Dovecot 2.3.21 Fallback MOVE to COPY on read-only namespaces

Hi I’m running Dovecot 2.3.21 with additional namespaces that point to read-only maildir snapshots. The setup works fine for browsing and copying messages, but when using Roundcube Webmail 1.5.3, there is a problem with the IMAP MOVE command.

• If I try to move a message from a read-only namespace, Roundcube issues UID MOVE, which fails (as expected, since MOVE = COPY + DELETE, and DELETE is impossible).
• What I would need is a way for Roundcube to fallback to COPY when the source/destination namespace is read-only ?

I already tested:

• imap_move = false in Roundcube config
• Overriding capabilities in Dovecot (imap_capability) to remove MOVE, but this does not fully work.
• Using INDEX=MEMORY / CONTROL outside snapshot for namespaces.

What I’m looking for:

• workaround in Dovecot to hide MOVE capability only for specific namespaces.
• or Roundcube plugin or patch that intercepts MOVE and replaces it with COPY for read-only namespaces.