fix(views): correct container reuse logic, fix flag validation, subprocess errors, port range, cleanup

[suradadhanush]

Changes

Container Reuse (resolves TODO in post())

The previous implementation called docker run unconditionally before checking if a container could be reused — causing orphaned containers on every reuse-eligible POST. Additionally, the reuse check compared a 12-char short ID from docker ps against the full 64-char container ID stored in the database, so reuse never triggered even when the container was healthy.

Fix: Attempt docker start directly first. docker start returns non-zero if the container doesn't exist — this is used as the fallback signal to create a new one. No docker ps check needed.

Flag Validation (resolves TODO in put())

Django does not parse PUT request bodies into request.POST. request.POST.get('flag') always returns None on a PUT request, causing the endpoint to always return 400.

Fix: Parse the request body directly using json.loads(request.body). SHA-256 hash comparison against the stored hashed_ prefixed flag is preserved correctly.

Subprocess error handling

Added stderr=subprocess.PIPE and returncode != 0 checks to all subprocess.Popen calls — previously silent failures returned 200 with a garbage container_id.

Other fixes

• Port scan starts at 8001 instead of 8000 — app runs on 8000, scanning from 8000 wastes a check every time
• Removed unused import csrf_exempt (Flake8 F401)
• Fixed typo: challange → challenge in put() method parameter