Environment halting and Agents pausing

[hlloreda]

Description

Remaining things:

• Clean
• Remove old todos
• Fix broken test

Self Check:

Strike through any lines that are not applicable (~~line~~) then check the box

• Attached issue to pull request
• Changelog entry
• Type annotations are present
• Code is clear and sufficiently documented
• No (preventable) type errors (check using make mypy or make mypy-diff)
• Sufficient test cases (reproduces the bug/tests the requested feature)
• Correct, in line with design
• End user documentation is included or an issue is created for end-user documentation (add ref to issue here: )
• If this PR fixes a race condition in the test suite, also push the fix to the relevant stable branche(s) (see test-fixes for more info)