From 3f57077a8b495752783dcda3a25e05f43c215347 Mon Sep 17 00:00:00 2001
From: Scott Idem <stidem@gmail.com>
Date: Tue, 10 Mar 2026 14:21:51 -0400
Subject: [PATCH] Pres mgmt: migrate session liveQueries to $derived.by()
 pattern

Replace $derived(liveQuery(...)) with $derived.by(() => { const id = ...; return liveQuery(...) })
for lq__event_presenter_obj and lq__auth__event_presenter_obj in the
session page.

$derived.by() captures only the specific ID at derivation time, so
unrelated store changes do not recreate the observable. Plain $derived
closes over the entire $events_slct store object, causing unnecessary
observable recreation on any store mutation.
---
 .../session/[session_id]/+page.svelte         | 27 ++++++++++---------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/src/routes/events/[event_id]/(pres_mgmt)/session/[session_id]/+page.svelte b/src/routes/events/[event_id]/(pres_mgmt)/session/[session_id]/+page.svelte
index ea729648..3c4b3877 100644
--- a/src/routes/events/[event_id]/(pres_mgmt)/session/[session_id]/+page.svelte
+++ b/src/routes/events/[event_id]/(pres_mgmt)/session/[session_id]/+page.svelte
@@ -6,7 +6,7 @@
     }
 
     let { data }: Props = $props();
-    let log_lvl: number = $state(1);
+    let log_lvl: number = $state(0);
 
     // Imports
     import { Modal } from 'flowbite-svelte';
@@ -68,20 +68,23 @@
         liveQuery(async () => await db_events.event.get(url_event_id))
     );
 
-    let lq__event_presenter_obj = $derived(
-        liveQuery(async () => {
-            if (!$events_slct.event_presenter_id) return null;
-            return await db_events.presenter.get($events_slct.event_presenter_id);
-        })
-    );
+    // $derived.by: capture only the specific ID so that unrelated store changes
+    // don't needlessly recreate the liveQuery observable.
+    let lq__event_presenter_obj = $derived.by(() => {
+        const id = $events_slct.event_presenter_id;
+        return liveQuery(async () => {
+            if (!id) return null;
+            return await db_events.presenter.get(id);
+        });
+    });
 
-    let lq__auth__event_presenter_obj = $derived(
-        liveQuery(async () => {
-            const pid = $events_loc.auth__person?.presenter_id;
+    let lq__auth__event_presenter_obj = $derived.by(() => {
+        const pid = $events_loc.auth__person?.presenter_id;
+        return liveQuery(async () => {
             if (!pid) return null;
             return await db_events.presenter.get(pid);
-        })
-    );
+        });
+    });
 
     if (!$events_loc.pres_mgmt) $events_loc.pres_mgmt = {};
     if (!$events_sess.pres_mgmt) $events_sess.pres_mgmt = {};