diff --git a/.changeset/angry-ideas-listen.md b/.changeset/angry-ideas-listen.md
new file mode 100644
index 0000000000..cb2bf00d1c
--- /dev/null
+++ b/.changeset/angry-ideas-listen.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: proactively defer effects in pending boundary
diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 08cc994494..8f23fb1a2e 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -1,7 +1,6 @@
 /** @import { Effect, Source, TemplateNode, } from '#client' */
 import {
 	BOUNDARY_EFFECT,
-	COMMENT_NODE,
 	DIRTY,
 	EFFECT_PRESERVED,
 	EFFECT_TRANSPARENT,
@@ -202,7 +201,7 @@ export class Boundary {
 					this.#pending_effect = null;
 				});
 
-				this.is_pending = false;
+				this.#resolve();
 			}
 		});
 	}
@@ -224,13 +223,33 @@ export class Boundary {
 				const pending = /** @type {(anchor: Node) => void} */ (this.#props.pending);
 				this.#pending_effect = branch(() => pending(this.#anchor));
 			} else {
-				this.is_pending = false;
+				this.#resolve();
 			}
 		} catch (error) {
 			this.error(error);
 		}
 	}
 
+	#resolve() {
+		this.is_pending = false;
+
+		// any effects that were previously deferred should be rescheduled —
+		// after the next traversal (which will happen immediately, due to the
+		// same update that brought us here) the effects will be flushed
+		for (const e of this.#dirty_effects) {
+			set_signal_status(e, DIRTY);
+			schedule_effect(e);
+		}
+
+		for (const e of this.#maybe_dirty_effects) {
+			set_signal_status(e, MAYBE_DIRTY);
+			schedule_effect(e);
+		}
+
+		this.#dirty_effects.clear();
+		this.#maybe_dirty_effects.clear();
+	}
+
 	/**
 	 * Defer an effect inside a pending boundary until the boundary resolves
 	 * @param {Effect} effect
@@ -294,24 +313,7 @@ export class Boundary {
 		this.#pending_count += d;
 
 		if (this.#pending_count === 0) {
-			this.is_pending = false;
-
-			// any effects that were encountered and deferred during traversal
-			// should be rescheduled — after the next traversal (which will happen
-			// immediately, due to the same update that brought us here)
-			// the effects will be flushed
-			for (const e of this.#dirty_effects) {
-				set_signal_status(e, DIRTY);
-				schedule_effect(e);
-			}
-
-			for (const e of this.#maybe_dirty_effects) {
-				set_signal_status(e, MAYBE_DIRTY);
-				schedule_effect(e);
-			}
-
-			this.#dirty_effects.clear();
-			this.#maybe_dirty_effects.clear();
+			this.#resolve();
 
 			if (this.#pending_effect) {
 				pause_effect(this.#pending_effect, () => {
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index b5a2651b2a..297049fd6b 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -18,7 +18,8 @@ import {
 	EAGER_EFFECT,
 	HEAD_EFFECT,
 	ERROR_VALUE,
-	MANAGED_EFFECT
+	MANAGED_EFFECT,
+	REACTION_RAN
 } from '#client/constants';
 import { async_mode_flag } from '../../flags/index.js';
 import { deferred, define_property, includes } from '../../shared/utils.js';
@@ -246,9 +247,6 @@ export class Batch {
 
 		var effect = root.first;
 
-		/** @type {Effect | null} */
-		var pending_boundary = null;
-
 		while (effect !== null) {
 			var flags = effect.f;
 			var is_branch = (flags & (BRANCH_EFFECT | ROOT_EFFECT)) !== 0;
@@ -256,26 +254,9 @@ export class Batch {
 
 			var skip = is_skippable_branch || (flags & INERT) !== 0 || this.#skipped_branches.has(effect);
 
-			// Inside a `<svelte:boundary>` with a pending snippet,
-			// all effects are deferred until the boundary resolves
-			// (except block/async effects, which run immediately)
-			if (
-				async_mode_flag &&
-				pending_boundary === null &&
-				(flags & BOUNDARY_EFFECT) !== 0 &&
-				effect.b?.is_pending
-			) {
-				pending_boundary = effect;
-			}
-
 			if (!skip && effect.fn !== null) {
 				if (is_branch) {
 					effect.f ^= CLEAN;
-				} else if (
-					pending_boundary !== null &&
-					(flags & (EFFECT | RENDER_EFFECT | MANAGED_EFFECT)) !== 0
-				) {
-					/** @type {Boundary} */ (pending_boundary.b).defer_effect(effect);
 				} else if ((flags & EFFECT) !== 0) {
 					effects.push(effect);
 				} else if (async_mode_flag && (flags & (RENDER_EFFECT | MANAGED_EFFECT)) !== 0) {
@@ -294,10 +275,6 @@ export class Batch {
 			}
 
 			while (effect !== null) {
-				if (effect === pending_boundary) {
-					pending_boundary = null;
-				}
-
 				var next = effect.next;
 
 				if (next !== null) {
@@ -839,6 +816,19 @@ function depends_on(reaction, sources, checked) {
 export function schedule_effect(signal) {
 	var effect = (last_scheduled_effect = signal);
 
+	var boundary = effect.b;
+
+	// defer render effects inside a pending boundary
+	// TODO the `REACTION_RAN` check is only necessary because of legacy `$:` effects AFAICT — we can remove later
+	if (
+		boundary?.is_pending &&
+		(signal.f & (EFFECT | RENDER_EFFECT | MANAGED_EFFECT)) !== 0 &&
+		(signal.f & REACTION_RAN) === 0
+	) {
+		boundary.defer_effect(signal);
+		return;
+	}
+
 	while (effect.parent !== null) {
 		effect = effect.parent;
 		var flags = effect.f;
@@ -850,13 +840,18 @@ export function schedule_effect(signal) {
 			is_flushing &&
 			effect === active_effect &&
 			(flags & BLOCK_EFFECT) !== 0 &&
-			(flags & HEAD_EFFECT) === 0
+			(flags & HEAD_EFFECT) === 0 &&
+			(flags & REACTION_RAN) !== 0
 		) {
 			return;
 		}
 
 		if ((flags & (ROOT_EFFECT | BRANCH_EFFECT)) !== 0) {
-			if ((flags & CLEAN) === 0) return;
+			if ((flags & CLEAN) === 0) {
+				// branch is already dirty, bail
+				return;
+			}
+
 			effect.f ^= CLEAN;
 		}
 	}