I'm aware of a practical framework that social movements along other kinds of organizations can use. There are different versions of this framework, for example, in start-up culture. I'm going to use the version I'm familiar with from social movements. I haven't taken the time yet to look up in the OHSM if this is a framework widely and effectively employed by social movements overall.

A mission is what a movement seeks to ultimately accomplish. It's usually the very thing that inspires the creation of a movement. It's so vast it often goes unstated. For example, the global climate change movement has a mission of 'stopping the catastrophic impact of climate change'. Yet that's so obvious it's not like at meetings environmentalists need to establish the fact they've gathered is to stop climate change. It's common knowledge.

The mission of effective altruism is, more or less, "to do the most good". Cause areas exist in other movements similarly broad to effective altruism, but they're not the same thing as a mission. The cause area someone focuses on will be due to their perception of how to do the most good, or their evaluation of how they can personally do the most good. So each cause area in EA represents a different interpretation of how to do the most good, as opposed to being a mission or goal in and of itself.

Goals are the factors a movement believes are the milestones to be completed to complete a mission. The movement believes each goal by itself is a necessary factor in completing the mission, and that the full set of goals combined fulfills the sufficient condition to complete the mission. So for the examples you gave, the set up would be as follows:

Cause: Global poverty alleviation

Mission: End extreme global poverty.

Goals: Improve trade and foreign aid.

Cause: Factory Farming

Mission: End factory farming.

Goals: Gain popular support for legal and corporate reforms.

Cause: Existential risk reduction

Mission: Avoid extinction.

Goals: MItigate extinction risk from AI, pandemics, and nuclear weapons.

Cause: Climate Change

Mission: Address climate change.

Goals: Pursue cap-and-trade, carbon taxes and clean tech

Cause: Wild Animal Welfare

Mission: Improve the welfare of wild animals.

Goals: Do research to figure out how to do that.

Having laid it out like this, it’s easier to see (1), why a “cause” isn’t a “mission” or “goal”; and, (2), how this framework can be crucial for clarifying what a movement is about at the highest level of abstraction. For example, while the mission of the cause of ‘global poverty alleviation’ is ‘eliminate extreme global poverty’, the goals of systemic international policy reform don’t match up to what EA primarily focuses on to alleviate global poverty, which is a lot of fundraising, philanthropy, research and field activity, focused on global health, not public policy. Your framing assumes ‘existential risk reduction’ refers to ‘extinction risk’, but ‘existential risk’ has been defined as long-term outcomes that permanently and irreversibly alter the trajectory of life, humanity, intelligence and civilization on Earth or in the universe. That includes extinction risks but can also include risks of astronomical suffering. If nitpicking the difference between missions and goals seems like needless semantics, remember that because EA as a community doesn’t have a clear and common framework for defining these things, we’ve been debating and discussing them for years.

Below goals are strategy and tactics. The strategy is the framework a movement employs for how to achieve the goals. Tactics are the set of concrete, action-oriented steps the movement takes to implement the strategy. The mission is to the goals as the strategy is to the tactics. There is more to get into about strategy and tactics, but this is too abstract a discussion to get into that. For figuring out what an effective social movement is, and how it becomes effective, it’s enough to start thinking in terms of mission and goals.