diff --git a/.changeset/cold-teachers-turn.md b/.changeset/cold-teachers-turn.md
new file mode 100644
index 0000000000..e86ffbcdfe
--- /dev/null
+++ b/.changeset/cold-teachers-turn.md
@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: correct start of `{:else if}` and `{:else}`
diff --git a/.changeset/few-cheetahs-taste.md b/.changeset/few-cheetahs-taste.md
new file mode 100644
index 0000000000..34da32f362
--- /dev/null
+++ b/.changeset/few-cheetahs-taste.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: reorder reactive statements during migration
diff --git a/.changeset/hip-garlics-tap.md b/.changeset/hip-garlics-tap.md
new file mode 100644
index 0000000000..0913e45d87
--- /dev/null
+++ b/.changeset/hip-garlics-tap.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+breaking: play transitions on `mount` by default
diff --git a/.changeset/light-hounds-carry.md b/.changeset/light-hounds-carry.md
new file mode 100644
index 0000000000..9e124f900f
--- /dev/null
+++ b/.changeset/light-hounds-carry.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: make `<select>` `<option value>` behavior consistent
diff --git a/.changeset/mighty-paws-smash.md b/.changeset/mighty-paws-smash.md
new file mode 100644
index 0000000000..56f707e10e
--- /dev/null
+++ b/.changeset/mighty-paws-smash.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: stricter control flow syntax validation in runes mode
diff --git a/.changeset/pre.json b/.changeset/pre.json
index b16dc711eb..7a33c7fb8d 100644
--- a/.changeset/pre.json
+++ b/.changeset/pre.json
@@ -78,6 +78,7 @@
     "cold-cheetahs-judge",
     "cold-lamps-accept",
     "cold-masks-learn",
+    "cold-teachers-turn",
     "cool-actors-tan",
     "cool-ants-leave",
     "cool-comics-marry",
@@ -133,6 +134,7 @@
     "eighty-lizards-notice",
     "eleven-avocados-walk",
     "eleven-beers-yell",
+    "eleven-cows-judge",
     "eleven-cycles-applaud",
     "eleven-hounds-pump",
     "empty-bags-heal",
@@ -157,6 +159,7 @@
     "fast-donkeys-pay",
     "fast-penguins-matter",
     "fast-weeks-clean",
+    "few-cheetahs-taste",
     "few-clouds-shop",
     "few-mugs-fail",
     "few-teachers-know",
@@ -242,6 +245,7 @@
     "heavy-ducks-leave",
     "heavy-ears-rule",
     "hip-balloons-begin",
+    "hip-garlics-tap",
     "hip-pumpkins-boil",
     "honest-buses-add",
     "honest-dragons-turn",
@@ -302,6 +306,7 @@
     "lemon-trees-act",
     "light-badgers-glow",
     "light-days-clean",
+    "light-hounds-carry",
     "light-humans-hang",
     "light-penguins-invent",
     "light-pens-watch",
@@ -340,6 +345,7 @@
     "mighty-cooks-scream",
     "mighty-files-hammer",
     "mighty-frogs-obey",
+    "mighty-paws-smash",
     "mighty-shoes-nail",
     "modern-apricots-promise",
     "modern-fishes-double",
@@ -398,6 +404,7 @@
     "pink-bikes-agree",
     "pink-goats-promise",
     "pink-mayflies-tie",
+    "plenty-clouds-reply",
     "plenty-elephants-fry",
     "plenty-starfishes-dress",
     "plenty-zoos-fix",
@@ -498,6 +505,7 @@
     "silver-sheep-knock",
     "six-bears-trade",
     "six-boats-shave",
+    "six-chicken-kneel",
     "six-gorillas-obey",
     "sixty-items-crash",
     "sixty-numbers-hope",
@@ -517,6 +525,7 @@
     "slow-plums-chew",
     "slow-wombats-reply",
     "small-apples-eat",
+    "small-owls-remain",
     "small-papayas-laugh",
     "small-sheep-type",
     "small-spiders-fail",
@@ -527,6 +536,7 @@
     "smart-spiders-fetch",
     "smart-turkeys-tell",
     "smart-zebras-pay",
+    "smart-zoos-vanish",
     "smooth-kids-protect",
     "smooth-pens-protect",
     "smooth-rings-rush",
@@ -621,6 +631,7 @@
     "tidy-chefs-taste",
     "tidy-deers-hope",
     "tidy-fans-relax",
+    "tidy-lizards-happen",
     "tidy-starfishes-allow",
     "tiny-kings-whisper",
     "tiny-meals-deliver",
@@ -658,9 +669,11 @@
     "wet-wombats-repeat",
     "wicked-clouds-exercise",
     "wicked-doors-train",
+    "wicked-emus-drive",
     "wicked-hairs-cheer",
     "wicked-wasps-allow",
     "wicked-ways-reply",
+    "wild-cows-chew",
     "wild-foxes-wonder",
     "wild-moose-compare",
     "wise-apples-care",
diff --git a/.changeset/six-chicken-kneel.md b/.changeset/six-chicken-kneel.md
new file mode 100644
index 0000000000..f7fcbd14c6
--- /dev/null
+++ b/.changeset/six-chicken-kneel.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: resolve legacy component props equality for mutations
diff --git a/.changeset/small-owls-remain.md b/.changeset/small-owls-remain.md
new file mode 100644
index 0000000000..a63ff64935
--- /dev/null
+++ b/.changeset/small-owls-remain.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: align warning and error objects, add frame property
diff --git a/.changeset/smart-zoos-vanish.md b/.changeset/smart-zoos-vanish.md
new file mode 100644
index 0000000000..b06583fd41
--- /dev/null
+++ b/.changeset/smart-zoos-vanish.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: reconnected deep derived signals to graph
diff --git a/.changeset/tidy-lizards-happen.md b/.changeset/tidy-lizards-happen.md
new file mode 100644
index 0000000000..1b280937a0
--- /dev/null
+++ b/.changeset/tidy-lizards-happen.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: make `$state` component exports settable
diff --git a/.changeset/wicked-emus-drive.md b/.changeset/wicked-emus-drive.md
new file mode 100644
index 0000000000..96629d079d
--- /dev/null
+++ b/.changeset/wicked-emus-drive.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure `$effect.root` is ignored on the server
diff --git a/.changeset/wild-cows-chew.md b/.changeset/wild-cows-chew.md
new file mode 100644
index 0000000000..55e5163e7b
--- /dev/null
+++ b/.changeset/wild-cows-chew.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: enable local transitions on `svelte:element`
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index f231e1eb45..9b4bf29159 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,43 @@
 # svelte
 
+## 5.0.0-next.178
+
+### Patch Changes
+
+- fix: reconnected deep derived signals to graph ([#12350](https://github.com/sveltejs/svelte/pull/12350))
+
+## 5.0.0-next.177
+
+### Patch Changes
+
+- breaking: play transitions on `mount` by default ([#12351](https://github.com/sveltejs/svelte/pull/12351))
+
+- fix: make `<select>` `<option value>` behavior consistent ([#12316](https://github.com/sveltejs/svelte/pull/12316))
+
+- chore: stricter control flow syntax validation in runes mode ([#12342](https://github.com/sveltejs/svelte/pull/12342))
+
+- fix: resolve legacy component props equality for mutations ([#12348](https://github.com/sveltejs/svelte/pull/12348))
+
+- fix: make `$state` component exports settable ([#12345](https://github.com/sveltejs/svelte/pull/12345))
+
+## 5.0.0-next.176
+
+### Patch Changes
+
+- fix: correct start of `{:else if}` and `{:else}` ([#12043](https://github.com/sveltejs/svelte/pull/12043))
+
+- fix: reverse parent/child order in invalid HTML warning ([#12336](https://github.com/sveltejs/svelte/pull/12336))
+
+- fix: reorder reactive statements during migration ([#12329](https://github.com/sveltejs/svelte/pull/12329))
+
+- feat: better `<svelte:element>` SSR output ([#12339](https://github.com/sveltejs/svelte/pull/12339))
+
+- chore: align warning and error objects, add frame property ([#12326](https://github.com/sveltejs/svelte/pull/12326))
+
+- fix: ensure `$effect.root` is ignored on the server ([#12332](https://github.com/sveltejs/svelte/pull/12332))
+
+- fix: enable local transitions on `svelte:element` ([#12346](https://github.com/sveltejs/svelte/pull/12346))
+
 ## 5.0.0-next.175
 
 ### Patch Changes
diff --git a/packages/svelte/messages/compile-errors/template.md b/packages/svelte/messages/compile-errors/template.md
index 2bb4197a1d..517e5e730f 100644
--- a/packages/svelte/messages/compile-errors/template.md
+++ b/packages/svelte/messages/compile-errors/template.md
@@ -88,6 +88,10 @@
 
 > Block was left open
 
+## block_unexpected_character
+
+> Expected a `%character%` character immediately following the opening bracket
+
 ## block_unexpected_close
 
 > Unexpected block closing tag
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 2df9ed138b..81755cefe2 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.0.0-next.175",
+  "version": "5.0.0-next.178",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/scripts/process-messages/templates/compile-errors.js b/packages/svelte/scripts/process-messages/templates/compile-errors.js
index e129eef9f6..349e0b38ef 100644
--- a/packages/svelte/scripts/process-messages/templates/compile-errors.js
+++ b/packages/svelte/scripts/process-messages/templates/compile-errors.js
@@ -1,54 +1,17 @@
-/** @import { Location } from 'locate-character' */
-import * as state from './state.js';
+import { CompileDiagnostic } from './utils/compile_diagnostic.js';
 
 /** @typedef {{ start?: number, end?: number }} NodeLike */
 
-export class InternalCompileError extends Error {
+export class InternalCompileError extends CompileDiagnostic {
 	name = 'CompileError';
 
-	filename = state.filename;
-
-	/** @type {[number, number] | undefined} */
-	position = undefined;
-
-	/** @type {Location | undefined} */
-	start = undefined;
-
-	/** @type {Location | undefined} */
-	end = undefined;
-
 	/**
-	 *
 	 * @param {string} code
 	 * @param {string} message
 	 * @param {[number, number] | undefined} position
 	 */
 	constructor(code, message, position) {
-		super(message);
-
-		this.code = code;
-		this.position = position;
-
-		if (position) {
-			this.start = state.locator(position[0]);
-			this.end = state.locator(position[1]);
-		}
-	}
-
-	toString() {
-		let out = `${this.name}: ${this.message}`;
-
-		out += `\n(${this.code})`;
-
-		if (this.filename) {
-			out += `\n${this.filename}`;
-
-			if (this.start) {
-				out += `${this.start.line}:${this.start.column}`;
-			}
-		}
-
-		return out;
+		super(code, message, position);
 	}
 }
 
@@ -65,7 +28,7 @@ function e(node, code, message) {
 	throw new InternalCompileError(
 		code,
 		message,
-		start !== undefined && end !== undefined ? [start, end] : undefined
+		start !== undefined ? [start, end ?? start] : undefined
 	);
 }
 
diff --git a/packages/svelte/scripts/process-messages/templates/compile-warnings.js b/packages/svelte/scripts/process-messages/templates/compile-warnings.js
index d6a0cd6a0b..c8bd7993c0 100644
--- a/packages/svelte/scripts/process-messages/templates/compile-warnings.js
+++ b/packages/svelte/scripts/process-messages/templates/compile-warnings.js
@@ -1,7 +1,21 @@
-import { filename, locator, warnings, ignore_stack, ignore_map } from './state.js';
+import { warnings, ignore_stack, ignore_map } from './state.js';
+import { CompileDiagnostic } from './utils/compile_diagnostic.js';
 
 /** @typedef {{ start?: number, end?: number }} NodeLike */
 
+export class InternalCompileWarning extends CompileDiagnostic {
+	name = 'CompileWarning';
+
+	/**
+	 * @param {string} code
+	 * @param {string} message
+	 * @param {[number, number] | undefined} position
+	 */
+	constructor(code, message, position) {
+		super(code, message, position);
+	}
+}
+
 /**
  * @param {null | NodeLike} node
  * @param {string} code
@@ -14,13 +28,13 @@ function w(node, code, message) {
 	}
 	if (stack && stack.at(-1)?.has(code)) return;
 
-	warnings.push({
-		code,
-		message,
-		filename,
-		start: node?.start !== undefined ? locator(node.start) : undefined,
-		end: node?.end !== undefined ? locator(node.end) : undefined
-	});
+	warnings.push(
+		new InternalCompileWarning(
+			code,
+			message,
+			node && node.start !== undefined ? [node.start, node.end ?? node.start] : undefined
+		)
+	);
 }
 
 export const codes = CODES;
diff --git a/packages/svelte/src/compiler/errors.js b/packages/svelte/src/compiler/errors.js
index c26586fb1c..b092e262db 100644
--- a/packages/svelte/src/compiler/errors.js
+++ b/packages/svelte/src/compiler/errors.js
@@ -1,50 +1,18 @@
 /* This file is generated by scripts/process-messages/index.js. Do not edit! */
 
-/** @import { Location } from 'locate-character' */
-import * as state from './state.js';
+import { CompileDiagnostic } from './utils/compile_diagnostic.js';
 
 /** @typedef {{ start?: number, end?: number }} NodeLike */
-export class InternalCompileError extends Error {
+export class InternalCompileError extends CompileDiagnostic {
 	name = 'CompileError';
-	filename = state.filename;
-	/** @type {[number, number] | undefined} */
-	position = undefined;
-	/** @type {Location | undefined} */
-	start = undefined;
-	/** @type {Location | undefined} */
-	end = undefined;
 
 	/**
-	 *
 	 * @param {string} code
 	 * @param {string} message
 	 * @param {[number, number] | undefined} position
 	 */
 	constructor(code, message, position) {
-		super(message);
-		this.code = code;
-		this.position = position;
-
-		if (position) {
-			this.start = state.locator(position[0]);
-			this.end = state.locator(position[1]);
-		}
-	}
-
-	toString() {
-		let out = `${this.name}: ${this.message}`;
-
-		out += `\n(${this.code})`;
-
-		if (this.filename) {
-			out += `\n${this.filename}`;
-
-			if (this.start) {
-				out += `${this.start.line}:${this.start.column}`;
-			}
-		}
-
-		return out;
+		super(code, message, position);
 	}
 }
 
@@ -58,7 +26,7 @@ function e(node, code, message) {
 	const start = typeof node === 'number' ? node : node?.start;
 	const end = typeof node === 'number' ? node : node?.end;
 
-	throw new InternalCompileError(code, message, start !== undefined && end !== undefined ? [start, end] : undefined);
+	throw new InternalCompileError(code, message, start !== undefined ? [start, end ?? start] : undefined);
 }
 
 /**
@@ -762,6 +730,16 @@ export function block_unclosed(node) {
 	e(node, "block_unclosed", "Block was left open");
 }
 
+/**
+ * Expected a `%character%` character immediately following the opening bracket
+ * @param {null | number | NodeLike} node
+ * @param {string} character
+ * @returns {never}
+ */
+export function block_unexpected_character(node, character) {
+	e(node, "block_unexpected_character", `Expected a \`${character}\` character immediately following the opening bracket`);
+}
+
 /**
  * Unexpected block closing tag
  * @param {null | number | NodeLike} node
diff --git a/packages/svelte/src/compiler/legacy.js b/packages/svelte/src/compiler/legacy.js
index caa7f8238e..da0ba058d3 100644
--- a/packages/svelte/src/compiler/legacy.js
+++ b/packages/svelte/src/compiler/legacy.js
@@ -353,11 +353,12 @@ export function convert(source, ast) {
 					};
 				}
 
+				const start = node.elseif ? node.consequent.nodes[0].start : node.start;
 				remove_surrounding_whitespace_nodes(node.consequent.nodes);
 
 				return {
 					type: 'IfBlock',
-					start: node.start,
+					start,
 					end: node.end,
 					expression: node.test,
 					children: node.consequent.nodes.map(
diff --git a/packages/svelte/src/compiler/migrate/index.js b/packages/svelte/src/compiler/migrate/index.js
index b5a1e5596e..308f5ab235 100644
--- a/packages/svelte/src/compiler/migrate/index.js
+++ b/packages/svelte/src/compiler/migrate/index.js
@@ -145,6 +145,47 @@ export function migrate(source) {
 			}
 		}
 
+		/**
+		 * If true, then we need to move all reactive statements to the end of the script block,
+		 * in their correct order. Svelte 4 reordered reactive statements, $derived/$effect.pre
+		 * don't have this behavior.
+		 */
+		let needs_reordering = false;
+
+		for (const [node, { dependencies }] of state.analysis.reactive_statements) {
+			/** @type {Compiler.Binding[]} */
+			let ids = [];
+			if (
+				node.body.type === 'ExpressionStatement' &&
+				node.body.expression.type === 'AssignmentExpression'
+			) {
+				ids = extract_identifiers(node.body.expression.left)
+					.map((id) => state.scope.get(id.name))
+					.filter((id) => !!id);
+			}
+
+			if (
+				dependencies.some(
+					(dep) =>
+						!ids.includes(dep) &&
+						/** @type {number} */ (dep.node.start) > /** @type {number} */ (node.start)
+				)
+			) {
+				needs_reordering = true;
+				break;
+			}
+		}
+
+		if (needs_reordering) {
+			const nodes = Array.from(state.analysis.reactive_statements.keys());
+			for (const node of nodes) {
+				const { start, end } = get_node_range(source, node);
+				str.appendLeft(end, '\n');
+				str.move(start, end, /** @type {number} */ (parsed.instance?.content.end));
+				str.remove(start - (source[start - 2] === '\r' ? 2 : 1), start);
+			}
+		}
+
 		if (state.needs_run && !added_legacy_import) {
 			if (parsed.instance) {
 				str.appendRight(
@@ -377,7 +418,7 @@ const instance_script = {
 					/** @type {number} */ (node.body.expression.start),
 					'let '
 				);
-				state.str.prependLeft(
+				state.str.prependRight(
 					/** @type {number} */ (node.body.expression.right.start),
 					'$derived('
 				);
@@ -388,14 +429,14 @@ const instance_script = {
 						');'
 					);
 				} else {
-					state.str.appendRight(/** @type {number} */ (node.end), ');');
+					state.str.appendLeft(/** @type {number} */ (node.end), ');');
 				}
 				return;
 			} else {
 				for (const binding of reassigned_bindings) {
 					if (binding && ids.includes(binding.node)) {
 						// implicitly-declared variable which we need to make explicit
-						state.str.prependLeft(
+						state.str.prependRight(
 							/** @type {number} */ (node.start),
 							`let ${binding.node.name}${binding.kind === 'state' ? ' = $state()' : ''};\n${state.indent}`
 						);
@@ -428,7 +469,7 @@ const instance_script = {
 					[/** @type {number} */ (node.body.end), state.end]
 				]
 			});
-			state.str.appendRight(/** @type {number} */ (node.end), `\n${state.indent}});`);
+			state.str.appendLeft(/** @type {number} */ (node.end), `\n${state.indent}});`);
 		}
 	}
 };
@@ -808,6 +849,30 @@ function get_indent(state, ...nodes) {
 	return indent;
 }
 
+/**
+ * Returns start and end of the node. If the start is preceeded with white-space-only before a line break,
+ * the start will be the start of the line.
+ * @param {string} source
+ * @param {Node} node
+ */
+function get_node_range(source, node) {
+	let start = /** @type {number} */ (node.start);
+	let end = /** @type {number} */ (node.end);
+
+	let idx = start;
+	while (source[idx - 1] !== '\n' && source[idx - 1] !== '\r') {
+		idx--;
+		if (source[idx] !== ' ' && source[idx] !== '\t') {
+			idx = start;
+			break;
+		}
+	}
+
+	start = idx;
+
+	return { start, end };
+}
+
 /**
  * @param {Compiler.OnDirective} last
  * @param {State} state
diff --git a/packages/svelte/src/compiler/phases/1-parse/state/tag.js b/packages/svelte/src/compiler/phases/1-parse/state/tag.js
index baa86783b0..f5beb7b79a 100644
--- a/packages/svelte/src/compiler/phases/1-parse/state/tag.js
+++ b/packages/svelte/src/compiler/phases/1-parse/state/tag.js
@@ -39,7 +39,8 @@ export default function tag(parser) {
 
 /** @param {import('../index.js').Parser} parser */
 function open(parser) {
-	const start = parser.index - 2;
+	let start = parser.index - 2;
+	while (parser.template[start] !== '{') start -= 1;
 
 	if (parser.eat('if')) {
 		parser.require_whitespace();
@@ -343,9 +344,12 @@ function next(parser) {
 			parser.allow_whitespace();
 			parser.eat('}', true);
 
+			let elseif_start = start - 1;
+			while (parser.template[elseif_start] !== '{') elseif_start -= 1;
+
 			/** @type {ReturnType<typeof parser.append<import('#compiler').IfBlock>>} */
 			const child = parser.append({
-				start: parser.index,
+				start: elseif_start,
 				end: -1,
 				type: 'IfBlock',
 				elseif: true,
diff --git a/packages/svelte/src/compiler/phases/2-analyze/index.js b/packages/svelte/src/compiler/phases/2-analyze/index.js
index 4a15f0e46f..aab31869cd 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/index.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/index.js
@@ -1010,6 +1010,9 @@ const runes_scope_tweaker = {
 			name: node.local.name,
 			alias: node.exported.name
 		});
+
+		const binding = state.scope.get(node.local.name);
+		if (binding) binding.reassigned = true;
 	},
 	ExportNamedDeclaration(node, { next, state }) {
 		if (!node.declaration || state.ast_type !== 'instance') {
diff --git a/packages/svelte/src/compiler/phases/2-analyze/validation.js b/packages/svelte/src/compiler/phases/2-analyze/validation.js
index b2097e60ce..882b0a0e46 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/validation.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/validation.js
@@ -1090,6 +1090,20 @@ function validate_no_const_assignment(node, argument, scope, is_binding) {
 	}
 }
 
+/**
+ * Validates that the opening of a control flow block is `{` immediately followed by the expected character.
+ * In legacy mode whitespace is allowed inbetween. TODO remove once legacy mode is gone and move this into parser instead.
+ * @param {{start: number; end: number}} node
+ * @param {import('./types.js').AnalysisState} state
+ * @param {string} expected
+ */
+function validate_opening_tag(node, state, expected) {
+	if (state.analysis.source[node.start + 1] !== expected) {
+		// avoid a sea of red and only mark the first few characters
+		e.block_unexpected_character({ start: node.start, end: node.start + 5 }, expected);
+	}
+}
+
 /**
  * @param {import('estree').AssignmentExpression | import('estree').UpdateExpression} node
  * @param {import('estree').Pattern | import('estree').Expression} argument
@@ -1217,6 +1231,8 @@ export const validation_runes = merge(validation, a11y_validators, {
 		validate_call_expression(node, state.scope, path);
 	},
 	EachBlock(node, { next, state }) {
+		validate_opening_tag(node, state, '#');
+
 		const context = node.context;
 		if (
 			context.type === 'Identifier' &&
@@ -1226,6 +1242,51 @@ export const validation_runes = merge(validation, a11y_validators, {
 		}
 		next({ ...state });
 	},
+	IfBlock(node, { state, path }) {
+		const parent = path.at(-1);
+		const expected =
+			path.at(-2)?.type === 'IfBlock' && parent?.type === 'Fragment' && parent.nodes.length === 1
+				? ':'
+				: '#';
+		validate_opening_tag(node, state, expected);
+	},
+	AwaitBlock(node, { state }) {
+		validate_opening_tag(node, state, '#');
+
+		if (node.value) {
+			const start = /** @type {number} */ (node.value.start);
+			const match = state.analysis.source.substring(start - 10, start).match(/{(\s*):then\s+$/);
+			if (match && match[1] !== '') {
+				e.block_unexpected_character({ start: start - 10, end: start }, ':');
+			}
+		}
+
+		if (node.error) {
+			const start = /** @type {number} */ (node.error.start);
+			const match = state.analysis.source.substring(start - 10, start).match(/{(\s*):catch\s+$/);
+			if (match && match[1] !== '') {
+				e.block_unexpected_character({ start: start - 10, end: start }, ':');
+			}
+		}
+	},
+	KeyBlock(node, { state }) {
+		validate_opening_tag(node, state, '#');
+	},
+	SnippetBlock(node, { state }) {
+		validate_opening_tag(node, state, '#');
+	},
+	ConstTag(node, { state }) {
+		validate_opening_tag(node, state, '@');
+	},
+	HtmlTag(node, { state }) {
+		validate_opening_tag(node, state, '@');
+	},
+	DebugTag(node, { state }) {
+		validate_opening_tag(node, state, '@');
+	},
+	RenderTag(node, { state }) {
+		validate_opening_tag(node, state, '@');
+	},
 	VariableDeclarator(node, { state }) {
 		ensure_no_module_import_conflict(node, state);
 
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
index d0dd2315a5..a8438c0aca 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
@@ -198,14 +198,38 @@ export function client_component(source, analysis, options) {
 	}
 
 	/** @type {Array<ESTree.Property | ESTree.SpreadElement>} */
-	const component_returned_object = analysis.exports.map(({ name, alias }) => {
+	const component_returned_object = analysis.exports.flatMap(({ name, alias }) => {
+		const binding = instance_state.scope.get(name);
 		const expression = serialize_get_binding(b.id(name), instance_state);
+		const getter = b.get(alias ?? name, [b.return(expression)]);
+
+		if (expression.type === 'Identifier') {
+			if (binding?.declaration_kind === 'let' || binding?.declaration_kind === 'var') {
+				return [
+					getter,
+					b.set(alias ?? name, [b.stmt(b.assignment('=', expression, b.id('$$value')))])
+				];
+			} else if (!options.dev) {
+				return b.init(alias ?? name, expression);
+			}
+		}
 
-		if (expression.type === 'Identifier' && !options.dev) {
-			return b.init(alias ?? name, expression);
+		if (binding?.kind === 'state' || binding?.kind === 'frozen_state') {
+			return [
+				getter,
+				b.set(alias ?? name, [
+					b.stmt(
+						b.call(
+							'$.set',
+							b.id(name),
+							b.call(binding.kind === 'state' ? '$.proxy' : '$.freeze', b.id('$$value'))
+						)
+					)
+				])
+			];
 		}
 
-		return b.get(alias ?? name, [b.return(expression)]);
+		return getter;
 	});
 
 	const properties = [...analysis.instance.scope.declarations].filter(
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/utils.js b/packages/svelte/src/compiler/phases/3-transform/client/utils.js
index 6137cfaecc..e77ee236ef 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/utils.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/utils.js
@@ -454,7 +454,6 @@ export function serialize_proxy_reassignment(value, proxy_reference, state) {
 		? b.call(
 				'$.proxy',
 				value,
-				b.true,
 				b.null,
 				typeof proxy_reference === 'string'
 					? b.id(proxy_reference)
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js
index d4460b6817..3cdee5a161 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js
@@ -617,7 +617,16 @@ function serialize_element_special_value_attribute(element, node_id, attribute,
 
 	if (is_reactive) {
 		const id = state.scope.generate(`${node_id.name}_value`);
-		serialize_update_assignment(state, id, undefined, value, update);
+		serialize_update_assignment(
+			state,
+			id,
+			// `<option>` is a special case: The value property reflects to the DOM. If the value is set to undefined,
+			// that means the value should be set to the empty string. To be able to do that when the value is
+			// initially undefined, we need to set a value that is guaranteed to be different.
+			element === 'option' ? b.object([]) : undefined,
+			value,
+			update
+		);
 		return true;
 	} else {
 		state.init.push(update);
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/transform-server.js b/packages/svelte/src/compiler/phases/3-transform/server/transform-server.js
index 48d495258f..04274a0d7e 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/transform-server.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/transform-server.js
@@ -412,11 +412,8 @@ const global_visitors = {
 		}
 
 		if (rune === '$effect.root') {
-			const args = /** @type {import('estree').Expression[]} */ (
-				node.arguments.map((arg) => context.visit(arg))
-			);
-			// Just call the function directly
-			return b.call(args[0]);
+			// ignore $effect.root() calls, just return a noop which mimics the cleanup function
+			return b.arrow([], b.block([]));
 		}
 
 		if (rune === '$state.snapshot') {
diff --git a/packages/svelte/src/compiler/state.js b/packages/svelte/src/compiler/state.js
index 1e094d95fd..64b9fe591c 100644
--- a/packages/svelte/src/compiler/state.js
+++ b/packages/svelte/src/compiler/state.js
@@ -14,6 +14,12 @@ export let warnings = [];
  */
 export let filename;
 
+/**
+ * The original source code
+ * @type {string}
+ */
+export let source;
+
 export let locator = getLocator('', { offsetLine: 1 });
 
 /**
@@ -43,10 +49,11 @@ export function pop_ignore() {
 }
 
 /**
- * @param {string} source
+ * @param {string} _source
  * @param {{ filename?: string, rootDir?: string }} options
  */
-export function reset(source, options) {
+export function reset(_source, options) {
+	source = _source;
 	const root_dir = options.rootDir?.replace(/\\/g, '/');
 	filename = options.filename?.replace(/\\/g, '/');
 
diff --git a/packages/svelte/src/compiler/types/index.d.ts b/packages/svelte/src/compiler/types/index.d.ts
index 129b5da175..9574491756 100644
--- a/packages/svelte/src/compiler/types/index.d.ts
+++ b/packages/svelte/src/compiler/types/index.d.ts
@@ -6,13 +6,12 @@ import type {
 	Identifier,
 	ImportDeclaration
 } from 'estree';
-import type { Location } from 'locate-character';
 import type { SourceMap } from 'magic-string';
 import type { Context } from 'zimmerframe';
 import type { Scope } from '../phases/scope.js';
 import type { Css } from './css.js';
 import type { EachBlock, Namespace, SvelteNode, SvelteOptions } from './template.js';
-import type { InternalCompileError } from '../errors.js';
+import type { ICompileDiagnostic } from '../utils/compile_diagnostic.js';
 
 /** The return value of `compile` from `svelte/compiler` */
 export interface CompileResult {
@@ -51,16 +50,9 @@ export interface CompileResult {
 	ast: any;
 }
 
-export interface Warning {
-	start?: Location;
-	end?: Location;
-	// TODO there was pos: number in Svelte 4 - do we want to add it back?
-	code: string;
-	message: string;
-	filename?: string;
-}
+export interface Warning extends ICompileDiagnostic {}
 
-export interface CompileError extends InternalCompileError {}
+export interface CompileError extends ICompileDiagnostic {}
 
 export type CssHashGetter = (args: {
 	name: string;
diff --git a/packages/svelte/src/compiler/utils/compile_diagnostic.js b/packages/svelte/src/compiler/utils/compile_diagnostic.js
new file mode 100644
index 0000000000..fa36416a06
--- /dev/null
+++ b/packages/svelte/src/compiler/utils/compile_diagnostic.js
@@ -0,0 +1,105 @@
+/** @import { Location } from 'locate-character' */
+import * as state from '../state.js';
+
+const regex_tabs = /^\t+/;
+
+/**
+ * @param {string} str
+ */
+function tabs_to_spaces(str) {
+	return str.replace(regex_tabs, (match) => match.split('\t').join('  '));
+}
+
+/**
+ * @param {string} source
+ * @param {number} line
+ * @param {number} column
+ */
+function get_code_frame(source, line, column) {
+	const lines = source.split('\n');
+	const frame_start = Math.max(0, line - 2);
+	const frame_end = Math.min(line + 3, lines.length);
+	const digits = String(frame_end + 1).length;
+	return lines
+		.slice(frame_start, frame_end)
+		.map((str, i) => {
+			const is_error_line = frame_start + i === line;
+			const line_num = String(i + frame_start + 1).padStart(digits, ' ');
+			if (is_error_line) {
+				const indicator =
+					' '.repeat(digits + 2 + tabs_to_spaces(str.slice(0, column)).length) + '^';
+				return `${line_num}: ${tabs_to_spaces(str)}\n${indicator}`;
+			}
+			return `${line_num}: ${tabs_to_spaces(str)}`;
+		})
+		.join('\n');
+}
+
+/**
+ * @typedef {{
+ * 	code: string;
+ * 	message: string;
+ * 	filename?: string;
+ * 	start?: Location;
+ * 	end?: Location;
+ * 	position?: [number, number];
+ * 	frame?: string;
+ * }} ICompileDiagnostic */
+
+/** @implements {ICompileDiagnostic} */
+export class CompileDiagnostic extends Error {
+	name = 'CompileDiagnostic';
+
+	/**
+	 * @param {string} code
+	 * @param {string} message
+	 * @param {[number, number] | undefined} position
+	 */
+	constructor(code, message, position) {
+		super(message);
+		this.code = code;
+
+		if (state.filename) {
+			this.filename = state.filename;
+		}
+
+		if (position) {
+			this.position = position;
+			this.start = state.locator(position[0]);
+			this.end = state.locator(position[1]);
+			if (this.start && this.end) {
+				this.frame = get_code_frame(state.source, this.start.line - 1, this.end.column);
+			}
+		}
+	}
+
+	toString() {
+		let out = `${this.code}: ${this.message}`;
+
+		if (this.filename) {
+			out += `\n${this.filename}`;
+
+			if (this.start) {
+				out += `:${this.start.line}:${this.start.column}`;
+			}
+		}
+
+		if (this.frame) {
+			out += `\n${this.frame}`;
+		}
+
+		return out;
+	}
+
+	toJSON() {
+		return {
+			code: this.code,
+			message: this.message,
+			filename: this.filename,
+			start: this.start,
+			end: this.end,
+			position: this.position,
+			frame: this.frame
+		};
+	}
+}
diff --git a/packages/svelte/src/compiler/warnings.js b/packages/svelte/src/compiler/warnings.js
index 7f40eec02b..2518c6c38a 100644
--- a/packages/svelte/src/compiler/warnings.js
+++ b/packages/svelte/src/compiler/warnings.js
@@ -1,14 +1,22 @@
 /* This file is generated by scripts/process-messages/index.js. Do not edit! */
 
-import {
-	filename,
-	locator,
-	warnings,
-	ignore_stack,
-	ignore_map
-} from './state.js';
+import { warnings, ignore_stack, ignore_map } from './state.js';
+import { CompileDiagnostic } from './utils/compile_diagnostic.js';
 
 /** @typedef {{ start?: number, end?: number }} NodeLike */
+export class InternalCompileWarning extends CompileDiagnostic {
+	name = 'CompileWarning';
+
+	/**
+	 * @param {string} code
+	 * @param {string} message
+	 * @param {[number, number] | undefined} position
+	 */
+	constructor(code, message, position) {
+		super(code, message, position);
+	}
+}
+
 /**
  * @param {null | NodeLike} node
  * @param {string} code
@@ -22,14 +30,7 @@ function w(node, code, message) {
 	}
 
 	if (stack && stack.at(-1)?.has(code)) return;
-
-	warnings.push({
-		code,
-		message,
-		filename,
-		start: node?.start !== undefined ? locator(node.start) : undefined,
-		end: node?.end !== undefined ? locator(node.end) : undefined
-	});
+	warnings.push(new InternalCompileWarning(code, message, node && node.start !== undefined ? [node.start, node.end ?? node.start] : undefined));
 }
 
 export const codes = [
diff --git a/packages/svelte/src/internal/client/dev/hmr.js b/packages/svelte/src/internal/client/dev/hmr.js
index 20f205ade8..0d0edd4ddc 100644
--- a/packages/svelte/src/internal/client/dev/hmr.js
+++ b/packages/svelte/src/internal/client/dev/hmr.js
@@ -1,9 +1,7 @@
 /** @import { Source, Effect } from '#client' */
-import { empty } from '../dom/operations.js';
 import { block, branch, destroy_effect } from '../reactivity/effects.js';
 import { set_should_intro } from '../render.js';
 import { get } from '../runtime.js';
-import { check_target } from './legacy.js';
 
 /**
  * @template {(anchor: Comment, props: any) => any} Component
@@ -20,6 +18,8 @@ export function hmr(source) {
 		/** @type {Effect} */
 		let effect;
 
+		let ran = false;
+
 		block(() => {
 			const component = get(source);
 
@@ -30,7 +30,9 @@ export function hmr(source) {
 			}
 
 			effect = branch(() => {
-				set_should_intro(false);
+				// when the component is invalidated, replace it without transitions
+				if (ran) set_should_intro(false);
+
 				// preserve getters/setters
 				Object.defineProperties(
 					instance,
@@ -39,10 +41,13 @@ export function hmr(source) {
 						new.target ? new component(anchor, props) : component(anchor, props)
 					)
 				);
-				set_should_intro(true);
+
+				if (ran) set_should_intro(true);
 			});
 		});
 
+		ran = true;
+
 		return instance;
 	};
 }
diff --git a/packages/svelte/src/internal/client/dom/blocks/slot.js b/packages/svelte/src/internal/client/dom/blocks/slot.js
new file mode 100644
index 0000000000..c4ed14200b
--- /dev/null
+++ b/packages/svelte/src/internal/client/dom/blocks/slot.js
@@ -0,0 +1,21 @@
+import { hydrate_next, hydrating } from '../hydration.js';
+
+/**
+ * @param {Comment} anchor
+ * @param {void | ((anchor: Comment, slot_props: Record<string, unknown>) => void)} slot_fn
+ * @param {Record<string, unknown>} slot_props
+ * @param {null | ((anchor: Comment) => void)} fallback_fn
+ */
+export function slot(anchor, slot_fn, slot_props, fallback_fn) {
+	if (hydrating) {
+		hydrate_next();
+	}
+
+	if (slot_fn === undefined) {
+		if (fallback_fn !== null) {
+			fallback_fn(anchor);
+		}
+	} else {
+		slot_fn(anchor, slot_props);
+	}
+}
diff --git a/packages/svelte/src/internal/client/dom/blocks/svelte-element.js b/packages/svelte/src/internal/client/dom/blocks/svelte-element.js
index 6edcdb63c7..266bb2f5f7 100644
--- a/packages/svelte/src/internal/client/dom/blocks/svelte-element.js
+++ b/packages/svelte/src/internal/client/dom/blocks/svelte-element.js
@@ -20,6 +20,7 @@ import { current_each_item, set_current_each_item } from './each.js';
 import { current_component_context, current_effect } from '../../runtime.js';
 import { DEV } from 'esm-env';
 import { noop } from '../../../shared/utils.js';
+import { EFFECT_TRANSPARENT } from '../../constants.js';
 
 /**
  * @param {Comment | Element} node
@@ -157,7 +158,7 @@ export function element(node, get_tag, is_svg, render_fn, get_namespace, locatio
 		// Inert effects are proactively detached from the effect tree. Returning a noop
 		// teardown function is an easy way to ensure that this is not discarded
 		return noop;
-	});
+	}, EFFECT_TRANSPARENT);
 
 	if (was_hydrating) {
 		set_hydrating(true);
diff --git a/packages/svelte/src/internal/client/dom/elements/attributes.js b/packages/svelte/src/internal/client/dom/elements/attributes.js
index c65acc9a24..5856e5e65e 100644
--- a/packages/svelte/src/internal/client/dom/elements/attributes.js
+++ b/packages/svelte/src/internal/client/dom/elements/attributes.js
@@ -155,6 +155,7 @@ export function set_custom_element_data(node, prop, value) {
 export function set_attributes(element, prev, next, lowercase_attributes, css_hash) {
 	var has_hash = css_hash.length !== 0;
 	var current = prev || {};
+	var is_option_element = element.tagName === 'OPTION';
 
 	for (var key in prev) {
 		if (!(key in next)) {
@@ -178,6 +179,26 @@ export function set_attributes(element, prev, next, lowercase_attributes, css_ha
 	for (const key in next) {
 		// let instead of var because referenced in a closure
 		let value = next[key];
+
+		// Up here because we want to do this for the initial value, too, even if it's undefined,
+		// and this wouldn't be reached in case of undefined because of the equality check below
+		if (is_option_element && key === 'value' && value == null) {
+			// The <option> element is a special case because removing the value attribute means
+			// the value is set to the text content of the option element, and setting the value
+			// to null or undefined means the value is set to the string "null" or "undefined".
+			// To align with how we handle this case in non-spread-scenarios, this logic is needed.
+			// There's a super-edge-case bug here that is left in in favor of smaller code size:
+			// Because of the "set missing props to null" logic above, we can't differentiate
+			// between a missing value and an explicitly set value of null or undefined. That means
+			// that once set, the value attribute of an <option> element can't be removed. This is
+			// a very rare edge case, and removing the attribute altogether isn't possible either
+			// for the <option value={undefined}> case, so we're not losing any functionality here.
+			// @ts-ignore
+			element.value = element.__value = '';
+			current[key] = value;
+			continue;
+		}
+
 		var prev_value = current[key];
 		if (value === prev_value) continue;
 
diff --git a/packages/svelte/src/internal/client/index.js b/packages/svelte/src/internal/client/index.js
index 342708a067..3231b5f5d1 100644
--- a/packages/svelte/src/internal/client/index.js
+++ b/packages/svelte/src/internal/client/index.js
@@ -15,6 +15,7 @@ export { key_block as key } from './dom/blocks/key.js';
 export { css_props } from './dom/blocks/css-props.js';
 export { index, each } from './dom/blocks/each.js';
 export { html } from './dom/blocks/html.js';
+export { slot } from './dom/blocks/slot.js';
 export { snippet, wrap_snippet } from './dom/blocks/snippet.js';
 export { component } from './dom/blocks/svelte-component.js';
 export { element } from './dom/blocks/svelte-element.js';
@@ -119,7 +120,7 @@ export {
 	update_pre_store,
 	update_store
 } from './reactivity/store.js';
-export { append_styles, sanitize_slots, set_text, slot } from './render.js';
+export { append_styles, sanitize_slots, set_text } from './render.js';
 export {
 	get,
 	invalidate_inner_signals,
diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index 78d835dec4..f5900ba957 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -11,7 +11,7 @@ import {
 	object_prototype
 } from './utils.js';
 import { check_ownership, widen_ownership } from './dev/ownership.js';
-import { mutable_source, source, set } from './reactivity/sources.js';
+import { source, set } from './reactivity/sources.js';
 import { STATE_FROZEN_SYMBOL, STATE_SYMBOL } from './constants.js';
 import { UNINITIALIZED } from '../../constants.js';
 import * as e from './errors.js';
@@ -19,12 +19,11 @@ import * as e from './errors.js';
 /**
  * @template T
  * @param {T} value
- * @param {boolean} [immutable]
  * @param {import('#client').ProxyMetadata | null} [parent]
  * @param {import('#client').Source<T>} [prev] dev mode only
  * @returns {import('#client').ProxyStateObject<T> | T}
  */
-export function proxy(value, immutable = true, parent = null, prev) {
+export function proxy(value, parent = null, prev) {
 	if (
 		typeof value === 'object' &&
 		value != null &&
@@ -59,7 +58,6 @@ export function proxy(value, immutable = true, parent = null, prev) {
 					s: new Map(),
 					v: source(0),
 					a: is_array(value),
-					i: immutable,
 					p: proxy,
 					t: value
 				}),
@@ -169,7 +167,7 @@ const state_proxy_handler = {
 			const metadata = target[STATE_SYMBOL];
 
 			const s = metadata.s.get(prop);
-			if (s !== undefined) set(s, proxy(descriptor.value, metadata.i, metadata));
+			if (s !== undefined) set(s, proxy(descriptor.value, metadata));
 		}
 
 		return Reflect.defineProperty(target, prop, descriptor);
@@ -215,7 +213,7 @@ const state_proxy_handler = {
 
 		// create a source, but only if it's an own property and not a prototype property
 		if (s === undefined && (!(prop in target) || get_descriptor(target, prop)?.writable)) {
-			s = (metadata.i ? source : mutable_source)(proxy(target[prop], metadata.i, metadata));
+			s = source(proxy(target[prop], metadata));
 			metadata.s.set(prop, s);
 		}
 
@@ -256,9 +254,7 @@ const state_proxy_handler = {
 			(current_effect !== null && (!has || get_descriptor(target, prop)?.writable))
 		) {
 			if (s === undefined) {
-				s = (metadata.i ? source : mutable_source)(
-					has ? proxy(target[prop], metadata.i, metadata) : UNINITIALIZED
-				);
+				s = source(has ? proxy(target[prop], metadata) : UNINITIALIZED);
 				metadata.s.set(prop, s);
 			}
 			const value = get(s);
@@ -283,7 +279,7 @@ const state_proxy_handler = {
 			s = metadata.s.get(prop);
 		}
 		if (s !== undefined) {
-			set(s, proxy(value, metadata.i, metadata));
+			set(s, proxy(value, metadata));
 		}
 		const is_array = metadata.a;
 		const not_has = !(prop in target);
diff --git a/packages/svelte/src/internal/client/render.js b/packages/svelte/src/internal/client/render.js
index 08103cbe56..34e3e3c3da 100644
--- a/packages/svelte/src/internal/client/render.js
+++ b/packages/svelte/src/internal/client/render.js
@@ -31,8 +31,8 @@ export const root_event_handles = new Set();
 
 /**
  * This is normally true — block effects should run their intro transitions —
- * but is false during hydration and mounting (unless `options.intro` is `true`)
- * and when creating the children of a `<svelte:element>` that just changed tag
+ * but is false during hydration (unless `options.intro` is `true`) and
+ * when creating the children of a `<svelte:element>` that just changed tag
  */
 export let should_intro = true;
 
@@ -57,27 +57,8 @@ export function set_text(text, value) {
 }
 
 /**
- * @param {Comment} anchor
- * @param {void | ((anchor: Comment, slot_props: Record<string, unknown>) => void)} slot_fn
- * @param {Record<string, unknown>} slot_props
- * @param {null | ((anchor: Comment) => void)} fallback_fn
- */
-export function slot(anchor, slot_fn, slot_props, fallback_fn) {
-	if (hydrating) {
-		hydrate_next();
-	}
-
-	if (slot_fn === undefined) {
-		if (fallback_fn !== null) {
-			fallback_fn(anchor);
-		}
-	} else {
-		slot_fn(anchor, slot_props);
-	}
-}
-
-/**
- * Mounts a component to the given target and returns the exports and potentially the props (if compiled with `accessors: true`) of the component
+ * Mounts a component to the given target and returns the exports and potentially the props (if compiled with `accessors: true`) of the component.
+ * Transitions will play during the initial render unless the `intro` option is set to `false`.
  *
  * @template {Record<string, any>} Props
  * @template {Record<string, any>} Exports
@@ -137,6 +118,7 @@ export function hydrate(component, options) {
 		validate_component(component);
 	}
 
+	options.intro = options.intro ?? false;
 	const target = options.target;
 	const was_hydrating = hydrating;
 
@@ -213,7 +195,7 @@ export function hydrate(component, options) {
  * 	}} options
  * @returns {Exports}
  */
-function _mount(Component, { target, anchor, props = {}, events, context, intro = false }) {
+function _mount(Component, { target, anchor, props = {}, events, context, intro = true }) {
 	init_operations();
 
 	const registered_events = new Set();
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index e699183d02..370e5e3d6d 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -171,8 +171,17 @@ export function check_dirtiness(reaction) {
 
 		if (dependencies !== null) {
 			var is_unowned = (flags & UNOWNED) !== 0;
+			var i;
+
+			if ((flags & DISCONNECTED) !== 0) {
+				for (i = 0; i < dependencies.length; i++) {
+					(dependencies[i].reactions ??= []).push(reaction);
+				}
 
-			for (var i = 0; i < dependencies.length; i++) {
+				reaction.f ^= DISCONNECTED;
+			}
+
+			for (i = 0; i < dependencies.length; i++) {
 				var dependency = dependencies[i];
 
 				if (check_dirtiness(/** @type {import('#client').Derived} */ (dependency))) {
@@ -771,25 +780,6 @@ export function get(signal) {
 		if (check_dirtiness(derived)) {
 			update_derived(derived);
 		}
-
-		if ((flags & DISCONNECTED) !== 0) {
-			// reconnect to the graph
-			deps = derived.deps;
-
-			if (deps !== null) {
-				for (var i = 0; i < deps.length; i++) {
-					var dep = deps[i];
-					var reactions = dep.reactions;
-					if (reactions === null) {
-						dep.reactions = [derived];
-					} else if (!reactions.includes(derived)) {
-						reactions.push(derived);
-					}
-				}
-			}
-
-			derived.f ^= DISCONNECTED;
-		}
 	}
 
 	return signal.v;
diff --git a/packages/svelte/src/internal/client/types.d.ts b/packages/svelte/src/internal/client/types.d.ts
index 0d2d5a29c2..78b1d8d6fd 100644
--- a/packages/svelte/src/internal/client/types.d.ts
+++ b/packages/svelte/src/internal/client/types.d.ts
@@ -180,8 +180,6 @@ export interface ProxyMetadata<T = Record<string | symbol, any>> {
 	v: Source<number>;
 	/** `true` if the proxified object is an array */
 	a: boolean;
-	/** Immutable: Whether to use a source or mutable source under the hood */
-	i: boolean;
 	/** The associated proxy */
 	p: ProxyStateObject<T>;
 	/** The original target this proxy was created for */
diff --git a/packages/svelte/src/legacy/legacy-client.js b/packages/svelte/src/legacy/legacy-client.js
index d2eba5be9c..334fe34e14 100644
--- a/packages/svelte/src/legacy/legacy-client.js
+++ b/packages/svelte/src/legacy/legacy-client.js
@@ -1,8 +1,9 @@
 /** @import { ComponentConstructorOptions, ComponentType, SvelteComponent, Component } from 'svelte' */
-import { proxy } from '../internal/client/proxy.js';
+import { mutable_source, get, set } from 'svelte/internal/client';
 import { user_pre_effect } from '../internal/client/reactivity/effects.js';
 import { hydrate, mount, unmount } from '../internal/client/render.js';
 import { define_property } from '../internal/client/utils.js';
+import { safe_not_equal } from '../internal/client/reactivity/equality.js';
 
 /**
  * Takes the same options as a Svelte 4 component and the component function and returns a Svelte 4 compatible component.
@@ -69,15 +70,43 @@ class Svelte4Component {
 	 * }} options
 	 */
 	constructor(options) {
-		// Using proxy state here isn't completely mirroring the Svelte 4 behavior, because mutations to a property
-		// cause fine-grained updates to only the places where that property is used, and not the entire property.
-		// Reactive statements and actions (the things where this matters) are handling this properly regardless, so it should be fine in practise.
-		const props = proxy({ ...(options.props || {}), $$events: {} }, false);
+		var sources = new Map();
+
+		/**
+		 * @param {string | symbol} key
+		 * @param {unknown} value
+		 */
+		var add_source = (key, value) => {
+			var s = mutable_source(value);
+			sources.set(key, s);
+			return s;
+		};
+
+		// Replicate coarse-grained props through a proxy that has a version source for
+		// each property, which is increment on updates to the property itself. Do not
+		// use our $state proxy because that one has fine-grained reactivity.
+		const props = new Proxy(
+			{ ...(options.props || {}), $$events: {} },
+			{
+				get(target, prop) {
+					return get(sources.get(prop) ?? add_source(prop, Reflect.get(target, prop)));
+				},
+				has(target, prop) {
+					get(sources.get(prop) ?? add_source(prop, Reflect.get(target, prop)));
+					return Reflect.has(target, prop);
+				},
+				set(target, prop, value) {
+					set(sources.get(prop) ?? add_source(prop, value), value);
+					return Reflect.set(target, prop, value);
+				}
+			}
+		);
+
 		this.#instance = (options.hydrate ? hydrate : mount)(options.component, {
 			target: options.target,
 			props,
 			context: options.context,
-			intro: options.intro,
+			intro: options.intro ?? false,
 			recover: options.recover
 		});
 
@@ -100,6 +129,7 @@ class Svelte4Component {
 		this.#instance.$set = /** @param {Record<string, any>} next */ (next) => {
 			Object.assign(props, next);
 		};
+
 		this.#instance.$destroy = () => {
 			unmount(this.#instance);
 		};
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index e2ef71d9cf..724d93fcf6 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -6,5 +6,5 @@
  * https://svelte.dev/docs/svelte-compiler#svelte-version
  * @type {string}
  */
-export const VERSION = '5.0.0-next.175';
+export const VERSION = '5.0.0-next.178';
 export const PUBLIC_VERSION = '5';
diff --git a/packages/svelte/tests/css/test.ts b/packages/svelte/tests/css/test.ts
index d17f7e9c6b..b4b25fc479 100644
--- a/packages/svelte/tests/css/test.ts
+++ b/packages/svelte/tests/css/test.ts
@@ -10,6 +10,8 @@ import type { CompileOptions, Warning } from '#compiler';
 
 function normalize_warning(warning: Warning) {
 	delete warning.filename;
+	delete warning.position;
+	delete warning.frame;
 	return warning;
 }
 
diff --git a/packages/svelte/tests/migrate/samples/reactive-statements-reorder-1/input.svelte b/packages/svelte/tests/migrate/samples/reactive-statements-reorder-1/input.svelte
new file mode 100644
index 0000000000..fe4c6724b2
--- /dev/null
+++ b/packages/svelte/tests/migrate/samples/reactive-statements-reorder-1/input.svelte
@@ -0,0 +1,7 @@
+<script>
+	$: mobile = width < 640;
+	$: x = !mobile;
+	let width = 0;
+</script>
+
+{width / mobile / x}
diff --git a/packages/svelte/tests/migrate/samples/reactive-statements-reorder-1/output.svelte b/packages/svelte/tests/migrate/samples/reactive-statements-reorder-1/output.svelte
new file mode 100644
index 0000000000..bf54a1fd7c
--- /dev/null
+++ b/packages/svelte/tests/migrate/samples/reactive-statements-reorder-1/output.svelte
@@ -0,0 +1,7 @@
+<script>
+	let width = 0;
+	let mobile = $derived(width < 640);
+	let x = $derived(!mobile);
+</script>
+
+{width / mobile / x}
\ No newline at end of file
diff --git a/packages/svelte/tests/migrate/samples/reactive-statements-reorder-2/input.svelte b/packages/svelte/tests/migrate/samples/reactive-statements-reorder-2/input.svelte
new file mode 100644
index 0000000000..ca6d5941c2
--- /dev/null
+++ b/packages/svelte/tests/migrate/samples/reactive-statements-reorder-2/input.svelte
@@ -0,0 +1,7 @@
+<script>
+	let width = 0;
+	$: console.log(mobile);
+	$: mobile = width < 640;
+</script>
+
+{width / mobile}
diff --git a/packages/svelte/tests/migrate/samples/reactive-statements-reorder-2/output.svelte b/packages/svelte/tests/migrate/samples/reactive-statements-reorder-2/output.svelte
new file mode 100644
index 0000000000..52c57f5669
--- /dev/null
+++ b/packages/svelte/tests/migrate/samples/reactive-statements-reorder-2/output.svelte
@@ -0,0 +1,11 @@
+<script>
+	import { run } from 'svelte/legacy';
+
+	let width = 0;
+	let mobile = $derived(width < 640);
+	run(() => {
+		console.log(mobile);
+	});
+</script>
+
+{width / mobile}
\ No newline at end of file
diff --git a/packages/svelte/tests/parser-modern/samples/if-block-else/input.svelte b/packages/svelte/tests/parser-modern/samples/if-block-else/input.svelte
new file mode 100644
index 0000000000..28b41c046c
--- /dev/null
+++ b/packages/svelte/tests/parser-modern/samples/if-block-else/input.svelte
@@ -0,0 +1,5 @@
+{#if foo}
+	<p>foo</p>
+{:else}
+	<p>not foo</p>
+{/if}
diff --git a/packages/svelte/tests/parser-modern/samples/if-block-else/output.json b/packages/svelte/tests/parser-modern/samples/if-block-else/output.json
new file mode 100644
index 0000000000..1193af156e
--- /dev/null
+++ b/packages/svelte/tests/parser-modern/samples/if-block-else/output.json
@@ -0,0 +1,116 @@
+{
+	"css": null,
+	"js": [],
+	"start": 0,
+	"end": 51,
+	"type": "Root",
+	"fragment": {
+		"type": "Fragment",
+		"nodes": [
+			{
+				"type": "IfBlock",
+				"elseif": false,
+				"start": 0,
+				"end": 51,
+				"test": {
+					"type": "Identifier",
+					"start": 5,
+					"end": 8,
+					"loc": {
+						"start": {
+							"line": 1,
+							"column": 5
+						},
+						"end": {
+							"line": 1,
+							"column": 8
+						}
+					},
+					"name": "foo"
+				},
+				"consequent": {
+					"type": "Fragment",
+					"nodes": [
+						{
+							"type": "Text",
+							"start": 9,
+							"end": 11,
+							"raw": "\n\t",
+							"data": "\n\t"
+						},
+						{
+							"type": "RegularElement",
+							"start": 11,
+							"end": 21,
+							"name": "p",
+							"attributes": [],
+							"fragment": {
+								"type": "Fragment",
+								"nodes": [
+									{
+										"type": "Text",
+										"start": 14,
+										"end": 17,
+										"raw": "foo",
+										"data": "foo"
+									}
+								],
+								"transparent": true
+							}
+						},
+						{
+							"type": "Text",
+							"start": 21,
+							"end": 22,
+							"raw": "\n",
+							"data": "\n"
+						}
+					],
+					"transparent": false
+				},
+				"alternate": {
+					"type": "Fragment",
+					"nodes": [
+						{
+							"type": "Text",
+							"start": 29,
+							"end": 31,
+							"raw": "\n\t",
+							"data": "\n\t"
+						},
+						{
+							"type": "RegularElement",
+							"start": 31,
+							"end": 45,
+							"name": "p",
+							"attributes": [],
+							"fragment": {
+								"type": "Fragment",
+								"nodes": [
+									{
+										"type": "Text",
+										"start": 34,
+										"end": 41,
+										"raw": "not foo",
+										"data": "not foo"
+									}
+								],
+								"transparent": true
+							}
+						},
+						{
+							"type": "Text",
+							"start": 45,
+							"end": 46,
+							"raw": "\n",
+							"data": "\n"
+						}
+					],
+					"transparent": false
+				}
+			}
+		],
+		"transparent": false
+	},
+	"options": null
+}
diff --git a/packages/svelte/tests/parser-modern/samples/if-block-elseif/input.svelte b/packages/svelte/tests/parser-modern/samples/if-block-elseif/input.svelte
new file mode 100644
index 0000000000..2566aef258
--- /dev/null
+++ b/packages/svelte/tests/parser-modern/samples/if-block-elseif/input.svelte
@@ -0,0 +1,5 @@
+{#if x > 10}
+	<p>x is greater than 10</p>
+{:else if x < 5}
+	<p>x is less than 5</p>
+{/if}
diff --git a/packages/svelte/tests/parser-modern/samples/if-block-elseif/output.json b/packages/svelte/tests/parser-modern/samples/if-block-elseif/output.json
new file mode 100644
index 0000000000..e68b154a55
--- /dev/null
+++ b/packages/svelte/tests/parser-modern/samples/if-block-elseif/output.json
@@ -0,0 +1,211 @@
+{
+	"css": null,
+	"js": [],
+	"start": 0,
+	"end": 89,
+	"type": "Root",
+	"fragment": {
+		"type": "Fragment",
+		"nodes": [
+			{
+				"type": "IfBlock",
+				"elseif": false,
+				"start": 0,
+				"end": 89,
+				"test": {
+					"type": "BinaryExpression",
+					"start": 5,
+					"end": 11,
+					"loc": {
+						"start": {
+							"line": 1,
+							"column": 5
+						},
+						"end": {
+							"line": 1,
+							"column": 11
+						}
+					},
+					"left": {
+						"type": "Identifier",
+						"start": 5,
+						"end": 6,
+						"loc": {
+							"start": {
+								"line": 1,
+								"column": 5
+							},
+							"end": {
+								"line": 1,
+								"column": 6
+							}
+						},
+						"name": "x"
+					},
+					"operator": ">",
+					"right": {
+						"type": "Literal",
+						"start": 9,
+						"end": 11,
+						"loc": {
+							"start": {
+								"line": 1,
+								"column": 9
+							},
+							"end": {
+								"line": 1,
+								"column": 11
+							}
+						},
+						"value": 10,
+						"raw": "10"
+					}
+				},
+				"consequent": {
+					"type": "Fragment",
+					"nodes": [
+						{
+							"type": "Text",
+							"start": 12,
+							"end": 14,
+							"raw": "\n\t",
+							"data": "\n\t"
+						},
+						{
+							"type": "RegularElement",
+							"start": 14,
+							"end": 41,
+							"name": "p",
+							"attributes": [],
+							"fragment": {
+								"type": "Fragment",
+								"nodes": [
+									{
+										"type": "Text",
+										"start": 17,
+										"end": 37,
+										"raw": "x is greater than 10",
+										"data": "x is greater than 10"
+									}
+								],
+								"transparent": true
+							}
+						},
+						{
+							"type": "Text",
+							"start": 41,
+							"end": 42,
+							"raw": "\n",
+							"data": "\n"
+						}
+					],
+					"transparent": false
+				},
+				"alternate": {
+					"type": "Fragment",
+					"nodes": [
+						{
+							"start": 42,
+							"end": 89,
+							"type": "IfBlock",
+							"elseif": true,
+							"test": {
+								"type": "BinaryExpression",
+								"start": 52,
+								"end": 57,
+								"loc": {
+									"start": {
+										"line": 3,
+										"column": 10
+									},
+									"end": {
+										"line": 3,
+										"column": 15
+									}
+								},
+								"left": {
+									"type": "Identifier",
+									"start": 52,
+									"end": 53,
+									"loc": {
+										"start": {
+											"line": 3,
+											"column": 10
+										},
+										"end": {
+											"line": 3,
+											"column": 11
+										}
+									},
+									"name": "x"
+								},
+								"operator": "<",
+								"right": {
+									"type": "Literal",
+									"start": 56,
+									"end": 57,
+									"loc": {
+										"start": {
+											"line": 3,
+											"column": 14
+										},
+										"end": {
+											"line": 3,
+											"column": 15
+										}
+									},
+									"value": 5,
+									"raw": "5"
+								}
+							},
+							"consequent": {
+								"type": "Fragment",
+								"nodes": [
+									{
+										"type": "Text",
+										"start": 58,
+										"end": 60,
+										"raw": "\n\t",
+										"data": "\n\t"
+									},
+									{
+										"type": "RegularElement",
+										"start": 60,
+										"end": 83,
+										"name": "p",
+										"attributes": [],
+										"fragment": {
+											"type": "Fragment",
+											"nodes": [
+												{
+													"type": "Text",
+													"start": 63,
+													"end": 79,
+													"raw": "x is less than 5",
+													"data": "x is less than 5"
+												}
+											],
+											"transparent": true
+										}
+									},
+									{
+										"type": "Text",
+										"start": 83,
+										"end": 84,
+										"raw": "\n",
+										"data": "\n"
+									}
+								],
+								"transparent": false
+							},
+							"alternate": null
+						}
+					],
+					"transparent": false
+				}
+			}
+		],
+		"transparent": false
+	},
+	"options": null
+}
diff --git a/packages/svelte/tests/parser-modern/samples/if-block/input.svelte b/packages/svelte/tests/parser-modern/samples/if-block/input.svelte
new file mode 100644
index 0000000000..5851347a88
--- /dev/null
+++ b/packages/svelte/tests/parser-modern/samples/if-block/input.svelte
@@ -0,0 +1 @@
+{#if foo}bar{/if}
diff --git a/packages/svelte/tests/parser-modern/samples/if-block/output.json b/packages/svelte/tests/parser-modern/samples/if-block/output.json
new file mode 100644
index 0000000000..965f2b5614
--- /dev/null
+++ b/packages/svelte/tests/parser-modern/samples/if-block/output.json
@@ -0,0 +1,50 @@
+{
+	"css": null,
+	"js": [],
+	"start": 0,
+	"end": 17,
+	"type": "Root",
+	"fragment": {
+		"type": "Fragment",
+		"nodes": [
+			{
+				"type": "IfBlock",
+				"elseif": false,
+				"start": 0,
+				"end": 17,
+				"test": {
+					"type": "Identifier",
+					"start": 5,
+					"end": 8,
+					"loc": {
+						"start": {
+							"line": 1,
+							"column": 5
+						},
+						"end": {
+							"line": 1,
+							"column": 8
+						}
+					},
+					"name": "foo"
+				},
+				"consequent": {
+					"type": "Fragment",
+					"nodes": [
+						{
+							"type": "Text",
+							"start": 9,
+							"end": 12,
+							"raw": "bar",
+							"data": "bar"
+						}
+					],
+					"transparent": false
+				},
+				"alternate": null
+			}
+		],
+		"transparent": false
+	},
+	"options": null
+}
diff --git a/packages/svelte/tests/runtime-legacy/samples/component-props-added/_config.js b/packages/svelte/tests/runtime-legacy/samples/component-props-added/_config.js
new file mode 100644
index 0000000000..bed8824577
--- /dev/null
+++ b/packages/svelte/tests/runtime-legacy/samples/component-props-added/_config.js
@@ -0,0 +1,15 @@
+import { test } from '../../test';
+
+export default test({
+	get props() {
+		return {};
+	},
+
+	html: '',
+
+	async test({ assert, component, target }) {
+		await component.$set({ message: 'goodbye' });
+
+		assert.htmlEqual(target.innerHTML, '<p>goodbye</p>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-legacy/samples/component-props-added/main.svelte b/packages/svelte/tests/runtime-legacy/samples/component-props-added/main.svelte
new file mode 100644
index 0000000000..8ee7f80adf
--- /dev/null
+++ b/packages/svelte/tests/runtime-legacy/samples/component-props-added/main.svelte
@@ -0,0 +1,3 @@
+{#if 'message' in $$props}
+	<p>{$$props.message}</p>
+{/if}
diff --git a/packages/svelte/tests/runtime-legacy/samples/component-props-mutated/_config.js b/packages/svelte/tests/runtime-legacy/samples/component-props-mutated/_config.js
new file mode 100644
index 0000000000..91d0aaa0d3
--- /dev/null
+++ b/packages/svelte/tests/runtime-legacy/samples/component-props-mutated/_config.js
@@ -0,0 +1,24 @@
+import { test } from '../../test';
+
+const data = {
+	message: 'hello'
+};
+
+export default test({
+	get props() {
+		data.message = 'hello';
+
+		return {
+			data
+		};
+	},
+
+	html: '<p>hello</p>',
+
+	async test({ assert, component, target }) {
+		data.message = 'goodbye';
+		await component.$set({ data });
+
+		assert.htmlEqual(target.innerHTML, '<p>goodbye</p>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-legacy/samples/component-props-mutated/main.svelte b/packages/svelte/tests/runtime-legacy/samples/component-props-mutated/main.svelte
new file mode 100644
index 0000000000..30195a0836
--- /dev/null
+++ b/packages/svelte/tests/runtime-legacy/samples/component-props-mutated/main.svelte
@@ -0,0 +1,5 @@
+<script>
+	export let data;
+</script>
+
+<p>{data.message}</p>
diff --git a/packages/svelte/tests/runtime-legacy/shared.ts b/packages/svelte/tests/runtime-legacy/shared.ts
index ed32d2f0c1..62a85c182f 100644
--- a/packages/svelte/tests/runtime-legacy/shared.ts
+++ b/packages/svelte/tests/runtime-legacy/shared.ts
@@ -61,7 +61,7 @@ export interface RuntimeTest<Props extends Record<string, any> = Record<string,
 		warnings: any[];
 		hydrate: Function;
 	}) => void | Promise<void>;
-	test_ssr?: (args: { assert: Assert }) => void | Promise<void>;
+	test_ssr?: (args: { logs: any[]; assert: Assert }) => void | Promise<void>;
 	accessors?: boolean;
 	immutable?: boolean;
 	intro?: boolean;
@@ -285,6 +285,7 @@ async function run_test_variant(
 
 			if (config.test_ssr) {
 				await config.test_ssr({
+					logs,
 					// @ts-expect-error
 					assert: {
 						...assert,
diff --git a/packages/svelte/tests/runtime-runes/samples/dynamic-element-transition/_config.js b/packages/svelte/tests/runtime-runes/samples/dynamic-element-transition/_config.js
new file mode 100644
index 0000000000..8c0ebf93e3
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/dynamic-element-transition/_config.js
@@ -0,0 +1,21 @@
+import { test } from '../../test';
+import { flushSync } from 'svelte';
+
+export default test({
+	async test({ assert, target, raf }) {
+		const btn = target.querySelector('button');
+
+		raf.tick(0);
+		btn?.click();
+		flushSync();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>Toggle</button> <div style="opacity: 0;">DIV</div>`
+		);
+
+		raf.tick(100);
+
+		assert.htmlEqual(target.innerHTML, `<button>Toggle</button> <div style="">DIV</div>`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/dynamic-element-transition/main.svelte b/packages/svelte/tests/runtime-runes/samples/dynamic-element-transition/main.svelte
new file mode 100644
index 0000000000..f9be144969
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/dynamic-element-transition/main.svelte
@@ -0,0 +1,12 @@
+<script>
+	import { fade } from 'svelte/transition';
+
+	let element = $state('div');
+	let show = $state(false);
+</script>
+
+<button onclick={() => (show = !show)}>Toggle</button>
+
+{#if show}
+	<svelte:element this={element} transition:fade={{ duration: 100 }}>DIV</svelte:element>
+{/if}
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-root-4/_config.js b/packages/svelte/tests/runtime-runes/samples/effect-root-4/_config.js
new file mode 100644
index 0000000000..4aac5eed85
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-root-4/_config.js
@@ -0,0 +1,18 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: '<button>cleanup</button>',
+
+	async test({ assert, target, logs }) {
+		const btn = target.querySelector('button');
+
+		btn?.click();
+		flushSync();
+
+		assert.deepEqual(logs, ['effect1', 'effect2']);
+	},
+	test_ssr({ assert, logs }) {
+		assert.deepEqual(logs, []);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-root-4/main.svelte b/packages/svelte/tests/runtime-runes/samples/effect-root-4/main.svelte
new file mode 100644
index 0000000000..2239445619
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-root-4/main.svelte
@@ -0,0 +1,10 @@
+<script>
+	$effect.root(() => {
+		console.log('effect1');
+	});
+	const cleanup = $effect.root(() => {
+		console.log('effect2');
+	});
+</script>
+
+<button onclick={cleanup}>cleanup</button>
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-root/_config.js b/packages/svelte/tests/runtime-runes/samples/effect-root/_config.js
index fe2a8bb499..cd072d087f 100644
--- a/packages/svelte/tests/runtime-runes/samples/effect-root/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/effect-root/_config.js
@@ -24,5 +24,8 @@ export default test({
 		});
 
 		assert.deepEqual(logs, [0, 1, 'cleanup 1', 'cleanup 2']);
+	},
+	test_ssr({ assert, logs }) {
+		assert.deepEqual(logs, []);
 	}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/event-store-no-hoisting/main.svelte b/packages/svelte/tests/runtime-runes/samples/event-store-no-hoisting/main.svelte
index b895081916..e827a9bfe9 100644
--- a/packages/svelte/tests/runtime-runes/samples/event-store-no-hoisting/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/event-store-no-hoisting/main.svelte
@@ -5,8 +5,7 @@
 
 	function setStore() {
 		store = writable(0, () => {
-			console.log('start');
-			return () => console.log('stop');
+			return () => {};
 		});
 	}
 </script>
diff --git a/packages/svelte/tests/runtime-runes/samples/exports-3/_config.js b/packages/svelte/tests/runtime-runes/samples/exports-3/_config.js
index cf22671d9f..807fed2aa6 100644
--- a/packages/svelte/tests/runtime-runes/samples/exports-3/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/exports-3/_config.js
@@ -4,10 +4,9 @@ import { test } from '../../test';
 export default test({
 	test({ assert, target }) {
 		assert.htmlEqual(target.innerHTML, `0 0 <button>0 / 0</button>`);
-		const [btn] = target.querySelectorAll('button');
+		const btn = target.querySelector('button');
 
-		btn?.click();
-		flushSync();
+		flushSync(() => btn?.click());
 		assert.htmlEqual(target.innerHTML, '1 2 <button>1 / 2</button>');
 	}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/exports-3/main.svelte b/packages/svelte/tests/runtime-runes/samples/exports-3/main.svelte
index b1cabb399f..a68a40f300 100644
--- a/packages/svelte/tests/runtime-runes/samples/exports-3/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/exports-3/main.svelte
@@ -1,5 +1,5 @@
 <script>
-	import Sub from './sub.svelte'
+	import Sub from './sub.svelte';
 	let sub = $state();
 </script>
 
diff --git a/packages/svelte/tests/runtime-runes/samples/exports-4/_config.js b/packages/svelte/tests/runtime-runes/samples/exports-4/_config.js
new file mode 100644
index 0000000000..807fed2aa6
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/exports-4/_config.js
@@ -0,0 +1,12 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	test({ assert, target }) {
+		assert.htmlEqual(target.innerHTML, `0 0 <button>0 / 0</button>`);
+		const btn = target.querySelector('button');
+
+		flushSync(() => btn?.click());
+		assert.htmlEqual(target.innerHTML, '1 2 <button>1 / 2</button>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/exports-4/main.svelte b/packages/svelte/tests/runtime-runes/samples/exports-4/main.svelte
new file mode 100644
index 0000000000..85adcffbe3
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/exports-4/main.svelte
@@ -0,0 +1,7 @@
+<script>
+	import Sub from './sub.svelte';
+	let sub = $state();
+</script>
+
+<Sub bind:this={sub} />
+<button on:click={() => sub.count++}>{sub?.count} / {sub?.doubled}</button>
diff --git a/packages/svelte/tests/runtime-runes/samples/exports-4/sub.svelte b/packages/svelte/tests/runtime-runes/samples/exports-4/sub.svelte
new file mode 100644
index 0000000000..75b0091235
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/exports-4/sub.svelte
@@ -0,0 +1,9 @@
+<script>
+	let count = $state(0);
+	let doubled = $derived(count * 2);
+
+	export { count, doubled };
+</script>
+
+{count}
+{doubled}
diff --git a/packages/svelte/tests/runtime-runes/samples/mount-intro-transition/Component.svelte b/packages/svelte/tests/runtime-runes/samples/mount-intro-transition/Component.svelte
new file mode 100644
index 0000000000..f9c91fb840
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/mount-intro-transition/Component.svelte
@@ -0,0 +1,5 @@
+<script>
+	import { fade } from 'svelte/transition';
+</script>
+
+<div in:fade|global={{ duration: 100 }}>DIV</div>
diff --git a/packages/svelte/tests/runtime-runes/samples/mount-intro-transition/_config.js b/packages/svelte/tests/runtime-runes/samples/mount-intro-transition/_config.js
new file mode 100644
index 0000000000..114f6f0cbf
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/mount-intro-transition/_config.js
@@ -0,0 +1,21 @@
+import { flushSync } from 'svelte';
+import { ok, test } from '../../test';
+
+export default test({
+	async test({ assert, target, raf }) {
+		const [btn1, btn2] = target.querySelectorAll('button');
+		const div = target.querySelector('div');
+		ok(div);
+
+		btn1.click();
+		flushSync();
+		assert.htmlEqual(div.innerHTML, `<div style="opacity: 0;">DIV</div>`);
+
+		raf.tick(100);
+		assert.htmlEqual(div.innerHTML, `<div style="">DIV</div>`);
+
+		btn2.click();
+		flushSync();
+		assert.htmlEqual(div.innerHTML, `<div>DIV</div>`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/mount-intro-transition/main.svelte b/packages/svelte/tests/runtime-runes/samples/mount-intro-transition/main.svelte
new file mode 100644
index 0000000000..83021fa537
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/mount-intro-transition/main.svelte
@@ -0,0 +1,21 @@
+<script>
+	import { mount, unmount } from 'svelte';
+	import Component from './Component.svelte';
+
+	let el;
+	let instance;
+
+	function intro(animate) {
+		if (instance) unmount(instance);
+
+		instance = mount(Component, {
+			target: el,
+			intro: animate
+		});
+	}
+</script>
+
+<div bind:this={el}></div>
+
+<button onclick={() => intro()}>mount with intro transition</button>
+<button onclick={() => intro(false)}>mount without intro transition</button>
diff --git a/packages/svelte/tests/runtime-runes/samples/select-falsy-value/_config.js b/packages/svelte/tests/runtime-runes/samples/select-falsy-value/_config.js
new file mode 100644
index 0000000000..5d535db521
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/select-falsy-value/_config.js
@@ -0,0 +1,32 @@
+import { test } from '../../test';
+
+// <option value> is special because falsy values should result in an empty string value attribute
+export default test({
+	mode: ['client'],
+	test({ assert, target }) {
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+			<select>
+				<option value="">Default</option>
+			</select>
+
+			<select>
+				<option value="">Default</option>
+			</select>
+
+			<select>
+				<option value="">Default</option>
+			</select>
+
+			<select>
+				<option value="">Default</option>
+			</select>
+
+			<select>
+				<option value="">Default</option>
+			</select>
+		`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/select-falsy-value/main.svelte b/packages/svelte/tests/runtime-runes/samples/select-falsy-value/main.svelte
new file mode 100644
index 0000000000..95e96c6d19
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/select-falsy-value/main.svelte
@@ -0,0 +1,26 @@
+<script>
+	let nonreactive = undefined;
+	let reactive = $state();
+	let nonreactive_spread = { value: undefined };
+	let reactive_spread = $state({ value: undefined });
+</script>
+
+<select>
+	<option value={undefined}>Default</option>
+</select>
+
+<select>
+	<option value={nonreactive}>Default</option>
+</select>
+
+<select>
+	<option value={reactive}>Default</option>
+</select>
+
+<select>
+	<option {...nonreactive_spread}>Default</option>
+</select>
+
+<select>
+	<option {...reactive_spread}>Default</option>
+</select>
diff --git a/packages/svelte/tests/signals/test.ts b/packages/svelte/tests/signals/test.ts
index 555beb0526..b66d25793f 100644
--- a/packages/svelte/tests/signals/test.ts
+++ b/packages/svelte/tests/signals/test.ts
@@ -550,6 +550,40 @@ describe('signals', () => {
 		};
 	});
 
+	test('deriveds update upon reconnection #3', () => {
+		let a = source(false);
+		let b = source(false);
+
+		let c = derived(() => $.get(a) || $.get(b));
+		let d = derived(() => $.get(c));
+		let e = derived(() => $.get(d));
+
+		return () => {
+			const log: string[] = [];
+			let destroy = effect_root(() => {
+				render_effect(() => {
+					$.get(e);
+					log.push('init');
+				});
+			});
+			destroy();
+
+			destroy = effect_root(() => {
+				render_effect(() => {
+					$.get(e);
+					log.push('update');
+				});
+			});
+
+			assert.deepEqual(log, ['init', 'update']);
+
+			set(a, true);
+			flushSync();
+
+			assert.deepEqual(log, ['init', 'update', 'update']);
+		};
+	});
+
 	test('unowned deriveds are not added as reactions', () => {
 		var count = source(0);
 
diff --git a/packages/svelte/tests/validator/samples/if-block-whitespace-legacy/errors.json b/packages/svelte/tests/validator/samples/if-block-whitespace-legacy/errors.json
new file mode 100644
index 0000000000..fe51488c70
--- /dev/null
+++ b/packages/svelte/tests/validator/samples/if-block-whitespace-legacy/errors.json
@@ -0,0 +1 @@
+[]
diff --git a/packages/svelte/tests/validator/samples/if-block-whitespace-legacy/input.svelte b/packages/svelte/tests/validator/samples/if-block-whitespace-legacy/input.svelte
new file mode 100644
index 0000000000..8640f21e1a
--- /dev/null
+++ b/packages/svelte/tests/validator/samples/if-block-whitespace-legacy/input.svelte
@@ -0,0 +1,8 @@
+<svelte:options runes={false} />
+
+<!-- prettier-ignore -->
+<div>
+	{ #if true}
+		<p>hi</p>
+	{/if}
+</div>
diff --git a/packages/svelte/tests/validator/samples/if-block-whitespace-runes/errors.json b/packages/svelte/tests/validator/samples/if-block-whitespace-runes/errors.json
new file mode 100644
index 0000000000..83ff498556
--- /dev/null
+++ b/packages/svelte/tests/validator/samples/if-block-whitespace-runes/errors.json
@@ -0,0 +1,14 @@
+[
+	{
+		"code": "block_unexpected_character",
+		"message": "Expected a `#` character immediately following the opening bracket",
+		"start": {
+			"line": 5,
+			"column": 1
+		},
+		"end": {
+			"line": 5,
+			"column": 6
+		}
+	}
+]
diff --git a/packages/svelte/tests/validator/samples/if-block-whitespace-runes/input.svelte b/packages/svelte/tests/validator/samples/if-block-whitespace-runes/input.svelte
new file mode 100644
index 0000000000..39b11dd5e1
--- /dev/null
+++ b/packages/svelte/tests/validator/samples/if-block-whitespace-runes/input.svelte
@@ -0,0 +1,8 @@
+<svelte:options runes={true} />
+
+<!-- prettier-ignore -->
+<div>
+	{ #if true}
+		<p>hi</p>
+	{/if}
+</div>
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index 305e1240db..c63e6366ba 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -366,7 +366,8 @@ declare module 'svelte' {
 	/** Anything except a function */
 	type NotFunction<T> = T extends Function ? never : T;
 	/**
-	 * Mounts a component to the given target and returns the exports and potentially the props (if compiled with `accessors: true`) of the component
+	 * Mounts a component to the given target and returns the exports and potentially the props (if compiled with `accessors: true`) of the component.
+	 * Transitions will play during the initial render unless the `intro` option is set to `false`.
 	 *
 	 * */
 	export function mount<Props extends Record<string, any>, Exports extends Record<string, any>>(component: ComponentType<SvelteComponent<Props>> | Component<Props, Exports, any>, options: {} extends Props ? {
@@ -562,9 +563,9 @@ declare module 'svelte/animate' {
 
 declare module 'svelte/compiler' {
 	import type { AssignmentExpression, ClassDeclaration, Expression, FunctionDeclaration, Identifier, ImportDeclaration, ArrayExpression, MemberExpression, ObjectExpression, Pattern, ArrowFunctionExpression, VariableDeclaration, VariableDeclarator, FunctionExpression, Node, Program, ChainExpression, SimpleCallExpression } from 'estree';
-	import type { Location } from 'locate-character';
 	import type { SourceMap } from 'magic-string';
 	import type { Context } from 'zimmerframe';
+	import type { Location } from 'locate-character';
 	/**
 	 * `compile` converts your `.svelte` source code into a JavaScript module that exports a component
 	 *
@@ -714,16 +715,9 @@ declare module 'svelte/compiler' {
 		ast: any;
 	}
 
-	export interface Warning {
-		start?: Location;
-		end?: Location;
-		// TODO there was pos: number in Svelte 4 - do we want to add it back?
-		code: string;
-		message: string;
-		filename?: string;
-	}
+	export interface Warning extends ICompileDiagnostic {}
 
-	export interface CompileError extends InternalCompileError {}
+	export interface CompileError extends ICompileDiagnostic {}
 
 	type CssHashGetter = (args: {
 		name: string;
@@ -1882,18 +1876,15 @@ declare module 'svelte/compiler' {
 		content: Program;
 		attributes: Attribute[];
 	}
-	class InternalCompileError extends Error {
-		
-		constructor(code: string, message: string, position: [number, number] | undefined);
-		filename: string | undefined;
-		
-		position: [number, number] | undefined;
-		
-		start: Location | undefined;
-		
-		end: Location | undefined;
+	type ICompileDiagnostic = {
 		code: string;
-	}
+		message: string;
+		filename?: string;
+		start?: Location;
+		end?: Location;
+		position?: [number, number];
+		frame?: string;
+	};
 
 	export {};
 }
@@ -2539,14 +2530,7 @@ declare module 'svelte/types/compiler/interfaces' {
 	export type CompileOptions = CompileOptions_1;
 	/** @deprecated import this from 'svelte' instead */
 	export type Warning = Warning_1;
-	interface Warning_1 {
-		start?: Location;
-		end?: Location;
-		// TODO there was pos: number in Svelte 4 - do we want to add it back?
-		code: string;
-		message: string;
-		filename?: string;
-	}
+	interface Warning_1 extends ICompileDiagnostic {}
 
 	type CssHashGetter = (args: {
 		name: string;
@@ -2709,6 +2693,15 @@ declare module 'svelte/types/compiler/interfaces' {
 	 *               (also see https://github.com/sveltejs/svelte/pull/5652)
 	 */
 	type Namespace = 'html' | 'svg' | 'mathml' | 'foreign';
+	type ICompileDiagnostic = {
+		code: string;
+		message: string;
+		filename?: string;
+		start?: Location;
+		end?: Location;
+		position?: [number, number];
+		frame?: string;
+	};
 
 	export {};
 }declare module '*.svelte' {
diff --git a/sites/svelte-5-preview/src/routes/docs/content/03-appendix/02-breaking-changes.md b/sites/svelte-5-preview/src/routes/docs/content/03-appendix/02-breaking-changes.md
index 5b08103d80..8de2bfbfe4 100644
--- a/sites/svelte-5-preview/src/routes/docs/content/03-appendix/02-breaking-changes.md
+++ b/sites/svelte-5-preview/src/routes/docs/content/03-appendix/02-breaking-changes.md
@@ -281,3 +281,7 @@ In Svelte 4, `<svelte:element this="div">` is valid code. This makes little sens
 ```
 
 Note that whereas Svelte 4 would treat `<svelte:element this="input">` (for example) identically to `<input>` for the purposes of determining which `bind:` directives could be applied, Svelte 5 does not.
+
+### `mount` plays transitions by default
+
+The `mount` function used to render a component tree plays transitions by default unless the `intro` option is set to `false`. This is different from legacy class components which, when manually instantiated, didn't play transitions by default.