Pathfinder 1E – How to Magically Heal Summons and Eidolons?

Funnily enough, works by RAW.

There is no prohibition of magical healing in construct traits, though some constructs are explicitly immune to magic except select few effects.

There is also no prohibition in the heal spell.

Technically, you can do it, but expect a heavy book thrown by your DM. He will also probably houserule it away, at least I personally would.

Note:

Can't remember anything on that in 3.5 either, though the description of Warforged contrasts the possibility of both special and positive-energy healing (emphasis mine):

As living constructs, warforged can be affected by spells that target living creatures as well as by those that target constructs. Damage dealt to a warforged can be healed by a cure light wounds spell or a repair light damage spell, for example, and a warforged is vulnerable to disable construct and harm. However, spells from the healing subschool and supernatural abilities that cure hit point damage or ability damage provide only half their normal effect to a warforged.

That leads one to the implication of impossibility of positive-energy based healing for a regular construct, even if it is not stated anywhere.

While a summoned monster does initially act on the turn of the person summoning, it has its own initiative track. If later it delays its action, or uses a spell or ability that changes its initiative, its initiative changes to a different count than the summoner's (or vice versa).

The rule you're quoting only says that it gets to act on the turn it was summoned, on the same initiative as the summoner, not that their initiative can't change individually later on.