fix: add safe bare-skill fallback for native OpenCode skill loading

[DevNewbie1826]

Summary

• Add a safe bare-skill fallback for the native OpenCode skill tool.
• Preserve native direction (no reintroduction of custom use_skill/find_skills flow).
• Rewrite only unambiguous bare names to superpowers/<name>.

Problem

When users entered bare skill names such as brainstorming, they could hit:
Skill or command "brainstorming" not found. Did you mean: superpowers/brainstorming, /superpowers:brainstorming?
This created avoidable friction because the first attempt often failed.

Root Cause

• Native skill resolution in OpenCode expects namespaced identifiers for superpowers skills.
• There was no compatibility fallback for bare names.

Changes

• Hooked tool.execute.before in the superpowers plugin and only intercept the native skill tool call.
• Added bare-name resolver with strict guards:
  1. Keep explicit namespaced/path input unchanged.
  2. Keep project/user exact matches unchanged (preserve priority).
  3. Rewrite to superpowers/<name> only when that superpowers skill is known.
• Added tests and runner integration for alias fallback behavior.

Files

• .opencode/plugins/superpowers.js
• .opencode/skill-alias.js
• tests/opencode/test-skill-alias-unit.mjs
• tests/opencode/test-skill-alias.sh
• tests/opencode/run-tests.sh

Verification

• node tests/opencode/test-skill-alias-unit.mjs ✅
• bash tests/opencode/run-tests.sh --test test-skill-alias.sh ✅
• Runtime check:
  • opencode run "Use the skill tool to load brainstorming ..." -> Skill "superpowers/brainstorming" ✅
  • Unknown bare skill remains not found (no over-rewrite) ✅

Risk / Compatibility

• Scoped to native skill tool only.
• No behavior change for explicit namespaced skills.
• Unknown/ambiguous names are not force-rewritten.

[obra]

Thanks for investigating this, @DevNewbie1826. We tested on OpenCode v1.3.2 and bare skill names (e.g., brainstorming without the superpowers/ prefix) work correctly with the native skill tool. The underlying issue was a plugin system timing bug in OpenCode v1.1.x where config.skills.paths mutations from plugin config hooks weren't propagating to the skill registry. This was fixed upstream in OpenCode v1.3.0 (PR anomalyco/opencode#18280). Closing since the fix is upstream rather than in superpowers.