Global time range (LFE-10497)

The global time filter that persists across views within a project (Home ↔ Trace ↔ Sessions …). Foundation for the date picker (LFE-8156), which is the editor that reads/writes this state.

Owner map

• globalDateRangeStore.ts — global singleton Zustand store (with persist). Single source of truth for the per-user default, namespaced by project (defaultsByProject: Record<projectId, token>), in relative meta-format. Owns the localStorage boundary (one key, langfuse-global-date-range). The store is global because the default is cross-route product state; the data is per-project because switching projects must give each its own range.
• useGlobalDateRange.ts — composition hook. Pure, no effects: derives the displayed TimeRange from the URL ?dateRange= (route source of truth) ⊕ the store default (presence-XOR, no merging), via resolveTimeRange. The only writer is setTimeRange (explicit pick) → URL + store default.
• resolveTimeRange / rangeToString / rangeFromString — pure encoding + XOR resolution, in @/src/utils/date-range-utils.ts (co-located with the other range utilities); covered by date-range-utils.clienttest.ts.

Consumers don't use these directly: useDashboardDateRange and useTableDateRange (in @/src/hooks/) are thin per-view delegators that pass the view's allowed presets + fallback.

Data flow (one-way)

URL ?dateRange  (route SoT, explicit) ─┐
                                       ├─ resolveTimeRange (pure) ─▶ timeRange ─▶ views
store default   (per-project, persisted)┘
        ▲
   setTimeRange  ──▶ setQueryParams(URL) + store.setProjectDefault ──▶ persist→localStorage

The default is never auto-written to the URL: clean navigations read the store default and leave the URL clean, so shared links carry only explicitly-set params.

Next slice

If project-scoped client state recurs (column/view prefs, drafts), promote the "select this project's slice" pattern into a shared <ProjectScope> provider; useGlobalDateRange already reads only the active project's slice, so it can move without consumer churn.