Model adjustments caught during validation

[lukelowry]

Description

These are the last few issues I ran into during validation. Mostly initialization and parameter guard fixes.

Lots of tiny edge cases in the full unmodified cases that we did not account for.

Proposed changes

• one
• two

Checklist

• All tests pass.
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows GridKit™ style guidelines.
• There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.
• I have updated CHANGELOG.md to reflect the changes in this PR. If this is a minor PR that is part of a larger fix already included in the file, state so.

Further comments

Looking very good. Draft until others are merged