Fix agent configuration merge order

[logvik]

At this case we will be able to override configuration from opencode.json config file. At the case, if we want to choose another model, for example, not codex.

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Summary by cubic

Fix agent configuration merge order so values in opencode.json take precedence over defaults. This lets users override agent options, like choosing a non-codex model.

^{Written for commit 90106c1. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 1 file

[vtemian]

Hey @logvik, thanks for the PR!

Before we merge this, could you clarify the specific use case you're trying to solve?

The current merge order is intentional — octto.json is designed to be the more specific configuration layer that takes precedence over opencode.json. Flipping the precedence would mean octto.json agent settings become defaults that opencode.json can silently override, which defeats the purpose of having octto-specific configuration.

Could you describe the scenario where you need opencode.json to override octto.json? There might be a better way to support your use case without changing the precedence for everyone.

[logvik]

Hi. I have described my case above. I wanted to try another model, because "codex" is the hard coded model now.