I think the benefits of maintainability and separation of responsibilities far outweigh any performance considerations. You can always add more CPU and storage.

What's the purpose of the "first mapping?" Data enrichment, canonicalization of message format(s), fixing message sequencing issues (the last is common in Epic environments)?

Are you using VS Code? With the Intersystems plugins installed, IRIS Terminal Lite is available on version 2025.1.

Unless the Linux system admin has set session timeouts for ssh, you shouldn't be timing out. The default settings (for Redhat and Ubuntu, at least) do not time you out.

Is the routing rule attempting to filter/route based on content embedded in the RTF? And how large is the message?