Ok just a quick simple question and if you can tell me where the source is that would be great. Lets say our champion Alan is attacked and reduced to -7HP, our cleric casts a Cure light wounds on Alan and he gains 6HP would Alan be at a total HP of -1HP or 6HP?
-1. (Rysky is correct)
But there is an advantage here, a character at -7hp is probably bleeding out (losing 1hp/round). After healing them up to -1 hp they stabilise (stop losing 1hp/round) & assuming nothing comes to kill them they will eventually regain that 1 hp wake up again.
I don't understand where you would need the source from. Magical healing just takes the total amount healed and adds it to your HP total. It's basic math with negative numbers. -7 + 6 = -1. Negative HP isn't suddenly treated as 0 for magical healing.
Pages 189-191 of the core rulebook describe injury and healing. Note that the rules describe what happens with any healing, if a character is healed to 0 hit points or above 0, because it doesn't always succeed.