fix: reuse `batch_values`

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

@@ -68,14 +68,6 @@ export let previous_batch = null;
  */
 export let batch_values = null;
 
-/**
- * When time travelling (i.e. working in one batch, while other batches
- * still have ongoing work), we ignore the real values of affected
- * signals in favour of their values within the batch
- * @type {Map<Value, any> | null}
- */
-export let forked_derived_values = null;
-
 // TODO this should really be a property of `batch`
 /** @type {Effect[]} */
 let queued_root_effects = [];
@@ -966,15 +958,14 @@ export function fork(fn) {
 
 	var batch = Batch.ensure();
 	batch.is_fork = true;
+	batch_values = new Map();
 
 	var committed = false;
 	var settled = batch.settled();
 
-	forked_derived_values = new Map();
-
 	flushSync(fn);
 
-	forked_derived_values = null;
+	batch_values = null;
 
 	// revert state changes
 	for (var [source, value] of batch.previous) {

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

@@ -34,7 +34,7 @@ import { async_mode_flag, tracing_mode_flag } from '../../flags/index.js';
 import { Boundary } from '../dom/blocks/boundary.js';
 import { component_context } from '../context.js';
 import { UNINITIALIZED } from '../../../constants.js';
-import { batch_values, current_batch, forked_derived_values } from './batch.js';
+import { batch_values, current_batch } from './batch.js';
 import { unset_context } from './async.js';
 import { deferred } from '../../shared/utils.js';
 
@@ -360,10 +360,8 @@ export function update_derived(derived) {
 		// the underlying value will be updated when the fork is committed.
 		// otherwise, the next time we get here after a 'real world' state
 		// change, `derived.equals` may incorrectly return `true`
-		if (!forked_derived_values) {
+		if (!current_batch?.is_fork) {
 			derived.v = value;
-		} else {
-			forked_derived_values.set(derived, value);
 		}
 
 		derived.wv = increment_write_version();
@@ -380,7 +378,7 @@ export function update_derived(derived) {
 	if (batch_values !== null) {
 		// only cache the value if we're in a tracking context, otherwise we won't
 		// clear the cache in `mark_reactions` when dependencies are updated
-		if (effect_tracking()) {
+		if (effect_tracking() || current_batch?.is_fork) {
 			batch_values.set(derived, value);
 		}
 	} else {

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

@@ -43,13 +43,7 @@ import {
 	set_dev_stack
 } from './context.js';
 import * as w from './warnings.js';
-import {
-	Batch,
-	batch_values,
-	flushSync,
-	forked_derived_values,
-	schedule_effect
-} from './reactivity/batch.js';
+import { Batch, batch_values, flushSync, schedule_effect } from './reactivity/batch.js';
 import { handle_error } from './error-handling.js';
 import { UNINITIALIZED } from '../../constants.js';
 import { captured_signals } from './legacy.js';
@@ -627,10 +621,6 @@ export function get(signal) {
 		if (is_updating_effect && effect_tracking() && (derived.f & CONNECTED) === 0) {
 			reconnect(derived);
 		}
-
-		if (forked_derived_values?.has(derived)) {
-			return forked_derived_values.get(derived);
-		}
 	}
 
 	if (batch_values?.has(signal)) {