Add OpenCode support design document

- Native OpenCode plugin approach using their JavaScript plugin system
- Shared core module (lib/skills-core.js) for code reuse with Codex
- Custom tools: use_skill and find_skills
- Session startup hook for automatic bootstrap
- Three-phase implementation plan

docs/plans/2025-11-22-opencode-support-design.md

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+# OpenCode Support Design
+
+**Date:** 2025-11-22
+**Author:** Bot & Jesse
+**Status:** Design Complete, Awaiting Implementation
+
+## Overview
+
+Add full superpowers support for OpenCode.ai using a native OpenCode plugin architecture that shares core functionality with the existing Codex implementation.
+
+## Background
+
+OpenCode.ai is a coding agent similar to Claude Code and Codex. Previous attempts to port superpowers to OpenCode (PR #93, PR #116) used file-copying approaches. This design takes a different approach: building a native OpenCode plugin using their JavaScript/TypeScript plugin system while sharing code with the Codex implementation.
+
+### Key Differences Between Platforms
+
+- **Claude Code**: Native Anthropic plugin system + file-based skills
+- **Codex**: No plugin system → bootstrap markdown + CLI script
+- **OpenCode**: JavaScript/TypeScript plugins with event hooks and custom tools API
+
+### OpenCode's Agent System
+
+- **Primary agents**: Build (default, full access) and Plan (restricted, read-only)
+- **Subagents**: General (research, searching, multi-step tasks)
+- **Invocation**: Automatic dispatch by primary agents OR manual `@mention` syntax
+- **Configuration**: Custom agents in `opencode.json` or `~/.config/opencode/agent/`
+
+## Architecture
+
+### High-Level Structure
+
+1. **Shared Core Module** (`lib/skills-core.js`)
+   - Common skill discovery and parsing logic
+   - Used by both Codex and OpenCode implementations
+
+2. **Platform-Specific Wrappers**
+   - Codex: CLI script (`.codex/superpowers-codex`)
+   - OpenCode: Plugin module (`.opencode/plugin/superpowers.js`)
+
+3. **Skill Directories**
+   - Core: `~/.config/opencode/superpowers/skills/` (or installed location)
+   - Personal: `~/.config/opencode/skills/` (shadows core skills)
+
+### Code Reuse Strategy
+
+Extract common functionality from `.codex/superpowers-codex` into shared module:
+
+```javascript
+// lib/skills-core.js
+module.exports = {
+  extractFrontmatter(filePath),      // Parse name + description from YAML
+  findSkillsInDir(dir, maxDepth),    // Recursive SKILL.md discovery
+  findAllSkills(dirs),                // Scan multiple directories
+  resolveSkillPath(skillName, dirs), // Handle shadowing (personal > core)
+  checkForUpdates(repoDir)           // Git fetch/status check
+};
+```
+
+### Skill Frontmatter Format
+
+Current format (no `when_to_use` field):
+
+```yaml
+---
+name: skill-name
+description: Use when [condition] - [what it does]; [additional context]
+---
+```
+
+## OpenCode Plugin Implementation
+
+### Custom Tools
+
+**Tool 1: `use_skill`**
+
+Loads a specific skill's content into the conversation (equivalent to Claude's Skill tool).
+
+```javascript
+{
+  name: 'use_skill',
+  description: 'Load and read a specific skill to guide your work',
+  schema: z.object({
+    skill_name: z.string().describe('Name of skill (e.g., "superpowers:brainstorming")')
+  }),
+  execute: async ({ skill_name }) => {
+    const { skillPath, content, frontmatter } = resolveAndReadSkill(skill_name);
+    const skillDir = path.dirname(skillPath);
+
+    return `# ${frontmatter.name}
+# ${frontmatter.description}
+# Supporting tools and docs are in ${skillDir}
+# ============================================
+
+${content}`;
+  }
+}
+```
+
+**Tool 2: `find_skills`**
+
+Lists all available skills with metadata.
+
+```javascript
+{
+  name: 'find_skills',
+  description: 'List all available skills',
+  schema: z.object({}),
+  execute: async () => {
+    const skills = discoverAllSkills();
+    return skills.map(s =>
+      `${s.namespace}:${s.name}
+  ${s.description}
+  Directory: ${s.directory}
+`).join('\n');
+  }
+}
+```
+
+### Session Startup Hook
+
+When a new session starts (`session.started` event):
+
+1. **Inject using-superpowers content**
+   - Full content of the using-superpowers skill
+   - Establishes mandatory workflows
+
+2. **Run find_skills automatically**
+   - Display full list of available skills upfront
+   - Include skill directories for each
+
+3. **Inject tool mapping instructions**
+   ```markdown
+   **Tool Mapping for OpenCode:**
+   When skills reference tools you don't have, substitute:
+   - `TodoWrite` → `update_plan`
+   - `Task` with subagents → Use OpenCode subagent system (@mention)
+   - `Skill` tool → `use_skill` custom tool
+   - Read, Write, Edit, Bash → Your native equivalents
+
+   **Skill directories contain:**
+   - Supporting scripts (run with bash)
+   - Additional documentation (read with read tool)
+   - Utilities specific to that skill
+   ```
+
+4. **Check for updates** (non-blocking)
+   - Quick git fetch with timeout
+   - Notify if updates available
+
+### Plugin Structure
+
+```javascript
+// .opencode/plugin/superpowers.js
+const skillsCore = require('../../lib/skills-core');
+const path = require('path');
+const fs = require('fs');
+const { z } = require('zod');
+
+export const SuperpowersPlugin = async ({ client, directory, $ }) => {
+  const superpowersDir = path.join(process.env.HOME, '.config/opencode/superpowers');
+  const personalDir = path.join(process.env.HOME, '.config/opencode/skills');
+
+  return {
+    'session.started': async () => {
+      const usingSuperpowers = await readSkill('using-superpowers');
+      const skillsList = await findAllSkills();
+      const toolMapping = getToolMappingInstructions();
+
+      return {
+        context: `${usingSuperpowers}\n\n${skillsList}\n\n${toolMapping}`
+      };
+    },
+
+    tools: [
+      {
+        name: 'use_skill',
+        description: 'Load and read a specific skill',
+        schema: z.object({
+          skill_name: z.string()
+        }),
+        execute: async ({ skill_name }) => {
+          // Implementation using skillsCore
+        }
+      },
+      {
+        name: 'find_skills',
+        description: 'List all available skills',
+        schema: z.object({}),
+        execute: async () => {
+          // Implementation using skillsCore
+        }
+      }
+    ]
+  };
+};
+```
+
+## File Structure
+
+```
+superpowers/
+├── lib/
+│   └── skills-core.js           # NEW: Shared skill logic
+├── .codex/
+│   ├── superpowers-codex        # UPDATED: Use skills-core
+│   ├── superpowers-bootstrap.md
+│   └── INSTALL.md
+├── .opencode/
+│   ├── plugin/
+│   │   └── superpowers.js       # NEW: OpenCode plugin
+│   └── INSTALL.md               # NEW: Installation guide
+└── skills/                       # Unchanged
+```
+
+## Implementation Plan
+
+### Phase 1: Refactor Shared Core
+
+1. Create `lib/skills-core.js`
+   - Extract frontmatter parsing from `.codex/superpowers-codex`
+   - Extract skill discovery logic
+   - Extract path resolution (with shadowing)
+   - Update to use only `name` and `description` (no `when_to_use`)
+
+2. Update `.codex/superpowers-codex` to use shared core
+   - Import from `../lib/skills-core.js`
+   - Remove duplicated code
+   - Keep CLI wrapper logic
+
+3. Test Codex implementation still works
+   - Verify bootstrap command
+   - Verify use-skill command
+   - Verify find-skills command
+
+### Phase 2: Build OpenCode Plugin
+
+1. Create `.opencode/plugin/superpowers.js`
+   - Import shared core from `../../lib/skills-core.js`
+   - Implement plugin function
+   - Define custom tools (use_skill, find_skills)
+   - Implement session.started hook
+
+2. Create `.opencode/INSTALL.md`
+   - Installation instructions
+   - Directory setup
+   - Configuration guidance
+
+3. Test OpenCode implementation
+   - Verify session startup bootstrap
+   - Verify use_skill tool works
+   - Verify find_skills tool works
+   - Verify skill directories are accessible
+
+### Phase 3: Documentation & Polish
+
+1. Update README with OpenCode support
+2. Add OpenCode installation to main docs
+3. Update RELEASE-NOTES
+4. Test both Codex and OpenCode work correctly
+
+## Next Steps
+
+1. **Create isolated workspace** (using git worktrees)
+   - Branch: `feature/opencode-support`
+
+2. **Follow TDD where applicable**
+   - Test shared core functions
+   - Test skill discovery and parsing
+   - Integration tests for both platforms
+
+3. **Incremental implementation**
+   - Phase 1: Refactor shared core + update Codex
+   - Verify Codex still works before moving on
+   - Phase 2: Build OpenCode plugin
+   - Phase 3: Documentation and polish
+
+4. **Testing strategy**
+   - Manual testing with real OpenCode installation
+   - Verify skill loading, directories, scripts work
+   - Test both Codex and OpenCode side-by-side
+   - Verify tool mappings work correctly
+
+5. **PR and merge**
+   - Create PR with complete implementation
+   - Test in clean environment
+   - Merge to main
+
+## Benefits
+
+- **Code reuse**: Single source of truth for skill discovery/parsing
+- **Maintainability**: Bug fixes apply to both platforms
+- **Extensibility**: Easy to add future platforms (Cursor, Windsurf, etc.)
+- **Native integration**: Uses OpenCode's plugin system properly
+- **Consistency**: Same skill experience across all platforms