next.js

7b6f9536 - Enable experimental.appShells by default with cacheComponents (#94516)

Enable experimental.appShells by default with cacheComponents (#94516) Turns on `experimental.appShells` by default for projects already on `cacheComponents`, unless explicitly disabled. Thanks to the preceding router-act change, most prefetch tests pass unchanged once App Shells is enabled. A few tests are genuinely coupled to the non-App-Shells behavior — they assert on per-link or runtime prefetch responses that App Shells instead defers to navigation — so the fixtures for those tests set `appShells` back to `false`. I'll address those in follow-ups. <!-- NEXT_JS_LLM_PR -->