The San Francisco 49ers on Thursday placed offensive tackle Andre Dillard on season-ending injured reserve, three days after the swing-tackle candidate was activated from the physically-unable-to-perform list following offseason ankle surgery. His move to IR leaves Spencer Burford and Austen Pleasants as the club’s primary backup options at tackle. The roster decision preceded a two-hour joint practice with the Las Vegas Raiders in Henderson, Nevada, where injuries continued to mount. Defensive end Nick Bosa sat out with neck soreness, and rookie defensive tackle CJ West was diagnosed with a hyperextended left knee— the second first-year lineman in as many weeks to suffer that injury after Mykel Williams. To bolster depth, San Francisco signed edge rushers William Bradley-King and Demone Harris and waived defensive tackle Michael Dwumfour. Despite a skeletal defensive front and temperatures that touched 98°F, the 49ers’ offense controlled much of the 15-period session. Quarterback Brock Purdy split the safeties for a long touchdown to first-round receiver Ricky Pearsall and connected repeatedly with running back Christian McCaffrey, who logged eight carries and six catches in what coach Kyle Shanahan called a sign he is “ready for the season.” Practice ended without the fights Raiders pass rusher Maxx Crosby had predicted, thanks in part to interventions by left tackle Trent Williams and Raiders coach Pete Carroll. Purdy is expected to start Saturday’s preseason game in Las Vegas, while the club assesses its shrinking depth chart in the trenches.