I've nearly got sanity cache revalidation via tags working but I'm getting a strange error after the first deployless content update happens:

Unhandled Promise Rejection     {"errorType":"Runtime.UnhandledPromiseRejection","errorMessage":"Error: EROFS: read-only file system, mkdir '/var/task/apps/next-marketing-site/public'","reason":{"errorType":"Error","errorMessage":"EROFS: read-only file system, mkdir '/var/task/apps/next-marketing-site/public'","code":"EROFS","errno":-30,"syscall":"mkdir","path":"/var/task/apps/next-marketing-site/public","stack":["Error: EROFS: read-only file system, mkdir '/var/task/apps/next-marketing-site/public'"]},"promise":{},"stack":["Runtime.UnhandledPromiseRejection: Error: EROFS: read-only file system, mkdir '/var/task/apps/next-marketing-site/public'","    at process.<anonymous> (file:///var/runtime/index.mjs:1276:17)","    at process.emit (node:events:529:35)","    at emit (node:internal/process/promises:149:20)","    at processPromiseRejections (node:internal/process/promises:283:27)","    at process.processTicksAndRejections (node:internal/process/task_queues:96:32)"]}
Unknown application error occurred
Runtime.Unknown

Does anyone have any insight here?