Previously CellValue had three variants: Number, Text, and Empty.
The Empty variant acted as a null sentinel, but the compiler could not
distinguish between "this is a real value" and "this might be empty".
Code that received a CellValue could use it without checking for Empty,
because there was no type-level enforcement.
Now CellValue has only Number and Text. The absence of a value is
represented as None at every API boundary:
DataStore::get() → Option<&CellValue> (was &CellValue / Empty)
Model::get_cell() → Option<&CellValue> (was &CellValue / Empty)
Model::evaluate() → Option<CellValue> (was CellValue::Empty)
eval_formula() → Option<CellValue> (was CellValue::Empty)
Model gains clear_cell() for explicit key removal; ClearCell dispatch
calls it instead of set_cell(key, CellValue::Empty).
The compiler now forces every caller of evaluate/get_cell to handle
the None case explicitly — accidental use of an empty value as if it
were real is caught at compile time rather than silently computing
wrong results.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
ImportPipeline holds all data and logic (raw JSON, records, proposals,
model_name, build_model). ImportWizard wraps it with UI-only state
(step, cursor, message). Rename WizardState → WizardStep throughout.
Headless import in dispatch.rs now constructs ImportPipeline directly.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
