feat(infra/clock): injectable Clock with Real and Fake implementations

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
+}