How can one reconcile contentment with what Allah Almighty has decreed with unfulfilled worldly hopes and demands, as well as with planning, striving, and toiling in the pursuit of sustenance and reliance upon Allah?

Reliance on Allah does not contradict taking precautions and means. The Prophet, peace and blessings be upon him, the master of those who rely on Allah, used to take precautions, and he commanded that the camel be tied and then to rely on Allah. The reality of reliance is an action of the heart, which is depending on Allah and trusting in Him, and knowing His Oneness in bringing benefit and harm. This action of the heart must influence the actions of the limbs by taking precautions. Abandoning precautions is a sign of helplessness, not reliance. A servant's management of their livelihood and their striving to earn provision is a form of taking precautions. What is blameworthy is the heart's attachment to management and abandoning reliance on Allah. When what one intended does not materialize, one should recall the preordainment of destiny and surrender to Allah's will. Allah's management for His servant is better than the servant's management for themselves, and this leads to contentment and tranquility. Mere worldly aspirations do not negate contentment, and when they do not materialize, one must believe that the affliction is by Allah's permission, and whoever believes in Allah, He guides their heart and compensates them with good.