feat: shared file-based logging to /mnt/converter/logs/

Both frontend and backend now write rotating log files to
/mnt/converter/logs/ (shared between host and LXC):

  /mnt/converter/logs/vm-bench.log          (frontend)
  /mnt/converter/logs/vm-bench-backend.log   (backend)

- RotatingFileHandler: 10 MB per file, 5 backups
- Console handler still writes to systemd journal
- Logs/ directory is gitignored and auto-created on startup
- Install script creates logs/ directory

.gitignore

@@ -1,6 +1,7 @@
 # Staging data — not code
 /in/
 /out/
+/logs/
 
 # Python
 __pycache__/

README.md

@@ -48,7 +48,8 @@ Browser            vm-bench LXC             Proxmox Host (srv2)
 │   └── requirements.txt
 ├── open-api.yaml              # API spec (single source of truth)
 ├── in/                        # Shared staging directory (gitignored)
-└── out/                       # Shared output directory (gitignored)
+├── out/                       # Shared output directory (gitignored)
+├── logs/                       # Shared log files (gitignored)
 ```
 
 ## Features
@@ -287,5 +288,21 @@ large virtual disk, but only a fraction is used.
 progress. Replace with real `qm create`, `qm importdisk`, and `qm set` commands
 when deploying to the Proxmox host.
 
-**Staging files**: `/mnt/converter/in/` and `/mnt/converter/out/` are gitignored —
-they contain user data, not code.
+**Staging files**: `/mnt/converter/in/`, `/mnt/converter/out/`, and `/mnt/converter/logs/` are gitignored —
+they contain runtime data, not code.
+
+## Logging
+
+Both services write to two locations simultaneously:
+
+| Destination | How to access |
+|-------------|---------------|
+| **File** (shared) | `tail -f /mnt/converter/logs/vm-bench.log` (frontend) or `vm-bench-backend.log` (backend) |
+| **Journal** (per-service) | `journalctl -u vm-bench -f` (frontend) or `journalctl -u vm-bench-backend -f` (backend) |
+
+Log files rotate automatically at 10 MB, keeping 5 historical files
+(e.g. `vm-bench.log`, `vm-bench.log.1`, `vm-bench.log.2`, …).
+
+The file logs are the authoritative source — they're written to the shared
+`/mnt/converter/logs/` directory, accessible from both the Proxmox host and
+the LXC container.

backend/app.py

@@ -9,6 +9,9 @@ Matches open-api.yaml v1.1.0 spec exactly.
 from __future__ import annotations
 
 import logging
+from logging.handlers import RotatingFileHandler
+from pathlib import Path
+
 from fastapi import FastAPI, HTTPException, Request
 from fastapi.middleware.cors import CORSMiddleware
 
@@ -28,11 +31,24 @@ from provisioner import submit_job, get_job_status, cleanup_staging
 # ---------------------------------------------------------------------------
 # Logging
 # ---------------------------------------------------------------------------
-logging.basicConfig(
-    level=logging.INFO,
-    format="%(asctime)s %(levelname)s %(message)s",
-)
 logger = logging.getLogger("backend")
+logger.setLevel(logging.INFO)
+
+# Console → systemd journal
+_ch = logging.StreamHandler()
+_ch.setFormatter(logging.Formatter("%(asctime)s %(levelname)s %(message)s"))
+logger.addHandler(_ch)
+
+# File handler → shared log directory
+LOG_DIR = Path("/mnt/converter/logs")
+LOG_DIR.mkdir(parents=True, exist_ok=True)
+_fh = RotatingFileHandler(
+    LOG_DIR / "vm-bench-backend.log", maxBytes=10 * 1024 * 1024, backupCount=5,
+)
+_fh.setFormatter(logging.Formatter("%(asctime)s %(levelname)s %(name)s %(message)s"))
+logger.addHandler(_fh)
+
+logger.info("Backend starting — log file: %s", LOG_DIR / "vm-bench-backend.log")
 
 # ---------------------------------------------------------------------------
 # Constants

backend/install.sh

@@ -60,6 +60,7 @@ for d in \
     "$CONVERTER_ROOT" \
     "$CONVERTER_ROOT/in" \
     "$CONVERTER_ROOT/out" \
+    "$CONVERTER_ROOT/logs" \
     "$CONVERTER_ROOT/backend" \
     "$CONVERTER_ROOT/frontend" \
     "$CONVERTER_ROOT/frontend/templates" \

frontend/app.py

@@ -16,6 +16,7 @@ Routes:
 from __future__ import annotations
 
 import logging
+from logging.handlers import RotatingFileHandler
 import os
 import shutil
 import subprocess
@@ -48,7 +49,23 @@ STAGING = Path("/mnt/converter/in")
 api = ApiClient()
 
 logger = logging.getLogger("vm-bench")
-logging.basicConfig(level=logging.INFO, format="%(asctime)s %(levelname)s %(message)s")
+logger.setLevel(logging.INFO)
+
+# Console handler → systemd journal via stdout
+_ch = logging.StreamHandler()
+_ch.setFormatter(logging.Formatter("%(asctime)s %(levelname)s %(message)s"))
+logger.addHandler(_ch)
+
+# File handler → shared log directory on /mnt/converter
+LOG_DIR = Path("/mnt/converter/logs")
+LOG_DIR.mkdir(parents=True, exist_ok=True)
+_fh = RotatingFileHandler(
+    LOG_DIR / "vm-bench.log", maxBytes=10 * 1024 * 1024, backupCount=5,
+)
+_fh.setFormatter(logging.Formatter("%(asctime)s %(levelname)s %(name)s %(message)s"))
+logger.addHandler(_fh)
+
+logger.info("Frontend starting — log file: %s", LOG_DIR / "vm-bench.log")
 
 # Config
 VM_ID_MIN = 21000