Implement `computeInitialValues` to calculate the starting state of
declared variables and seed them into the journal stream store during
the completions initialization process.
Add support for `role=declare` blocks in markdown to allow for
dynamic variable declarations and tag-based modifiers.
- Implement `declare-parser` to parse CSV-formatted declaration blocks.
- Implement `var-reactivity` to manage dependency graphs, topological
sorting, and cascading updates when variables change.
- Implement `variable-expression` to evaluate arithmetic, dice rolls,
and math functions within expressions.
hypercross