diff --git a/src/lib/actions/auth-guard.ts b/src/lib/actions/auth-guard.ts
new file mode 100644
index 0000000..8346053
--- /dev/null
+++ b/src/lib/actions/auth-guard.ts
@@ -0,0 +1,60 @@
+/**
+ * Authentication Guard for Server Actions
+ *
+ * Provides a reusable `withAuth` wrapper that handles Supabase client creation
+ * and user authentication, eliminating the repeated 4-line auth boilerplate
+ * across all Server Actions.
+ *
+ * @example
+ * ```ts
+ * // Before: repeated in every action
+ * const supabase = await createClient()
+ * const { data: { user }, error } = await supabase.auth.getUser()
+ * if (error || !user) throw new Error('Authentication required')
+ *
+ * // After: single-line wrapper
+ * export const deleteBoard = (id: string) =>
+ *   withAuth(async (supabase, user) => { ... })
+ * ```
+ */
+
+'use server'
+
+import type { SupabaseClient, User } from '@supabase/supabase-js'
+
+import { createClient } from '@/lib/supabase/server'
+import type { Database } from '@/lib/supabase/types'
+
+/**
+ * Wraps a Server Action with authentication, providing an authenticated
+ * Supabase client and the current user.
+ *
+ * @param action - Async function receiving authenticated supabase client and user
+ * @returns The action's return value, or throws if not authenticated
+ * @throws {Error} 'Authentication required' when user is not logged in
+ *
+ * @example
+ * export const createBoard = (name: string) =>
+ *   withAuth(async (supabase, user) => {
+ *     const { data, error } = await supabase
+ *       .from('board')
+ *       .insert({ name, user_id: user.id })
+ *     if (error) throw error
+ *     return data
+ *   })
+ */
+export async function withAuth<T>(
+  action: (supabase: SupabaseClient<Database>, user: User) => Promise<T>,
+): Promise<T> {
+  const supabase = await createClient()
+  const {
+    data: { user },
+    error: authError,
+  } = await supabase.auth.getUser()
+
+  if (authError || !user) {
+    throw new Error('Authentication required')
+  }
+
+  return action(supabase, user)
+}
diff --git a/src/lib/actions/board.ts b/src/lib/actions/board.ts
index 47de5bb..4df2e3f 100644
--- a/src/lib/actions/board.ts
+++ b/src/lib/actions/board.ts
@@ -9,6 +9,7 @@
 
 import * as Sentry from '@sentry/nextjs'
 
+import { withAuth } from '@/lib/actions/auth-guard'
 import type {
   StatusListDomain,
   RepoCardDomain,
@@ -221,23 +222,23 @@ export async function updateStatusList(
   if (updates.name !== undefined) statusListNameSchema.parse(updates.name)
   if (updates.color !== undefined) statusListColorSchema.parse(updates.color)
 
-  const supabase = await createClient()
-
-  const updateData: Record<string, unknown> = {}
-  if (updates.name !== undefined) updateData.name = updates.name
-  if (updates.color !== undefined) updateData.color = updates.color
-
-  const { error } = await supabase
-    .from('statuslist')
-    .update(updateData)
-    .eq('id', statusId)
-
-  if (error) {
-    Sentry.captureException(error, {
-      extra: { context: 'Update status list', statusId, updates },
-    })
-    throw new Error('Failed to update status list')
-  }
+  return withAuth(async (supabase) => {
+    const updateData: Record<string, unknown> = {}
+    if (updates.name !== undefined) updateData.name = updates.name
+    if (updates.color !== undefined) updateData.color = updates.color
+
+    const { error } = await supabase
+      .from('statuslist')
+      .update(updateData)
+      .eq('id', statusId)
+
+    if (error) {
+      Sentry.captureException(error, {
+        extra: { context: 'Update status list', statusId, updates },
+      })
+      throw new Error('Failed to update status list')
+    }
+  })
 }
 
 /**
@@ -284,23 +285,23 @@ export async function updateStatusListPosition(
   // Validate grid position (P2-4)
   gridPositionSchema.parse({ gridRow, gridCol })
 
-  const supabase = await createClient()
-
-  const { error } = await supabase
-    .from('statuslist')
-    .update({
-      grid_row: gridRow,
-      grid_col: gridCol,
-      updated_at: new Date().toISOString(),
-    })
-    .eq('id', id)
-
-  if (error) {
-    Sentry.captureException(error, {
-      extra: { context: 'Update status list position', id, gridRow, gridCol },
-    })
-    throw new Error('Failed to update column position')
-  }
+  return withAuth(async (supabase) => {
+    const { error } = await supabase
+      .from('statuslist')
+      .update({
+        grid_row: gridRow,
+        grid_col: gridCol,
+        updated_at: new Date().toISOString(),
+      })
+      .eq('id', id)
+
+    if (error) {
+      Sentry.captureException(error, {
+        extra: { context: 'Update status list position', id, gridRow, gridCol },
+      })
+      throw new Error('Failed to update column position')
+    }
+  })
 }
 
 /**
@@ -319,23 +320,23 @@ export async function swapStatusListPositions(
   id1: string,
   id2: string,
 ): Promise<void> {
-  const supabase = await createClient()
+  return withAuth(async (supabase) => {
+    const { error } = await supabase.rpc('swap_statuslist_positions', {
+      id_a: id1,
+      id_b: id2,
+    })
 
-  const { error } = await supabase.rpc('swap_statuslist_positions', {
-    id_a: id1,
-    id_b: id2,
+    if (error) {
+      Sentry.captureException(error, {
+        extra: {
+          context: 'Swap status list positions (RPC)',
+          id1,
+          id2,
+        },
+      })
+      throw new Error('Failed to swap column positions')
+    }
   })
-
-  if (error) {
-    Sentry.captureException(error, {
-      extra: {
-        context: 'Swap status list positions (RPC)',
-        id1,
-        id2,
-      },
-    })
-    throw new Error('Failed to swap column positions')
-  }
 }
 
 /**
@@ -352,26 +353,26 @@ export async function swapStatusListPositions(
 export async function batchUpdateStatusListPositions(
   updates: Array<{ id: string; gridRow: number; gridCol: number }>,
 ): Promise<void> {
-  const supabase = await createClient()
+  return withAuth(async (supabase) => {
+    // Atomic batch update via PostgreSQL RPC — all updates succeed or all fail
+    const { error } = await supabase.rpc('batch_update_statuslist_positions', {
+      p_updates: updates.map(({ id, gridRow, gridCol }) => ({
+        id,
+        grid_row: gridRow,
+        grid_col: gridCol,
+      })),
+    })
 
-  // Atomic batch update via PostgreSQL RPC — all updates succeed or all fail
-  const { error } = await supabase.rpc('batch_update_statuslist_positions', {
-    p_updates: updates.map(({ id, gridRow, gridCol }) => ({
-      id,
-      grid_row: gridRow,
-      grid_col: gridCol,
-    })),
+    if (error) {
+      Sentry.captureException(error, {
+        extra: {
+          context: 'Batch update status list positions (RPC)',
+          updateCount: updates.length,
+        },
+      })
+      throw new Error('Failed to update column positions')
+    }
   })
-
-  if (error) {
-    Sentry.captureException(error, {
-      extra: {
-        context: 'Batch update status list positions (RPC)',
-        updateCount: updates.length,
-      },
-    })
-    throw new Error('Failed to update column positions')
-  }
 }
 
 // ========================================
@@ -432,23 +433,28 @@ export async function updateRepoCardPosition(
   statusId: string,
   order: number,
 ): Promise<void> {
-  const supabase = await createClient()
-
-  const { error } = await supabase
-    .from('repocard')
-    .update({
-      status_id: statusId,
-      order: order,
-      updated_at: new Date().toISOString(),
-    })
-    .eq('id', cardId)
-
-  if (error) {
-    Sentry.captureException(error, {
-      extra: { context: 'Update repo card position', cardId, statusId, order },
-    })
-    throw new Error('Failed to update repo card position')
-  }
+  return withAuth(async (supabase) => {
+    const { error } = await supabase
+      .from('repocard')
+      .update({
+        status_id: statusId,
+        order: order,
+        updated_at: new Date().toISOString(),
+      })
+      .eq('id', cardId)
+
+    if (error) {
+      Sentry.captureException(error, {
+        extra: {
+          context: 'Update repo card position',
+          cardId,
+          statusId,
+          order,
+        },
+      })
+      throw new Error('Failed to update repo card position')
+    }
+  })
 }
 
 /**
@@ -458,26 +464,26 @@ export async function updateRepoCardPosition(
 export async function batchUpdateRepoCardOrders(
   updates: Array<{ id: string; statusId: string; order: number }>,
 ): Promise<void> {
-  const supabase = await createClient()
+  return withAuth(async (supabase) => {
+    // Atomic batch update via PostgreSQL RPC — all updates succeed or all fail
+    const { error } = await supabase.rpc('batch_update_repocard_orders', {
+      p_updates: updates.map(({ id, statusId, order }) => ({
+        id,
+        status_id: statusId,
+        order,
+      })),
+    })
 
-  // Atomic batch update via PostgreSQL RPC — all updates succeed or all fail
-  const { error } = await supabase.rpc('batch_update_repocard_orders', {
-    p_updates: updates.map(({ id, statusId, order }) => ({
-      id,
-      status_id: statusId,
-      order,
-    })),
+    if (error) {
+      Sentry.captureException(error, {
+        extra: {
+          context: 'Batch update repo card orders (RPC)',
+          updateCount: updates.length,
+        },
+      })
+      throw new Error('Failed to update some repo cards')
+    }
   })
-
-  if (error) {
-    Sentry.captureException(error, {
-      extra: {
-        context: 'Batch update repo card orders (RPC)',
-        updateCount: updates.length,
-      },
-    })
-    throw new Error('Failed to update some repo cards')
-  }
 }
 
 // ========================================
@@ -615,16 +621,16 @@ export async function updateBoardPositions(
  * Delete a board
  */
 export async function deleteBoard(boardId: string): Promise<void> {
-  const supabase = await createClient()
-
-  const { error } = await supabase.from('board').delete().eq('id', boardId)
-
-  if (error) {
-    Sentry.captureException(error, {
-      extra: { context: 'Delete board', boardId },
-    })
-    throw new Error('Failed to delete board')
-  }
+  return withAuth(async (supabase) => {
+    const { error } = await supabase.from('board').delete().eq('id', boardId)
+
+    if (error) {
+      Sentry.captureException(error, {
+        extra: { context: 'Delete board', boardId },
+      })
+      throw new Error('Failed to delete board')
+    }
+  })
 }
 
 /**
@@ -634,19 +640,19 @@ export async function updateBoard(
   boardId: string,
   updates: { name?: string },
 ): Promise<void> {
-  const supabase = await createClient()
-
-  const { error } = await supabase
-    .from('board')
-    .update(updates)
-    .eq('id', boardId)
-
-  if (error) {
-    Sentry.captureException(error, {
-      extra: { context: 'Update board', boardId, updates },
-    })
-    throw new Error('Failed to update board')
-  }
+  return withAuth(async (supabase) => {
+    const { error } = await supabase
+      .from('board')
+      .update(updates)
+      .eq('id', boardId)
+
+    if (error) {
+      Sentry.captureException(error, {
+        extra: { context: 'Update board', boardId, updates },
+      })
+      throw new Error('Failed to update board')
+    }
+  })
 }
 
 // ========================================