[ENHANCEMENT] improves test coverage across codebase (helpers, execution lifecyle, SSE/exec error paths etc)

[Ishita-190]

Fixes issue #117

Fixes this issue

Adds a set of unit tests covering JSONL helpers, execution lifecycle helpers, session parsing, command-history helpers, and some SSE/exec error paths.

Overall coverage increased from 54% to 70%.

Changes made

• Added test_app_helpers.py : helpers, jsonl, reliability rebuild, session parsing, command history
• Added test_execution_lifecycle.py : _cleanup_execution unit tests and exec timeout branch
• Modified test_reliability.py , test_security.py , test_sse.py : improved coverage in these files as well

Testing and validation

python -m pytest --cov=. --cov-report=term-missing --cov-report=html

start htmlcov\index.html

Screenshots and logs

Checklist

• No breaking changes
• Tests added or updated
• Documentation added or updated
• Branch is up to date with main

[Ishita-190]

@siddu-k please take a look at this!