[FEATURE]: Expose set flags using configuration

[hosseinalipour]

Feature hasn't been suggested before.

• [x] I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Several useful options are only available as environment variables (defined in flag.ts).

I wish if These would be configurable via opencode.json for better discoverability and easier management without needing to set environment variables, or even better, to be configurable in the agent level too. I would be interested to submit a PR for this.

Proposed: { flags: { disable_prune: false, disable_autocompact: false, disable_autoupdate: false, enable_exa: true } }

[github-actions[bot]]

This issue might be a duplicate of existing issues. Please check:

• #3011: [Feature Request] Configurable Retry Mechanism via opencode.json - similar request to make environment-variable options configurable via opencode.json
• #4702: [FEATURE]: Add config to change shell for bash tool - requests configuring shell options via config file instead of environment variables
• #4683: [FEATURE]: allow multiple shell setups and allow switching them at runtime via TUI command - related approach to exposing environment-variable options through configuration

All these issues share the same pattern of requesting that environment-variable-based options be made configurable through opencode.json. Feel free to ignore if your specific case differs from these.