fix leak

packages/svelte/src/internal/client/dom/blocks/branches.js

@@ -1,5 +1,4 @@
 /** @import { Effect, TemplateNode } from '#client' */
-import { is_runes } from '../../context.js';
 import { Batch, current_batch } from '../../reactivity/batch.js';
 import {
 	branch,
@@ -8,7 +7,6 @@ import {
 	pause_effect,
 	resume_effect
 } from '../../reactivity/effects.js';
-import { set_should_intro, should_intro } from '../../render.js';
 import { hydrate_node, hydrating } from '../hydration.js';
 import { create_text, should_defer_append } from '../operations.js';
 
@@ -126,6 +124,22 @@ export class BranchManager {
 		}
 	};
 
+	/**
+	 * @param {Batch} batch
+	 */
+	#discard = (batch) => {
+		this.#batches.delete(batch);
+
+		const keys = Array.from(this.#batches.values());
+
+		for (const [k, branch] of this.#offscreen) {
+			if (!keys.includes(k)) {
+				destroy_effect(branch.effect);
+				this.#offscreen.delete(k);
+			}
+		}
+	};
+
 	/**
 	 *
 	 * @param {any} key
@@ -173,7 +187,8 @@ export class BranchManager {
 				}
 			}
 
-			batch.add_callback(this.#commit);
+			batch.oncommit(this.#commit);
+			batch.ondiscard(this.#discard);
 		} else {
 			if (hydrating) {
 				this.anchor = hydrate_node;

packages/svelte/src/internal/client/dom/blocks/each.js

@@ -310,7 +310,7 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 					}
 				}
 
-				batch.add_callback(commit);
+				batch.oncommit(commit);
 			} else {
 				commit();
 			}

packages/svelte/src/internal/client/reactivity/batch.js

@@ -108,7 +108,12 @@ export class Batch {
 	 * and append new ones by calling the functions added inside (if/each/key/etc) blocks
 	 * @type {Set<() => void>}
 	 */
-	#callbacks = new Set();
+	#commit_callbacks = new Set();
+
+	/**
+	 * If a fork is discarded, we need to destroy any effects that are no longer needed
+	 */
+	#discard_callbacks = new Set();
 
 	/**
 	 * The number of async effects that are currently in flight
@@ -328,11 +333,16 @@ export class Batch {
 		}
 	}
 
+	discard() {
+		for (const fn of this.#discard_callbacks) fn(this);
+		this.#discard_callbacks.clear();
+	}
+
 	#resolve() {
 		if (this.#blocking_pending === 0) {
 			// append/remove branches
-			for (const fn of this.#callbacks) fn();
-			this.#callbacks.clear();
+			for (const fn of this.#commit_callbacks) fn();
+			this.#commit_callbacks.clear();
 		}
 
 		if (this.#pending === 0) {
@@ -463,8 +473,13 @@ export class Batch {
 	}
 
 	/** @param {() => void} fn */
-	add_callback(fn) {
-		this.#callbacks.add(fn);
+	oncommit(fn) {
+		this.#commit_callbacks.add(fn);
+	}
+
+	/** @param {(batch: Batch) => void} fn */
+	ondiscard(fn) {
+		this.#discard_callbacks.add(fn);
 	}
 
 	settled() {
@@ -943,7 +958,10 @@ export function fork(fn) {
 			await settled;
 		},
 		discard: () => {
+			if (batches.has(batch)) {
 				batches.delete(batch);
+				batch.discard();
+			}
 		}
 	};
 }