Remove or narrow dm-agent-sync OpenCode plugin so Data Machine owns identity

[chubes4]

Problem

bridges/kimaki/plugins/dm-agent-sync.ts dynamically writes OpenCode config.agent.build.prompt and config.agent.plan.prompt, and registers all active Data Machine agents into OpenCode's agent switcher.

wp-coding-agents already migrated persisted agent.*.prompt away because that shape can override OpenCode's canonical system prompt opening and break Anthropic Claude Max OAuth. The runtime plugin appears to reintroduce the same class of behavior dynamically. It also conflicts with the channel-bound Data Machine identity model by choosing the first listed Data Machine agent as the build/plan identity.

Scope

• Decide whether dm-agent-sync.ts should be removed entirely or reduced to a safer behavior.
• Stop mutating config.agent.build.prompt / config.agent.plan.prompt.
• Stop registering all Data Machine agents into OpenCode by default unless there is an explicit, channel-safe routing design.
• Keep Data Machine memory identity in top-level instructions / AGENTS.md composition, not implicit OpenCode agent slots.

Acceptance criteria

• Runtime plugin no longer reintroduces agent.*.prompt identity injection.
• Build/plan identity stays channel/Data-Machine-bound.
• Tests are updated to prove the safer behavior.
• Generated/repair opencode.json expectations stay consistent with the new plugin list.

AI assistance

This issue was identified during an OpenCode GPT-5.5 review of wp-coding-agents against Kimaki 0.13.0.