【后端接口】宠物技能书：技能槽解锁与顶替规则

local SKILL_SLOT_MAX = 4
function PetSkill.unlockSlot(actor, petIdx)
    local pet = actor:GetPet(petIdx)
    local unlocked = pet.skillSlotCount or 1
    if unlocked >= SKILL_SLOT_MAX then return false, "技能槽已满" end
    if not actor:TakeItemByName("技能槽钥匙", 1) then return false, "缺少钥匙" end
    pet.skillSlotCount = unlocked + 1
    sendmsg(actor, 1, "技能槽解锁成功，当前 " .. (unlocked + 1) .. " 个槽位")
    return true
end

function PetSkill.learn(actor, petIdx, bookId)
    local pet = actor:GetPet(petIdx)
    local book = SKILL_BOOK_DEF[bookId]
    local emptySlot = PetSkill.findEmpty(pet)
    if emptySlot then
        pet.skills[emptySlot] = book.skillId
    else
        -- 满槽时随机顶替一个技能
        local replaceIdx = math.random(1, #pet.skills)
        local old = pet.skills[replaceIdx]
        pet.skills[replaceIdx] = book.skillId
        sendmsg(actor, 1, old .. " 被顶替为 " .. book.skillId)
    end
    actor:TakeItemByName(bookId, 1)
    PetSkill.recalc(pet)
    return true
end