From f48e4e2ec503c9b3f1ca2ea8ac12b549a8e93adc Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 23 Mar 2026 21:11:42 -0400
Subject: [PATCH] WIP

---
 .../src/internal/client/reactivity/batch.js   |  2 +-
 .../src/internal/client/reactivity/effects.js |  3 ++-
 .../src/internal/client/reactivity/sources.js |  2 +-
 .../src/internal/client/reactivity/status.js  |  2 +-
 .../src/internal/client/reactivity/types.d.ts |  5 ++---
 .../svelte/src/internal/client/runtime.js     | 21 +++++++++++--------
 6 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index 3b10d6ebe6..cc00df4a5f 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -39,7 +39,7 @@ import { UNINITIALIZED } from '../../../constants.js';
 import { set_signal_status } from './status.js';
 import { legacy_is_updating_store } from './store.js';
 import { invariant } from '../../shared/dev.js';
-import { log_effect_tree } from '../dev/debug.js';
+import { log_effect_tree, root } from '../dev/debug.js';
 
 /** @type {Set<Batch>} */
 const batches = new Set();
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index 54c8a17d79..bf8ae97ca1 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -103,7 +103,7 @@ function create_effect(type, fn) {
 		ctx: component_context,
 		deps: null,
 		nodes: null,
-		f: type | DIRTY | CONNECTED,
+		f: type | CLEAN | CONNECTED,
 		first: null,
 		fn,
 		last: null,
@@ -113,6 +113,7 @@ function create_effect(type, fn) {
 		prev: null,
 		teardown: null,
 		wv: 0,
+		rv: -1,
 		ac: null
 	};
 
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index 3ccde0f211..279c0cf465 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -371,7 +371,7 @@ function mark_reactions(signal, status, updated_during_traversal) {
 
 				mark_reactions(derived, MAYBE_DIRTY, updated_during_traversal);
 			}
-		} else if (not_dirty) {
+		} else {
 			var effect = /** @type {Effect} */ (reaction);
 
 			if ((flags & BLOCK_EFFECT) !== 0 && eager_block_effects !== null) {
diff --git a/packages/svelte/src/internal/client/reactivity/status.js b/packages/svelte/src/internal/client/reactivity/status.js
index 024285e73a..b8d2e23b2f 100644
--- a/packages/svelte/src/internal/client/reactivity/status.js
+++ b/packages/svelte/src/internal/client/reactivity/status.js
@@ -8,7 +8,7 @@ const STATUS_MASK = ~(DIRTY | MAYBE_DIRTY | CLEAN);
  * @param {number} status
  */
 export function set_signal_status(signal, status) {
-	signal.f = (signal.f & STATUS_MASK) | status;
+	// signal.f = (signal.f & STATUS_MASK) | status;
 }
 
 /**
diff --git a/packages/svelte/src/internal/client/reactivity/types.d.ts b/packages/svelte/src/internal/client/reactivity/types.d.ts
index 8477917991..546a403434 100644
--- a/packages/svelte/src/internal/client/reactivity/types.d.ts
+++ b/packages/svelte/src/internal/client/reactivity/types.d.ts
@@ -11,6 +11,8 @@ import type { Boundary } from '../dom/blocks/boundary';
 export interface Signal {
 	/** Flags bitmask */
 	f: number;
+	/** Read version */
+	rv: number;
 	/** Write version */
 	wv: number;
 }
@@ -20,11 +22,8 @@ export interface Value<V = unknown> extends Signal {
 	equals: Equals;
 	/** Signals that read from this signal */
 	reactions: null | Reaction[];
-	/** Read version */
-	rv: number;
 	/** The latest value for this signal */
 	v: V;
-
 	// dev-only
 	/** A label (e.g. the `foo` in `let foo = $state(...)`) used for `$inspect.trace()` */
 	label?: string;
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 906d68fbf0..5c8f3875af 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -156,26 +156,25 @@ export function increment_write_version() {
 export function is_dirty(reaction) {
 	var flags = reaction.f;
 
-	if ((flags & DIRTY) !== 0) {
-		return true;
-	}
-
 	if (flags & DERIVED) {
 		reaction.f &= ~WAS_MARKED;
 	}
 
-	if ((flags & MAYBE_DIRTY) !== 0) {
-		var dependencies = /** @type {Value[]} */ (reaction.deps);
+	var dependencies = /** @type {Value[]} */ (reaction.deps);
+
+	if (dependencies !== null) {
 		var length = dependencies.length;
 
 		for (var i = 0; i < length; i++) {
 			var dependency = dependencies[i];
 
-			if (is_dirty(/** @type {Derived} */ (dependency))) {
-				update_derived(/** @type {Derived} */ (dependency));
+			if ((dependency.f & DERIVED) !== 0) {
+				if (is_dirty(/** @type {Derived} */ (dependency))) {
+					update_derived(/** @type {Derived} */ (dependency));
+				}
 			}
 
-			if (dependency.wv > reaction.wv) {
+			if (dependency.wv > reaction.rv) {
 				return true;
 			}
 		}
@@ -190,6 +189,8 @@ export function is_dirty(reaction) {
 		}
 	}
 
+	reaction.rv = write_version;
+
 	return false;
 }
 
@@ -254,6 +255,8 @@ export function update_reaction(reaction) {
 	}
 
 	try {
+		reaction.wv = reaction.rv = write_version;
+
 		reaction.f |= REACTION_IS_UPDATING;
 		var fn = /** @type {Function} */ (reaction.fn);
 		var result = fn();