feat(agent): add per-agent skills filtering

[IgorWarzocha]

Don't shoot the messenger, purely vibecoded.

Summary

Add ability to filter which skills are visible to each agent via a new skills field in agent configuration.

This addresses the issue where all discovered skills are loaded into the system prompt for every agent, causing:

• Skill leakage across inappropriate agent contexts
• No way to scope skills to specific agent types
• Unnecessary context in specialized agents

Usage

In opencode.json:

{
  "agent": {
    "excel-maestro": {
      "skills": {
        "spreadsheets": true
      }
    },
    "read-only-explorer": {
      "skills": {
        "git-*": false
      }
    }
  }
}

In agent markdown frontmatter (.opencode/agent/excel-maestro.md):

---
mode: all
skills:
  spreadsheets: true
---

Behavior

• Whitelist mode: When any true values are present, only skills matching a true pattern are shown
• Blacklist mode: When only false values are present, all skills except those matching false patterns are shown
• No config: All skills visible (backwards compatible)

Uses the same wildcard pattern matching as existing tools filtering.

Changes

• config/config.ts: Added skills field to Agent schema
• agent/agent.ts: Added skills to Agent.Info type and state builder
• skill/skill.ts: Added filter() and forAgent() functions
• session/system.ts: Updated skills() to accept optional filter parameter
• session/prompt.ts: Pass agent's skills filter to SystemPrompt.skills()
• Tests for filtering logic and markdown frontmatter support

[thdxr]

hang onto this - we're reworking a bunch of permissions stuff and this can come after that

[airtonix]

Looks like https://github.com/sst/opencode/pull/6000 makes this not needed?

[malhashemi]

Looks like https://github.com/sst/opencode/pull/6000 makes this not needed?

True denied skills are already filtered out of agents context

[IgorWarzocha]

See, the original idea was similar, I am now leaning towards an entirely different thing.

Current implementation basically loads all the skills into all agents unless you edit them. There needs to be something that allows easier allow/deny skills and I believe they should all be disabled as default.

opencode agent create should probably include a step to add/remove skills to the agent config. and I believe we're getting to a point where opencode agent edit just to edit the frontmatter is a necessity.

https://github.com/sst/opencode/pull/6103

[malhashemi]

See, the original idea was similar, I am now leaning towards an entirely different thing.

Current implementation basically loads all the skills into all agents unless you edit them. There needs to be something that allows easier allow/deny skills and I believe they should all be disabled as default.

opencode agent create should probably include a step to add/remove skills to the agent config. and I believe we're getting to a point where opencode agent edit just to edit the frontmatter is a necessity.

Actually global deny is very easy in your config simply:

permission.skill: {* : deny}

Would deny it globally this is how I have it setup at the moment. Also there is a new permission system in the works so lets hold on till release.

[malhashemi]

Having said that I agree that some guided configurations on the agent setup process would be nice to have. So thats a direction worth taking

[IgorWarzocha]

See, the original idea was similar, I am now leaning towards an entirely different thing. Current implementation basically loads all the skills into all agents unless you edit them. There needs to be something that allows easier allow/deny skills and I believe they should all be disabled as default. opencode agent create should probably include a step to add/remove skills to the agent config. and I believe we're getting to a point where opencode agent edit just to edit the frontmatter is a necessity.

Actually global deny is very easy in your config simply:

permission.skill: {* : deny}

Would deny it globally this is how I have it setup at the moment. Also there is a new permission system in the works so lets hold on till release.

Yeah agree but it's the defaults that are the problem - creating a build agent config is not something that everyone does. I can see how having all the skills enabled as default can be problematic