feat: add Agent Skills for experimental artifact workflow

Implements Task #3 from the experimental release plan:
- Create skill templates for openspec-new-change and openspec-continue-change
- Add artifact-experimental-setup CLI command
- Generate Agent Skills in .claude/skills/ directory
- Support cross-editor compatibility (Claude Code, Cursor, Windsurf)

Skills follow the Agent Skills specification and provide:
- Natural language invocation by AI assistants
- Step-by-step artifact creation workflow
- Dependency-driven change management

Author: TabishB

docs/experimental-release-plan.md

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+# OpenSpec Experimental Release Plan
+
+This document outlines the plan to release the experimental artifact workflow system for user testing.
+
+## Overview
+
+The goal is to allow users to test the new artifact-driven workflow system alongside the existing OpenSpec commands. This experimental system (`opsx`) provides a more granular, step-by-step approach to creating change artifacts.
+
+## Three Workflow Modes
+
+### 1. Old Workflow (Current Production)
+- **Commands**: `/openspec:proposal`, `/openspec:apply`, `/openspec:archive`
+- **Behavior**: Hardcoded slash commands that generate all artifacts in one command
+- **Status**: Production, unchanged
+
+### 2. New Artifact System - Batch Mode (Future)
+- **Commands**: Refactored `/openspec:proposal` using schemas
+- **Behavior**: Schema-driven but generates all artifacts at once (like legacy)
+- **Status**: Not in scope for this experimental release
+- **Note**: This is a future refactor to unify the old system with schemas
+
+### 3. New Artifact System - Granular Mode (Experimental)
+- **Commands**: `/opsx:new`, `/opsx:continue`
+- **Behavior**: One artifact at a time, dependency-driven, iterative
+- **Status**: Target for this experimental release
+
+---
+
+## Work Items
+
+### 1. Rename AWF to OPSX
+
+**Current State:**
+- Commands: `/awf:start`, `/awf:continue`
+- Files: `.claude/commands/awf/start.md`, `.claude/commands/awf/continue.md`
+
+**Target State:**
+- Commands: `/opsx:new`, `/opsx:continue`
+- Files: `.claude/commands/opsx/new.md`, `.claude/commands/opsx/continue.md`
+
+**Tasks:**
+- [x] Create `.claude/commands/opsx/` directory
+- [x] Rename `start.md` → `new.md` and update content
+- [x] Copy `continue.md` with updated references
+- [x] Update all references from "awf" to "opsx" in command content
+- [x] Update frontmatter (name, description) to use "opsx" naming
+- [x] Remove `.claude/commands/awf/` directory
+
+**CLI Commands:**
+The underlying CLI commands (`openspec status`, `openspec next`, `openspec instructions`, etc.) remain unchanged. Only the slash command names change.
+
+---
+
+### 2. Remove WF Skill Files
+
+**Current State:**
+- `.claude/commands/wf/start.md` - References non-existent `openspec wf` commands
+- `.claude/commands/wf/continue.md` - References non-existent `openspec wf` commands
+
+**Target State:**
+- Directory and files removed
+
+**Tasks:**
+- [x] Delete `.claude/commands/wf/start.md`
+- [x] Delete `.claude/commands/wf/continue.md`
+- [x] Delete `.claude/commands/wf/` directory
+
+---
+
+### 3. Add Agent Skills for Experimental Workflow
+
+**Purpose:**
+Generate experimental workflow skills using the [Agent Skills](https://agentskills.io/specification) open standard.
+
+**Why Skills Instead of Slash Commands:**
+- **Cross-editor compatibility**: Skills work in Claude Code, Cursor, Windsurf, and other compatible editors automatically
+- **Simpler implementation**: Single directory (`.claude/skills/`) instead of 18+ editor-specific configurators
+- **Standard format**: Open standard with simple YAML frontmatter + markdown
+- **User invocation**: Users explicitly invoke skills when they want to use them
+
+**Behavior:**
+1. Create `.claude/skills/` directory if it doesn't exist
+2. Generate two skills using the Agent Skills specification:
+   - `openspec-new-change/SKILL.md` - Start a new change with artifact workflow
+   - `openspec-continue-change/SKILL.md` - Continue working on a change (create next artifact)
+3. Skills are added **alongside** existing `/openspec:*` commands (not replacing)
+
+**Supported Editors:**
+- Claude Code (native support)
+- Cursor (native support via Settings → Rules → Import Settings)
+- Windsurf (imports `.claude` configs)
+- Cline, Codex, and other Agent Skills-compatible editors
+
+**Tasks:**
+- [x] Create skill template content for `openspec-new-change` (based on current opsx:new)
+- [x] Create skill template content for `openspec-continue-change` (based on current opsx:continue)
+- [x] Add temporary `artifact-experimental-setup` command to CLI
+- [x] Implement skill file generation (YAML frontmatter + markdown body)
+- [x] Add success message with usage instructions
+
+**Note:** The `artifact-experimental-setup` command is temporary and will be merged into `openspec init` once the experimental workflow is promoted to stable.
+
+**Skill Format:**
+Each skill is a directory with a `SKILL.md` file:
+```
+.claude/skills/
+├── openspec-new-change/
+│   └── SKILL.md          # name, description, instructions
+└── openspec-continue-change/
+    └── SKILL.md          # name, description, instructions
+```
+
+**CLI Interface:**
+```bash
+openspec artifact-experimental-setup
+
+# Output:
+# 🧪 Experimental Artifact Workflow Setup
+#
+# Created .claude/skills/openspec-new-change/SKILL.md
+# Created .claude/skills/openspec-continue-change/SKILL.md
+#
+# ✅ Skills are now available in:
+#   - Claude Code (auto-detected)
+#   - Cursor (enable in Settings → Rules → Import Settings)
+#   - Windsurf (auto-imported from .claude directory)
+#
+# 📖 To use:
+#   Ask Claude naturally:
+#   • "I want to start a new OpenSpec change to add <feature>"
+#   • "Continue working on this change"
+#
+#   Claude will automatically use the appropriate skill.
+#
+# 💡 This is an experimental feature. Feedback welcome at:
+#    https://github.com/your-org/openspec/issues
+```
+
+**Implementation Notes:**
+- Simple file writing: Create directories and write templated `SKILL.md` files (no complex logic)
+- Use existing `FileSystemUtils.writeFile()` pattern like slash command configurators
+- Template structure: YAML frontmatter + markdown body
+- Keep existing `/opsx:*` slash commands for now (manual cleanup later)
+- Skills use invocation model (user explicitly asks Claude to use them)
+- Skill `description` field guides when Claude suggests using the skill
+- Each `SKILL.md` has required fields: `name` (matches directory) and `description`
+
+---
+
+### 4. Update `/opsx:new` Command Content
+
+**Current Behavior (awf:start):**
+1. Ask user what they want to build (if no input)
+2. Create change directory
+3. Show artifact status
+4. Show what's ready
+5. Get instructions for proposal
+6. STOP and wait
+
+**New Behavior (opsx:new):**
+Same flow but with updated naming:
+- References to "awf" → "opsx"
+- References to `/awf:continue` → `/opsx:continue`
+- Update frontmatter name/description
+
+**Tasks:**
+- [x] Update all "awf" references to "opsx"
+- [x] Update command references in prompt text
+- [x] Verify CLI commands still work (they use `openspec`, not `awf`)
+
+---
+
+### 5. Update `/opsx:continue` Command Content
+
+**Current Behavior (awf:continue):**
+1. Prompt for change selection (if not provided)
+2. Check current status
+3. Create ONE artifact based on what's ready
+4. Show progress and what's unlocked
+5. STOP
+
+**New Behavior (opsx:continue):**
+Same flow with updated naming.
+
+**Tasks:**
+- [x] Update all "awf" references to "opsx"
+- [x] Update command references in prompt text
+
+---
+
+### 6. End-to-End Testing
+
+**Objective:**
+Run through a complete workflow with Claude using the new skills to create a real feature, validating the entire flow works.
+
+**Test Scenario:**
+Use a real OpenSpec feature as the test case (dog-fooding).
+
+**Test Flow:**
+1. Run `openspec artifact-experimental-setup` to create skills
+2. Verify `.claude/skills/openspec-new-change/SKILL.md` created
+3. Verify `.claude/skills/openspec-continue-change/SKILL.md` created
+4. Ask Claude: "I want to start a new OpenSpec change to add feature X"
+5. Verify Claude invokes the `openspec-new-change` skill
+6. Verify change directory created at `openspec/changes/add-feature-x/`
+7. Verify proposal template shown
+8. Ask Claude: "Continue working on this change"
+9. Verify Claude invokes the `openspec-continue-change` skill
+10. Verify `proposal.md` created with content
+11. Ask Claude: "Continue" (create specs)
+12. Verify `specs/*.md` created
+13. Ask Claude: "Continue" (create design)
+14. Verify `design.md` created
+15. Ask Claude: "Continue" (create tasks)
+16. Verify `tasks.md` created
+17. Verify status shows 4/4 complete
+18. Implement the feature based on tasks
+19. Run `/openspec:archive` to archive the change
+
+**Validation Checklist:**
+- [ ] `openspec artifact-experimental-setup` creates correct directory structure
+- [ ] Skills are auto-detected in Claude Code
+- [ ] Skill descriptions trigger appropriate invocations
+- [ ] Skills create change directory and show proposal template
+- [ ] Skills correctly identify ready artifacts
+- [ ] Skills create artifacts with meaningful content
+- [ ] Dependency detection works (specs requires proposal, etc.)
+- [ ] Progress tracking is accurate
+- [ ] Template content is useful and well-structured
+- [ ] Error handling works (invalid names, missing changes, etc.)
+- [ ] Works with different schemas (spec-driven, tdd)
+- [ ] Test in Cursor (Settings → Rules → Import Settings)
+
+**Document Results:**
+- Create test log documenting what worked and what didn't
+- Note any friction points or confusing UX
+- Identify bugs or improvements needed before user release
+
+---
+
+### 7. Documentation for Users
+
+**Create user-facing documentation explaining:**
+
+1. **What is the experimental workflow?**
+   - A new way to create OpenSpec changes step-by-step using Agent Skills
+   - One artifact at a time with dependency tracking
+   - More interactive and iterative than the batch approach
+   - Works across Claude Code, Cursor, Windsurf, and other compatible editors
+
+2. **How to set up experimental workflow**
+   ```bash
+   openspec artifact-experimental-setup
+   ```
+
+   Note: This is a temporary command that will be integrated into `openspec init` once promoted to stable.
+
+3. **Available skills**
+   - `openspec-new-change` - Start a new change with artifact workflow
+   - `openspec-continue-change` - Continue working (create next artifact)
+
+4. **How to use**
+   - **Claude Code**: Skills are auto-detected, just ask Claude naturally
+     - "I want to start a new OpenSpec change to add X"
+     - "Continue working on this change"
+   - **Cursor**: Enable in Settings → Rules → Import Settings
+   - **Windsurf**: Auto-imports `.claude` directory
+
+5. **Example workflow**
+   - Step-by-step walkthrough with natural language interactions
+   - Show how Claude invokes skills based on user requests
+
+6. **Feedback mechanism**
+   - GitHub issue template for feedback
+   - What to report (bugs, UX issues, suggestions)
+
+**Tasks:**
+- [ ] Create `docs/experimental-workflow.md` user guide
+- [ ] Add GitHub issue template for experimental feedback
+- [ ] Update README with mention of experimental features
+
+---
+
+## Dependency Graph
+
+```
+1. Remove WF skill files
+   └── (no dependencies)
+
+2. Rename AWF to OPSX
+   └── (no dependencies)
+
+3. Add Agent Skills
+   └── Depends on: Rename AWF to OPSX (uses opsx content as templates)
+
+4. Update opsx:new content
+   └── Depends on: Rename AWF to OPSX
+
+5. Update opsx:continue content
+   └── Depends on: Rename AWF to OPSX
+
+6. E2E Testing
+   └── Depends on: Add Agent Skills (tests the skills workflow)
+
+7. User Documentation
+   └── Depends on: E2E Testing (need to know final behavior)
+```
+
+---
+
+## Out of Scope
+
+The following are explicitly NOT part of this experimental release:
+
+1. **Batch mode refactor** - Making legacy `/openspec:proposal` use schemas
+2. **New schemas** - Only shipping with existing `spec-driven` and `tdd`
+3. **Schema customization UI** - No `openspec schema list` or similar
+4. **Multiple editor support in CLI** - Skills work cross-editor automatically via `.claude/skills/`
+5. **Replacing existing commands** - Skills are additive, not replacing `/openspec:*` or `/opsx:*`
+
+---
+
+## Success Criteria
+
+The experimental release is ready when:
+
+1. `openspec-new-change` and `openspec-continue-change` skills work end-to-end
+2. `openspec artifact-experimental-setup` creates skills in `.claude/skills/`
+3. Skills work in Claude Code and are compatible with Cursor/Windsurf
+4. At least one complete workflow has been tested manually
+5. User documentation exists explaining how to generate and use skills
+6. Feedback mechanism is in place
+7. WF skill files are removed
+8. No references to "awf" remain in user-facing content
+
+---
+
+## Open Questions
+
+1. **Schema selection** - Should `opsx:new` allow selecting a schema, or always use `spec-driven`?
+   - Current: Always uses `spec-driven` as default
+   - Consider: Add `--schema tdd` option or prompt
+
+2. **Namespace in CLI** - Should experimental CLI commands be namespaced?
+   - Current: `openspec status`, `openspec next` (no namespace)
+   - Alternative: `openspec opsx status` (explicit experimental namespace)
+   - Recommendation: Keep current, less typing for users
+
+3. **Deprecation path** - If opsx becomes the default, how do we migrate?
+   - Not needed for experimental release
+   - Document that command names may change
+
+---
+
+## Estimated Work Breakdown
+
+| Item | Complexity | Notes |
+|------|------------|-------|
+| Remove WF files | Trivial | Just delete 2 files + directory |
+| Rename AWF → OPSX | Low | File renames + content updates |
+| Add Agent Skills | **Low** | **Simple: 3-4 files, single output directory, standard format** |
+| Update opsx:new content | Low | Text replacements |
+| Update opsx:continue content | Low | Text replacements |
+| E2E Testing | Medium | Manual testing, documenting results |
+| User Documentation | Medium | New docs, issue template |
+
+**Key Improvement:** Switching to Agent Skills reduces complexity significantly:
+- **Before:** 20+ files (type definitions, 18+ editor configurators, editor selection UI)
+- **After:** 3-4 files (skill templates, simple CLI command)
+- **Cross-editor:** Works automatically in Claude Code, Cursor, Windsurf without extra code
+
+---
+
+## Next Steps
+
+1. Review this plan and confirm scope
+2. Create tasks/issues for each work item
+3. Execute in dependency order
+4. Conduct E2E testing
+5. Write user docs
+6. Release to test users