fix: purge all old staging path references — full code review cleanup

Bugs found and fixed:
- converter.py: STAGING_IN.iterdir() → extract_base.iterdir()
  (checked wrong dir when source was in session subdir)
- vm-bench.service: TMPDIR=/mnt/converter/in → /mnt/converter/tmp
  (old path poisoned all temp file writes)
- backend/app.py: removed unused STAGING_IN constant
- converter.py: removed unused STAGING_OUT constant
- install.sh: removed creation of old /in and /out dirs

backend/app.py

@@ -54,7 +54,6 @@ logger.info("Backend starting — log file: %s", LOG_DIR / "vm-bench-backend.log
 # ---------------------------------------------------------------------------
 # Constants
 # ---------------------------------------------------------------------------
-STAGING_IN = "/mnt/converter/in"
 API_PREFIX = "/api/v1"
 
 # ---------------------------------------------------------------------------

backend/converter.py

@@ -17,7 +17,6 @@ from typing import Optional
 
 STAGING_ROOT = Path("/mnt/converter/tmp")
 STAGING_IN = STAGING_ROOT / "in"
-STAGING_OUT = STAGING_ROOT / "out"
 
 logger = logging.getLogger("backend.converter")
 
@@ -108,7 +107,7 @@ def extract_if_needed(filename: str) -> Path:
         raise RuntimeError(f"{tool} failed: {result.stderr.strip()[:500]}")
 
     # Determine what was created
-    after = set(STAGING_IN.iterdir())
+    after = set(extract_base.iterdir())
     new_items = after - before
 
     # If the archive had a single top-level directory matching the stem, use it

backend/install.sh

@@ -58,8 +58,6 @@ echo "[1/6] Creating directory structure..."
 
 for d in \
     "$CONVERTER_ROOT" \
-    "$CONVERTER_ROOT/in" \
-    "$CONVERTER_ROOT/out" \
     "$CONVERTER_ROOT/logs" \
     "$CONVERTER_ROOT/tmp" \
     "$CONVERTER_ROOT/backend" \

frontend/vm-bench.service

@@ -8,7 +8,7 @@ User=root
 WorkingDirectory=/mnt/converter/frontend
 Environment=PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
 Environment=BACKEND_URL=http://10.2.0.2:9000
-Environment=TMPDIR=/mnt/converter/in
+Environment=TMPDIR=/mnt/converter/tmp
 ExecStart=/usr/bin/python3 -m uvicorn app:app --host 0.0.0.0 --port 5000 --timeout-keep-alive 300
 Restart=always
 RestartSec=3