fix: don't restore batch in #await (#17051)

#16977 had one slight regression which might contribute to #16990: The batch from earlier was restored, but that doesn't make sense in this situations since this has nothing to do with our new async logic of batches suspending until pending work is done. As a result you could end up with a batch being created, and then the restore then instead reverting to an earlier batch that was already done, which means a ghost-batch ends up in the set of batches, subsequently triggering time traveling when it shouldn't. This may help with #16990 No test because basically impossible to do so

Author: dummdidumm

.changeset/shaky-jars-cut.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: don't restore batch in `#await`

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

@@ -12,7 +12,7 @@ import {
 import { queue_micro_task } from '../task.js';
 import { HYDRATION_START_ELSE, UNINITIALIZED } from '../../../../constants.js';
 import { is_runes } from '../../context.js';
-import { flushSync, is_flushing_sync } from '../../reactivity/batch.js';
+import { Batch, flushSync, is_flushing_sync } from '../../reactivity/batch.js';
 import { BranchManager } from './branches.js';
 import { capture, unset_context } from '../../reactivity/async.js';
 
@@ -69,7 +69,11 @@ export function await_block(node, get_input, pending_fn, then_fn, catch_fn) {
 if (destroyed) return;
 
 resolved = true;
-restore();
+// We don't want to restore the previous batch here; {#await} blocks don't follow the async logic
+// we have elsewhere, instead pending/resolve/fail states are each their own batch so to speak.
+restore(false);
+// Make sure we have a batch, since the branch manager expects one to exist
+Batch.ensure();
 
 if (hydrating) {
 // `restore()` could set `hydrating` to `true`, which we very much

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

@@ -33,7 +33,6 @@ import {
 set_hydrating,
 skip_nodes
 } from '../dom/hydration.js';
-import { create_text } from '../dom/operations.js';
 
 /**
  *
@@ -102,11 +101,11 @@ export function capture() {
 var previous_dev_stack = dev_stack;
 }
 
-return function restore() {
+return function restore(activate_batch = true) {
 set_active_effect(previous_effect);
 set_active_reaction(previous_reaction);
 set_component_context(previous_component_context);
-previous_batch?.activate();
+if (activate_batch) previous_batch?.activate();
 
 if (was_hydrating) {
 set_hydrating(true);