diff --git a/.claude/guidelines/authentication.md b/.claude/guidelines/authentication.md
index fe885da13..d0f9a5dae 100644
--- a/.claude/guidelines/authentication.md
+++ b/.claude/guidelines/authentication.md
@@ -32,11 +32,37 @@ All authentication is handled by **Mana Core Auth**, a centralized authenticatio
         │<──────────────────────│                       │
 ```
 
+## User ID Format
+
+**CRITICAL**: Mana Core Auth uses Better Auth, which generates **non-UUID user IDs**.
+
+```
+Example user ID: otUe1YrfENPdHnrF3g1vSBfpkQfambCZ
+```
+
+**Format details:**
+- 32 characters
+- Base62 alphabet (a-z, A-Z, 0-9)
+- ~190 bits of entropy (more than UUID's 122 bits)
+- NOT a valid UUID format
+
+**Database schema implications:**
+
+```typescript
+// CORRECT - use text for user_id
+userId: text('user_id').notNull(),
+
+// WRONG - will cause "invalid input syntax for type uuid" errors
+userId: uuid('user_id').notNull(),
+```
+
+Always use `text` type for `user_id` columns in all database schemas.
+
 ## Token Structure (EdDSA JWT)
 
 ```json
 {
-  "sub": "user-uuid-123",
+  "sub": "otUe1YrfENPdHnrF3g1vSBfpkQfambCZ",
   "email": "user@example.com",
   "role": "user",
   "sid": "session-id-456",
@@ -47,6 +73,8 @@ All authentication is handled by **Mana Core Auth**, a centralized authenticatio
 }
 ```
 
+**Note**: The `sub` claim contains the Better Auth user ID (not a UUID).
+
 **Important**: Keep claims minimal. Do NOT include:
 - Credit balance (changes frequently)
 - Organization data (use API instead)
diff --git a/.claude/guidelines/database.md b/.claude/guidelines/database.md
index a503f86cd..285803ff3 100644
--- a/.claude/guidelines/database.md
+++ b/.claude/guidelines/database.md
@@ -101,6 +101,26 @@ src/db/
 └── migrations/            # Generated migrations
 ```
 
+### User ID Column Type
+
+**CRITICAL**: Always use `text` for `user_id` columns, NOT `uuid`.
+
+Mana Core Auth (Better Auth) generates non-UUID user IDs:
+
+```
+Example: otUe1YrfENPdHnrF3g1vSBfpkQfambCZ
+```
+
+```typescript
+// CORRECT
+userId: text('user_id').notNull(),
+
+// WRONG - causes "invalid input syntax for type uuid" errors
+userId: uuid('user_id').notNull(),
+```
+
+See [Authentication Guidelines](./authentication.md#user-id-format) for details.
+
 ### Table Definition Pattern
 
 ```typescript
@@ -123,8 +143,10 @@ export const files = pgTable(
 		// Primary key - always UUID with auto-generation
 		id: uuid('id').primaryKey().defaultRandom(),
 
-		// Foreign keys
-		userId: varchar('user_id', { length: 255 }).notNull(),
+		// User ID - always TEXT (Better Auth uses non-UUID format)
+		userId: text('user_id').notNull(),
+
+		// Foreign keys to other tables (UUIDs are fine)
 		parentFolderId: uuid('parent_folder_id').references(() => folders.id, { onDelete: 'set null' }),
 
 		// Required fields
diff --git a/apps/todo/CLAUDE.md b/apps/todo/CLAUDE.md
index c12462a3e..affb10e98 100644
--- a/apps/todo/CLAUDE.md
+++ b/apps/todo/CLAUDE.md
@@ -156,9 +156,11 @@ pnpm preview                     # Preview build
 
 ## Database Schema
 
+> **Note**: `user_id` columns use TEXT type (not UUID) because Mana Core Auth generates non-UUID user IDs.
+
 ### projects
 - `id` (UUID) - Primary key
-- `user_id` (UUID) - Owner
+- `user_id` (TEXT) - Owner (Better Auth format)
 - `name` (VARCHAR) - Project name
 - `color` (VARCHAR) - Hex color
 - `icon` (VARCHAR) - Icon name
@@ -169,7 +171,7 @@ pnpm preview                     # Preview build
 ### tasks
 - `id` (UUID) - Primary key
 - `project_id` (UUID) - FK to projects (nullable = Inbox)
-- `user_id` (UUID) - Owner
+- `user_id` (TEXT) - Owner (Better Auth format)
 - `title` (VARCHAR) - Task title
 - `description` (TEXT) - Description
 - `due_date` (TIMESTAMP) - Due date
@@ -182,7 +184,7 @@ pnpm preview                     # Preview build
 
 ### labels
 - `id` (UUID) - Primary key
-- `user_id` (UUID) - Owner
+- `user_id` (TEXT) - Owner (Better Auth format)
 - `name` (VARCHAR) - Label name
 - `color` (VARCHAR) - Hex color
 
@@ -193,6 +195,7 @@ pnpm preview                     # Preview build
 ### reminders
 - `id` (UUID) - Primary key
 - `task_id` (UUID) - FK to tasks
+- `user_id` (TEXT) - Owner (Better Auth format)
 - `minutes_before` (INTEGER) - Offset
 - `type` (VARCHAR) - push/email/both
 - `status` (VARCHAR) - pending/sent/failed
diff --git a/apps/todo/apps/backend/src/db/schema/kanban-boards.schema.ts b/apps/todo/apps/backend/src/db/schema/kanban-boards.schema.ts
index 1245668e8..1d074c7cc 100644
--- a/apps/todo/apps/backend/src/db/schema/kanban-boards.schema.ts
+++ b/apps/todo/apps/backend/src/db/schema/kanban-boards.schema.ts
@@ -1,11 +1,20 @@
-import { pgTable, uuid, timestamp, varchar, boolean, integer, index } from 'drizzle-orm/pg-core';
+import {
+	pgTable,
+	uuid,
+	text,
+	timestamp,
+	varchar,
+	boolean,
+	integer,
+	index,
+} from 'drizzle-orm/pg-core';
 import { projects } from './projects.schema';
 
 export const kanbanBoards = pgTable(
 	'kanban_boards',
 	{
 		id: uuid('id').primaryKey().defaultRandom(),
-		userId: uuid('user_id').notNull(),
+		userId: text('user_id').notNull(),
 		projectId: uuid('project_id').references(() => projects.id, { onDelete: 'cascade' }),
 
 		// Board properties
diff --git a/apps/todo/apps/backend/src/db/schema/kanban-columns.schema.ts b/apps/todo/apps/backend/src/db/schema/kanban-columns.schema.ts
index 3764e4872..98a8faddd 100644
--- a/apps/todo/apps/backend/src/db/schema/kanban-columns.schema.ts
+++ b/apps/todo/apps/backend/src/db/schema/kanban-columns.schema.ts
@@ -1,4 +1,13 @@
-import { pgTable, uuid, timestamp, varchar, boolean, integer, index } from 'drizzle-orm/pg-core';
+import {
+	pgTable,
+	uuid,
+	text,
+	timestamp,
+	varchar,
+	boolean,
+	integer,
+	index,
+} from 'drizzle-orm/pg-core';
 import { kanbanBoards } from './kanban-boards.schema';
 
 // Define locally to avoid circular dependency with tasks.schema
@@ -8,7 +17,7 @@ export const kanbanColumns = pgTable(
 	'kanban_columns',
 	{
 		id: uuid('id').primaryKey().defaultRandom(),
-		userId: uuid('user_id').notNull(),
+		userId: text('user_id').notNull(),
 		boardId: uuid('board_id')
 			.references(() => kanbanBoards.id, { onDelete: 'cascade' })
 			.notNull(),
diff --git a/apps/todo/apps/backend/src/db/schema/labels.schema.ts b/apps/todo/apps/backend/src/db/schema/labels.schema.ts
index 64e1f0bf0..55add9f7f 100644
--- a/apps/todo/apps/backend/src/db/schema/labels.schema.ts
+++ b/apps/todo/apps/backend/src/db/schema/labels.schema.ts
@@ -1,10 +1,10 @@
-import { pgTable, uuid, timestamp, varchar, index } from 'drizzle-orm/pg-core';
+import { pgTable, uuid, text, timestamp, varchar, index } from 'drizzle-orm/pg-core';
 
 export const labels = pgTable(
 	'labels',
 	{
 		id: uuid('id').primaryKey().defaultRandom(),
-		userId: uuid('user_id').notNull(),
+		userId: text('user_id').notNull(),
 		name: varchar('name', { length: 100 }).notNull(),
 		color: varchar('color', { length: 7 }).default('#6B7280'),
 		createdAt: timestamp('created_at', { withTimezone: true }).defaultNow().notNull(),
diff --git a/apps/todo/apps/backend/src/db/schema/projects.schema.ts b/apps/todo/apps/backend/src/db/schema/projects.schema.ts
index f1b507042..b45b7e92f 100644
--- a/apps/todo/apps/backend/src/db/schema/projects.schema.ts
+++ b/apps/todo/apps/backend/src/db/schema/projects.schema.ts
@@ -21,7 +21,7 @@ export const projects = pgTable(
 	'projects',
 	{
 		id: uuid('id').primaryKey().defaultRandom(),
-		userId: uuid('user_id').notNull(),
+		userId: text('user_id').notNull(),
 		name: varchar('name', { length: 255 }).notNull(),
 		description: text('description'),
 		color: varchar('color', { length: 7 }).default('#3B82F6'),
diff --git a/apps/todo/apps/backend/src/db/schema/reminders.schema.ts b/apps/todo/apps/backend/src/db/schema/reminders.schema.ts
index fdb3f6e7f..63a1e9ce5 100644
--- a/apps/todo/apps/backend/src/db/schema/reminders.schema.ts
+++ b/apps/todo/apps/backend/src/db/schema/reminders.schema.ts
@@ -1,4 +1,4 @@
-import { pgTable, uuid, timestamp, varchar, integer, index } from 'drizzle-orm/pg-core';
+import { pgTable, uuid, text, timestamp, varchar, integer, index } from 'drizzle-orm/pg-core';
 import { tasks } from './tasks.schema';
 
 export type ReminderType = 'push' | 'email' | 'both';
@@ -11,7 +11,7 @@ export const reminders = pgTable(
 		taskId: uuid('task_id')
 			.notNull()
 			.references(() => tasks.id, { onDelete: 'cascade' }),
-		userId: uuid('user_id').notNull(),
+		userId: text('user_id').notNull(),
 
 		// Timing
 		minutesBefore: integer('minutes_before').notNull(),
diff --git a/apps/todo/apps/backend/src/db/schema/tasks.schema.ts b/apps/todo/apps/backend/src/db/schema/tasks.schema.ts
index 573937582..8d3596fa5 100644
--- a/apps/todo/apps/backend/src/db/schema/tasks.schema.ts
+++ b/apps/todo/apps/backend/src/db/schema/tasks.schema.ts
@@ -45,7 +45,7 @@ export const tasks = pgTable(
 	{
 		id: uuid('id').primaryKey().defaultRandom(),
 		projectId: uuid('project_id').references(() => projects.id, { onDelete: 'set null' }),
-		userId: uuid('user_id').notNull(),
+		userId: text('user_id').notNull(),
 		parentTaskId: uuid('parent_task_id'),
 
 		// Content