fix(launcher): use $derived.by for session liveQueries to fix stale presentation/presenter data

When switching sessions within the same location, presentations and presenters
were not updating. The root cause: plain $derived(liveQuery(...)) never recreates
the Observable when slct__event_session_id changes, because liveQuery's async
callback runs in Dexie's zone where Svelte tracking is off. Dexie's range-level
change detection then ignores new session data (it arrives under a different
event_session_id index value, outside the originally observed range).

Replaced all four liveQuery declarations with $derived.by(() => { const id = ...;
return liveQuery(...id...); }) — the same pattern already used in +layout.svelte
for location-dependent queries. Svelte tracks the id read in the outer closure
and recreates the Observable on every session change.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/routes/events/[event_id]/(launcher)/launcher_session_view.svelte

@@ -50,10 +50,17 @@ import {
     Users
 } from '@lucide/svelte';
 // Event Session (Main View Trigger)
-// WHY: We use a simple derived observable. The template handles the $ prefix.
+// WHY: $derived.by captures the id in the outer closure so Svelte tracks it as a
-let lq__event_session_obj = $derived(
+// reactive dependency and recreates the Observable when slct__event_session_id changes.
-    liveQuery(() => db_events.session.get(slct__event_session_id))
+// Plain $derived(liveQuery(...)) does NOT work here: liveQuery's async callback runs in
-);
+// Dexie's zone where Svelte tracking is off, so $derived never sees the id read and never
+// recreates the Observable when the session changes. Dexie's range-level change tracking
+// then keeps the stale Observable alive — it only re-fires when data in the originally
+// observed key range changes, not when a different session's data arrives.
+let lq__event_session_obj = $derived.by(() => {
+    const id = slct__event_session_id;
+    return liveQuery(() => db_events.session.get(id));
+});
 
 // WHY: type_code drives poster vs. oral UI branching throughout this component.
 // It was previously a prop that was never passed by the parent, so all poster
@@ -62,65 +69,63 @@ let lq__event_session_obj = $derived(
 let type_code = $derived($lq__event_session_obj?.type_code ?? '');
 
 // Event File (for a Session)
-// WHY: Pure data retrieval. Side effects (updating global stores) are removed
+// WHY: $derived.by — same reason as lq__event_session_obj above. Without recreating
-// to prevent circular reactivity loops during rapid navigation.
+// the Observable when slct__event_session_id changes, Dexie never re-fires for the new
-let lq__event_file_obj_li = $derived(
+// session's files (they land in a different for_id range than what was originally observed).
-    liveQuery(async () => {
+let lq__event_file_obj_li = $derived.by(() => {
-        if (!slct__event_session_id) return [];
+    const id = slct__event_session_id;
+    return liveQuery(async () => {
+        if (!id) return [];
 
         if (log_lvl > 1) {
-            console.log(
+            console.log(`[LQ] Fetching files for session: ${id}`);
-                `[LQ] Fetching files for session: ${slct__event_session_id}`
-            );
         }
 
         return await db_events.file
             .where('for_id')
-            .equals(slct__event_session_id)
+            .equals(id)
             .reverse()
             .sortBy('created_on');
-    })
+    });
-);
+});
 
 // Event Presentation
-let lq__event_presentation_obj_li = $derived(
+// WHY: $derived.by — same reason as above. Captures both id and sort_by in the outer
-    liveQuery(async () => {
+// closure so a new Observable is created whenever the session or its type changes.
-        if (!slct__event_session_id) return [];
+let lq__event_presentation_obj_li = $derived.by(() => {
+    const id = slct__event_session_id;
+    const sort_by = type_code == 'poster' ? 'name' : 'start_datetime';
+    return liveQuery(async () => {
+        if (!id) return [];
 
         if (log_lvl > 1) {
-            console.log(
+            console.log(`[LQ] Fetching presentations for session: ${id}`);
-                `[LQ] Fetching presentations for session: ${slct__event_session_id}`
-            );
         }
 
-        let sort_by = 'start_datetime';
-        if (type_code == 'poster') {
-            sort_by = 'name';
-        }
         return await db_events.presentation
             .where('event_session_id')
-            .equals(slct__event_session_id)
+            .equals(id)
             .sortBy(sort_by);
-    })
+    });
-);
+});
 
 // Event Presenter
-let lq__event_presenter_obj_li = $derived(
+// WHY: $derived.by — same reason as above.
-    liveQuery(async () => {
+let lq__event_presenter_obj_li = $derived.by(() => {
-        if (!slct__event_session_id) return [];
+    const id = slct__event_session_id;
+    return liveQuery(async () => {
+        if (!id) return [];
 
         if (log_lvl > 1) {
-            console.log(
+            console.log(`[LQ] Fetching presenters for session: ${id}`);
-                `[LQ] Fetching presenters for session: ${slct__event_session_id}`
-            );
         }
 
         return await db_events.presenter
             .where('event_session_id')
-            .equals(slct__event_session_id)
+            .equals(id)
             .sortBy('full_name');
-    })
+    });
-);
+});
 
 // let show_modal_upload_files: boolean = false;
 // let link_to_type: null|string = null;