Phase 6: remote backup destinations — SFTP & S3 (0.6.0)

- BackupDestination model + backup_destination_service (SFTP via paramiko,
  S3-compatible via boto3): upload/list/download/delete/test.
- routers/destinations.py: destinations CRUD (secrets masked, merge-on-update),
  test, list/delete remote backups. backups.py: POST /{id}/backup/push and
  POST /restore-from (download from a destination + restore, volumes included).
- Frontend: Settings → Backup destinations (SFTP/S3 forms + test); Backup dialog
  can push to a destination; Restore dialog can pick a destination + backup.
- deps: paramiko 3.5.0, boto3 1.35.99.

Verified end-to-end against live MinIO + atmoz/sftp: create/test destinations,
push (incl. volumes), list, restore-from to a fresh stack (volume data intact),
delete remote backup.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/routers/destinations.py

@@ -0,0 +1,171 @@
+"""Backup destination management (SFTP / S3-compatible)."""
+from __future__ import annotations
+
+import asyncio
+import json
+
+from fastapi import APIRouter, Depends, HTTPException, Request
+from sqlmodel import Session, select
+
+from auth import get_current_user, require_admin
+from database import get_session
+from models.backup_destination import (
+    DESTINATION_TYPES,
+    SECRET_KEYS,
+    BackupDestination,
+    DestinationCreate,
+    DestinationRead,
+    DestinationUpdate,
+)
+from models.user import User
+from services import audit_service, backup_destination_service as dest_service
+
+router = APIRouter(prefix="/api/backups/destinations", tags=["backups"])
+
+
+def _ip(request: Request) -> str:
+    return request.client.host if request.client else "unknown"
+
+
+def _mask(config: dict) -> dict:
+    return {k: ("••••••" if k in SECRET_KEYS and v else v) for k, v in config.items()}
+
+
+def _to_read(d: BackupDestination) -> DestinationRead:
+    return DestinationRead(
+        id=d.id,
+        name=d.name,
+        type=d.type,
+        config=_mask(dest_service.parse_config(d)),
+        created_at=d.created_at,
+    )
+
+
+def _get_or_404(session: Session, dest_id: int) -> BackupDestination:
+    d = session.get(BackupDestination, dest_id)
+    if not d:
+        raise HTTPException(status_code=404, detail=f"Destination {dest_id} not found")
+    return d
+
+
+@router.get("", response_model=list[DestinationRead])
+def list_destinations(
+    session: Session = Depends(get_session),
+    _user: User = Depends(require_admin),
+) -> list[DestinationRead]:
+    rows = session.exec(select(BackupDestination).order_by(BackupDestination.id)).all()
+    return [_to_read(d) for d in rows]
+
+
+@router.post("", response_model=DestinationRead, status_code=201)
+def create_destination(
+    body: DestinationCreate,
+    request: Request,
+    session: Session = Depends(get_session),
+    user: User = Depends(require_admin),
+) -> DestinationRead:
+    if body.type not in DESTINATION_TYPES:
+        raise HTTPException(status_code=400, detail=f"Unknown type '{body.type}'")
+    d = BackupDestination(name=body.name, type=body.type, config=json.dumps(body.config))
+    session.add(d)
+    session.commit()
+    session.refresh(d)
+    audit_service.record(
+        session, user=user.username, action="destination.create", target=body.name,
+        detail=body.type, ip=_ip(request),
+    )
+    return _to_read(d)
+
+
+@router.put("/{dest_id}", response_model=DestinationRead)
+def update_destination(
+    dest_id: int,
+    body: DestinationUpdate,
+    request: Request,
+    session: Session = Depends(get_session),
+    user: User = Depends(require_admin),
+) -> DestinationRead:
+    d = _get_or_404(session, dest_id)
+    if body.name is not None:
+        d.name = body.name
+    if body.config is not None:
+        # Merge so masked/blank secrets don't wipe stored ones.
+        existing = dest_service.parse_config(d)
+        for k, v in body.config.items():
+            if k in SECRET_KEYS and (v == "" or v == "••••••"):
+                continue  # keep existing secret
+            existing[k] = v
+        d.config = json.dumps(existing)
+    session.add(d)
+    session.commit()
+    session.refresh(d)
+    audit_service.record(
+        session, user=user.username, action="destination.update", target=d.name,
+        ip=_ip(request),
+    )
+    return _to_read(d)
+
+
+@router.delete("/{dest_id}")
+def delete_destination(
+    dest_id: int,
+    request: Request,
+    session: Session = Depends(get_session),
+    user: User = Depends(require_admin),
+) -> dict:
+    d = _get_or_404(session, dest_id)
+    name = d.name
+    session.delete(d)
+    session.commit()
+    audit_service.record(
+        session, user=user.username, action="destination.delete", target=name,
+        ip=_ip(request),
+    )
+    return {"ok": True}
+
+
+@router.post("/{dest_id}/test")
+async def test_destination(
+    dest_id: int,
+    session: Session = Depends(get_session),
+    _user: User = Depends(require_admin),
+) -> dict:
+    d = _get_or_404(session, dest_id)
+    try:
+        await asyncio.to_thread(dest_service.test, d)
+        return {"ok": True}
+    except dest_service.DestinationError as exc:
+        return {"ok": False, "error": str(exc)}
+
+
+@router.get("/{dest_id}/backups")
+async def list_destination_backups(
+    dest_id: int,
+    session: Session = Depends(get_session),
+    _user: User = Depends(require_admin),
+) -> list[dict]:
+    d = _get_or_404(session, dest_id)
+    try:
+        return await asyncio.to_thread(dest_service.list_backups, d)
+    except dest_service.DestinationError as exc:
+        raise HTTPException(status_code=502, detail=str(exc)) from exc
+
+
+@router.delete("/{dest_id}/backups/{name}")
+async def delete_destination_backup(
+    dest_id: int,
+    name: str,
+    request: Request,
+    session: Session = Depends(get_session),
+    user: User = Depends(require_admin),
+) -> dict:
+    d = _get_or_404(session, dest_id)
+    try:
+        await asyncio.to_thread(dest_service.delete, d, name)
+    except dest_service.DestinationError as exc:
+        raise HTTPException(status_code=502, detail=str(exc)) from exc
+    audit_service.record(
+        session, user=user.username, action="destination.backup.delete",
+        target=f"{d.name}/{name}", ip=_ip(request),
+    )
+    return {"ok": True}