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/backups.py

@@ -1,18 +1,26 @@
 """Stack backup (incl. volumes) and restore."""
 from __future__ import annotations
 
+import asyncio
 import os
 import tempfile
 
 from fastapi import APIRouter, Depends, File, Form, HTTPException, Query, Request, UploadFile
 from fastapi.responses import FileResponse
+from pydantic import BaseModel
 from sqlmodel import Session
 
 from auth import require_admin
 from database import get_session
+from models.backup_destination import BackupDestination
 from models.stack import Stack
 from models.user import User
-from services import audit_service, backup_service, compose_service
+from services import (
+    audit_service,
+    backup_destination_service as dest_service,
+    backup_service,
+    compose_service,
+)
 
 router = APIRouter(prefix="/api/stacks", tags=["backups"])
 
@@ -21,6 +29,12 @@ def _ip(request: Request) -> str:
     return request.client.host if request.client else "unknown"
 
 
+def _backup_filename(stack_id: str, include_volumes: bool) -> str:
+    date = compose_service.now().strftime("%Y%m%d-%H%M%S")
+    suffix = "full" if include_volumes else "config"
+    return f"backup-{stack_id}-{suffix}-{date}.tar.gz"
+
+
 @router.get("/{stack_id}/backup")
 async def backup_stack(
     stack_id: str,
@@ -43,12 +57,10 @@ async def backup_stack(
         session, user=user.username, action="stack.backup", target=stack_id,
         detail=f"volumes={include_volumes}", ip=_ip(request),
     )
-    date = compose_service.now().strftime("%Y%m%d-%H%M%S")
-    suffix = "full" if include_volumes else "config"
     return FileResponse(
         path,
         media_type="application/gzip",
-        filename=f"backup-{stack_id}-{suffix}-{date}.tar.gz",
+        filename=_backup_filename(stack_id, include_volumes),
     )
 
 
@@ -94,3 +106,105 @@ async def restore_stack(
     finally:
         if os.path.exists(tmp.name):
             os.unlink(tmp.name)
+
+
+# --------------------------------------------------------------------------- #
+# Push to / restore from a remote destination
+# --------------------------------------------------------------------------- #
+
+
+class PushBody(BaseModel):
+    destination_id: int
+    include_volumes: bool = True
+    stop_first: bool = True
+
+
+class RestoreFromBody(BaseModel):
+    destination_id: int
+    name: str
+    target_id: str | None = None
+    overwrite: bool = False
+    restore_volumes: bool = True
+
+
+def _get_dest(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.post("/{stack_id}/backup/push")
+async def push_backup(
+    stack_id: str,
+    body: PushBody,
+    request: Request,
+    session: Session = Depends(get_session),
+    user: User = Depends(require_admin),
+) -> dict:
+    stack = session.get(Stack, stack_id)
+    if not stack:
+        raise HTTPException(status_code=404, detail=f"Stack '{stack_id}' not found")
+    dest = _get_dest(session, body.destination_id)
+    try:
+        path = await backup_service.create_backup(
+            stack_id, stack.name,
+            include_volumes=body.include_volumes, stop_first=body.stop_first,
+        )
+    except backup_service.BackupError as exc:
+        raise HTTPException(status_code=400, detail=str(exc)) from exc
+
+    filename = _backup_filename(stack_id, body.include_volumes)
+    try:
+        remote = await asyncio.to_thread(dest_service.upload, dest, path, filename)
+    except dest_service.DestinationError as exc:
+        raise HTTPException(status_code=502, detail=str(exc)) from exc
+    finally:
+        if os.path.exists(path):
+            os.unlink(path)
+
+    audit_service.record(
+        session, user=user.username, action="stack.backup.push",
+        target=stack_id, detail=f"{dest.name}:{filename}", ip=_ip(request),
+    )
+    return {"ok": True, "destination": dest.name, "name": filename, "remote": remote}
+
+
+@router.post("/restore-from")
+async def restore_from_destination(
+    body: RestoreFromBody,
+    request: Request,
+    session: Session = Depends(get_session),
+    user: User = Depends(require_admin),
+) -> dict:
+    dest = _get_dest(session, body.destination_id)
+    tmp = tempfile.NamedTemporaryFile(delete=False, suffix=".tar.gz")
+    tmp.close()
+    try:
+        try:
+            await asyncio.to_thread(dest_service.download, dest, body.name, tmp.name)
+        except dest_service.DestinationError as exc:
+            raise HTTPException(status_code=502, detail=str(exc)) from exc
+
+        target = compose_service.slugify(body.target_id) if body.target_id else None
+        try:
+            result = backup_service.restore_backup(
+                tmp.name, target_id=target,
+                overwrite=body.overwrite, restore_volumes=body.restore_volumes,
+            )
+        except backup_service.BackupError as exc:
+            code = 409 if "already exists" in str(exc) else 400
+            raise HTTPException(status_code=code, detail=str(exc)) from exc
+
+        stack_id = result["stack_id"]
+        if not session.get(Stack, stack_id):
+            session.add(Stack(id=stack_id, name=result.get("name", stack_id)))
+            session.commit()
+        audit_service.record(
+            session, user=user.username, action="stack.restore",
+            target=stack_id, detail=f"from {dest.name}:{body.name}", ip=_ip(request),
+        )
+        return result
+    finally:
+        if os.path.exists(tmp.name):
+            os.unlink(tmp.name)