fix: distinguish task deadlines from child operation timeouts

internal/handler/task_deadline.go

@@ -0,0 +1,13 @@
+package handler
+
+import (
+	"context"
+	"errors"
+)
+
+// taskDeadlineExceeded distinguishes the task's deadline from a child operation's
+// timeout. A run error (including a cancellation cause) may wrap DeadlineExceeded
+// while the task itself still has time remaining; it must not exhaust the task budget.
+func taskDeadlineExceeded(taskCtx context.Context) bool {
+	return taskCtx != nil && errors.Is(taskCtx.Err(), context.DeadlineExceeded)
+}