os-ddclient generates empty ddclient.conf although account exists in config.xml/json

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Title
os-ddclient: account is stored in config.xml/json but ddclient.conf stays empty

Describe the bug
When configuring Dynamic DNS with the os-ddclient plugin, the account is correctly saved in /conf/config.xml and rendered into /usr/local/etc/ddclient.json, but /usr/local/etc/ddclient.conf only contains the header lines:

syslog=yes
pid=/var/run/ddclient.pid

No actual account configuration is written into ddclient.conf.

As a result, ddclient_opn may appear to start or run, but it has no usable account configuration.

I was able to verify that the DynDNS provider itself is working: a manual ddclient test with the same Infomaniak credentials works successfully from the shell.

I do not know the last known working version.

To Reproduce
Steps to reproduce the behavior:

1. Go to Services -> Dynamic DNS -> Settings
2. Create a Dynamic DNS account using os-ddclient
3. I tested both:
   • service dyndns2
   • service custom with protocol dyndns2
4. Save and apply the configuration
5. Check the generated files:
   • /conf/config.xml
   • /usr/local/etc/ddclient.json
   • /usr/local/etc/ddclient.conf
6. Observe that:
   • the account exists in config.xml
   • the account exists in ddclient.json
   • ddclient.conf only contains the header lines and no account entries

Expected behavior
I expect os-ddclient to render a complete and usable /usr/local/etc/ddclient.conf containing the configured account, for example protocol/server/login/password/hostname related entries, so that ddclient_opn can actually perform updates.

Screenshots
If needed, I can provide screenshots showing:

• the configured DynDNS account in the GUI
• /usr/local/etc/ddclient.json containing the account
• /usr/local/etc/ddclient.conf only containing the header lines

Relevant log files
/var/log/system/latest.log showed:
WARNING: failed to start ddclient_opn

/var/log/configd/latest.log showed template generation succeeds:

• generate template OPNsense/ddclient
• generated //usr/local/etc/ddclient.conf
• generated //usr/local/etc/ddclient.json

But the generated ddclient.conf still only contains:
syslog=yes
pid=/var/run/ddclient.pid

Relevant observations:

• /conf/config.xml contains the DynDNS account
• /usr/local/etc/ddclient.json contains the DynDNS account
• /usr/local/etc/ddclient.conf does not contain the DynDNS account

A manual ddclient test worked successfully with the same provider credentials, which suggests the issue is not the provider itself but the plugin/template/runtime generation.

Additional context
Provider used: Infomaniak DynDNS

Manual shell test with ddclient works when using:

• protocol: dyndns2
• server: infomaniak.com
• valid credentials
• valid hostname
• explicit IP or otherwise correct IP detection

This strongly suggests that:

• provider credentials are valid
• provider endpoint is working
• the issue is specific to os-ddclient generating or using ddclient.conf

I also tested a custom entry with:

• service: custom
• protocol: dyndns2
• server: infomaniak.com

The account was again present in config.xml and ddclient.json, but ddclient.conf still remained empty except for the header lines.

Environment
Opnsense 26.1.9

Hardware:
Intel(R) N150
4x Intel I226-V 2.5G interfaces
1U rack firewall appliance (PcZinophyte / Topton-style system, N150, no SFP)

Start by comparing the account data in /conf/config.xml and /usr/local/etc/ddclient.json with the generated /usr/local/etc/ddclient.conf, then trace the OPNsense/ddclient template generation entry point and ddclient_opn startup. Done means a configured account is rendered into a usable ddclient.conf and ddclient_opn can start with that configuration.