test: Improve test coverage for CLI commands

[allenporter]

Adds test coverage for CLI subcommands, fields flag injection, and CLI session handlers.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.38%. Comparing base (e60d657) to head (5dbcd0b).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #49       +/-   ##
===========================================
+ Coverage   82.09%   93.38%   +11.29%     
===========================================
  Files          30       30               
  Lines        3100     3100               
===========================================
+ Hits         2545     2895      +350     
+ Misses        555      205      -350     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.