feat: task 2.7 event picker (subscription driver)

- src/data/events.ts: useUserEvents() TanStack Query (5-min stale,
  sort -starts_at). EventSummary type is a Pick of EventRow.
- src/live/active-event.ts: useActiveEventOrchestration() returns the
  swap fn — unsubscribe previous + clearForEvent + subscribe new +
  applySnapshot on success + persist to localStorage. Out-of-order
  safety via per-call version counter. Plus readSavedActiveEventId().
- src/ui/components/event-picker.tsx: <EventPicker> dropdown.
  useState + click-outside; rows show name + date + discipline.
- src/live/index.ts: re-exports active-event helpers.
- src/routes/_authed/monitor.tsx: auto-select effect (one-shot via
  initializedRef, gated on events loaded + WS connected); renders
  <EventPicker> wired to setActiveEvent.

Deviations:
1. Vanilla div + useState dropdown instead of shadcn Popover —
   no new shadcn primitive add; easy to swap later for keyboard nav.
2. Auto-select gated on connectionStatus === 'connected' so the
   subscribe call gets the snapshot path (not 'not-connected').
3. Logout-clears-saved-event-id deferred to a small Phase 1.8
   follow-up; documented in task risks.

Bundle: 395KB / 120KB gz (~1KB up from 2.6).

src/data/events.ts

@@ -0,0 +1,38 @@
+import { readItems, type Query } from '@directus/sdk';
+import { useQuery, type UseQueryResult } from '@tanstack/react-query';
+import { useDirectus, type EventRow, type Schema } from '@/auth';
+
+/**
+ * The subset of `EventRow` the SPA reads when listing events. Trims the
+ * payload (no `regulation_doc_url`, `notes`) — those load on demand.
+ */
+export type EventSummary = Pick<
+  EventRow,
+  'id' | 'name' | 'slug' | 'discipline' | 'starts_at' | 'ends_at' | 'organization_id'
+>;
+
+/**
+ * Fetch the events the current user has access to. Directus's permission
+ * policies (Phase 4 territory) determine the result set; for now all
+ * authenticated users see all events.
+ *
+ * Sorted most-recent-start-date first so the dogfood event is at the top.
+ * 5-minute stale time — events change daily at most.
+ */
+export function useUserEvents(): UseQueryResult<EventSummary[]> {
+  const directus = useDirectus();
+  return useQuery({
+    queryKey: ['events', 'user-accessible'],
+    queryFn: async (): Promise<EventSummary[]> => {
+      const result = await directus.request(
+        readItems<Schema, 'events', Query<Schema, EventRow>>('events', {
+          fields: ['id', 'name', 'slug', 'discipline', 'starts_at', 'ends_at', 'organization_id'],
+          sort: ['-starts_at'],
+          limit: -1,
+        }),
+      );
+      return result as EventSummary[];
+    },
+    staleTime: 5 * 60 * 1000,
+  });
+}

src/live/active-event.ts

@@ -0,0 +1,89 @@
+import { useCallback, useRef } from 'react';
+import { getLiveClient } from './bootstrap';
+import { usePositionStore } from './position-store';
+
+const ACTIVE_EVENT_LS_KEY = 'trm-active-event-id';
+
+/**
+ * Returns a stored active-event id from `localStorage`, or `null`.
+ * The orchestration's caller validates that the id still resolves to a
+ * known event before passing it back in.
+ */
+export function readSavedActiveEventId(): string | null {
+  try {
+    return localStorage.getItem(ACTIVE_EVENT_LS_KEY);
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * Hook returning a function that switches the active event:
+ *
+ * 1. Unsubscribes from the previous topic if any (best-effort).
+ * 2. Clears the position store of the previous event's state.
+ * 3. Subscribes to the new event topic.
+ * 4. On success → `applySnapshot(eventId, snapshot)` + persist eventId.
+ * 5. On failure → log + leave previous state alone (caller can retry).
+ *
+ * Out-of-order safety: a per-call version counter discards the result
+ * if the user kicked off another `setActiveEvent(...)` while this one
+ * was still in flight. Without it, an old subscribe's snapshot could
+ * arrive after a newer subscribe and overwrite the user's selection.
+ *
+ * Pass `null` to clear the active event without subscribing to a new
+ * one (used on logout).
+ */
+export function useActiveEventOrchestration(): (eventId: string | null) => Promise<void> {
+  const versionRef = useRef(0);
+
+  return useCallback(async (eventId: string | null): Promise<void> => {
+    const myVersion = ++versionRef.current;
+
+    // Tear down previous subscription, if any.
+    const prevEventId = usePositionStore.getState().activeEventId;
+    if (prevEventId) {
+      try {
+        const client = getLiveClient();
+        await client.unsubscribe(`event:${prevEventId}`);
+      } catch {
+        // Silent — even if unsubscribe fails, we drop local state.
+      }
+      usePositionStore.getState().clearForEvent();
+    }
+
+    if (eventId === null) {
+      try {
+        localStorage.removeItem(ACTIVE_EVENT_LS_KEY);
+      } catch {
+        // Ignore localStorage failures (private browsing, quota).
+      }
+      return;
+    }
+
+    let client;
+    try {
+      client = getLiveClient();
+    } catch (err) {
+      // <LiveBootstrap> hasn't mounted yet — caller should retry once
+      // auth resolves and the live client is up.
+      console.warn('setActiveEvent: live client not ready', err);
+      return;
+    }
+
+    const result = await client.subscribe(`event:${eventId}`);
+    if (versionRef.current !== myVersion) return; // superseded; ignore
+
+    if (!result.ok) {
+      console.warn('setActiveEvent: subscribe failed', result);
+      return;
+    }
+
+    usePositionStore.getState().applySnapshot(eventId, result.snapshot);
+    try {
+      localStorage.setItem(ACTIVE_EVENT_LS_KEY, eventId);
+    } catch {
+      // Ignore.
+    }
+  }, []);
+}

src/live/index.ts

@@ -1,4 +1,5 @@
 export { LiveBootstrap, getLiveClient } from './bootstrap';
+export { readSavedActiveEventId, useActiveEventOrchestration } from './active-event';
 export { createCoalescer, type Coalescer } from './coalescer';
 export { useConnectionStore, type ConnectionStatus } from './connection-store';
 export { usePositionStore } from './position-store';

src/routes/_authed/monitor.tsx

@@ -1,15 +1,45 @@
+import { useEffect, useRef } from 'react';
 import { createFileRoute } from '@tanstack/react-router';
+import { useUserEvents } from '@/data/events';
+import {
+  readSavedActiveEventId,
+  useActiveEventOrchestration,
+  useConnectionStore,
+  usePositionStore,
+} from '@/live';
 import { BasemapSwitcher } from '@/map/core/basemap-switcher';
 import { MapView } from '@/map/core/map-view';
 import { TrailsToggle } from '@/map/core/trails-toggle';
 import { MapPositions } from '@/map/layers/map-positions';
 import { MapTrails } from '@/map/layers/map-trails';
+import { EventPicker } from '@/ui/components/event-picker';
 
 export const Route = createFileRoute('/_authed/monitor')({
   component: MonitorPage,
 });
 
 function MonitorPage() {
+  const activeEventId = usePositionStore((s) => s.activeEventId);
+  const setActiveEvent = useActiveEventOrchestration();
+  const events = useUserEvents();
+  const connectionStatus = useConnectionStore((s) => s.status);
+  const initializedRef = useRef(false);
+
+  // Auto-select on first mount: prefer the previously-saved event id;
+  // otherwise the most recent. Gated on the WS being connected so the
+  // subscribe call doesn't immediately resolve with `not-connected`.
+  useEffect(() => {
+    if (initializedRef.current) return;
+    if (!events.data || events.data.length === 0) return;
+    if (connectionStatus !== 'connected') return;
+    initializedRef.current = true;
+
+    const saved = readSavedActiveEventId();
+    const target =
+      saved && events.data.some((e) => e.id === saved) ? saved : (events.data[0]?.id ?? null);
+    if (target) void setActiveEvent(target);
+  }, [events.data, connectionStatus, setActiveEvent]);
+
   return (
     // 3.5rem ≈ 56 px reserved for a future top-bar (Phase 3 chrome).
     // For now the parent _authed layout has no top-bar, so the map can
@@ -20,6 +50,12 @@ function MonitorPage() {
           UI controls. Floating cards positioned absolutely inside
           <MapView>'s wrapper.
         */}
+        <EventPicker
+          activeEventId={activeEventId}
+          onChange={(id) => {
+            void setActiveEvent(id);
+          }}
+        />
         <BasemapSwitcher />
         <TrailsToggle />
         {/*

src/ui/components/event-picker.tsx

@@ -0,0 +1,115 @@
+import { useEffect, useRef, useState } from 'react';
+import { ChevronDown } from 'lucide-react';
+import { useUserEvents, type EventSummary } from '@/data/events';
+import { cn } from '@/lib/utils';
+
+export type EventPickerProps = {
+  activeEventId: string | null;
+  onChange: (eventId: string) => void;
+};
+
+/**
+ * Top-left dropdown listing the events the current user can see, sorted
+ * most-recent first. Click to open; click an event to switch.
+ */
+export function EventPicker({ activeEventId, onChange }: EventPickerProps) {
+  const { data: events = [], isLoading, isError } = useUserEvents();
+  const [open, setOpen] = useState(false);
+  const containerRef = useRef<HTMLDivElement>(null);
+
+  // Click-outside to close.
+  useEffect(() => {
+    if (!open) return;
+    const handler = (ev: MouseEvent): void => {
+      if (containerRef.current && !containerRef.current.contains(ev.target as Node)) {
+        setOpen(false);
+      }
+    };
+    document.addEventListener('mousedown', handler);
+    return () => {
+      document.removeEventListener('mousedown', handler);
+    };
+  }, [open]);
+
+  const active = events.find((e) => e.id === activeEventId);
+
+  const buttonLabel = (() => {
+    if (active) return active.name;
+    if (isLoading) return 'Loading events…';
+    if (isError) return 'Failed to load events';
+    if (events.length === 0) return 'No events available';
+    return 'Select event';
+  })();
+
+  return (
+    <div ref={containerRef} className="absolute top-3 left-3 z-10">
+      <button
+        type="button"
+        onClick={() => setOpen((o) => !o)}
+        disabled={isLoading || isError || events.length === 0}
+        className="flex items-center gap-2 bg-background border border-border rounded-md shadow-sm px-3 py-1.5 text-sm font-medium hover:bg-accent/50 disabled:opacity-60 disabled:cursor-not-allowed"
+      >
+        <span className="truncate max-w-xs">{buttonLabel}</span>
+        <ChevronDown
+          className={cn('size-4 transition-transform', open && 'rotate-180')}
+          aria-hidden
+        />
+      </button>
+      {open && events.length > 0 && (
+        <ul className="absolute mt-1 left-0 min-w-72 max-w-md max-h-80 overflow-y-auto bg-background border border-border rounded-md shadow-md">
+          {events.map((e) => (
+            <EventRow
+              key={e.id}
+              event={e}
+              isActive={e.id === activeEventId}
+              onClick={() => {
+                onChange(e.id);
+                setOpen(false);
+              }}
+            />
+          ))}
+        </ul>
+      )}
+    </div>
+  );
+}
+
+function EventRow({
+  event,
+  isActive,
+  onClick,
+}: {
+  event: EventSummary;
+  isActive: boolean;
+  onClick: () => void;
+}) {
+  return (
+    <li>
+      <button
+        type="button"
+        onClick={onClick}
+        className={cn(
+          'w-full text-left px-3 py-2 transition-colors border-b border-border last:border-b-0',
+          isActive ? 'bg-accent text-accent-foreground' : 'hover:bg-accent/50',
+        )}
+      >
+        <div className="text-sm font-medium truncate">{event.name}</div>
+        <div className="text-xs text-muted-foreground mt-0.5">
+          {formatDate(event.starts_at)} · {event.discipline}
+        </div>
+      </button>
+    </li>
+  );
+}
+
+function formatDate(iso: string): string {
+  // Compact date-only render. Browser's locale formatter is fine for v1;
+  // i18n is Phase 4. Ditches the time component — operators care about
+  // which event, not which start time.
+  try {
+    const d = new Date(iso);
+    return d.toLocaleDateString(undefined, { year: 'numeric', month: 'short', day: 'numeric' });
+  } catch {
+    return iso.slice(0, 10);
+  }
+}