diff --git a/server/src/auth.js b/server/src/auth.js
index 55b538c..7a655ba 100644
--- a/server/src/auth.js
+++ b/server/src/auth.js
@@ -1,7 +1,7 @@
 import crypto from 'node:crypto'
 import bcrypt from 'bcryptjs'
 import { getCookie, setCookie, deleteCookie } from 'hono/cookie'
-import { createSession, getSession, deleteSession, createUser, getUserByUsername, getUserById, updateUser } from './db.js'
+import { createSession, getSession, deleteSession, renewSessionIfDue, createUser, getUserByUsername, getUserById, updateUser } from './db.js'
 import { config } from './config.js'
 
 const COOKIE_NAME = 'helios_session'
@@ -143,6 +143,18 @@ export function requireAuth(db) {
   return async (c, next) => {
     const session = sessionIdFromCookie(db, c)
     if (!session) return c.json({ error: 'no autorizado' }, 401)
+    // Expiración deslizante (#130): si la sesión queda por debajo de la mitad
+    // del TTL, extender su vida y re-emitir la cookie con maxAge fresco.
+    if (renewSessionIfDue(db, session.id, config.sessionTtlMs)) {
+      const isHttps = c.req.header('x-forwarded-proto') === 'https' || c.req.url.startsWith('https://')
+      setCookie(c, COOKIE_NAME, `${session.id}.${sign(db, session.id)}`, {
+        httpOnly: true,
+        sameSite: 'Lax',
+        secure: isHttps,
+        maxAge: Math.floor(config.sessionTtlMs / 1000),
+        path: '/',
+      })
+    }
     c.set('userId', session.userId)
     return next()
   }
diff --git a/server/src/db.js b/server/src/db.js
index 3ed020f..19314ef 100644
--- a/server/src/db.js
+++ b/server/src/db.js
@@ -295,6 +295,19 @@ export function deleteSession(db, id) {
   db.prepare('DELETE FROM sessions WHERE id = ?').run(id)
 }
 
+// Expiración deslizante: si a la sesión le queda menos de la mitad del TTL,
+// extiende expires_at un TTL completo desde ahora. Un usuario activo no pierde
+// la sesión en el límite fijo. Devuelve true si renovó (el caller re-emite la
+// cookie con maxAge fresco).
+export function renewSessionIfDue(db, id, ttlMs) {
+  const row = db.prepare('SELECT expires_at FROM sessions WHERE id = ?').get(id)
+  if (!row) return false
+  const now = Date.now()
+  if (row.expires_at - now >= ttlMs / 2) return false
+  db.prepare('UPDATE sessions SET expires_at = ? WHERE id = ?').run(now + ttlMs, id)
+  return true
+}
+
 export function cleanSessions(db) {
   db.prepare('DELETE FROM sessions WHERE expires_at < ?').run(Date.now())
   const oneHourAgo = Date.now() - 3600 * 1000
diff --git a/server/test/auth.test.js b/server/test/auth.test.js
index 738e77f..7777fbd 100644
--- a/server/test/auth.test.js
+++ b/server/test/auth.test.js
@@ -1,7 +1,7 @@
 import { describe, it, expect, beforeEach } from 'vitest'
 import Database from 'better-sqlite3'
 import { initSchema, getUserByUsername } from '../src/db.js'
-import { loginRateLimited, registerLoginFail, loginOk, registerUser, handleLogin, ensureBootstrapAdmin, changeOwnPassword } from '../src/auth.js'
+import { loginRateLimited, registerLoginFail, loginOk, registerUser, handleLogin, ensureBootstrapAdmin, changeOwnPassword, requireAuth } from '../src/auth.js'
 
 function mockContext(ip, cookie) {
   const headers = new Headers()
@@ -13,6 +13,7 @@ function mockContext(ip, cookie) {
       raw: { headers },
     },
     header: () => {},
+    set: () => {},
     res: { headers: { append: () => {} } },
     env: {},
   }
@@ -112,3 +113,55 @@ describe('rate-limit de login (SQLite)', () => {
     expect(loginRateLimited(db, b)).toBe(false)
   })
 })
+
+describe('expiración deslizante de sesiones (#130)', () => {
+  const TTL_MS = 30 * 24 * 3600 * 1000
+
+  async function loginCapturingCookie(username, password) {
+    const c = mockContext('1.1.1.1')
+    const captured = []
+    c.header = (k, v) => captured.push([k, v])
+    const res = await handleLogin(db, c, { username, password })
+    const setCookie = captured.find(([k]) => k === 'Set-Cookie')?.[1] || ''
+    const cookie = setCookie.split(';')[0] // helios_session=<id>.<sig>
+    return { res, cookie }
+  }
+
+  it('sesión por debajo de la mitad del TTL: renueva expires_at y re-emite cookie', async () => {
+    await registerUser(db, 'slide', 'secreto123')
+    const { cookie } = await loginCapturingCookie('slide', 'secreto123')
+    expect(cookie).toMatch(/^helios_session=.+\..+/)
+    const sessionId = cookie.split('=')[1].split('.')[0]
+    const soon = Date.now() + 10 * 24 * 3600 * 1000 // 10 días < 15 (mitad del TTL)
+    db.prepare('UPDATE sessions SET expires_at = ? WHERE id = ?').run(soon, sessionId)
+
+    const c2 = mockContext('1.1.1.1', cookie)
+    const captured = []
+    c2.header = (k, v) => captured.push([k, v])
+    let nextCalled = false
+    await requireAuth(db)(c2, async () => { nextCalled = true })
+    expect(nextCalled).toBe(true)
+    const renewed = captured.find(([k]) => k === 'Set-Cookie')?.[1] || ''
+    expect(renewed).toMatch(/^helios_session=.+\..+/)
+    expect(renewed).toMatch(/Max-Age=2592000/)
+    const after = db.prepare('SELECT expires_at FROM sessions WHERE id = ?').get(sessionId).expires_at
+    expect(after).toBeGreaterThan(Date.now() + 25 * 24 * 3600 * 1000)
+  })
+
+  it('sesión por encima de la mitad del TTL: no renueva ni re-emite cookie', async () => {
+    await registerUser(db, 'fresh', 'secreto123')
+    const { cookie } = await loginCapturingCookie('fresh', 'secreto123')
+    const sessionId = cookie.split('=')[1].split('.')[0]
+    const fresh = Date.now() + 20 * 24 * 3600 * 1000 // 20 días > 15
+    db.prepare('UPDATE sessions SET expires_at = ? WHERE id = ?').run(fresh, sessionId)
+
+    const c2 = mockContext('1.1.1.1', cookie)
+    const captured = []
+    c2.header = (k, v) => captured.push([k, v])
+    let nextCalled = false
+    await requireAuth(db)(c2, async () => { nextCalled = true })
+    expect(nextCalled).toBe(true)
+    expect(captured.find(([k]) => k === 'Set-Cookie')).toBeUndefined()
+    expect(db.prepare('SELECT expires_at FROM sessions WHERE id = ?').get(sessionId).expires_at).toBe(fresh)
+  })
+})