border-radius: 20px;
+  background: #161923;
+  color: var(--text);
+  box-shadow: 0 30px 100px rgba(0, 0, 0, .65);
+}
+
+.batch-preview-modal::backdrop {
+  background: rgba(4, 5, 8, .78);
+  backdrop-filter: blur(7px);
+}
+
+.modal-heading,
+.modal-actions,
+.modal-safety {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 14px;
+}
+
+.modal-heading h2 {
+  margin: 0;
+  font-size: 23px;
+  letter-spacing: -.03em;
+}
+
+.modal-heading > button {
+  border: 0;
+  background: transparent;
+  color: var(--muted);
+  font-size: 28px;
+  cursor: pointer;
+}
+
+#batch-preview-summary {
+  color: var(--muted);
+  font-size: 12px;
+}
+
+.batch-preview-list {
+  display: grid;
+  gap: 10px;
+  max-height: 390px;
+  margin: 18px 0;
+  padding-right: 4px;
+  overflow: auto;
+}
+
+.preview-decision {
+  display: grid;
+  grid-template-columns: 80px 1fr 1fr;
+  gap: 13px;
+  padding: 14px;
+  border: 1px solid var(--line);
+  border-radius: 13px;
+  background: rgba(255, 255, 255, .025);
+}
+
+.preview-decision > span,
+.preview-decision b {
+  color: var(--muted);
+  font-size: 9px;
+  text-transform: uppercase;
+  letter-spacing: .08em;
+}
+
+.winner-path,
+.replaced-paths {
+  min-width: 0;
+}
+
+.winner-path strong,
+.winner-path small,
+.replaced-paths small {
+  display: block;
+  margin-top: 5px;
+  overflow-wrap: anywhere;
+}
+
+.winner-path strong {
+  color: #8ce4b8;
+  font-size: 11px;
+}
+
+.winner-path small,
+.replaced-paths small {
+  color: var(--muted);
+  font-size: 9px;
+  line-height: 1.45;
+}
+
+.modal-safety {
+  justify-content: flex-start;
+  padding: 13px;
+  border: 1px solid rgba(102, 217, 232, .2);
+  border-radius: 12px;
+  background: rgba(102, 217, 232, .05);
+}
+
+.modal-safety > span {
+  color: var(--cyan);
+}
+
+.modal-safety p,
+.modal-safety strong,
+.modal-safety small {
+  display: block;
+  margin: 0;
+}
+
+.modal-safety strong {
+  font-size: 11px;
+}
+
+.modal-safety small {
+  margin-top: 4px;
+  color: var(--muted);
+  font-size: 9px;
+  line-height: 1.45;
+}
+
+.modal-actions {
+  justify-content: flex-end;
+  margin-top: 16px;
+}
+
+.modal-actions button {
+  border: 1px solid var(--line);
+  border-radius: 10px;
+  padding: 10px 13px;
+  background: rgba(255, 255, 255, .04);
+  color: var(--text);
+  font: 700 11px/1 inherit;
+  cursor: pointer;
+}
+
+#accept-preview {
+  border-color: transparent;
+  background: #6f5bd0;
+}
+
+@media (max-width: 620px) {
+  .preview-decision {
+    grid-template-columns: 1fr;
+  }
+
+  .modal-actions {
+    align-items: stretch;
+    flex-direction: column-reverse;
+  }
+}
+
+.file-compare-row {
+  display: grid;
+  gap: 8px;
+  padding: 9px 0;
+  border-top: 1px solid rgba(255, 255, 255, .05);
+}
+
+.file-compare-row:first-child {
+  border-top: 0;
+}
+
+.file-compare-row div,
+.file-actions {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 7px;
+}
+
+.file-compare-row button,
+.file-actions button {
+  border: 1px solid rgba(155, 135, 245, .25);
+  border-radius: 8px;
+  padding: 7px 9px;
+  background: rgba(155, 135, 245, .08);
+  color: #d8d2f6;
+  font: 700 10px/1 inherit;
+  cursor: pointer;
+}
+
+.keeper-option {
+  justify-content: space-between;
+}
+
+.keeper-option > label {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  min-width: 0;
+  cursor: pointer;
+}
+
+.audio-preview {
+  position: fixed;
+  right: 24px;
+  bottom: 20px;
+  display: grid;
+  grid-template-columns: minmax(150px, .7fr) minmax(240px, 1.3fr) auto;
+  align-items: center;
+  gap: 16px;
+  width: min(720px, calc(100vw - 48px));
+  padding: 13px 14px;
+  border: 1px solid rgba(102, 217, 232, .3);
+  border-radius: 14px;
+  background: rgba(16, 21, 29, .96);
+  box-shadow: 0 16px 48px rgba(0, 0, 0, .45);
+  z-index: 5;
+}
+
+.audio-preview[hidden] {
+  display: none;
+}
+
+.audio-preview span,
+.audio-preview strong {
+  display: block;
+}
+
+.audio-preview span {
+  color: var(--cyan);
+  font-size: 9px;
+  text-transform: uppercase;
+  letter-spacing: .1em;
+}
+
+.audio-preview strong {
+  max-width: 360px;
+  margin-top: 4px;
+  overflow: hidden;
+  color: var(--text);
+  font-size: 11px;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.audio-preview audio {
+  width: 100%;
+  height: 34px;
+}
+
+.audio-preview > button {
+  border: 0;
+  background: transparent;
+  color: var(--muted);
+  font-size: 22px;
+  cursor: pointer;
+}
+
+@media (max-width: 680px) {
+  .keeper-option,
+  .audio-preview {
+    align-items: stretch;
+    grid-template-columns: 1fr;
+  }
+
+  .keeper-option {
+    flex-direction: column;
+  }
+}

serato_doctor/webui/recovery.css

@@ -0,0 +1 @@
+.recovery-panel{margin-top:18px;padding:25px}.recovery-panel>p{color:var(--muted);font-size:12px;line-height:1.6}.recovery-panel .section-heading button{border:1px solid rgba(155,135,245,.35);border-radius:10px;padding:9px 12px;background:rgba(155,135,245,.12);color:#ddd8fa;font:700 11px inherit;cursor:pointer}.recovery-panel button:disabled{opacity:.5;cursor:not-allowed}.backup-summary{padding:11px 13px;border-radius:11px;background:rgba(255,255,255,.03);color:#bfc4cf;font-size:11px;margin:15px 0 10px}.backup-list{display:grid;gap:9px}.backup-item{display:flex;align-items:center;justify-content:space-between;gap:18px;padding:14px;border:1px solid var(--line);border-radius:13px;background:rgba(255,255,255,.025)}.backup-item>div{min-width:0}.backup-item strong,.backup-item small{display:block}.backup-item strong{font-size:12px;margin:7px 0}.backup-item small{font-size:10px;color:var(--muted);line-height:1.5;overflow-wrap:anywhere}.backup-item>button{flex:0 0 auto;border:0;border-radius:10px;padding:10px 13px;background:#6f5bd0;color:#fff;font:700 11px inherit;cursor:pointer}.backup-status{display:inline-block;padding:4px 7px;border-radius:999px;font-size:9px;text-transform:uppercase;letter-spacing:.08em;color:var(--cyan);background:rgba(102,217,232,.1)}.backup-status.restored{color:#aeb4c2;background:rgba(255,255,255,.06)}@media(max-width:520px){.backup-item{align-items:stretch;flex-direction:column}.backup-item>button{width:100%}}

tests/test_repair.py

@@ -0,0 +1,101 @@
+from pathlib import Path
+
+import pytest
+
+from serato_doctor.repair import (
+    BACKUP_FOLDER,
+    apply_duplicate_repair,
+    apply_duplicate_repair_batch,
+    list_backups,
+    plan_duplicate_repair,
+    restore_backup,
+    rotate_backups,
+)
+
+
+def library(tmp_path):
+    serato = tmp_path / "_Serato_"
+    crate = serato / "Subcrates" / "House.crate"
+    crate.parent.mkdir(parents=True)
+    crate.write_bytes(b"crate-data")
+    (serato / "database V2").write_bytes(b"database-data")
+    music = tmp_path / "Music"
+    keeper = music / "Main" / "Track.mp3"
+    duplicate = music / "Old" / "Track.mp3"
+    keeper.parent.mkdir(parents=True)
+    duplicate.parent.mkdir(parents=True)
+    keeper.write_bytes(b"keeper")
+    duplicate.write_bytes(b"duplicate")
+    return serato, keeper, duplicate
+
+
+def test_duplicate_repair_backs_up_then_preserves_old_path_as_link(tmp_path):
+    serato, keeper, duplicate = library(tmp_path)
+    plan = plan_duplicate_repair(keeper, (keeper, duplicate), serato)
+
+    receipt = apply_duplicate_repair(plan, serato, backup_limit=3)
+
+    assert duplicate.is_symlink()
+    assert duplicate.resolve() == keeper.resolve()
+    assert (receipt.backup / "manifest.json").is_file()
+    assert any((receipt.backup / "serato-metadata").rglob("House.crate"))
+    assert any((receipt.backup / "serato-metadata").rglob("database V2"))
+
+    history = list_backups(serato)
+    assert len(history) == 1
+    assert history[0].status == "ready"
+    assert history[0].size_bytes > 0
+
+    restored = restore_backup(receipt.backup)
+    assert restored == (duplicate.resolve(),)
+    assert not duplicate.is_symlink()
+    assert duplicate.read_bytes() == b"duplicate"
+    assert list_backups(serato)[0].status == "restored"
+
+
+def test_plan_rejects_keeper_outside_duplicate_group(tmp_path):
+    serato, keeper, duplicate = library(tmp_path)
+    outsider = tmp_path / "outsider.mp3"
+    outsider.write_bytes(b"other")
+
+    with pytest.raises(ValueError, match="must belong"):
+        plan_duplicate_repair(outsider, (keeper, duplicate), serato)
+
+
+def test_backup_rotation_can_be_limited_or_unlimited(tmp_path):
+    root = tmp_path / BACKUP_FOLDER
+    for name in ("001", "002", "003"):
+        backup = root / name
+        backup.mkdir(parents=True)
+        (backup / "manifest.json").write_text("{}", encoding="utf-8")
+
+    rotate_backups(root, None)
+    assert len(list(root.iterdir())) == 3
+    rotate_backups(root, 2)
+    assert {path.name for path in root.iterdir()} == {"002", "003"}
+
+
+def test_batch_repair_uses_one_backup_and_restores_every_group(tmp_path):
+    serato, first_keeper, first_duplicate = library(tmp_path)
+    second_keeper = tmp_path / "Music" / "Main" / "Other.mp3"
+    second_duplicate = tmp_path / "Music" / "Old" / "Other.mp3"
+    second_keeper.write_bytes(b"other-keeper")
+    second_duplicate.write_bytes(b"other-duplicate")
+    plans = (
+        plan_duplicate_repair(
+            first_keeper, (first_keeper, first_duplicate), serato
+        ),
+        plan_duplicate_repair(
+            second_keeper, (second_keeper, second_duplicate), serato
+        ),
+    )
+
+    receipt = apply_duplicate_repair_batch(plans, serato, backup_limit=10)
+
+    assert first_duplicate.is_symlink()
+    assert second_duplicate.is_symlink()
+    assert len(list((serato / BACKUP_FOLDER).iterdir())) == 1
+    assert len(receipt.replaced) == 2
+    restore_backup(receipt.backup)
+    assert first_duplicate.read_bytes() == b"duplicate"
+    assert second_duplicate.read_bytes() == b"other-duplicate"

tests/test_web.py

@@ -3,7 +3,14 @@ from pathlib import Path
 
 import pytest
 
-from serato_doctor.web import STATIC_FILES, analyze_paths
+from serato_doctor.web import (
+    STATIC_FILES,
+    _file_token,
+    _verified_audio,
+    analyze_paths,
+    duplicate_repair,
+    duplicate_repair_batch,
+)
 
 
 def test_web_analysis_uses_production_health_pipeline(tmp_path):
@@ -40,12 +47,101 @@ def test_web_analysis_rejects_missing_folders(tmp_path):
 def test_web_static_assets_are_declared_and_packaged():
     asset_root = Path(__file__).parents[1] / "serato_doctor" / "webui"
 
-    assert set(STATIC_FILES) == {"/", "/app.css", "/app.js"}
+    assert set(STATIC_FILES) == {
+        "/",
+        "/app.css",
+        "/recovery.css",
+        "/layout-fixes.css",
+        "/app.js",
+    }
     assert all((asset_root / filename).is_file() for filename, _ in STATIC_FILES.values())
     html = (asset_root / "index.html").read_text(encoding="utf-8")
     assert "Missing tracks in Serato" in html
     assert "Old crate references" in html
     assert "Choose a diagnostic" in html
+    assert "Backup recovery" in html
+    assert "Here’s exactly what will happen" in html
+    assert 'id="batch-preview-modal"' in html
     assert 'data-detail="database_missing_tracks"' in html
     assert 'data-detail="old_crate_references"' in html
     assert html.count('class="info-button"') >= 10
+
+
+def test_duplicate_repair_preview_does_not_change_files(tmp_path):
+    serato = tmp_path / "_Serato_"
+    serato.mkdir()
+    music = tmp_path / "Music"
+    first = music / "A" / "Track.mp3"
+    second = music / "B" / "Track.mp3"
+    first.parent.mkdir(parents=True)
+    second.parent.mkdir(parents=True)
+    first.write_bytes(b"first")
+    second.write_bytes(b"second")
+
+    result = duplicate_repair(
+        serato, music, first, (first, second), backup_limit=10
+    )
+
+    assert result["applied"] is False
+    assert result["database_v2_modified"] is False
+    assert second.read_bytes() == b"second"
+    assert not second.is_symlink()
+
+
+def test_audio_preview_tokens_only_open_signed_audio(tmp_path):
+    track = tmp_path / "Track.mp3"
+    track.write_bytes(b"audio")
+
+    token = _file_token(track)
+
+    assert _verified_audio(token) == track
+    with pytest.raises(ValueError, match="Invalid or expired"):
+        _verified_audio(token + "changed")
+
+
+def test_duplicate_details_include_preview_and_finder_controls(tmp_path):
+    serato = tmp_path / "_Serato_"
+    serato.mkdir()
+    music = tmp_path / "Music"
+    first = music / "A" / "Track.mp3"
+    second = music / "B" / "Track.mp3"
+    first.parent.mkdir(parents=True)
+    second.parent.mkdir(parents=True)
+    first.write_bytes(b"first")
+    second.write_bytes(b"second")
+
+    result = analyze_paths(serato, music)
+    group = result["details"]["duplicate_filenames"]["items"][0]
+
+    assert len(group["file_previews"]) == 2
+    assert group["file_previews"][0]["audio_url"].startswith("/api/audio?")
+    assert group["file_previews"][0]["reveal_token"]
+
+
+def test_batch_preview_combines_approved_groups_without_changes(tmp_path):
+    serato = tmp_path / "_Serato_"
+    serato.mkdir()
+    music = tmp_path / "Music"
+    choices = []
+    for filename in ("First.mp3", "Second.mp3"):
+        keeper = music / "A" / filename
+        duplicate = music / "B" / filename
+        keeper.parent.mkdir(parents=True, exist_ok=True)
+        duplicate.parent.mkdir(parents=True, exist_ok=True)
+        keeper.write_bytes(b"keeper")
+        duplicate.write_bytes(b"duplicate")
+        choices.append(
+            {"keeper": str(keeper), "group_files": [str(keeper), str(duplicate)]}
+        )
+
+    result = duplicate_repair_batch(
+        serato, music, choices, backup_limit=10
+    )
+
+    assert result["applied"] is False
+    assert result["choice_count"] == 2
+    assert len(result["replaced"]) == 2
+    assert len(result["decisions"]) == 2
+    assert result["decisions"][0]["keeper"].endswith("First.mp3")
+    assert len(result["decisions"][0]["replaced"]) == 1
+    assert all(not Path(choice["group_files"][1]).is_symlink() for choice in choices)