fix(compose): move atomic backup out of stack folder, silence stale stats 404s (#498)

The Skipper/Admiral atomic deploy/update path used to create
.sencho-backup/ inside the user's stack folder, which silently failed
with EACCES whenever a container had chowned the bind mount (swag,
tautulli, linuxserver/* images, etc). That broke auto-rollback and the
manual rollback endpoint for those stacks. Stack backups now live under
<DATA_DIR>/backups/<stackName>/ next to sencho.db, which is always
writable by the Sencho user.

While stress-testing the same scenario, MonitorService also flooded the
error log with "Error parsing stats for container ... 404 no such
container" because per-container stats polls (30s tick) raced with
docker compose recreating containers. The 404 case is now skipped
silently; non-404 stats failures still log at error level.

backend/src/__tests__/filesystem-backup.test.ts

@@ -0,0 +1,102 @@
+/**
+ * Verifies that FileSystemService stores stack backups under
+ * <DATA_DIR>/backups/<stackName>/ rather than inside the user's compose
+ * folder. The old in-stack-folder location failed with EACCES whenever a
+ * container had chowned the bind mount, breaking the atomic rollback
+ * feature for those stacks.
+ */
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import path from 'path';
+import os from 'os';
+import { promises as fsPromises } from 'fs';
+
+// Mutable state the mocked NodeRegistry reads. Each test rewrites these
+// before instantiating FileSystemService.
+const mockState = { composeDir: '' };
+
+vi.mock('../services/NodeRegistry', () => ({
+  NodeRegistry: {
+    getInstance: () => ({
+      getComposeDir: () => mockState.composeDir,
+      getDefaultNodeId: () => 1,
+    }),
+  },
+}));
+
+import { FileSystemService } from '../services/FileSystemService';
+
+describe('FileSystemService backup location', () => {
+  let composeDir: string;
+  let dataDir: string;
+  let originalDataDir: string | undefined;
+
+  beforeEach(async () => {
+    composeDir = await fsPromises.mkdtemp(path.join(os.tmpdir(), 'sencho-compose-'));
+    dataDir = await fsPromises.mkdtemp(path.join(os.tmpdir(), 'sencho-data-'));
+    mockState.composeDir = composeDir;
+    originalDataDir = process.env.DATA_DIR;
+    process.env.DATA_DIR = dataDir;
+  });
+
+  afterEach(async () => {
+    if (originalDataDir === undefined) delete process.env.DATA_DIR;
+    else process.env.DATA_DIR = originalDataDir;
+    await fsPromises.rm(composeDir, { recursive: true, force: true });
+    await fsPromises.rm(dataDir, { recursive: true, force: true });
+  });
+
+  it('writes backups under <DATA_DIR>/backups/<stackName>/, not inside the stack folder', async () => {
+    const stackName = 'web';
+    const stackDir = path.join(composeDir, stackName);
+    await fsPromises.mkdir(stackDir, { recursive: true });
+    await fsPromises.writeFile(path.join(stackDir, 'compose.yaml'), 'services: {}\n', 'utf-8');
+    await fsPromises.writeFile(path.join(stackDir, '.env'), 'FOO=bar\n', 'utf-8');
+
+    const service = FileSystemService.getInstance();
+    await service.backupStackFiles(stackName);
+
+    const newBackupDir = path.join(dataDir, 'backups', stackName);
+    const oldBackupDir = path.join(stackDir, '.sencho-backup');
+
+    // New location has every backed-up file
+    await expect(fsPromises.access(path.join(newBackupDir, 'compose.yaml'))).resolves.toBeUndefined();
+    await expect(fsPromises.access(path.join(newBackupDir, '.env'))).resolves.toBeUndefined();
+    const ts = await fsPromises.readFile(path.join(newBackupDir, '.timestamp'), 'utf-8');
+    expect(parseInt(ts, 10)).toBeGreaterThan(0);
+
+    // Old location must NOT be created
+    await expect(fsPromises.access(oldBackupDir)).rejects.toMatchObject({ code: 'ENOENT' });
+  });
+
+  it('getBackupInfo reads from the new location', async () => {
+    const stackName = 'api';
+    await fsPromises.mkdir(path.join(composeDir, stackName), { recursive: true });
+    await fsPromises.writeFile(path.join(composeDir, stackName, 'compose.yaml'), 'services: {}\n', 'utf-8');
+
+    const service = FileSystemService.getInstance();
+    const before = await service.getBackupInfo(stackName);
+    expect(before).toEqual({ exists: false, timestamp: null });
+
+    await service.backupStackFiles(stackName);
+    const after = await service.getBackupInfo(stackName);
+    expect(after.exists).toBe(true);
+    expect(typeof after.timestamp).toBe('number');
+  });
+
+  it('restoreStackFiles copies files from the new location back to the stack dir', async () => {
+    const stackName = 'db';
+    const stackDir = path.join(composeDir, stackName);
+    await fsPromises.mkdir(stackDir, { recursive: true });
+    await fsPromises.writeFile(path.join(stackDir, 'compose.yaml'), 'version: original\n', 'utf-8');
+
+    const service = FileSystemService.getInstance();
+    await service.backupStackFiles(stackName);
+
+    // Mutate the live stack file, then restore
+    await fsPromises.writeFile(path.join(stackDir, 'compose.yaml'), 'version: mutated\n', 'utf-8');
+    await service.restoreStackFiles(stackName);
+
+    const restored = await fsPromises.readFile(path.join(stackDir, 'compose.yaml'), 'utf-8');
+    expect(restored).toBe('version: original\n');
+  });
+});

backend/src/services/FileSystemService.ts

@@ -3,6 +3,16 @@ import { promises as fsPromises } from 'fs';
 import { spawn } from 'child_process';
 import { NodeRegistry } from './NodeRegistry';
 
+/**
+ * Resolves the writable Sencho data directory (same one DatabaseService /
+ * CryptoService use). Recomputed lazily so test harnesses that override
+ * `process.env.DATA_DIR` after module load still take effect.
+ */
+function getBackupBaseDir(): string {
+  const dataDir = process.env.DATA_DIR || path.join(process.cwd(), 'data');
+  return path.join(dataDir, 'backups');
+}
+
 /**
  * FileSystemService - local-only file I/O for compose stack management.
  *
@@ -289,11 +299,17 @@ export class FileSystemService {
   }
 
   /**
-   * Backup stack files (compose.yaml + .env) to .sencho-backup/ within the stack dir.
+   * Backup stack files (compose.yaml + .env) into Sencho's data dir.
+   *
+   * Backups live at <DATA_DIR>/backups/<stackName>/ (NOT inside the user's
+   * compose folder) so the operation always succeeds even when the stack
+   * folder is owned by another UID (e.g., a container running as root has
+   * chowned its bind mount). DATA_DIR is the same writable location that
+   * holds sencho.db and encryption.key.
    */
   async backupStackFiles(stackName: string): Promise<void> {
     const stackDir = path.join(this.baseDir, stackName);
-    const backupDir = path.join(stackDir, '.sencho-backup');
+    const backupDir = path.join(getBackupBaseDir(), stackName);
     await fsPromises.mkdir(backupDir, { recursive: true });
 
     // Copy compose file
@@ -327,12 +343,9 @@ export class FileSystemService {
     await fsPromises.writeFile(path.join(backupDir, '.timestamp'), Date.now().toString(), 'utf-8');
   }
 
-  /**
-   * Restore stack files from .sencho-backup/ back to the stack dir.
-   */
   async restoreStackFiles(stackName: string): Promise<void> {
     const stackDir = path.join(this.baseDir, stackName);
-    const backupDir = path.join(stackDir, '.sencho-backup');
+    const backupDir = path.join(getBackupBaseDir(), stackName);
 
     const items = await fsPromises.readdir(backupDir);
     for (const item of items) {
@@ -341,11 +354,8 @@ export class FileSystemService {
     }
   }
 
-  /**
-   * Get backup info for a stack.
-   */
   async getBackupInfo(stackName: string): Promise<{ exists: boolean; timestamp: number | null }> {
-    const backupDir = path.join(this.baseDir, stackName, '.sencho-backup');
+    const backupDir = path.join(getBackupBaseDir(), stackName);
     try {
       await fsPromises.access(backupDir);
       const tsFile = path.join(backupDir, '.timestamp');

backend/src/services/MonitorService.ts

@@ -294,6 +294,14 @@ export class MonitorService {
                             }
                         }
                     } catch (e) {
+                        // Containers can be removed between getRunningContainers() and the
+                        // per-container stats call (e.g., during a stack update). Dockerode
+                        // throws a 404 in that case. That's expected churn, not a real
+                        // error, so skip silently rather than flooding the logs.
+                        const err = e as { statusCode?: number; reason?: string };
+                        if (err?.statusCode === 404 || err?.reason === 'no such container') {
+                            continue;
+                        }
                         console.error(`Error parsing stats for container ${container.Id} on node ${node.name}`, e);
                     }
                 }