Fix missing workflow 404 handling and add regression tests

[Titas-Ghosh]

Fixes #323

Problem

GET /workflow/<serverID> could miss the intended 404 Not Found path because model and controller used different not-found contracts:

• WorkFlowModel.get() could return (False, 'Record Not Found')
• getWorkflow() checked only for None

This mismatch could lead to invalid downstream behavior instead of a clean 404.

Root Cause

Inconsistent API contract between:

• server/model/workflows.py
• server/controller/workflow.py

Changes

1. Standardized model contract:

• WorkFlowModel.get() now returns None when serverID is missing.

2. Hardened controller handling:

• Added isMissingWorkflow(...) guard in server/controller/workflow.py.
• Guard handles both:
  • new contract: None
  • legacy contract: (False, 'Record Not Found')
• Ensures GET /workflow/<serverID> consistently returns 404 for missing workflows.

3. Added regression tests:

• New file: server/tests/test_workflow_controller.py
• Covers:
  • missing workflow (None) -> 404
  • missing workflow (legacy tuple) -> 404
  • hash mismatch with X-Latest-Hash -> 400
  • hash match with X-Latest-Hash -> 200

Files Changed

• server/model/workflows.py
• server/controller/workflow.py
• server/tests/test_workflow_controller.py

Behavior After This PR

• GET /workflow/<missing-id> always returns 404 Not Found
• Behavior is consistent with and without X-Latest-Hash
• Legacy not-found return shape is still safely handled in controller

Validation

• Syntax check passed:
  • python -m py_compile server/controller/workflow.py server/model/workflows.py server/tests/test_workflow_controller.py
• Ran backend regression tests locally(from server/):
  • python -m unittest discover -s tests -p "test_*.py" -v
• Result: Ran 4 tests ... OK

Test Output Screenshot

Notes

This is backward-compatible at controller level while moving model behavior to a single clear not-found contract.