fix: ensure unowned derived dependencies are not duplicated when reactions are skipped

Author: trueadm

.changeset/stale-keys-taste.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure unowned derived dependencies are not duplicated when reactions are skipped

packages/svelte/src/internal/client/runtime.js

@@ -404,15 +404,9 @@ export function update_reaction(reaction) {
 	skipped_deps = 0;
 	untracked_writes = null;
 	active_reaction = (flags & (BRANCH_EFFECT | ROOT_EFFECT)) === 0 ? reaction : null;
-	// prettier-ignore
 	skip_reaction =
 		(flags & UNOWNED) !== 0 &&
-		(!is_flushing_effect ||
-			// If we were previously not in a reactive context and we're reading an unowned derived
-			// that was created inside another reaction, then we don't fully know the real owner and thus
-			// we need to skip adding any reactions for this unowned
-				((previous_reaction === null || previous_untracking) &&
-				/** @type {Derived} */ (reaction).parent !== null));
+		(!is_flushing_effect || previous_reaction === null || previous_untracking);
 
 	derived_sources = null;
 	set_component_context(reaction.ctx);
@@ -933,7 +927,10 @@ export function get(signal) {
 				skipped_deps++;
 			} else if (new_deps === null) {
 				new_deps = [signal];
-			} else {
+			} else if (!skip_reaction || !new_deps.includes(signal)) {
+				// Normally we can push duplicated dependencies to `new_deps`, but if we're inside
+				// an unowned derived because skip_reaction is true, then we need to ensure that
+				// we don't have duplicates
 				new_deps.push(signal);
 			}
 		}