InvestigationFilters is a normalized, serializable selection (days,
providers, projects, models, categories, PRs, project-scoped branches,
provider-scoped sessions) with OR within a dimension and AND across them.
Contribution math walks each row's segments and multiplies per-dimension
shares, so sums reconcile every dimension's aggregate exactly; rows without
segments are excluded and disclosed. NavState + the history stack back the
in-app Back/Forward (filters, sort, page depth, open drawer) and the
restart snapshot. The drawer shows metadata, full totals beside the
in-selection figures, and the per-model/category/branch/day/PR breakdowns
with an Escape-and-focus-return contract.
