Enable experimental.cachedNavigations by default with cacheComponents (#94012)

Turns on `experimental.cachedNavigations` by default for projects
already on `cacheComponents`. Last of the Sparkle stack.

Tied to `cacheComponents` rather than flipped unconditionally because
`cachedNavigations` is a no-op without it, and the existing validation
already throws if you set it without `cacheComponents` — so an
unconditional flip would break every non-Cache-Components project.

<!-- NEXT_JS_LLM_PR -->

packages/next/src/server/config.ts

@@ -2184,6 +2184,23 @@ function enforceExperimentalFeatures(
     }
   }
 
+  // Enable cachedNavigations by default when cacheComponents is enabled.
+  // cachedNavigations relies on Cache Components rendering to do anything
+  // useful, so the two features are tied together: we only flip the default
+  // for projects that are already using Cache Components. Done silently —
+  // we don't report this through `configuredExperimentalFeatures` because
+  // (a) the existing `cacheComponents` env-var auto-enable above is also
+  // silent, and (b) reporting it would force every snapshot test that has
+  // `cacheComponents: true` to take on a new line.
+  // TODO: Remove this once cachedNavigations is unconditionally the default.
+  if (
+    config.cacheComponents &&
+    (config.experimental.cachedNavigations === undefined ||
+      (isDefaultConfig && !config.experimental.cachedNavigations))
+  ) {
+    config.experimental.cachedNavigations = true
+  }
+
   // TODO: Remove this once appNewScrollHandler is the default.
   if (
     process.env.__NEXT_EXPERIMENTAL_APP_NEW_SCROLL_HANDLER === 'true' &&