docs(openspec): align add-update-command change with conventions and idempotency

Add init command for OpenSpec

openspec/changes/add-update-command/design.md

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+# Technical Design
+
+## Architecture Decisions
+
+### Simplicity First
+- No version tracking - always update when commanded
+- Full replacement for OpenSpec-managed files only (e.g., `openspec/README.md`)
+- Marker-based updates for user-owned files (e.g., `CLAUDE.md`)
+- Templates bundled with package - no network required
+- Minimal error handling - only check prerequisites
+
+### Template Strategy
+- Use existing template utilities
+  - `readmeTemplate` from `src/core/templates/readme-template.ts` for `openspec/README.md`
+  - `TemplateManager.getClaudeTemplate()` for `CLAUDE.md`
+- Directory name is fixed to `openspec` (from `OPENSPEC_DIR_NAME`)
+
+### File Operations
+- Use async utilities for consistency
+  - `FileSystemUtils.writeFile` for `openspec/README.md`
+  - `FileSystemUtils.updateFileWithMarkers` for `CLAUDE.md`
+- No atomic operations needed - users have git
+- Check directory existence before proceeding
+
+## Implementation
+
+### Update Command (`src/core/update.ts`)
+```typescript
+export class UpdateCommand {
+  async execute(projectPath: string): Promise<void> {
+    const openspecDirName = OPENSPEC_DIR_NAME;
+    const openspecPath = path.join(projectPath, openspecDirName);
+
+    // 1. Check openspec directory exists
+    if (!await FileSystemUtils.directoryExists(openspecPath)) {
+      throw new Error(`No OpenSpec directory found. Run 'openspec init' first.`);
+    }
+
+    // 2. Update README.md (full replacement)
+    const readmePath = path.join(openspecPath, 'README.md');
+    await FileSystemUtils.writeFile(readmePath, readmeTemplate);
+
+    // 3. Update CLAUDE.md (marker-based)
+    const claudePath = path.join(projectPath, 'CLAUDE.md');
+    const claudeContent = TemplateManager.getClaudeTemplate();
+    await FileSystemUtils.updateFileWithMarkers(
+      claudePath,
+      claudeContent,
+      OPENSPEC_MARKERS.start,
+      OPENSPEC_MARKERS.end
+    );
+
+    // 4. Success message (ASCII-safe, checkmark optional by terminal)
+    console.log('Updated OpenSpec instructions');
+  }
+}
+```
+
+## Why This Approach
+
+### Benefits
+- **Dead simple**: ~40 lines of code total
+- **Fast**: No version checks, minimal parsing
+- **Predictable**: Same result every time; idempotent
+- **Maintainable**: Reuses existing utilities
+
+### Trade-offs Accepted
+- No version tracking (unnecessary complexity)
+- Full overwrite only for OpenSpec-managed files
+- Marker-managed updates for user-owned files
+
+## Error Handling
+
+Only handle critical errors:
+- Missing `openspec` directory → throw error handled by CLI to present a friendly message
+- File write failures → let errors bubble up to CLI
+
+## Testing Strategy
+
+Manual smoke tests are sufficient initially:
+1. Run `openspec init` in a test project
+2. Modify both files (including custom content around markers in `CLAUDE.md`)
+3. Run `openspec update`
+4. Verify `openspec/README.md` fully replaced; `CLAUDE.md` OpenSpec block updated without altering user content outside markers
+5. Run the command twice to verify idempotency and no duplicate markers
+6. Test with missing `openspec` directory (expect failure)

openspec/changes/add-update-command/proposal.md

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+# Add Update Command
+
+## Why
+
+Users need a way to update their local OpenSpec instructions (README.md and CLAUDE.md) when the OpenSpec package releases new versions with improved AI agent instructions or structural conventions.
+
+## What Changes
+
+- Add new `openspec update` CLI command that updates OpenSpec instructions
+- Replace `openspec/README.md` with the latest template
+  - Safe because this file is fully OpenSpec-managed
+- Update only the OpenSpec-managed block in `CLAUDE.md` using markers
+  - Preserve all user content outside markers
+  - If `CLAUDE.md` is missing, create it with the managed block
+- Display success message after update (ASCII-safe): "Updated OpenSpec instructions"
+  - A leading checkmark MAY be shown when the terminal supports it
+  - Operation is idempotent (re-running yields identical results)
+
+## Impact
+
+- Affected specs: `cli-update` (new capability)
+- Affected code:
+  - `src/core/update.ts` (new command class, mirrors `InitCommand` placement)
+  - `src/cli/index.ts` (register new command)
+  - Uses existing templates via `TemplateManager` and `readmeTemplate`
+
+## Out of Scope
+
+- No `.openspec/config.json` is introduced by this change. The default directory name `openspec` is used.

openspec/changes/add-update-command/specs/cli-update/spec.md

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+# Update Command Specification
+
+## Purpose
+
+As a developer using OpenSpec, I want to update the OpenSpec instructions in my project when new versions are released, so that I can benefit from improvements to AI agent instructions.
+
+## Core Requirements
+
+### Update Behavior
+
+The update command SHALL update OpenSpec instruction files to the latest templates.
+
+WHEN a user runs `openspec update` THEN the command SHALL:
+- Check if the `openspec` directory exists
+- Replace `openspec/README.md` with the latest template (complete replacement)
+- Update the OpenSpec-managed block in `CLAUDE.md` using markers
+  - Preserve user content outside markers
+  - Create `CLAUDE.md` if missing
+- Display ASCII-safe success message: "Updated OpenSpec instructions"
+
+### Prerequisites
+
+The command SHALL require:
+- An existing `openspec` directory (created by `openspec init`)
+
+IF the `openspec` directory does not exist THEN:
+- Display error: "No OpenSpec directory found. Run 'openspec init' first."
+- Exit with code 1
+
+### File Handling
+
+The update command SHALL:
+- Completely replace `openspec/README.md` with the latest template
+- Update only the OpenSpec-managed block in `CLAUDE.md` using markers
+- Use the default directory name `openspec`
+- Be idempotent (repeated runs have no additional effect)
+
+## Edge Cases
+
+### File Permissions
+IF file write fails THEN let the error bubble up naturally with file path.
+
+### Missing CLAUDE.md
+IF CLAUDE.md doesn't exist THEN create it with the template content.
+
+### Custom Directory Name
+Not supported in this change. The default directory name `openspec` SHALL be used.
+
+## Success Criteria
+
+Users SHALL be able to:
+- Update OpenSpec instructions with a single command
+- Get the latest AI agent instructions
+- See clear confirmation of the update
+
+The update process SHALL be:
+- Simple and fast (no version checking)
+- Predictable (same result every time)
+- Self-contained (no network required)

openspec/changes/add-update-command/tasks.md

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+# Implementation Tasks
+
+## 1. Update Command Implementation
+- [ ] 1.1 Create `src/core/update.ts` with `UpdateCommand` class
+- [ ] 1.2 Check if `openspec` directory exists (use `FileSystemUtils.directoryExists`)
+- [ ] 1.3 Write `readmeTemplate` to `openspec/README.md` using `FileSystemUtils.writeFile`
+- [ ] 1.4 Update `CLAUDE.md` using markers via `FileSystemUtils.updateFileWithMarkers` and `TemplateManager.getClaudeTemplate()`
+- [ ] 1.5 Display ASCII-safe success message: `Updated OpenSpec instructions`
+
+## 2. CLI Integration
+- [ ] 2.1 Register `update` command in `src/cli/index.ts`
+- [ ] 2.2 Add command description: `Update OpenSpec instruction files`
+- [ ] 2.3 Handle errors with `ora().fail(...)` and exit code 1 (missing `openspec` directory, file write errors)
+
+## 3. Testing
+- [ ] 3.1 Verify `openspec/README.md` is fully replaced with latest template
+- [ ] 3.2 Verify `CLAUDE.md` OpenSpec block updates without altering user content outside markers
+- [ ] 3.3 Verify idempotency (running twice yields identical files, no duplicate markers)
+- [ ] 3.4 Verify error when `openspec` directory is missing with friendly message
+- [ ] 3.5 Verify success message displays properly in ASCII-only terminals

openspec/specs/cli-init/spec.md

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+# CLI Init Specification
+
+## Purpose
+
+The `openspec init` command SHALL create a complete OpenSpec directory structure in any project, enabling immediate adoption of OpenSpec conventions with support for multiple AI coding assistants.
+
+## Behavior
+
+### Progress Indicators
+
+WHEN executing initialization steps
+THEN validate environment silently in background (no output unless error)
+AND display progress with ora spinners:
+- Show spinner: "⠋ Creating OpenSpec structure..."
+- Then success: "✔ OpenSpec structure created"
+- Show spinner: "⠋ Configuring AI tools..."
+- Then success: "✔ AI tools configured"
+
+### Directory Creation
+
+WHEN `openspec init` is executed
+THEN create the following directory structure:
+```
+openspec/
+├── project.md
+├── README.md
+├── specs/
+└── changes/
+    └── archive/
+```
+
+### File Generation
+
+The command SHALL generate:
+- `README.md` containing complete OpenSpec instructions for AI assistants
+- `project.md` with project context template
+
+### AI Tool Configuration
+
+WHEN run interactively
+THEN prompt user to select AI tools to configure:
+- Claude Code (updates/creates CLAUDE.md with OpenSpec markers)
+- Cursor (future)
+- Aider (future)
+
+### AI Tool Configuration Details
+
+WHEN Claude Code is selected
+THEN create or update `CLAUDE.md` in the project root directory (not inside openspec/)
+
+WHEN CLAUDE.md does not exist
+THEN create new file with OpenSpec content wrapped in markers:
+```markdown
+<!-- OPENSPEC:START -->
+# OpenSpec Project
+
+This document provides instructions for AI coding assistants on how to use OpenSpec conventions for spec-driven development. Follow these rules precisely when working on OpenSpec-enabled projects.
+
+This project uses OpenSpec for spec-driven development. Specifications are the source of truth.
+
+See @openspec/README.md for detailed conventions and guidelines.
+<!-- OPENSPEC:END -->
+```
+
+WHEN CLAUDE.md already exists
+THEN preserve all existing content
+AND insert OpenSpec content at the beginning of the file using markers
+AND ensure markers don't duplicate if they already exist
+
+The marker system SHALL:
+- Use `<!-- OPENSPEC:START -->` to mark the beginning of managed content
+- Use `<!-- OPENSPEC:END -->` to mark the end of managed content
+- Allow OpenSpec to update its content without affecting user customizations
+- Preserve all content outside the markers intact
+
+WHY use markers:
+- Users may have existing CLAUDE.md instructions they want to keep
+- OpenSpec can update its instructions in future versions
+- Clear boundary between OpenSpec-managed and user-managed content
+
+### Interactive Mode
+
+WHEN run
+THEN prompt user with: "Which AI tool do you use?"
+AND show single-select menu with available tools:
+- Claude Code
+AND show disabled options as "coming soon" (not selectable):
+- Cursor (coming soon)
+- Aider (coming soon)  
+- Continue (coming soon)
+
+User navigation:
+- Use arrow keys to move between options
+- Press Enter to select the highlighted option
+
+### Safety Checks
+
+WHEN `openspec/` directory already exists
+THEN display error with ora fail indicator:
+"✖ Error: OpenSpec seems to already be initialized. Use 'openspec update' to update the structure."
+
+WHEN checking initialization feasibility
+THEN verify write permissions in the target directory silently
+AND only display error if permissions are insufficient
+
+### Success Output
+
+WHEN initialization completes successfully
+THEN display actionable prompts for AI-driven workflow:
+```
+✔ OpenSpec initialized successfully!
+
+Next steps - Copy these prompts to Claude:
+
+────────────────────────────────────────────────────────────
+1. Populate your project context:
+   "Please read openspec/project.md and help me fill it out
+    with details about my project, tech stack, and conventions"
+
+2. Create your first change proposal:
+   "I want to add [YOUR FEATURE HERE]. Please create an
+    OpenSpec change proposal for this feature"
+
+3. Learn the OpenSpec workflow:
+   "Please explain the OpenSpec workflow from openspec/README.md
+    and how I should work with you on this project"
+────────────────────────────────────────────────────────────
+```
+
+The prompts SHALL:
+- Be copy-pasteable for immediate use with AI tools
+- Guide users through the AI-driven workflow
+- Replace placeholder text ([YOUR FEATURE HERE]) with actual features
+
+### Exit Codes
+
+- 0: Success
+- 1: General error (including when OpenSpec directory already exists)
+- 2: Insufficient permissions (reserved for future use)
+- 3: User cancelled operation (reserved for future use)
+
+## Why
+
+Manual creation of OpenSpec structure is error-prone and creates adoption friction. A standardized init command ensures:
+- Consistent structure across all projects
+- Proper AI instruction files are always included
+- Quick onboarding for new projects
+- Clear conventions from the start