fix(core): restore Skill tool as allow by default

[shssoichiro]

Context

Access to the Skill tool was revoked from many agents, such as Plan, Ask, and Explore. This is undesirable. This change restores access to the Skill tool to all non-system agents as allow-by-default, so that the agent can load skills.

Screenshots

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[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (3 files)

• .changeset/skill-tool-default-agents.md
• packages/opencode/src/kilocode/agent/index.ts
• packages/opencode/test/kilocode/agent-skill-permissions.test.ts

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_{Reviewed by gpt-5.5-2026-04-23 · 179,307 tokens}

[marius-kilocode]

This makes sense. skill is permission-gated, and these agents use * = deny allowlists. Code mode still inherited * = allow, but Ask/Plan/Explore/Orchestrator never explicitly allowed skill, so once skills were filtered through agent permissions they disappeared for those modes instead of failing loudly.

The regression started with upstream 0f6bc8ae71 / OpenCode #17053, which moved skill discovery into the system prompt and skips it when Permission.disabled(["skill"], agent.permission) says the tool is disabled. That made missing skill: "allow" visible for allowlisted agents. Later upstream 17bd16667c / OpenCode #21795 moved the skill tool description into the registry and used the same skill.available(agent) permission filtering there too, so the tool description path had the same issue.

This PR adds skill: "allow" to the non-system allowlisted agents and keeps system agents denied, which matches the intended split. The regression test is the important part here so we don’t lose this again.

[marius-kilocode]

#9556 looks like the root cause

[marius-kilocode]

Thanks @shssoichiro