From 3c3ce570558a83f143c85c276f719b97ec65cb54 Mon Sep 17 00:00:00 2001
From: Ryan Hamamura <58859899+ryanhamamura@users.noreply.github.com>
Date: Fri, 20 Feb 2026 07:46:05 -1000
Subject: [PATCH] fix: signal-backed marker reactivity and stale signal re-push
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Two issues discovered during testing:

1. data-effect expressions for signal-backed markers short-circuited
   before reading $signalID when the map hadn't loaded yet. Datastar
   never tracked those signals as dependencies, so the effect never
   re-ran. Fix: read signal values unconditionally before the guard.

2. prepareSignalsForPatch never reset changed=false on regular signals
   (only computed ones), causing every SyncSignals() call to re-push
   all signals — including stale server-side values for the draggable
   pin, overwriting the client-side drag position.
---
 context.go     | 1 +
 maplibre/js.go | 9 ++++++---
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/context.go b/context.go
index dee6bac..52164e5 100644
--- a/context.go
+++ b/context.go
@@ -291,6 +291,7 @@ func (c *Context) prepareSignalsForPatch() map[string]any {
 			}
 			if sig.changed {
 				updatedSigs[sigID.(string)] = fmt.Sprintf("%v", sig.val)
+				sig.changed = false
 			}
 		case *computedSignal:
 			sig.recompute()
diff --git a/maplibre/js.go b/maplibre/js.go
index ee136dc..67952f1 100644
--- a/maplibre/js.go
+++ b/maplibre/js.go
@@ -233,12 +233,15 @@ func dragendHandlerJS(mapID, markerID string, mk Marker) string {
 // markerEffectExpr generates a data-effect expression that moves a signal-backed marker
 // when its signals change.
 func markerEffectExpr(mapID, markerID string, mk Marker) string {
+	// Read signals before the guard so Datastar tracks them as dependencies
+	// even when the map/marker hasn't loaded yet on first evaluation.
 	return fmt.Sprintf(
-		`var m=window.__via_maps&&window.__via_maps[%s];`+
+		`var lng=$%s,lat=$%s;`+
+			`var m=window.__via_maps&&window.__via_maps[%s];`+
 			`if(m&&m._via_markers[%s]){`+
-			`m._via_markers[%s].setLngLat([$%s,$%s])}`,
-		jsonStr(mapID), jsonStr(markerID), jsonStr(markerID),
+			`m._via_markers[%s].setLngLat([lng,lat])}`,
 		mk.LngSignal.ID(), mk.LatSignal.ID(),
+		jsonStr(mapID), jsonStr(markerID), jsonStr(markerID),
 	)
 }