diff --git a/apps/mana/apps/web/src/lib/data/current-user.ts b/apps/mana/apps/web/src/lib/data/current-user.ts
new file mode 100644
index 000000000..4c965a8f0
--- /dev/null
+++ b/apps/mana/apps/web/src/lib/data/current-user.ts
@@ -0,0 +1,36 @@
+/**
+ * Single source of truth for the current authenticated user id.
+ *
+ * Why a separate module?
+ *   The data layer (database.ts hooks) needs to know who is writing each
+ *   record so it can stamp `userId` automatically. Importing the auth store
+ *   directly would couple the data layer to UI state and create a circular
+ *   dependency. Instead, the root layout pushes the current user id here on
+ *   every auth state change.
+ *
+ * Guest mode: when no user is signed in, records are stamped with the
+ * `GUEST_USER_ID` sentinel. The mana-sync backend treats these as anonymous
+ * and rejects them at the RLS layer once auth is required.
+ */
+
+export const GUEST_USER_ID = 'guest';
+
+let currentUserId: string | null = null;
+
+/** Updates the active user. Pass `null` for sign-out / guest. */
+export function setCurrentUserId(id: string | null): void {
+	currentUserId = id;
+}
+
+/** Returns the active user id, or `null` if unauthenticated. */
+export function getCurrentUserId(): string | null {
+	return currentUserId;
+}
+
+/**
+ * Returns the user id to stamp on local records: real user when signed in,
+ * `GUEST_USER_ID` otherwise. Always non-null so it can be used as a key.
+ */
+export function getEffectiveUserId(): string {
+	return currentUserId ?? GUEST_USER_ID;
+}
diff --git a/apps/mana/apps/web/src/lib/data/database.ts b/apps/mana/apps/web/src/lib/data/database.ts
index 4b3fb9380..b5b5c39ce 100644
--- a/apps/mana/apps/web/src/lib/data/database.ts
+++ b/apps/mana/apps/web/src/lib/data/database.ts
@@ -11,6 +11,7 @@ import Dexie, { type EntityTable } from 'dexie';
 import { trackFirstContent } from '$lib/stores/funnel-tracking';
 import { fire as fireTrigger } from '$lib/triggers/registry';
 import { checkInlineSuggestion } from '$lib/triggers/inline-suggest';
+import { getEffectiveUserId } from './current-user';
 
 // ─── Database ──────────────────────────────────────────────
 
@@ -576,6 +577,14 @@ for (const [appId, tables] of Object.entries(SYNC_APP_MAP)) {
 			if (_applyingServerChanges) return;
 			const now = new Date().toISOString();
 
+			// Auto-stamp the active user. Module stores never set userId themselves,
+			// preventing accidental impersonation and removing all hardcoded
+			// 'guest'/'local' fallbacks scattered across query files.
+			const objRecord = obj as Record<string, unknown>;
+			if (objRecord.userId === undefined || objRecord.userId === null) {
+				objRecord.userId = getEffectiveUserId();
+			}
+
 			// Stamp every real field with the create-time so future LWW comparisons
 			// have a baseline. Mutates obj in place — Dexie persists the mutation.
 			const ft: Record<string, string> = {};
@@ -583,7 +592,7 @@ for (const [appId, tables] of Object.entries(SYNC_APP_MAP)) {
 				if (isInternalKey(key)) continue;
 				ft[key] = now;
 			}
-			(obj as Record<string, unknown>)[FIELD_TIMESTAMPS_KEY] = ft;
+			objRecord[FIELD_TIMESTAMPS_KEY] = ft;
 
 			// Build payload for pending-change WITHOUT the internal timestamp map
 			const { [FIELD_TIMESTAMPS_KEY]: _omit, ...dataForSync } = obj as Record<string, unknown>;
@@ -613,6 +622,12 @@ for (const [appId, tables] of Object.entries(SYNC_APP_MAP)) {
 			const now = new Date().toISOString();
 			const fields: Record<string, { value: unknown; updatedAt: string }> = {};
 
+			// userId is immutable after creation. Silently strip any attempt to
+			// reassign it from a local update so a buggy or malicious caller can
+			// never re-parent records to a different user.
+			const mods = modifications as Record<string, unknown>;
+			if ('userId' in mods) delete mods.userId;
+
 			// Merge field timestamps: keep existing, overwrite for each modified field
 			const existingFT =
 				((obj as Record<string, unknown>)[FIELD_TIMESTAMPS_KEY] as
diff --git a/apps/mana/apps/web/src/lib/data/guest-migration.ts b/apps/mana/apps/web/src/lib/data/guest-migration.ts
new file mode 100644
index 000000000..b2df98d02
--- /dev/null
+++ b/apps/mana/apps/web/src/lib/data/guest-migration.ts
@@ -0,0 +1,90 @@
+/**
+ * Guest → User data migration.
+ *
+ * In guest mode, the Dexie creating-hook stamps every record with
+ * `userId = GUEST_USER_ID`. Sync push is also a no-op while there is no
+ * auth token, so the records live purely in the local IndexedDB.
+ *
+ * When the user signs in for the first time we want their existing local
+ * data to be theirs. This module walks every sync-tracked table, finds
+ * records owned by `guest`, and re-creates them under the active user id.
+ *
+ * Why delete-and-re-add instead of an in-place update?
+ *   The Dexie updating-hook deliberately strips `userId` from modifications
+ *   (immutable once created), and even if we bypassed that, an `op: 'update'`
+ *   pending-change would only ship the userId field to the server — other
+ *   clients pulling the change would see a fresh record with just an id and
+ *   userId. By deleting and re-adding we generate a clean `op: 'insert'`
+ *   with the full record payload.
+ *
+ *   Deleting in guest mode is safe because nothing was ever pushed to the
+ *   server: `_pendingChanges` is cleared as part of the migration too, so the
+ *   delete is purely local and never reaches the sync layer.
+ */
+
+import { db, SYNC_APP_MAP, FIELD_TIMESTAMPS_KEY } from './database';
+import { GUEST_USER_ID } from './current-user';
+
+export interface GuestMigrationResult {
+	migratedRecords: number;
+	tablesTouched: number;
+}
+
+/**
+ * Re-stamps every `userId === 'guest'` record under the active user id.
+ *
+ * Caller must ensure `setCurrentUserId(newUserId)` was already invoked so
+ * that the Dexie creating-hook picks up the right id when re-inserting.
+ */
+export async function migrateGuestDataToUser(newUserId: string): Promise<GuestMigrationResult> {
+	if (!newUserId || newUserId === GUEST_USER_ID) {
+		return { migratedRecords: 0, tablesTouched: 0 };
+	}
+
+	// Drop any pending changes accumulated during guest mode — they were
+	// never pushed (no auth token) and reference the old guest userId. The
+	// re-inserts below will produce fresh pending changes that should NOT be
+	// wiped, so this MUST happen before the migration loop.
+	await db.table('_pendingChanges').clear();
+
+	let migratedRecords = 0;
+	let tablesTouched = 0;
+
+	for (const tables of Object.values(SYNC_APP_MAP)) {
+		for (const tableName of tables) {
+			const table = db.table(tableName);
+
+			// Filter scan: userId is not indexed (and we don't want to widen the
+			// schema for a one-shot migration). Tables are typically small at
+			// this point because guest mode only stores what one person typed.
+			const guestRecords = await table
+				.filter((r: unknown) => (r as Record<string, unknown>).userId === GUEST_USER_ID)
+				.toArray();
+
+			if (guestRecords.length === 0) continue;
+			tablesTouched++;
+
+			// One transaction per table keeps the delete+add pair atomic and
+			// avoids leaving the table half-migrated if Dexie throws partway.
+			await db.transaction('rw', table, async () => {
+				for (const oldRecord of guestRecords) {
+					const record = oldRecord as Record<string, unknown>;
+					const id = record.id as string;
+
+					// Strip the bookkeeping fields the creating-hook will rebuild.
+					// Importantly, drop `userId` so the hook stamps the new id from
+					// getEffectiveUserId() instead of preserving 'guest'.
+					const { userId: _oldUser, [FIELD_TIMESTAMPS_KEY]: _oldFt, ...clean } = record;
+					void _oldUser;
+					void _oldFt;
+
+					await table.delete(id);
+					await table.add({ ...clean, id });
+					migratedRecords++;
+				}
+			});
+		}
+	}
+
+	return { migratedRecords, tablesTouched };
+}
diff --git a/apps/mana/apps/web/src/lib/modules/calc/queries.ts b/apps/mana/apps/web/src/lib/modules/calc/queries.ts
index c7c71d40b..b8d8111ad 100644
--- a/apps/mana/apps/web/src/lib/modules/calc/queries.ts
+++ b/apps/mana/apps/web/src/lib/modules/calc/queries.ts
@@ -12,7 +12,7 @@ import type { Calculation, SavedFormula } from '@calc/shared';
 export function toCalculation(local: LocalCalculation): Calculation {
 	return {
 		id: local.id,
-		userId: 'local',
+		userId: local.userId ?? '',
 		mode: local.mode,
 		expression: local.expression,
 		result: local.result,
@@ -24,7 +24,7 @@ export function toCalculation(local: LocalCalculation): Calculation {
 export function toSavedFormula(local: LocalSavedFormula): SavedFormula {
 	return {
 		id: local.id,
-		userId: 'local',
+		userId: local.userId ?? '',
 		name: local.name,
 		expression: local.expression,
 		description: local.description ?? undefined,
diff --git a/apps/mana/apps/web/src/lib/modules/cards/queries.ts b/apps/mana/apps/web/src/lib/modules/cards/queries.ts
index c53c10934..5ffa55236 100644
--- a/apps/mana/apps/web/src/lib/modules/cards/queries.ts
+++ b/apps/mana/apps/web/src/lib/modules/cards/queries.ts
@@ -13,7 +13,6 @@ import type { LocalDeck, LocalCard, Deck, Card } from './types';
 export function toDeck(local: LocalDeck): Deck {
 	return {
 		id: local.id,
-		userId: 'local',
 		title: local.name,
 		description: local.description ?? undefined,
 		color: local.color,
diff --git a/apps/mana/apps/web/src/lib/modules/cards/types.ts b/apps/mana/apps/web/src/lib/modules/cards/types.ts
index c5f063040..03b333d0e 100644
--- a/apps/mana/apps/web/src/lib/modules/cards/types.ts
+++ b/apps/mana/apps/web/src/lib/modules/cards/types.ts
@@ -27,7 +27,6 @@ export interface LocalCard extends BaseRecord {
 
 export interface Deck {
 	id: string;
-	userId: string;
 	title: string;
 	description?: string;
 	color: string;
diff --git a/apps/mana/apps/web/src/lib/modules/chat/queries.ts b/apps/mana/apps/web/src/lib/modules/chat/queries.ts
index a3d82662b..050fdbe67 100644
--- a/apps/mana/apps/web/src/lib/modules/chat/queries.ts
+++ b/apps/mana/apps/web/src/lib/modules/chat/queries.ts
@@ -18,7 +18,6 @@ import type {
 export function toConversation(local: LocalConversation): Conversation {
 	return {
 		id: local.id,
-		userId: local.userId ?? 'guest',
 		modelId: local.modelId ?? '',
 		templateId: local.templateId ?? undefined,
 		spaceId: local.spaceId ?? undefined,
@@ -35,7 +34,6 @@ export function toConversation(local: LocalConversation): Conversation {
 export function toTemplate(local: LocalTemplate): Template {
 	return {
 		id: local.id,
-		userId: local.userId ?? 'guest',
 		name: local.name,
 		description: local.description || null,
 		systemPrompt: local.systemPrompt,
diff --git a/apps/mana/apps/web/src/lib/modules/chat/types.ts b/apps/mana/apps/web/src/lib/modules/chat/types.ts
index ae92084f0..56fd13e60 100644
--- a/apps/mana/apps/web/src/lib/modules/chat/types.ts
+++ b/apps/mana/apps/web/src/lib/modules/chat/types.ts
@@ -36,7 +36,6 @@ export interface LocalTemplate extends BaseRecord {
 
 export interface Conversation {
 	id: string;
-	userId: string;
 	modelId: string;
 	templateId?: string;
 	spaceId?: string;
@@ -60,7 +59,6 @@ export interface Message {
 
 export interface Template {
 	id: string;
-	userId: string;
 	name: string;
 	description: string | null;
 	systemPrompt: string;
diff --git a/apps/mana/apps/web/src/lib/modules/contacts/queries.ts b/apps/mana/apps/web/src/lib/modules/contacts/queries.ts
index fc6f80dea..f6879d7c5 100644
--- a/apps/mana/apps/web/src/lib/modules/contacts/queries.ts
+++ b/apps/mana/apps/web/src/lib/modules/contacts/queries.ts
@@ -15,7 +15,6 @@ export function toContact(local: LocalContact): Contact {
 
 	return {
 		id: local.id,
-		userId: 'local',
 		firstName,
 		lastName,
 		displayName,
diff --git a/apps/mana/apps/web/src/lib/modules/contacts/types.ts b/apps/mana/apps/web/src/lib/modules/contacts/types.ts
index 32fbc0d20..f41d01c8f 100644
--- a/apps/mana/apps/web/src/lib/modules/contacts/types.ts
+++ b/apps/mana/apps/web/src/lib/modules/contacts/types.ts
@@ -35,7 +35,6 @@ export interface LocalContact extends BaseRecord {
 
 export interface Contact {
 	id: string;
-	userId: string;
 	firstName?: string | null;
 	lastName?: string | null;
 	displayName?: string | null;
diff --git a/apps/mana/apps/web/src/lib/modules/memoro/types.ts b/apps/mana/apps/web/src/lib/modules/memoro/types.ts
index 12513f603..3c906bb60 100644
--- a/apps/mana/apps/web/src/lib/modules/memoro/types.ts
+++ b/apps/mana/apps/web/src/lib/modules/memoro/types.ts
@@ -7,7 +7,6 @@ import type { BaseRecord } from '@mana/local-store';
 export type ProcessingStatus = 'pending' | 'processing' | 'completed' | 'failed';
 
 export interface LocalMemo extends BaseRecord {
-	userId?: string;
 	title: string | null;
 	intro: string | null;
 	transcript: string | null;
@@ -45,7 +44,6 @@ export interface LocalMemo extends BaseRecord {
 
 export interface LocalMemory extends BaseRecord {
 	memoId: string;
-	userId?: string;
 	title: string;
 	content: string | null;
 	metadata?: Record<string, unknown>;
diff --git a/apps/mana/apps/web/src/lib/modules/planta/queries.ts b/apps/mana/apps/web/src/lib/modules/planta/queries.ts
index ed5c4aa83..509bf3b12 100644
--- a/apps/mana/apps/web/src/lib/modules/planta/queries.ts
+++ b/apps/mana/apps/web/src/lib/modules/planta/queries.ts
@@ -25,7 +25,6 @@ import type {
 export function toPlant(local: LocalPlant): Plant {
 	return {
 		id: local.id,
-		userId: 'local',
 		name: local.name,
 		scientificName: local.scientificName ?? undefined,
 		commonName: local.commonName ?? undefined,
@@ -49,7 +48,6 @@ export function toPlantPhoto(local: LocalPlantPhoto): PlantPhoto {
 	return {
 		id: local.id,
 		plantId: local.plantId,
-		userId: 'local',
 		storagePath: local.storagePath,
 		publicUrl: local.publicUrl ?? undefined,
 		filename: local.filename,
@@ -69,7 +67,6 @@ export function toWateringSchedule(local: LocalWateringSchedule): WateringSchedu
 	return {
 		id: local.id,
 		plantId: local.plantId,
-		userId: 'local',
 		frequencyDays: local.frequencyDays,
 		lastWateredAt: local.lastWateredAt ? new Date(local.lastWateredAt) : undefined,
 		nextWateringAt: local.nextWateringAt ? new Date(local.nextWateringAt) : undefined,
@@ -85,7 +82,6 @@ export function toWateringLog(local: LocalWateringLog): WateringLog {
 	return {
 		id: local.id,
 		plantId: local.plantId,
-		userId: 'local',
 		wateredAt: new Date(local.wateredAt),
 		notes: local.notes ?? undefined,
 		createdAt: new Date(local.createdAt ?? new Date().toISOString()),
diff --git a/apps/mana/apps/web/src/lib/modules/planta/types.ts b/apps/mana/apps/web/src/lib/modules/planta/types.ts
index 4437297e8..ce1a804d3 100644
--- a/apps/mana/apps/web/src/lib/modules/planta/types.ts
+++ b/apps/mana/apps/web/src/lib/modules/planta/types.ts
@@ -62,7 +62,6 @@ export interface LocalWateringLog extends BaseRecord {
 
 export interface Plant {
 	id: string;
-	userId: string;
 	name: string;
 	scientificName?: string;
 	commonName?: string;
@@ -83,7 +82,6 @@ export interface Plant {
 export interface PlantPhoto {
 	id: string;
 	plantId: string;
-	userId: string;
 	storagePath: string;
 	publicUrl?: string;
 	filename: string;
@@ -100,7 +98,6 @@ export interface PlantPhoto {
 export interface WateringSchedule {
 	id: string;
 	plantId: string;
-	userId: string;
 	frequencyDays: number;
 	lastWateredAt?: Date;
 	nextWateringAt?: Date;
@@ -113,7 +110,6 @@ export interface WateringSchedule {
 export interface WateringLog {
 	id: string;
 	plantId: string;
-	userId: string;
 	wateredAt: Date;
 	notes?: string;
 	createdAt: Date;
diff --git a/apps/mana/apps/web/src/lib/modules/presi/queries.ts b/apps/mana/apps/web/src/lib/modules/presi/queries.ts
index d548a415b..bf220fb64 100644
--- a/apps/mana/apps/web/src/lib/modules/presi/queries.ts
+++ b/apps/mana/apps/web/src/lib/modules/presi/queries.ts
@@ -14,7 +14,6 @@ import type { LocalDeck, LocalSlide, Deck, Slide } from './types';
 export function toDeck(local: LocalDeck): Deck {
 	return {
 		id: local.id,
-		userId: 'local',
 		title: local.title,
 		description: local.description ?? undefined,
 		themeId: local.themeId ?? undefined,
diff --git a/apps/mana/apps/web/src/lib/modules/presi/types.ts b/apps/mana/apps/web/src/lib/modules/presi/types.ts
index a0f4170a1..188a4c395 100644
--- a/apps/mana/apps/web/src/lib/modules/presi/types.ts
+++ b/apps/mana/apps/web/src/lib/modules/presi/types.ts
@@ -30,7 +30,6 @@ export interface SlideContent {
 
 export interface Deck {
 	id: string;
-	userId: string;
 	title: string;
 	description?: string;
 	themeId?: string;
diff --git a/apps/mana/apps/web/src/lib/modules/storage/queries.ts b/apps/mana/apps/web/src/lib/modules/storage/queries.ts
index 7e8a62a8c..00c43e22e 100644
--- a/apps/mana/apps/web/src/lib/modules/storage/queries.ts
+++ b/apps/mana/apps/web/src/lib/modules/storage/queries.ts
@@ -12,7 +12,6 @@ import type { LocalFile, LocalFolder, LocalFileTag } from './types';
 
 export interface StorageFile {
 	id: string;
-	userId: string;
 	name: string;
 	originalName: string;
 	mimeType: string;
@@ -30,7 +29,6 @@ export interface StorageFile {
 
 export interface StorageFolder {
 	id: string;
-	userId: string;
 	name: string;
 	description: string | null;
 	color: string | null;
@@ -46,7 +44,6 @@ export interface StorageFolder {
 
 export interface StorageTag {
 	id: string;
-	userId: string;
 	name: string;
 	color: string | null;
 	createdAt: string;
@@ -57,7 +54,6 @@ export interface StorageTag {
 export function toFile(local: LocalFile): StorageFile {
 	return {
 		id: local.id,
-		userId: 'local',
 		name: local.name,
 		originalName: local.originalName,
 		mimeType: local.mimeType,
@@ -77,7 +73,6 @@ export function toFile(local: LocalFile): StorageFile {
 export function toFolder(local: LocalFolder): StorageFolder {
 	return {
 		id: local.id,
-		userId: 'local',
 		name: local.name,
 		description: local.description ?? null,
 		color: local.color ?? null,
@@ -100,7 +95,6 @@ export function toTag(local: {
 }): StorageTag {
 	return {
 		id: local.id,
-		userId: 'local',
 		name: local.name,
 		color: local.color ?? null,
 		createdAt: local.createdAt ?? new Date().toISOString(),
diff --git a/apps/mana/apps/web/src/lib/modules/times/queries.ts b/apps/mana/apps/web/src/lib/modules/times/queries.ts
index 09013070b..dbf4f9889 100644
--- a/apps/mana/apps/web/src/lib/modules/times/queries.ts
+++ b/apps/mana/apps/web/src/lib/modules/times/queries.ts
@@ -130,7 +130,6 @@ export function toSettings(local: LocalSettings): TimesSettings {
 export function toAlarm(local: LocalAlarm): Alarm {
 	return {
 		id: local.id,
-		userId: 'local',
 		label: local.label,
 		time: local.time,
 		enabled: local.enabled,
@@ -146,7 +145,6 @@ export function toAlarm(local: LocalAlarm): Alarm {
 export function toCountdownTimer(local: LocalCountdownTimer): Timer {
 	return {
 		id: local.id,
-		userId: 'local',
 		label: local.label,
 		durationSeconds: local.durationSeconds,
 		remainingSeconds: local.remainingSeconds,
@@ -162,7 +160,6 @@ export function toCountdownTimer(local: LocalCountdownTimer): Timer {
 export function toWorldClock(local: LocalWorldClock): WorldClock {
 	return {
 		id: local.id,
-		userId: 'local',
 		timezone: local.timezone,
 		cityName: local.cityName,
 		sortOrder: local.sortOrder,
diff --git a/apps/mana/apps/web/src/lib/modules/times/stores/session-alarms.svelte.ts b/apps/mana/apps/web/src/lib/modules/times/stores/session-alarms.svelte.ts
index 2b04783ab..45dbfb976 100644
--- a/apps/mana/apps/web/src/lib/modules/times/stores/session-alarms.svelte.ts
+++ b/apps/mana/apps/web/src/lib/modules/times/stores/session-alarms.svelte.ts
@@ -62,7 +62,6 @@ export const sessionAlarmsStore = {
 		const now = new Date().toISOString();
 		const alarm: Alarm = {
 			id: generateSessionId(),
-			userId: 'guest',
 			label: input.label || null,
 			time: input.time,
 			enabled: input.enabled ?? true,
diff --git a/apps/mana/apps/web/src/lib/modules/times/stores/session-countdown-timers.svelte.ts b/apps/mana/apps/web/src/lib/modules/times/stores/session-countdown-timers.svelte.ts
index 8909191b6..e467010a7 100644
--- a/apps/mana/apps/web/src/lib/modules/times/stores/session-countdown-timers.svelte.ts
+++ b/apps/mana/apps/web/src/lib/modules/times/stores/session-countdown-timers.svelte.ts
@@ -63,7 +63,6 @@ export const sessionCountdownTimersStore = {
 		const now = new Date().toISOString();
 		const timer: Timer = {
 			id: generateSessionId(),
-			userId: 'guest',
 			label: input.label || null,
 			durationSeconds: input.durationSeconds,
 			remainingSeconds: input.durationSeconds,
diff --git a/apps/mana/apps/web/src/lib/modules/times/types.ts b/apps/mana/apps/web/src/lib/modules/times/types.ts
index 8c7121861..216586a8a 100644
--- a/apps/mana/apps/web/src/lib/modules/times/types.ts
+++ b/apps/mana/apps/web/src/lib/modules/times/types.ts
@@ -251,7 +251,6 @@ export type TimerStatus = 'idle' | 'running' | 'paused' | 'finished';
 
 export interface Alarm {
 	id: string;
-	userId: string;
 	label: string | null;
 	time: string; // HH:MM:SS format
 	enabled: boolean;
@@ -285,7 +284,6 @@ export interface UpdateAlarmInput {
 
 export interface Timer {
 	id: string;
-	userId: string;
 	label: string | null;
 	durationSeconds: number;
 	remainingSeconds: number | null;
@@ -311,7 +309,6 @@ export interface UpdateTimerInput {
 
 export interface WorldClock {
 	id: string;
-	userId: string;
 	timezone: string; // IANA timezone e.g. 'America/New_York'
 	cityName: string;
 	sortOrder: number;
diff --git a/apps/mana/apps/web/src/lib/modules/todo/queries.ts b/apps/mana/apps/web/src/lib/modules/todo/queries.ts
index 0337194d5..f25107265 100644
--- a/apps/mana/apps/web/src/lib/modules/todo/queries.ts
+++ b/apps/mana/apps/web/src/lib/modules/todo/queries.ts
@@ -20,7 +20,6 @@ export function toTask(local: LocalTask): Task {
 	return {
 		id: local.id,
 		projectId: (local as Record<string, unknown>).projectId as string | null | undefined,
-		userId: local.userId ?? 'guest',
 		title: local.title,
 		description: local.description,
 		dueDate: local.dueDate,
diff --git a/apps/mana/apps/web/src/lib/modules/todo/types.ts b/apps/mana/apps/web/src/lib/modules/todo/types.ts
index b20bcc6a5..f0db21e2d 100644
--- a/apps/mana/apps/web/src/lib/modules/todo/types.ts
+++ b/apps/mana/apps/web/src/lib/modules/todo/types.ts
@@ -24,7 +24,6 @@ export type TaskStatus = 'pending' | 'in_progress' | 'completed' | 'cancelled';
 export interface LocalTask extends BaseRecord {
 	title: string;
 	description?: string;
-	userId?: string;
 	projectId?: string | null;
 	priority: TaskPriority;
 	isCompleted: boolean;
@@ -45,7 +44,6 @@ export interface LocalTaskTag extends BaseRecord {
 
 export interface LocalReminder extends BaseRecord {
 	taskId: string;
-	userId?: string;
 	minutesBefore: number;
 	type: 'push' | 'email' | 'both';
 	status: 'pending' | 'sent' | 'failed';
@@ -101,7 +99,6 @@ export interface LocalTodoProject extends BaseRecord {
 export interface Task {
 	id: string;
 	projectId?: string | null;
-	userId: string;
 	title: string;
 	description?: string | null;
 	dueDate?: string | null;
diff --git a/apps/mana/apps/web/src/routes/+layout.svelte b/apps/mana/apps/web/src/routes/+layout.svelte
index 9ccb53d1e..a91a59ebb 100644
--- a/apps/mana/apps/web/src/routes/+layout.svelte
+++ b/apps/mana/apps/web/src/routes/+layout.svelte
@@ -5,24 +5,51 @@
 	import { authStore } from '$lib/stores/auth.svelte';
 	import { networkStore } from '$lib/stores/network.svelte';
 	import { loadAutomations } from '$lib/triggers';
+	import { setCurrentUserId } from '$lib/data/current-user';
+	import { migrateGuestDataToUser } from '$lib/data/guest-migration';
 	import SuggestionToast from '$lib/components/SuggestionToast.svelte';
 	import OfflineIndicator from '$lib/components/OfflineIndicator.svelte';
 	import PwaUpdatePrompt from '$lib/components/PwaUpdatePrompt.svelte';
 
 	let { children } = $props();
 
-	onMount(async () => {
+	// Tracks whether we have already attempted the guest → user migration in
+	// this app load. The migration is idempotent (no guest records → no-op)
+	// so this just prevents redundant table scans on every auth state change.
+	let guestMigrationAttempted = false;
+
+	// Push the active user id into the data layer whenever auth state changes.
+	// The Dexie creating-hook reads this to auto-stamp `userId` on every record,
+	// so module stores never need to know who the current user is.
+	$effect(() => {
+		const userId = authStore.user?.id ?? null;
+		setCurrentUserId(userId);
+
+		// First time we see an authenticated user in this session, lift any
+		// guest records into their account so the data they typed before
+		// signing up follows them.
+		if (userId && !guestMigrationAttempted) {
+			guestMigrationAttempted = true;
+			migrateGuestDataToUser(userId).catch((err) => {
+				console.error('[mana] guest → user migration failed:', err);
+			});
+		}
+	});
+
+	onMount(() => {
 		// Initialize theme
 		const cleanupTheme = theme.initialize();
 
 		// Initialize network status tracking
 		networkStore.initialize();
 
-		// Initialize auth
-		await authStore.initialize();
-
-		// Load cross-module automation triggers
-		await loadAutomations();
+		// Auth + automation loading is async — fire and forget. Returning
+		// cleanup from an async onMount would silently drop it, so the async
+		// work runs in an inner IIFE while the outer arrow stays sync.
+		void (async () => {
+			await authStore.initialize();
+			await loadAutomations();
+		})();
 
 		return () => {
 			cleanupTheme();
diff --git a/packages/local-store/src/types.ts b/packages/local-store/src/types.ts
index ac3e6fa4f..beda23192 100644
--- a/packages/local-store/src/types.ts
+++ b/packages/local-store/src/types.ts
@@ -5,6 +5,11 @@
 /** Base record that all local-store entities must extend. */
 export interface BaseRecord {
 	id: string;
+	/**
+	 * Owner of this record. Auto-stamped by the Dexie creating-hook from the
+	 * active session user; module stores must never set this themselves.
+	 */
+	userId?: string;
 	createdAt?: string;
 	updatedAt?: string;
 	deletedAt?: string | null;