diff --git a/internal/infra/clock/clock.go b/internal/infra/clock/clock.go
new file mode 100644
index 0000000..9ad7b64
--- /dev/null
+++ b/internal/infra/clock/clock.go
@@ -0,0 +1,18 @@
+// Package clock provides an injectable time source. Production code uses Real();
+// tests use NewFake(t) to make time-based logic deterministic.
+package clock
+
+import "time"
+
+// Clock is the abstraction over the system clock. Implementations must be
+// safe for concurrent use.
+type Clock interface {
+	Now() time.Time
+}
+
+type realClock struct{}
+
+// Real returns a Clock backed by time.Now.
+func Real() Clock { return realClock{} }
+
+func (realClock) Now() time.Time { return time.Now() }
diff --git a/internal/infra/clock/clock_test.go b/internal/infra/clock/clock_test.go
new file mode 100644
index 0000000..6d26022
--- /dev/null
+++ b/internal/infra/clock/clock_test.go
@@ -0,0 +1,54 @@
+package clock
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestRealClock_Now(t *testing.T) {
+	c := Real()
+	now := c.Now()
+	assert.WithinDuration(t, time.Now(), now, time.Second)
+}
+
+func TestFakeClock_NowReturnsSetTime(t *testing.T) {
+	t0 := time.Date(2026, 5, 5, 10, 0, 0, 0, time.UTC)
+	c := NewFake(t0)
+	assert.Equal(t, t0, c.Now())
+}
+
+func TestFakeClock_Advance(t *testing.T) {
+	t0 := time.Date(2026, 5, 5, 10, 0, 0, 0, time.UTC)
+	c := NewFake(t0)
+	c.Advance(2 * time.Hour)
+	assert.Equal(t, t0.Add(2*time.Hour), c.Now())
+}
+
+func TestFakeClock_AdvanceConcurrent(t *testing.T) {
+	c := NewFake(time.Now())
+	done := make(chan struct{})
+	go func() {
+		for i := 0; i < 1000; i++ {
+			c.Advance(time.Microsecond)
+		}
+		close(done)
+	}()
+	for i := 0; i < 1000; i++ {
+		_ = c.Now()
+	}
+	<-done
+}
+
+func TestFakeClock_Set(t *testing.T) {
+	c := NewFake(time.Date(2026, 5, 5, 10, 0, 0, 0, time.UTC))
+	t1 := time.Date(2027, 1, 1, 0, 0, 0, 0, time.UTC)
+	c.Set(t1)
+	assert.Equal(t, t1, c.Now())
+}
+
+var _ Clock = (*realClock)(nil)
+var _ Clock = (*FakeClock)(nil)
+var _ = require.New // keep import live; helper used by other packages
diff --git a/internal/infra/clock/fake.go b/internal/infra/clock/fake.go
new file mode 100644
index 0000000..b72f6d6
--- /dev/null
+++ b/internal/infra/clock/fake.go
@@ -0,0 +1,38 @@
+package clock
+
+import (
+	"sync"
+	"time"
+)
+
+// FakeClock is a controllable Clock for tests. Construct with NewFake; advance
+// time with Advance; jump to a specific time with Set. Safe for concurrent use.
+type FakeClock struct {
+	mu  sync.Mutex
+	now time.Time
+}
+
+// NewFake returns a FakeClock initialized to t.
+func NewFake(t time.Time) *FakeClock {
+	return &FakeClock{now: t}
+}
+
+func (c *FakeClock) Now() time.Time {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.now
+}
+
+// Advance moves the clock forward by d.
+func (c *FakeClock) Advance(d time.Duration) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.now = c.now.Add(d)
+}
+
+// Set jumps the clock to t.
+func (c *FakeClock) Set(t time.Time) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.now = t
+}