Collect and report failed declarations, failed tag modifier expressions, and
circular dependencies instead of swallowing them. Diagnostics are deduped,
logged with key/expression context, cleared on re-init, and exposed through
useJournalCompletions and the VariableView warning banner. A bad declaration
no longer aborts the rest of a cascade.
Reject malformed numeric literals in the tokenizer so inputs like "1.2.3"
throw instead of being truncated by parseFloat.
