fix: preserve agent step limits

[fengjikui]

Summary

• preserve existing OpenCode agent fields such as steps/maxSteps when micode overlays plugin agents
• allow steps and maxSteps through sanitized micode.json agent overrides
• add regression coverage for both config loading and plugin-agent merging

Root cause

micode built the plugin agent map and then spread those agents directly over config.agent. That replaced the existing OpenCode agent object, so fields configured outside the plugin overlay, including iteration limits such as steps, were silently dropped.

Validation

• bun run check
• bun run build
• git diff --check

Closes #53

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Summary by cubic

Preserves user-configured agent iteration limits (steps, maxSteps) when plugin agents overlay OpenCode defaults, and allows these fields in sanitized micode.json overrides.

• Bug Fixes
  • Merge plugin agents with existing config.agent via mergePluginAgents to keep fields like steps/maxSteps.
  • Allow steps and maxSteps in AgentOverride schema and safe properties.
  • Add regression tests for config loading and agent merge behavior.

^{Written for commit 86b62f0. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 5 files

_{Re-trigger cubic}