SAN FRANCISCO — The Cubs might not have all the answers they want for their bullpen as they approach next week’s trade deadline — especially after their 17th blown save in a loss Monday to the Giants.

But their rotation plans for the stretch run appear to be coming into focus as left-hander Cole Hamels (oblique strain) looked healthy in a minor-league rehab start Tuesday for Class AAA Iowa.

Hamels walked three in a scoreless 2„-inning start on a strict pitch limit. He pitched at his usual velocity, topping out at 93 mph, and his two strikeouts included one of Hernan Perez (8-for-16 lifetime in the majors against Hamels). He threw 35 pitches.

Barring a setback in how his body responds Wednesday or during a between-starts bullpen session Thursday, he could be on track to rejoin the rotation Sunday in Milwaukee.

That would put the Cubs’ opening five back together again, healthy, for the first time since the second week of June.

“We’ll just see how he feels [Wednesday] and make the next evaluation after that,” manager Joe Maddon said. “Hopefully, it’ll be sooner rather than later, but after he throws, we’ll know more.”

Hamels was one of the hottest pitchers in the majors in June (1.22 ERA) when he left his June 28 start after one inning because of the injury.

Catch 2-3?

The Cubs expect to activate Willson Contreras (foot) from the injured list Wednesday for Jon Lester’s start against the Giants and likely will carry three catchers on the roster at that point — as they have done down the stretch in recent years.

Maddon said such a decision hasn’t been “finalized” yet.

But, he said, “We have talked about it. There’s different ways to incorporate that.”

Using defensive whiz Martin Maldonado as the truer backup allows the Cubs to get Victor Caratini’s switch-hitting bat in the lineup at the same time as Contreras. Caratini and Contreras are converted players who can play other positions — Caratini more notably at corner infield spots and Contreras in left field.

“We’re pretty firm there; I’ll stack that up against anybody,” Maddon said of his catching corps. “That’s a good position to be stacked up with. Because when something happens there, you scramble.”

The Cubs expected to decide after the game Tuesday night whether they can get by with one fewer pitcher in the bullpen when Contreras is activated.

Russell reboot

After a series of mental lapses over the weekend, second baseman Addison Russell was out of the lineup for the third consecutive game.

It’s his longest stretch on the bench since returning from his domestic-violence suspension in May that didn’t involve his early-June hand injury.

“That’s what it’s all about now — we’ve really got to get beyond the mental mistakes,” Maddon said of Russell, who admittedly was missing signs and might have been in need of a review.

“He’s heard it for a couple of years. It’s not just happening on July whatever-this-is in 2019. It’s been an ongoing process, with him and everybody else to make sure we get all this stuff.”

Impressive rookie Robel Garcia got the start at second again.

“It gives [Russell] a chance to reboot a little bit, think about it a little bit, slow it down a little bit, so he can grasp all this stuff,” Maddon said.

Roster move

The day after making his second start filling in for Hamels, right-hander Alec Mills was optioned back to Iowa before the game against the Giants.

Left-hander Tim Collins was called up to join the bullpen.