chore: log a failed route-cache clear and spell out the read-only key rollback

The route-cache clear stays non-fatal but warns when it fails for any
reason other than a missing build id or cache. The api-key-read-only flag
says to revoke or replace read-only keys before rolling back.

Author: waleedlatif1

apps/sim/lib/core/config/feature-flags.ts

@@ -79,7 +79,7 @@ const FEATURE_FLAGS = {
   },
   'api-key-read-only': {
     description:
-      'Allow creating read-only API keys. Turn on only after every pod runs a release that enforces key access, since older pods treat a read-only key as full access. Before rolling back below the release that added read-only keys, turn this off first: that older code also serves every existing read-only key as full access. Enforcement of existing read-only keys never depends on this flag. Global; disabled by default.',
+      'Allow creating read-only API keys. Turn on only after every pod runs a release that enforces key access, since older pods treat a read-only key as full access. Before rolling back below the release that added read-only keys, turn this off and revoke or replace every existing read-only key: turning the flag off only stops new ones, and that older code serves existing read-only keys as full access. Enforcement of existing read-only keys never depends on this flag. Global; disabled by default.',
     fallback: 'API_KEY_READ_ONLY',
   },
   'mothership-model-selector': {

apps/sim/lib/core/utils/route-cache.ts

@@ -1,13 +1,18 @@
 import { readdir, readFile, rm, writeFile } from 'node:fs/promises'
 import { join } from 'node:path'
+import { createLogger } from '@sim/logger'
+import { getErrorMessage } from '@sim/utils/errors'
+
+const logger = createLogger('RouteCache')
 
 const BUILD_MARKER = '.build-id'
 
 /**
  * Clears Next's route cache when it was written by a different build. Its keys carry no build
  * id, and the image declares the directory a volume, so a container recreated from a newer
  * image would otherwise serve pages the old build rendered, pointing at chunks it no longer
- * ships. Never throws: a cache that cannot be read or cleared is left to Next.
+ * ships. Never throws: a cache that cannot be read or cleared is left to Next, with a warning
+ * unless there was simply no build id or cache to read.
  */
 export async function clearRouteCacheFromOtherBuild(nextDirectory: string): Promise<void> {
   const routeCache = join(nextDirectory, 'server', 'route-cache')
@@ -21,5 +26,10 @@ export async function clearRouteCacheFromOtherBuild(nextDirectory: string): Prom
       entries.map((entry) => rm(join(routeCache, entry), { recursive: true, force: true }))
     )
     await writeFile(join(routeCache, BUILD_MARKER), buildId)
-  } catch {}
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException).code === 'ENOENT') return
+    logger.warn('Could not clear the route cache from an earlier build', {
+      error: getErrorMessage(error),
+    })
+  }
 }