What rules determine whether "could" can be ambiguous in some sentences?

Solution 1:

"We didn't know that we could get caught in the trap, unfortunately."

"We could get caught in that trap, if we're not careful."

It appears to allow the same two interpretations as when talking about lifting rocks. Could (to be able) can be used instead of would (to will), to distinguish between something actually occurring vs. the potential for something to occur.

Solution 2:

The passive construction, in the example the get-passive, is not confined to the first sense you give.

In those days, there was tighter security around the gardens in the evening. We could get caught if we weren't very careful to stay away from the lit areas.

But the 'might be caught [in the future]' reading is the default one, and a rephrasing more likely with the 'past-state/occurrence' sense. This is especially true with minimal context. But some context, not necessarily in the same sentence, is almost mandatory in all these cases. With the 'past-state/occurrence' sense:

It was dangerous as well as exciting trespassing in the gardens. We might get caught. And then we would be without fail grounded for weeks.