Remote functions deploy (`rayfin up functions deploy`) returns 404 "Endpoint not found", is remote functions hosting supported in the current preview?

Summary

rayfin up functions deploy consistently fails with a 404 at the deploy endpoint. Before assuming a bug, I want to confirm whether remote functions deployment to a Fabric data app is actually supported in the current preview, or whether functions are local-host-only for now. The CLI labels the command [EXPERIMENTAL], which makes me suspect the latter.

Environment

• @microsoft/rayfin-cli 1.33.1
• Deploying to a Fabric workspace on a Fabric Trial capacity (Australia East)
• WSL2 Ubuntu,
• Tenant has "Fabric Apps (preview)" enabled

What works

The rest of the deploy is fully successful:

• Rayfin item created, runtime settings applied (auth, data, storage)
• Database configuration generated and applied (13 entities, all tables created)
• Static content built and deployed, app is live and reachable
• Functions build, typecheck, and package correctly (14 function(s), 11 files)

What fails

rayfin up functions deploy (and the functions step of rayfin up) fails after packaging:

🚀 Deploying functions...
⏳ Deploy endpoint not ready (404), retrying in 2s... (1/5)
... (retries 4s, 8s, 16s) ...
❌ Functions deploy failed (404): {"code":"InternalError", ... "Response Content = '{\"error\":\"Endpoint not found\"}'", "httpStatusCode":404 ...}

Target endpoint:

https://api.fabric.microsoft.com/v1/workspaces/<ws>/appBackends/<item>/__private/functions/deploy

What I've ruled out

• Not provisioning lag: identical 404 across attempts spanning ~1 hour.
• Not a packaging/build problem: packaging reports success (14 functions) before the deploy call.
• Not the missing runtime package: @microsoft/fabric-user-data-functions resolves from the bundled .tgz after functions init --force; TypeScript compilation succeeds.
• Not auth: the step authenticates successfully before the 404.
• The __private/ path segment and the [EXPERIMENTAL] label on rayfin up functions both suggest this endpoint may not be generally available yet.

Questions

1. Is remote functions deployment to a Fabric data app supported in the current preview, or are functions intended to run only via the local host (rayfin dev functions apply) for now?
2. If supported, is there a prerequisite I've missed, e.g. a tenant/capacity setting, or a capability that requires paid Fabric capacity rather than a trial?
3. Is the __private/functions/deploy endpoint expected to exist on a freshly deployed item, and if so, is there a way to verify/trigger its provisioning?

Happy to provide full verbose logs or the RootActivityId values from the failures.