fix: clarify openspec/README.md in tasks (AI instructions file)

The diff command now applies deltas and shows side-by-side
requirement comparison rather than just displaying delta instructions.

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

@@ -1,26 +0,0 @@
-# Implementation Tasks
-
-## 1. Core Implementation
-- [ ] 1.1 Create `src/core/list.ts` with list logic
-  - [ ] 1.1.1 Implement directory scanning (exclude archive/)
-  - [ ] 1.1.2 Implement task counting from tasks.md files
-  - [ ] 1.1.3 Format output as simple table
-- [ ] 1.2 Add list command to CLI in `src/cli/index.ts`
-  - [ ] 1.2.1 Register `openspec list` command
-  - [ ] 1.2.2 Connect to list.ts implementation
-
-## 2. Error Handling
-- [ ] 2.1 Handle missing openspec/changes/ directory
-- [ ] 2.2 Handle changes without tasks.md files
-- [ ] 2.3 Handle empty changes directory
-
-## 3. Testing
-- [ ] 3.1 Add tests for list functionality
-  - [ ] 3.1.1 Test with multiple changes
-  - [ ] 3.1.2 Test with completed changes
-  - [ ] 3.1.3 Test with no changes
-  - [ ] 3.1.4 Test error conditions
-
-## 4. Documentation
-- [ ] 4.1 Update CLI help text with list command
-- [ ] 4.2 Add list command to README if applicable

openspec/changes/adopt-delta-based-changes/proposal.md

@@ -0,0 +1,66 @@
+# Adopt Delta-Based Changes for Specifications
+
+## Why
+
+The current approach of storing complete future states in change proposals creates a poor review experience. When reviewing changes on GitHub, reviewers see entire spec files (often 100+ lines) as "added" in green, making it impossible to identify what actually changed. With the recent structured format adoption, we now have clear section boundaries that enable a better approach: storing only additions and modifications.
+
+## What Changes
+
+Store only the requirements that actually change, not complete future states:
+
+- **ADDED Requirements**: New capabilities being introduced
+- **MODIFIED Requirements**: Existing requirements being changed (must match current header)
+- **REMOVED Requirements**: Deprecated capabilities
+- **RENAMED Requirements**: Explicit header changes (e.g., `FROM: Old Name` → `TO: New Name`)
+
+The archive command will programmatically apply these deltas using normalized header matching (trim leading/trailing whitespace) instead of manually copying entire files.
+
+## Impact
+
+**Affected specs**: openspec-conventions, cli-archive, cli-diff
+
+**Benefits**:
+- GitHub diffs show only actual changes (25 lines instead of 150+)
+- Reviewers immediately see what's being added, modified, or removed
+- Conflicts are more apparent when two changes modify the same requirement
+- Archive command can programmatically apply changes
+
+**Format**: Delta format only - all changes must use ADDED/MODIFIED/REMOVED sections.
+
+## Example
+
+Instead of storing a 150-line complete future spec, store only:
+
+```markdown
+# User Authentication - Changes
+
+## ADDED Requirements
+
+### Requirement: OAuth Support
+Users SHALL authenticate via OAuth providers including Google and GitHub.
+
+#### Scenario: OAuth login flow
+- **WHEN** user selects OAuth provider
+- **THEN** redirect to provider authorization
+- **AND** exchange authorization code for tokens
+
+## MODIFIED Requirements
+
+### Requirement: Session Management
+Sessions SHALL expire after 30 minutes of inactivity.
+
+#### Scenario: Inactive session timeout  
+- **WHEN** no activity for 30 minutes ← (was 60 minutes)
+- **THEN** invalidate session token
+- **AND** require re-authentication
+
+## RENAMED Requirements
+- FROM: `### Requirement: Basic Authentication`
+- TO: `### Requirement: Email Authentication`
+```
+
+This makes reviews focused and changes explicit.
+
+## Conflict Resolution
+
+Git naturally detects conflicts when two changes modify the same requirement header. This is actually better than full-state storage where Git might silently merge incompatible changes.

openspec/changes/adopt-delta-based-changes/specs/cli-archive/spec.md

@@ -0,0 +1,46 @@
+# CLI Archive Command - Changes
+
+## MODIFIED Requirements
+
+### Requirement: Spec Update Process
+
+Before moving the change to archive, the command SHALL apply delta changes to main specs to reflect the deployed reality.
+
+#### Scenario: Applying delta changes
+
+- **WHEN** archiving a change with delta-based specs
+- **THEN** parse and apply delta changes as defined in openspec-conventions
+- **AND** validate all operations before applying
+
+#### Scenario: Validating delta changes
+
+- **WHEN** processing delta changes
+- **THEN** perform validations as specified in openspec-conventions
+- **AND** if validation fails, show specific errors and abort
+
+#### Scenario: Conflict detection
+
+- **WHEN** applying deltas would create duplicate requirement headers
+- **THEN** abort with error message showing the conflict
+- **AND** suggest manual resolution
+
+### Requirement: Display Output
+
+The command SHALL provide clear feedback about delta operations.
+
+#### Scenario: Showing delta application
+
+- **WHEN** applying delta changes
+- **THEN** display for each spec:
+  - Number of requirements added
+  - Number of requirements modified
+  - Number of requirements removed
+  - Number of requirements renamed
+- **AND** use standard output symbols (+ ~ - →) as defined in openspec-conventions:
+  ```
+  Applying changes to specs/user-auth/spec.md:
+    + 2 added
+    ~ 3 modified
+    - 1 removed
+    → 1 renamed
+  ```

openspec/changes/adopt-delta-based-changes/specs/cli-diff/spec.md

@@ -0,0 +1,35 @@
+# CLI Diff Command - Changes
+
+## REMOVED Requirements
+
+### Requirement: Display Format
+
+**Reason for removal**: The standard unified diff format is replaced by requirement-level side-by-side comparison that better shows semantic changes rather than line-by-line text differences.
+
+## MODIFIED Requirements
+
+### Requirement: Diff Output
+
+The command SHALL show a requirement-level comparison displaying only changed requirements.
+
+#### Scenario: Side-by-side comparison of changes
+
+- **WHEN** running `openspec diff <change>`
+- **THEN** display only requirements that have changed
+- **AND** show them in a side-by-side format that:
+  - Clearly shows the current version on the left
+  - Shows the future version on the right
+  - Indicates new requirements (not in current)
+  - Indicates removed requirements (not in future)
+  - Aligns modified requirements for easy comparison
+
+### Requirement: Validation
+
+The command SHALL validate that changes can be applied successfully.
+
+#### Scenario: Invalid delta references
+
+- **WHEN** delta references non-existent requirement
+- **THEN** show error message with specific requirement
+- **AND** continue showing other valid changes
+- **AND** clearly mark failed changes in the output

openspec/changes/adopt-delta-based-changes/specs/openspec-conventions/spec.md

@@ -0,0 +1,109 @@
+# OpenSpec Conventions - Changes
+
+## ADDED Requirements
+
+### Requirement: Header-Based Requirement Identification
+
+Requirement headers SHALL serve as unique identifiers for programmatic matching between current specs and proposed changes.
+
+#### Scenario: Matching requirements programmatically
+
+- **WHEN** processing delta changes
+- **THEN** use the `### Requirement: [Name]` header as the unique identifier
+- **AND** match using normalized headers: `normalize(header) = trim(header)`
+- **AND** compare headers with case-sensitive equality after normalization
+
+#### Scenario: Handling requirement renames
+
+- **WHEN** renaming a requirement
+- **THEN** use a special `## RENAMED Requirements` section
+- **AND** specify both old and new names explicitly:
+  ```markdown
+  ## RENAMED Requirements
+  - FROM: `### Requirement: Old Name`
+  - TO: `### Requirement: New Name`
+  ```
+- **AND** if content also changes, include under MODIFIED using the NEW header
+
+#### Scenario: Validating header uniqueness
+
+- **WHEN** creating or modifying requirements
+- **THEN** ensure no duplicate headers exist within a spec
+- **AND** validation tools SHALL flag duplicate headers as errors
+
+## MODIFIED Requirements
+
+### Requirement: Change Storage Convention
+
+Change proposals SHALL store only the additions, modifications, and removals to specifications, not complete future states.
+
+#### Scenario: Creating change proposals with additions
+
+- **WHEN** creating a change proposal that adds new requirements
+- **THEN** include only the new requirements under `## ADDED Requirements`
+- **AND** each requirement SHALL include its complete content
+- **AND** use the standard structured format for requirements and scenarios
+
+#### Scenario: Creating change proposals with modifications  
+
+- **WHEN** creating a change proposal that modifies existing requirements
+- **THEN** include the modified requirements under `## MODIFIED Requirements`
+- **AND** use the same header text as in the current spec (normalized)
+- **AND** include the complete modified requirement (not a diff)
+- **AND** optionally annotate what changed with inline comments like `← (was X)`
+
+#### Scenario: Creating change proposals with removals
+
+- **WHEN** creating a change proposal that removes requirements
+- **THEN** list them under `## REMOVED Requirements`
+- **AND** use the normalized header text for identification
+- **AND** include reason for removal
+- **AND** document any migration path if applicable
+
+
+The `changes/[name]/specs/` directory SHALL contain:
+- Delta files showing only what changes
+- Sections for ADDED, MODIFIED, REMOVED, and RENAMED requirements
+- Normalized header matching for requirement identification
+- Complete requirements using the structured format
+- Clear indication of change type for each requirement
+
+#### Scenario: Using standard output symbols
+
+- **WHEN** displaying delta operations in CLI output
+- **THEN** use these standard symbols:
+  - `+` for ADDED (green)
+  - `~` for MODIFIED (yellow)
+  - `-` for REMOVED (red)
+  - `→` for RENAMED (cyan)
+
+### Requirement: Archive Process Enhancement
+
+The archive process SHALL programmatically apply delta changes to current specifications using header-based matching.
+
+#### Scenario: Archiving changes with deltas
+
+- **WHEN** archiving a completed change
+- **THEN** the archive command SHALL:
+  1. Parse RENAMED sections first and apply renames
+  2. Parse REMOVED sections and remove by normalized header match
+  3. Parse MODIFIED sections and replace by normalized header match (using new names if renamed)
+  4. Parse ADDED sections and append new requirements
+- **AND** validate that all MODIFIED/REMOVED headers exist in current spec
+- **AND** validate that ADDED headers don't already exist
+- **AND** generate the updated spec in the main specs/ directory
+
+#### Scenario: Handling conflicts during archive
+
+- **WHEN** delta changes conflict with current spec state
+- **THEN** the archive command SHALL report specific conflicts
+- **AND** require manual resolution before proceeding
+- **AND** provide clear guidance on resolving conflicts
+
+## REMOVED Requirements
+
+### Requirement: Future State Storage
+
+**Reason for removal**: Replaced by delta-based change storage which provides better review experience and clearer change tracking.
+
+**Migration path**: All new changes must use delta format.

openspec/changes/adopt-delta-based-changes/tasks.md

@@ -0,0 +1,39 @@
+# Implementation Tasks
+
+## 1. Update Conventions
+- [ ] 1.1 Update openspec-conventions spec with delta-based approach
+- [ ] 1.2 Add Header-Based Requirement Identification
+- [ ] 1.3 Define ADDED/MODIFIED/REMOVED/RENAMED sections
+- [ ] 1.4 Document standard output symbols (+ ~ - →)
+- [ ] 1.5 Update openspec/README.md with delta-based conventions
+- [ ] 1.6 Update examples to use delta format
+
+## 2. Update Diff Command
+- [ ] 2.1 Update cli-diff spec with requirement-level comparison
+- [ ] 2.2 Parse specs into requirement-level structures
+- [ ] 2.3 Apply deltas to generate future state
+- [ ] 2.4 Implement side-by-side comparison view (changes only)
+- [ ] 2.5 Add tests for requirement-level comparison
+- [ ] 2.6 Add tests for side-by-side view formatting
+
+## 3. Update Archive Command
+- [ ] 3.1 Update cli-archive spec with delta processing behavior
+- [ ] 3.2 Implement normalized header matching (trim whitespace)
+- [ ] 3.3 Parse delta sections (ADDED/MODIFIED/REMOVED/RENAMED)
+- [ ] 3.4 Apply changes in order: RENAMED → REMOVED → MODIFIED → ADDED
+- [ ] 3.5 Validate delta operations:
+  - [ ] 3.5.1 MODIFIED/REMOVED requirements exist
+  - [ ] 3.5.2 ADDED requirements don't already exist
+  - [ ] 3.5.3 RENAMED FROM headers exist, TO headers don't
+  - [ ] 3.5.4 No duplicate headers within specs
+  - [ ] 3.5.5 Renamed requirements aren't also in ADDED
+- [ ] 3.6 Display operation counts (+ 2 added, ~ 3 modified, etc.)
+- [ ] 3.7 Add tests for header normalization
+- [ ] 3.8 Add tests for applying deltas in correct order
+- [ ] 3.9 Add tests for validation edge cases
+
+## Notes
+- Archive command is critical path - must work reliably
+- All new changes must use delta format
+- Header normalization: normalize(header) = trim(header)
+- Diff command shows only changed requirements in side-by-side comparison

openspec/changes/archive/2025-01-13-add-list-command/tasks.md

@@ -0,0 +1,26 @@
+# Implementation Tasks
+
+## 1. Core Implementation
+- [x] 1.1 Create `src/core/list.ts` with list logic
+  - [x] 1.1.1 Implement directory scanning (exclude archive/)
+  - [x] 1.1.2 Implement task counting from tasks.md files
+  - [x] 1.1.3 Format output as simple table
+- [x] 1.2 Add list command to CLI in `src/cli/index.ts`
+  - [x] 1.2.1 Register `openspec list` command
+  - [x] 1.2.2 Connect to list.ts implementation
+
+## 2. Error Handling
+- [x] 2.1 Handle missing openspec/changes/ directory
+- [x] 2.2 Handle changes without tasks.md files
+- [x] 2.3 Handle empty changes directory
+
+## 3. Testing
+- [x] 3.1 Add tests for list functionality
+  - [x] 3.1.1 Test with multiple changes
+  - [x] 3.1.2 Test with completed changes
+  - [x] 3.1.3 Test with no changes
+  - [x] 3.1.4 Test error conditions
+
+## 4. Documentation
+- [x] 4.1 Update CLI help text with list command
+- [x] 4.2 Add list command to README if applicable

openspec/changes/archive/2025-08-13-add-archive-command/proposal.md

@@ -0,0 +1,15 @@
+## Why
+Need a command to archive completed changes to the archive folder with proper date prefixing, following OpenSpec conventions. Currently changes must be manually moved and renamed.
+
+## What Changes
+- Add new `archive` command to CLI that moves changes to `changes/archive/YYYY-MM-DD-[change-name]/`
+- Check for incomplete tasks before archiving and warn user
+- Allow interactive selection of change to archive
+- Prevent archiving if target directory already exists
+- Update main specs from the change's future state specs (copy from `changes/[name]/specs/` to `openspec/specs/`)
+- Show confirmation prompt before updating specs, displaying which specs will be created/updated
+- Support `--yes` flag to skip confirmations for automation
+
+## Impact
+- Affected specs: cli-archive (new)
+- Affected code: src/cli/index.ts, src/core/archive.ts (new)

openspec/changes/archive/2025-08-13-add-archive-command/specs/cli-archive/spec.md

@@ -0,0 +1,111 @@
+# CLI Archive Command Specification
+
+## Purpose
+The archive command moves completed changes from the active changes directory to the archive folder with date-based naming, following OpenSpec conventions.
+
+## Command Syntax
+```bash
+openspec archive [change-name] [--yes|-y]
+```
+
+Options:
+- `--yes`, `-y`: Skip confirmation prompts (for automation)
+
+## Behavior
+
+### Change Selection
+WHEN no change-name is provided
+THEN display interactive list of available changes (excluding archive/)
+AND allow user to select one
+
+WHEN change-name is provided
+THEN use that change directly
+AND validate it exists
+
+### Task Completion Check
+The command SHALL scan the change's tasks.md file for incomplete tasks (marked with `- [ ]`)
+
+WHEN incomplete tasks are found
+THEN display all incomplete tasks to the user
+AND prompt for confirmation to continue
+AND default to "No" for safety
+
+WHEN all tasks are complete OR no tasks.md exists
+THEN proceed with archiving without prompting
+
+### Archive Process
+The archive operation SHALL:
+1. Create archive/ directory if it doesn't exist
+2. Generate target name as `YYYY-MM-DD-[change-name]` using current date
+3. Check if target directory already exists
+4. Update main specs from the change's future state specs (see Spec Update Process below)
+5. Move the entire change directory to the archive location
+
+WHEN target archive already exists
+THEN fail with error message
+AND do not overwrite existing archive
+
+WHEN move succeeds
+THEN display success message with archived name and list of updated specs
+
+### Spec Update Process
+Before moving the change to archive, the command SHALL update main specs to reflect the deployed reality:
+
+WHEN the change contains specs in `changes/[name]/specs/`
+THEN:
+1. Analyze which specs will be affected by comparing with existing specs
+2. Display a summary of spec updates to the user (see Confirmation Behavior below)
+3. Prompt for confirmation unless `--yes` flag is provided
+4. If confirmed, for each capability spec in the change directory:
+   - Copy the spec from `changes/[name]/specs/[capability]/spec.md` to `openspec/specs/[capability]/spec.md`
+   - Create the target directory structure if it doesn't exist
+   - Overwrite existing spec files (specs represent current reality, change specs are the new reality)
+   - Track which specs were updated for the success message
+
+WHEN no specs exist in the change
+THEN skip the spec update step
+AND proceed with archiving
+
+### Confirmation Behavior
+The spec update confirmation SHALL:
+- Display a clear summary showing:
+  - Which specs will be created (new capabilities)
+  - Which specs will be updated (existing capabilities)
+  - The source path for each spec
+- Format the confirmation prompt as:
+  ```
+  The following specs will be updated:
+  
+  NEW specs to be created:
+    - cli-archive (from changes/add-archive-command/specs/cli-archive/spec.md)
+  
+  EXISTING specs to be updated:
+    - cli-init (from changes/update-init-command/specs/cli-init/spec.md)
+  
+  Update 2 specs and archive 'add-archive-command'? [y/N]:
+  ```
+- Default to "No" for safety (require explicit "y" or "yes")
+- Skip confirmation when `--yes` or `-y` flag is provided
+
+WHEN user declines the confirmation
+THEN abort the entire archive operation
+AND display message: "Archive cancelled. No changes were made."
+AND exit with non-zero status code
+
+## Error Handling
+
+SHALL handle the following error conditions:
+- Missing openspec/changes/ directory
+- Change not found
+- Archive target already exists
+- File system permissions issues
+
+## Why These Decisions
+
+**Interactive selection**: Reduces typing and helps users see available changes
+**Task checking**: Prevents accidental archiving of incomplete work
+**Date prefixing**: Maintains chronological order and prevents naming conflicts
+**No overwrite**: Preserves historical archives and prevents data loss
+**Spec updates before archiving**: Specs in the main directory represent current reality; when a change is deployed and archived, its future state specs become the new reality and must replace the main specs
+**Confirmation for spec updates**: Provides visibility into what will change, prevents accidental overwrites, and ensures users understand the impact before specs are modified
+**--yes flag for automation**: Allows CI/CD pipelines to archive without interactive prompts while maintaining safety by default for manual use

openspec/changes/archive/2025-08-13-add-archive-command/tasks.md

@@ -0,0 +1,44 @@
+# Implementation Tasks
+
+## 1. Core Implementation
+- [ ] 1.1 Create `src/core/archive.ts` with ArchiveCommand class
+  - [ ] 1.1.1 Implement change selection (interactive if not provided)
+  - [ ] 1.1.2 Implement incomplete task checking from tasks.md
+  - [ ] 1.1.3 Implement confirmation prompt for incomplete tasks
+  - [ ] 1.1.4 Implement spec update functionality
+    - [ ] 1.1.4.1 Detect specs in change directory
+    - [ ] 1.1.4.2 Compare with existing main specs
+    - [ ] 1.1.4.3 Display summary of new vs updated specs
+    - [ ] 1.1.4.4 Show confirmation prompt for spec updates
+    - [ ] 1.1.4.5 Copy specs to main spec directory
+  - [ ] 1.1.5 Implement archive move with date prefixing
+  - [ ] 1.1.6 Support --yes flag to skip confirmations
+
+## 2. CLI Integration
+- [ ] 2.1 Add archive command to `src/cli/index.ts`
+  - [ ] 2.1.1 Import ArchiveCommand
+  - [ ] 2.1.2 Register command with commander
+  - [ ] 2.1.3 Add --yes/-y flag option
+  - [ ] 2.1.4 Add proper error handling
+
+## 3. Error Handling
+- [ ] 3.1 Handle missing openspec/changes/ directory
+- [ ] 3.2 Handle change not found
+- [ ] 3.3 Handle archive target already exists
+- [ ] 3.4 Handle user cancellation
+
+## 4. Testing
+- [ ] 4.1 Test with fully completed change
+- [ ] 4.2 Test with incomplete tasks (warning shown)
+- [ ] 4.3 Test interactive selection mode
+- [ ] 4.4 Test duplicate archive prevention
+- [ ] 4.5 Test spec update functionality
+  - [ ] 4.5.1 Test creating new specs
+  - [ ] 4.5.2 Test updating existing specs
+  - [ ] 4.5.3 Test confirmation prompt display
+  - [ ] 4.5.4 Test declining confirmation (no changes made)
+  - [ ] 4.5.5 Test --yes flag skips confirmation
+
+## 5. Build and Validation
+- [ ] 5.1 Ensure TypeScript compilation succeeds
+- [ ] 5.2 Test command execution

openspec/changes/archive/2025-08-13-add-diff-command/proposal.md

@@ -0,0 +1,19 @@
+# Add Diff Command to OpenSpec CLI
+
+## Why
+
+Developers need to easily view differences between proposed spec changes and current specs without manually comparing files.
+
+## What Changes
+
+- Add `openspec diff [change-name]` command that shows differences between change specs and current specs
+- Compare files in `changes/[change-name]/specs/` with corresponding files in `specs/`
+- Display unified diff output showing added/removed/modified lines
+- Support colored output for better readability
+
+## Impact
+
+- Affected specs: New capability `cli-diff` will be added
+- Affected code:
+  - `src/cli/index.ts` - Add diff command
+  - `src/core/diff.ts` - New file with diff logic (~80 lines)

openspec/changes/archive/2025-08-13-add-diff-command/specs/cli-diff/spec.md

@@ -0,0 +1,77 @@
+# CLI Diff Command Specification
+
+## Purpose
+
+The `openspec diff` command provides developers with a visual comparison between proposed spec changes and the current deployed specs.
+
+## Command Syntax
+
+```bash
+openspec diff [change-name]
+```
+
+## Behavior
+
+### Without Arguments
+
+WHEN running `openspec diff` without arguments
+THEN list all available changes in the `changes/` directory (excluding archive)
+AND prompt user to select a change
+
+### With Change Name
+
+WHEN running `openspec diff <change-name>`
+THEN compare all spec files in `changes/<change-name>/specs/` with corresponding files in `specs/`
+
+### Diff Output
+
+FOR each spec file in the change:
+- IF file exists in both locations THEN show unified diff
+- IF file only exists in change THEN show as new file (all lines with +)
+- IF file only exists in current specs THEN show as deleted (all lines with -)
+
+### Display Format
+
+The diff SHALL use standard unified diff format:
+- Lines prefixed with `-` for removed content
+- Lines prefixed with `+` for added content
+- Lines without prefix for unchanged context
+- File headers showing the paths being compared
+
+### Color Support
+
+WHEN terminal supports colors:
+- Removed lines displayed in red
+- Added lines displayed in green
+- File headers displayed in bold
+- Context lines in default color
+
+### Error Handling
+
+WHEN specified change doesn't exist THEN display error "Change '<name>' not found"
+WHEN no specs directory in change THEN display "No spec changes found for '<name>'"
+WHEN changes directory doesn't exist THEN display "No OpenSpec changes directory found"
+
+## Examples
+
+```bash
+# View diff for specific change
+$ openspec diff add-auth-feature
+
+--- specs/user-auth/spec.md
++++ changes/add-auth-feature/specs/user-auth/spec.md
+@@ -10,6 +10,8 @@
+ Users SHALL authenticate with email and password.
+ 
++Users MAY authenticate with OAuth providers.
++
+ WHEN credentials are valid THEN issue JWT token.
+
+# List all changes and select
+$ openspec diff
+Available changes:
+  1. add-auth-feature
+  2. update-payment-flow
+  3. add-status-command
+Select a change (1-3): 
+```

openspec/changes/archive/2025-08-13-add-diff-command/tasks.md

@@ -0,0 +1,23 @@
+# Implementation Tasks
+
+## 1. Core Implementation
+- [x] 1.1 Create `src/core/diff.ts` with diff logic
+- [x] 1.2 Implement change directory scanning
+- [x] 1.3 Implement file comparison using unified diff format
+- [x] 1.4 Add color support for terminal output
+
+## 2. CLI Integration
+- [x] 2.1 Add diff command to `src/cli/index.ts`
+- [x] 2.2 Implement interactive change selection when no argument provided
+- [x] 2.3 Add error handling for missing changes
+
+## 3. Enhancements
+- [x] 3.1 Replace with jest-diff for professional diff output
+- [x] 3.2 Improve file headers with status and statistics
+- [x] 3.3 Add summary view with file counts and line changes
+
+## 4. Testing
+- [ ] 4.1 Test diff generation for modified files
+- [ ] 4.2 Test handling of new files
+- [ ] 4.3 Test handling of deleted files
+- [ ] 4.4 Test interactive mode

openspec/changes/structured-spec-format/proposal.md

@@ -0,0 +1,36 @@
+## Why
+
+OpenSpec specifications lack a consistent structure that makes sections visually identifiable and programmatically parseable across different specs. This makes it harder to maintain consistency and build tooling.
+
+## What Changes
+
+**Specification Format Section**
+- From: No formal structure requirements for specifications
+- To: Structured format with `### Requirement:` and `#### Scenario:` headers
+- Reason: Visual consistency and parseability across all specs
+- Impact: Non-breaking - existing specs can migrate gradually
+
+**Keyword Formatting**
+- From: Inconsistent use of WHEN/THEN/AND keywords
+- To: Bold keywords (**WHEN**, **THEN**, **AND**) in scenario bullets
+- Reason: Improved readability and consistent visual hierarchy
+- Impact: Non-breaking - formatting enhancement only
+
+**Format Flexibility**
+- From: Implicit understanding that different content needs different formats
+- To: Explicit allowance for alternative formats (OpenAPI, JSON Schema, etc.)
+- Reason: Address concern that not all specs fit requirement/scenario pattern
+- Impact: Non-breaking - clarifies existing practice
+
+**Migration Guidelines**
+- From: No migration guidance
+- To: Documented gradual migration approach
+- Reason: Allows incremental adoption without disrupting existing specs
+- Impact: Non-breaking - opt-in migration as specs are modified
+
+## Impact
+
+- Affected specs: openspec-conventions (enhancement to existing capability)
+- Affected code: None initially - this is a documentation standard enhancement
+- Migration: Gradual - existing specs migrate as they're modified
+- Tooling: Enables future parsing tools but doesn't require them

openspec/changes/structured-spec-format/specs/openspec-conventions/spec.md

@@ -0,0 +1,180 @@
+# OpenSpec Conventions Specification
+
+## Purpose
+
+OpenSpec conventions SHALL define how system capabilities are documented, how changes are proposed and tracked, and how specifications evolve over time. This meta-specification serves as the source of truth for OpenSpec's own conventions.
+
+## Core Principles
+
+The system SHALL follow these principles:
+- Specs reflect what IS currently built and deployed
+- Changes contain proposals for what SHOULD be changed
+- AI drives the documentation process
+- Specs are living documentation kept in sync with deployed code
+
+## Directory Structure
+
+WHEN an OpenSpec project is initialized
+THEN it SHALL have this structure:
+```
+openspec/
+├── project.md              # Project-specific context
+├── README.md               # AI assistant instructions
+├── specs/                  # Current deployed capabilities
+│   └── [capability]/       # Single, focused capability
+│       ├── spec.md         # WHAT and WHY
+│       └── design.md       # HOW (optional, for established patterns)
+└── changes/                # Proposed changes
+    ├── [change-name]/      # Descriptive change identifier
+    │   ├── proposal.md     # Why, what, and impact
+    │   ├── tasks.md        # Implementation checklist
+    │   ├── design.md       # Technical decisions (optional)
+    │   └── specs/          # Complete future state
+    │       └── [capability]/
+    │           └── spec.md # Clean markdown (no diff syntax)
+    └── archive/            # Completed changes
+        └── YYYY-MM-DD-[name]/
+```
+
+## Specification Format
+
+### Requirement: Structured Format for Behavioral Specs
+
+Behavioral specifications SHALL use a structured format with consistent section headers and keywords to ensure visual consistency and parseability.
+
+#### Scenario: Writing requirement sections
+
+- **WHEN** documenting a requirement in a behavioral specification
+- **THEN** use a level-3 heading with format `### Requirement: [Name]`
+- **AND** immediately follow with a SHALL statement describing core behavior
+- **AND** keep requirement names descriptive and under 50 characters
+
+#### Scenario: Documenting scenarios
+
+- **WHEN** documenting specific behaviors or use cases
+- **THEN** use level-4 headings with format `#### Scenario: [Description]`
+- **AND** use bullet points with bold keywords for steps:
+  - **GIVEN** for initial state (optional)
+  - **WHEN** for conditions or triggers
+  - **THEN** for expected outcomes
+  - **AND** for additional outcomes or conditions
+
+#### Scenario: Adding implementation details
+
+- **WHEN** a step requires additional detail
+- **THEN** use sub-bullets under the main step
+- **AND** maintain consistent indentation
+  - Sub-bullets provide examples or specifics
+  - Keep sub-bullets concise
+
+### Requirement: Format Flexibility
+
+The structured format SHALL be the default for behavioral specifications, but alternative formats MAY be used when more appropriate for the content type.
+
+#### Scenario: Documenting API specifications
+
+- **WHEN** documenting REST API endpoints or GraphQL schemas
+- **THEN** OpenAPI, GraphQL SDL, or similar formats MAY be used
+- **AND** the spec SHALL clearly indicate the format being used
+- **AND** behavioral aspects SHALL still follow the structured format
+
+#### Scenario: Documenting data schemas
+
+- **WHEN** documenting data structures, database schemas, or configurations
+- **THEN** JSON Schema, SQL DDL, or similar formats MAY be used
+- **AND** include the structured format for behavioral rules and constraints
+
+#### Scenario: Using simplified format
+
+- **WHEN** documenting simple capabilities without complex scenarios
+- **THEN** a simplified WHEN/THEN format without full structure MAY be used
+- **AND** this should be consistent within the capability
+
+## Change Storage Convention
+
+### Future State Storage
+
+WHEN creating a change proposal
+THEN store the complete future state of affected specs
+AND use clean markdown without diff syntax
+
+The `changes/[name]/specs/` directory SHALL contain:
+- Complete spec files as they will exist after the change
+- Clean markdown without `+` or `-` prefixes
+- All formatting and structure of the final intended state
+
+### Proposal Format
+
+WHEN documenting what changes
+THEN the proposal SHALL explicitly describe each change:
+
+```markdown
+**[Section or Behavior Name]**
+- From: [current state/requirement]
+- To: [future state/requirement]
+- Reason: [why this change is needed]
+- Impact: [breaking/non-breaking, who's affected]
+```
+
+This explicit format compensates for not having inline diffs and ensures reviewers understand exactly what will change.
+
+## Change Lifecycle
+
+The change process SHALL follow these states:
+
+1. **Propose**: AI creates change with future state specs and explicit proposal
+2. **Review**: Humans review proposal and future state
+3. **Approve**: Change is approved for implementation
+4. **Implement**: Follow tasks.md checklist (can span multiple PRs)
+5. **Deploy**: Changes are deployed to production
+6. **Update**: Specs in `specs/` are updated to match deployed reality
+7. **Archive**: Change is moved to `archive/YYYY-MM-DD-[name]/`
+
+## Viewing Changes
+
+WHEN reviewing proposed changes
+THEN reviewers can compare using:
+- GitHub PR diff view when changes are committed
+- Command line: `diff -u specs/[capability]/spec.md changes/[name]/specs/[capability]/spec.md`
+- Any visual diff tool comparing current vs future state
+
+The system relies on tools to generate diffs rather than storing them.
+
+## Capability Naming
+
+Capabilities SHALL use:
+- Verb-noun patterns (e.g., `user-auth`, `payment-capture`)
+- Hyphenated lowercase names
+- Singular focus (one responsibility per capability)
+- No nesting (flat structure under `specs/`)
+
+## When Changes Require Proposals
+
+A proposal SHALL be created for:
+- New features or capabilities
+- Breaking changes to existing behavior
+- Architecture or pattern changes
+- Performance optimizations that change behavior
+- Security updates affecting access patterns
+
+A proposal is NOT required for:
+- Bug fixes restoring intended behavior
+- Typos or formatting fixes
+- Non-breaking dependency updates
+- Adding tests for existing behavior
+- Documentation clarifications
+
+## Why This Approach
+
+Clean future state storage provides:
+- **Readability**: No diff syntax pollution
+- **AI-compatibility**: Standard markdown that AI tools understand
+- **Simplicity**: No special parsing or processing needed
+- **Tool-agnostic**: Any diff tool can show changes
+- **Clear intent**: Explicit proposals document reasoning
+
+The structured format adds:
+- **Visual Consistency**: Requirement and Scenario prefixes make sections instantly recognizable
+- **Parseability**: Consistent structure enables tooling and automation
+- **Flexibility**: Alternative formats supported where appropriate
+- **Gradual Adoption**: Existing specs can migrate incrementally

openspec/changes/structured-spec-format/tasks.md

@@ -0,0 +1,19 @@
+## 1. Update OpenSpec Conventions Spec
+
+- [x] 1.1 Add "Specification Format" section to openspec-conventions
+- [x] 1.2 Document structured format with Requirement/Scenario headers
+- [x] 1.3 Define bold keyword usage (WHEN/THEN/AND) for scenarios
+- [x] 1.4 Include examples demonstrating the format within the spec itself
+
+## 2. Update Documentation
+
+- [x] 2.1 Update the "Why This Approach" section with structured format benefits
+- [x] 2.2 Ensure spec follows its own format as a demonstration
+
+## 3. Update Existing Specs
+
+- [x] 3.1 Update cli-init spec to use structured format in Behavior section
+- [x] 3.2 Update cli-list spec to use structured format in Behavior section
+- [x] 3.3 Update cli-update spec to use structured format in Behavior section
+- [x] 3.4 Update cli-diff spec to use structured format in Behavior section
+- [x] 3.5 Update cli-archive spec to use structured format in Behavior section

openspec/specs/cli-archive/spec.md

@@ -0,0 +1,155 @@
+# CLI Archive Command Specification
+
+## Purpose
+The archive command moves completed changes from the active changes directory to the archive folder with date-based naming, following OpenSpec conventions.
+
+## Command Syntax
+```bash
+openspec archive [change-name] [--yes|-y]
+```
+
+Options:
+- `--yes`, `-y`: Skip confirmation prompts (for automation)
+
+## Behavior
+
+### Requirement: Change Selection
+
+The command SHALL support both interactive and direct change selection methods.
+
+#### Scenario: Interactive selection
+
+- **WHEN** no change-name is provided
+- **THEN** display interactive list of available changes (excluding archive/)
+- **AND** allow user to select one
+
+#### Scenario: Direct selection
+
+- **WHEN** change-name is provided
+- **THEN** use that change directly
+- **AND** validate it exists
+
+### Requirement: Task Completion Check
+
+The command SHALL verify task completion status before archiving to prevent premature archival.
+
+#### Scenario: Incomplete tasks found
+
+- **WHEN** incomplete tasks are found (marked with `- [ ]`)
+- **THEN** display all incomplete tasks to the user
+- **AND** prompt for confirmation to continue
+- **AND** default to "No" for safety
+
+#### Scenario: All tasks complete
+
+- **WHEN** all tasks are complete OR no tasks.md exists
+- **THEN** proceed with archiving without prompting
+
+### Requirement: Archive Process
+
+The archive operation SHALL follow a structured process to safely move changes to the archive.
+
+#### Scenario: Performing archive
+
+- **WHEN** archiving a change
+- **THEN** execute these steps:
+  1. Create archive/ directory if it doesn't exist
+  2. Generate target name as `YYYY-MM-DD-[change-name]` using current date
+  3. Check if target directory already exists
+  4. Update main specs from the change's future state specs (see Spec Update Process below)
+  5. Move the entire change directory to the archive location
+
+#### Scenario: Archive already exists
+
+- **WHEN** target archive already exists
+- **THEN** fail with error message
+- **AND** do not overwrite existing archive
+
+#### Scenario: Successful archive
+
+- **WHEN** move succeeds
+- **THEN** display success message with archived name and list of updated specs
+
+### Requirement: Spec Update Process
+
+Before moving the change to archive, the command SHALL update main specs to reflect the deployed reality.
+
+#### Scenario: Updating specs from change
+
+- **WHEN** the change contains specs in `changes/[name]/specs/`
+- **THEN** execute these steps:
+  1. Analyze which specs will be affected by comparing with existing specs
+  2. Display a summary of spec updates to the user (see Confirmation Behavior below)
+  3. Prompt for confirmation unless `--yes` flag is provided
+  4. If confirmed, for each capability spec in the change directory:
+     - Copy the spec from `changes/[name]/specs/[capability]/spec.md` to `openspec/specs/[capability]/spec.md`
+     - Create the target directory structure if it doesn't exist
+     - Overwrite existing spec files (specs represent current reality, change specs are the new reality)
+     - Track which specs were updated for the success message
+
+#### Scenario: No specs in change
+
+- **WHEN** no specs exist in the change
+- **THEN** skip the spec update step
+- **AND** proceed with archiving
+
+### Requirement: Confirmation Behavior
+
+The spec update confirmation SHALL provide clear visibility into changes before they are applied.
+
+#### Scenario: Displaying confirmation
+
+- **WHEN** prompting for confirmation
+- **THEN** display a clear summary showing:
+  - Which specs will be created (new capabilities)
+  - Which specs will be updated (existing capabilities)
+  - The source path for each spec
+- **AND** format the confirmation prompt as:
+  ```
+  The following specs will be updated:
+  
+  NEW specs to be created:
+    - cli-archive (from changes/add-archive-command/specs/cli-archive/spec.md)
+  
+  EXISTING specs to be updated:
+    - cli-init (from changes/update-init-command/specs/cli-init/spec.md)
+  
+  Update 2 specs and archive 'add-archive-command'? [y/N]:
+  ```
+#### Scenario: Handling confirmation response
+
+- **WHEN** waiting for user confirmation
+- **THEN** default to "No" for safety (require explicit "y" or "yes")
+- **AND** skip confirmation when `--yes` or `-y` flag is provided
+
+#### Scenario: User declines confirmation
+
+- **WHEN** user declines the confirmation
+- **THEN** abort the entire archive operation
+- **AND** display message: "Archive cancelled. No changes were made."
+- **AND** exit with non-zero status code
+
+## Error Handling
+
+### Requirement: Error Conditions
+
+The command SHALL handle various error conditions gracefully.
+
+#### Scenario: Handling errors
+
+- **WHEN** errors occur
+- **THEN** handle the following conditions:
+  - Missing openspec/changes/ directory
+  - Change not found
+  - Archive target already exists
+  - File system permissions issues
+
+## Why These Decisions
+
+**Interactive selection**: Reduces typing and helps users see available changes
+**Task checking**: Prevents accidental archiving of incomplete work
+**Date prefixing**: Maintains chronological order and prevents naming conflicts
+**No overwrite**: Preserves historical archives and prevents data loss
+**Spec updates before archiving**: Specs in the main directory represent current reality; when a change is deployed and archived, its future state specs become the new reality and must replace the main specs
+**Confirmation for spec updates**: Provides visibility into what will change, prevents accidental overwrites, and ensures users understand the impact before specs are modified
+**--yes flag for automation**: Allows CI/CD pipelines to archive without interactive prompts while maintaining safety by default for manual use

openspec/specs/cli-diff/spec.md

@@ -0,0 +1,120 @@
+# CLI Diff Command Specification
+
+## Purpose
+
+The `openspec diff` command provides developers with a visual comparison between proposed spec changes and the current deployed specs.
+
+## Command Syntax
+
+```bash
+openspec diff [change-name]
+```
+
+## Behavior
+
+### Requirement: Without Arguments
+
+The command SHALL provide an interactive selection when no change is specified.
+
+#### Scenario: Running without arguments
+
+- **WHEN** running `openspec diff` without arguments
+- **THEN** list all available changes in the `changes/` directory (excluding archive)
+- **AND** prompt user to select a change
+
+### Requirement: With Change Name
+
+The command SHALL compare specs when a specific change is provided.
+
+#### Scenario: Running with change name
+
+- **WHEN** running `openspec diff <change-name>`
+- **THEN** compare all spec files in `changes/<change-name>/specs/` with corresponding files in `specs/`
+
+### Requirement: Diff Output
+
+The command SHALL generate appropriate diff output for all spec changes.
+
+#### Scenario: Comparing existing files
+
+- **WHEN** file exists in both locations
+- **THEN** show unified diff
+
+#### Scenario: New files
+
+- **WHEN** file only exists in change
+- **THEN** show as new file (all lines with +)
+
+#### Scenario: Deleted files
+
+- **WHEN** file only exists in current specs
+- **THEN** show as deleted (all lines with -)
+
+### Requirement: Display Format
+
+The command SHALL use standard unified diff format for consistency with existing tools.
+
+#### Scenario: Formatting diff output
+
+- **WHEN** displaying diff output
+- **THEN** use standard unified diff format:
+  - Lines prefixed with `-` for removed content
+  - Lines prefixed with `+` for added content
+  - Lines without prefix for unchanged context
+  - File headers showing the paths being compared
+
+### Requirement: Color Support
+
+The command SHALL enhance readability with colors when supported.
+
+#### Scenario: Terminal with color support
+
+- **WHEN** terminal supports colors
+- **THEN** display:
+  - Removed lines in red
+  - Added lines in green
+  - File headers in bold
+  - Context lines in default color
+
+### Requirement: Error Handling
+
+The command SHALL provide clear error messages for various failure conditions.
+
+#### Scenario: Change not found
+
+- **WHEN** specified change doesn't exist
+- **THEN** display error "Change '<name>' not found"
+
+#### Scenario: No specs in change
+
+- **WHEN** no specs directory in change
+- **THEN** display "No spec changes found for '<name>'"
+
+#### Scenario: Missing changes directory
+
+- **WHEN** changes directory doesn't exist
+- **THEN** display "No OpenSpec changes directory found"
+
+## Examples
+
+```bash
+# View diff for specific change
+$ openspec diff add-auth-feature
+
+--- specs/user-auth/spec.md
++++ changes/add-auth-feature/specs/user-auth/spec.md
+@@ -10,6 +10,8 @@
+ Users SHALL authenticate with email and password.
+ 
++Users MAY authenticate with OAuth providers.
++
+ WHEN credentials are valid THEN issue JWT token.
+
+# List all changes and select
+$ openspec diff
+Available changes:
+  1. add-auth-feature
+  2. update-payment-flow
+  3. add-status-command
+Select a change (1-3): 
+```

openspec/specs/cli-init/spec.md

@@ -6,20 +6,28 @@ The `openspec init` command SHALL create a complete OpenSpec directory structure
 
 ## Behavior
 
-### Progress Indicators
+### Requirement: 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"
+The command SHALL display progress indicators during initialization to provide clear feedback about each step.
 
-### Directory Creation
+#### Scenario: Displaying initialization progress
 
-WHEN `openspec init` is executed
-THEN create the following directory structure:
+- **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"
+
+### Requirement: Directory Creation
+
+The command SHALL create the complete OpenSpec directory structure with all required directories and files.
+
+#### Scenario: Creating OpenSpec structure
+
+- **WHEN** `openspec init` is executed
+- **THEN** create the following directory structure:
 ```
 openspec/
 ├── project.md
@@ -29,27 +37,41 @@ openspec/
     └── archive/
 ```
 
-### File Generation
+### Requirement: File Generation
 
-The command SHALL generate:
-- `README.md` containing complete OpenSpec instructions for AI assistants
-- `project.md` with project context template
+The command SHALL generate required template files with appropriate content for immediate use.
 
-### AI Tool Configuration
+#### Scenario: Generating template files
 
-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)
+- **WHEN** initializing OpenSpec
+- **THEN** generate `README.md` containing complete OpenSpec instructions for AI assistants
+- **AND** generate `project.md` with project context template
 
-### AI Tool Configuration Details
+### Requirement: AI Tool Configuration
 
-WHEN Claude Code is selected
-THEN create or update `CLAUDE.md` in the project root directory (not inside openspec/)
+The command SHALL configure AI coding assistants with OpenSpec instructions based on user selection.
 
-WHEN CLAUDE.md does not exist
-THEN create new file with OpenSpec content wrapped in markers:
+#### Scenario: Prompting for AI tool selection
+
+- **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)
+
+### Requirement: AI Tool Configuration Details
+
+The command SHALL properly configure selected AI tools with OpenSpec-specific instructions using a marker system.
+
+#### Scenario: Configuring Claude Code
+
+- **WHEN** Claude Code is selected
+- **THEN** create or update `CLAUDE.md` in the project root directory (not inside openspec/)
+
+#### Scenario: Creating new CLAUDE.md
+
+- **WHEN** CLAUDE.md does not exist
+- **THEN** create new file with OpenSpec content wrapped in markers:
 ```markdown
 <!-- OPENSPEC:START -->
 # OpenSpec Project
@@ -62,51 +84,71 @@ 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
+#### Scenario: Updating existing CLAUDE.md
 
-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
+- **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
+
+#### Scenario: Managing content with markers
+
+- **WHEN** using the marker system
+- **THEN** use `<!-- OPENSPEC:START -->` to mark the beginning of managed content
+- **AND** use `<!-- OPENSPEC:END -->` to mark the end of managed content
+- **AND** allow OpenSpec to update its content without affecting user customizations
+- **AND** 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
+### Requirement: 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)
+The command SHALL provide an interactive menu for AI tool selection with clear navigation instructions.
 
-User navigation:
-- Use arrow keys to move between options
-- Press Enter to select the highlighted option
+#### Scenario: Displaying interactive menu
 
-### Safety Checks
+- **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)
 
-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."
+#### Scenario: Navigating the menu
 
-WHEN checking initialization feasibility
-THEN verify write permissions in the target directory silently
-AND only display error if permissions are insufficient
+- **WHEN** user is in the menu
+- **THEN** allow arrow keys to move between options
+- **AND** allow Enter key to select the highlighted option
 
-### Success Output
+### Requirement: Safety Checks
 
-WHEN initialization completes successfully
-THEN display actionable prompts for AI-driven workflow:
+The command SHALL perform safety checks to prevent overwriting existing structures and ensure proper permissions.
+
+#### Scenario: Detecting existing initialization
+
+- **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."
+
+#### Scenario: Checking write permissions
+
+- **WHEN** checking initialization feasibility
+- **THEN** verify write permissions in the target directory silently
+- **AND** only display error if permissions are insufficient
+
+### Requirement: Success Output
+
+The command SHALL provide clear, actionable next steps upon successful initialization.
+
+#### Scenario: Displaying success message
+
+- **WHEN** initialization completes successfully
+- **THEN** display actionable prompts for AI-driven workflow:
 ```
 ✔ OpenSpec initialized successfully!
 
@@ -132,12 +174,18 @@ The prompts SHALL:
 - Guide users through the AI-driven workflow
 - Replace placeholder text ([YOUR FEATURE HERE]) with actual features
 
-### Exit Codes
+### Requirement: 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)
+The command SHALL use consistent exit codes to indicate different failure modes.
+
+#### Scenario: Returning exit codes
+
+- **WHEN** the command completes
+- **THEN** return appropriate exit code:
+  - 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
 

openspec/specs/cli-list/spec.md

@@ -0,0 +1,96 @@
+# List Command Specification
+
+## Purpose
+
+The `openspec list` command SHALL provide developers with a quick overview of all active changes in the project, showing their names and task completion status.
+
+## Behavior
+
+### Requirement: Command Execution
+
+The command SHALL scan and analyze all active changes to provide a comprehensive overview.
+
+#### Scenario: Scanning for changes
+
+- **WHEN** `openspec list` is executed
+- **THEN** scan the `openspec/changes/` directory for change directories
+- **AND** exclude the `archive/` subdirectory from results
+- **AND** parse each change's `tasks.md` file to count task completion
+
+### Requirement: Task Counting
+
+The command SHALL accurately count task completion status using standard markdown checkbox patterns.
+
+#### Scenario: Counting tasks in tasks.md
+
+- **WHEN** parsing a `tasks.md` file
+- **THEN** count tasks matching these patterns:
+  - Completed: Lines containing `- [x]`
+  - Incomplete: Lines containing `- [ ]`
+- **AND** calculate total tasks as the sum of completed and incomplete
+
+### Requirement: Output Format
+
+The command SHALL display changes in a clear, readable table format with progress indicators.
+
+#### Scenario: Displaying change list
+
+- **WHEN** displaying the list
+- **THEN** show a table with columns:
+  - Change name (directory name)
+  - Task progress (e.g., "3/5 tasks" or "✓ Complete")
+- **AND** use status indicators:
+  - `✓` for fully completed changes (all tasks done)
+  - Progress fraction for partial completion
+
+Example output:
+```
+Changes:
+  add-auth-feature     3/5 tasks
+  update-api-docs      ✓ Complete
+  fix-validation       0/2 tasks
+  add-list-command     1/4 tasks
+```
+
+### Requirement: Empty State
+
+The command SHALL provide clear feedback when no active changes are present.
+
+#### Scenario: Handling empty state
+
+- **WHEN** no active changes exist (only archive/ or empty changes/)
+- **THEN** display: "No active changes found."
+
+### Requirement: Error Handling
+
+The command SHALL gracefully handle missing files and directories with appropriate messages.
+
+#### Scenario: Missing tasks.md file
+
+- **WHEN** a change directory has no `tasks.md` file
+- **THEN** display the change with "No tasks" status
+
+#### Scenario: Missing changes directory
+
+- **WHEN** `openspec/changes/` directory doesn't exist
+- **THEN** display error: "No OpenSpec changes directory found. Run 'openspec init' first."
+- **AND** exit with code 1
+
+### Requirement: Sorting
+
+The command SHALL maintain consistent ordering of changes for predictable output.
+
+#### Scenario: Ordering changes
+
+- **WHEN** displaying multiple changes
+- **THEN** sort them in alphabetical order by change name
+
+## Why
+
+Developers need a quick way to:
+- See what changes are in progress
+- Identify which changes are ready to archive
+- Understand the overall project evolution status
+- Get a bird's-eye view without opening multiple files
+
+This command provides that visibility with minimal effort, following OpenSpec's philosophy of simplicity and clarity.

openspec/specs/cli-update/spec.md

@@ -6,45 +6,65 @@ As a developer using OpenSpec, I want to update the OpenSpec instructions in my
 
 ## Core Requirements
 
-### Update Behavior
+### Requirement: 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"
+#### Scenario: Running update command
 
-### Prerequisites
+- **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"
 
-The command SHALL require:
-- An existing `openspec` directory (created by `openspec init`)
+### Requirement: Prerequisites
 
-IF the `openspec` directory does not exist THEN:
-- Display error: "No OpenSpec directory found. Run 'openspec init' first."
-- Exit with code 1
+The command SHALL require an existing OpenSpec structure before allowing updates.
 
-### File Handling
+#### Scenario: Checking prerequisites
 
-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)
+- **GIVEN** the command requires an existing `openspec` directory (created by `openspec init`)
+- **WHEN** the `openspec` directory does not exist
+- **THEN** display error: "No OpenSpec directory found. Run 'openspec init' first."
+- **AND** exit with code 1
+
+### Requirement: File Handling
+
+The update command SHALL handle file updates in a predictable and safe manner.
+
+#### Scenario: Updating files
+
+- **WHEN** updating files
+- **THEN** completely replace `openspec/README.md` with the latest template
+- **AND** update only the OpenSpec-managed block in `CLAUDE.md` using markers
+- **AND** use the default directory name `openspec`
+- **AND** 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.
+### Requirement: Error Handling
 
-### Missing CLAUDE.md
-IF CLAUDE.md doesn't exist THEN create it with the template content.
+The command SHALL handle edge cases gracefully.
 
-### Custom Directory Name
-Not supported in this change. The default directory name `openspec` SHALL be used.
+#### Scenario: File permission errors
+
+- **WHEN** file write fails
+- **THEN** let the error bubble up naturally with file path
+
+#### Scenario: Missing CLAUDE.md
+
+- **WHEN** CLAUDE.md doesn't exist
+- **THEN** create it with the template content
+
+#### Scenario: Custom directory names
+
+- **WHEN** considering custom directory names
+- **THEN** not supported in this change
+- **AND** the default directory name `openspec` SHALL be used
 
 ## Success Criteria
 

openspec/specs/openspec-conventions/spec.md

@@ -14,8 +14,14 @@ The system SHALL follow these principles:
 
 ## Directory Structure
 
-WHEN an OpenSpec project is initialized
-THEN it SHALL have this structure:
+### Requirement: Project Structure
+
+An OpenSpec project SHALL maintain a consistent directory structure for specifications and changes.
+
+#### Scenario: Initializing project structure
+
+- **WHEN** an OpenSpec project is initialized
+- **THEN** it SHALL have this structure:
 ```
 openspec/
 ├── project.md              # Project-specific context
@@ -36,23 +42,63 @@ openspec/
         └── YYYY-MM-DD-[name]/
 ```
 
+## Specification Format
+
+### Requirement: Structured Format for Behavioral Specs
+
+Behavioral specifications SHALL use a structured format with consistent section headers and keywords to ensure visual consistency and parseability.
+
+#### Scenario: Writing requirement sections
+
+- **WHEN** documenting a requirement in a behavioral specification
+- **THEN** use a level-3 heading with format `### Requirement: [Name]`
+- **AND** immediately follow with a SHALL statement describing core behavior
+- **AND** keep requirement names descriptive and under 50 characters
+
+#### Scenario: Documenting scenarios
+
+- **WHEN** documenting specific behaviors or use cases
+- **THEN** use level-4 headings with format `#### Scenario: [Description]`
+- **AND** use bullet points with bold keywords for steps:
+  - **GIVEN** for initial state (optional)
+  - **WHEN** for conditions or triggers
+  - **THEN** for expected outcomes
+  - **AND** for additional outcomes or conditions
+
+#### Scenario: Adding implementation details
+
+- **WHEN** a step requires additional detail
+- **THEN** use sub-bullets under the main step
+- **AND** maintain consistent indentation
+  - Sub-bullets provide examples or specifics
+  - Keep sub-bullets concise
+
+
 ## Change Storage Convention
 
-### Future State Storage
+### Requirement: Future State Storage
 
-WHEN creating a change proposal
-THEN store the complete future state of affected specs
-AND use clean markdown without diff syntax
+Change proposals SHALL store complete future state specifications without diff syntax.
+
+#### Scenario: Creating change proposals
+
+- **WHEN** creating a change proposal
+- **THEN** store the complete future state of affected specs
+- **AND** use clean markdown without diff syntax
 
 The `changes/[name]/specs/` directory SHALL contain:
 - Complete spec files as they will exist after the change
 - Clean markdown without `+` or `-` prefixes
 - All formatting and structure of the final intended state
 
-### Proposal Format
+### Requirement: Proposal Format
 
-WHEN documenting what changes
-THEN the proposal SHALL explicitly describe each change:
+Proposals SHALL explicitly document all changes with clear from/to comparisons.
+
+#### Scenario: Documenting changes
+
+- **WHEN** documenting what changes
+- **THEN** the proposal SHALL explicitly describe each change:
 
 ```markdown
 **[Section or Behavior Name]**
@@ -78,8 +124,14 @@ The change process SHALL follow these states:
 
 ## Viewing Changes
 
-WHEN reviewing proposed changes
-THEN reviewers can compare using:
+### Requirement: Change Review
+
+The system SHALL support multiple methods for reviewing proposed changes.
+
+#### Scenario: Reviewing changes
+
+- **WHEN** reviewing proposed changes
+- **THEN** reviewers can compare using:
 - GitHub PR diff view when changes are committed
 - Command line: `diff -u specs/[capability]/spec.md changes/[name]/specs/[capability]/spec.md`
 - Any visual diff tool comparing current vs future state
@@ -117,4 +169,9 @@ Clean future state storage provides:
 - **AI-compatibility**: Standard markdown that AI tools understand
 - **Simplicity**: No special parsing or processing needed
 - **Tool-agnostic**: Any diff tool can show changes
-- **Clear intent**: Explicit proposals document reasoning
+- **Clear intent**: Explicit proposals document reasoning
+
+The structured format adds:
+- **Visual Consistency**: Requirement and Scenario prefixes make sections instantly recognizable
+- **Parseability**: Consistent structure enables tooling and automation
+- **Gradual Adoption**: Existing specs can migrate incrementally

package.json

@@ -53,7 +53,9 @@
   },
   "dependencies": {
     "@inquirer/prompts": "^7.8.0",
+    "chalk": "^5.5.0",
     "commander": "^14.0.0",
+    "jest-diff": "^30.0.5",
     "ora": "^8.2.0"
   }
 }

pnpm-lock.yaml

@@ -11,9 +11,15 @@ importers:
       '@inquirer/prompts':
         specifier: ^7.8.0
         version: 7.8.0(@types/node@24.2.0)
+      chalk:
+        specifier: ^5.5.0
+        version: 5.5.0
       commander:
         specifier: ^14.0.0
         version: 14.0.0
+      jest-diff:
+        specifier: ^30.0.5
+        version: 30.0.5
       ora:
         specifier: ^8.2.0
         version: 8.2.0
@@ -310,6 +316,18 @@ packages:
       '@types/node':
         optional: true
 
+  '@jest/diff-sequences@30.0.1':
+    resolution: {integrity: sha512-n5H8QLDJ47QqbCNn5SuFjCRDrOLEZ0h8vAHCK5RL9Ls7Xa8AQLa/YxAc9UjFqoEDM48muwtBGjtMY5cr0PLDCw==}
+    engines: {node: ^18.14.0 || ^20.0.0 || ^22.0.0 || >=24.0.0}
+
+  '@jest/get-type@30.0.1':
+    resolution: {integrity: sha512-AyYdemXCptSRFirI5EPazNxyPwAL0jXt3zceFjaj8NFiKP9pOi0bfXonf6qkf82z2t3QWPeLCWWw4stPBzctLw==}
+    engines: {node: ^18.14.0 || ^20.0.0 || ^22.0.0 || >=24.0.0}
+
+  '@jest/schemas@30.0.5':
+    resolution: {integrity: sha512-DmdYgtezMkh3cpU8/1uyXakv3tJRcmcXxBOcO0tbaozPwpmh4YMsnWrQm9ZmZMfa5ocbxzbFk6O4bDPEc/iAnA==}
+    engines: {node: ^18.14.0 || ^20.0.0 || ^22.0.0 || >=24.0.0}
+
   '@jridgewell/sourcemap-codec@1.5.4':
     resolution: {integrity: sha512-VT2+G1VQs/9oz078bLrYbecdZKs912zQlkelYpuf+SXF+QvZDYJlbx/LSx+meSAwdDFnF8FVXW92AVjjkVmgFw==}
 
@@ -416,6 +434,9 @@ packages:
     cpu: [x64]
     os: [win32]
 
+  '@sinclair/typebox@0.34.38':
+    resolution: {integrity: sha512-HpkxMmc2XmZKhvaKIZZThlHmx1L0I/V1hWK1NubtlFnr6ZqdiOpV72TKudZUNQjZNsyDBay72qFEhEvb+bcwcA==}
+
   '@types/chai@5.2.2':
     resolution: {integrity: sha512-8kB30R7Hwqf40JPiKhVzodJs2Qc1ZJ5zuT3uzw5Hq/dhNCl3G3l83jfpdI1e20BP348+fV7VIL/+FxaXkqBmWg==}
 
@@ -478,6 +499,10 @@ packages:
     resolution: {integrity: sha512-zbB9rCJAT1rbjiVDb2hqKFHNYLxgtk8NURxZ3IZwD3F6NtxbXZQCnnSi1Lkx+IDohdPlFp222wVALIheZJQSEg==}
     engines: {node: '>=8'}
 
+  ansi-styles@5.2.0:
+    resolution: {integrity: sha512-Cxwpt2SfTzTtXcfOlzGEee8O+c+MmUgGrNiBcXnuWxuFJHe6a5Hz7qwhwe5OgaSYI0IJvkLqWX1ASG+cJOkEiA==}
+    engines: {node: '>=10'}
+
   assertion-error@2.0.1:
     resolution: {integrity: sha512-Izi8RQcffqCeNVgFigKli1ssklIbpHnCYc6AknXGYoB6grJqyeby7jv12JUQgmTAnIDnbck1uxksT4dzN3PWBA==}
     engines: {node: '>=12'}
@@ -490,6 +515,10 @@ packages:
     resolution: {integrity: sha512-5nFxhUrX0PqtyogoYOA8IPswy5sZFTOsBFl/9bNsmDLgsxYTzSZQJDPppDnZPTQbzSEm0hqGjWPzRemQCYbD6A==}
     engines: {node: '>=18'}
 
+  chalk@4.1.2:
+    resolution: {integrity: sha512-oKnbhFyRIXpUuez8iBMmyEa4nbj4IOQyuhc/wy9kY7/WVPcwIO9VA668Pu8RkO7+0G76SLROeyw9CpQ061i4mA==}
+    engines: {node: '>=10'}
+
   chalk@5.5.0:
     resolution: {integrity: sha512-1tm8DTaJhPBG3bIkVeZt1iZM9GfSX2lzOeDVZH9R9ffRHpmHvxZ/QhgQH/aDTkswQVt+YHdXAdS/In/30OjCbg==}
     engines: {node: ^12.17.0 || ^14.13 || >=16.0.0}
@@ -585,6 +614,10 @@ packages:
     resolution: {integrity: sha512-vpeMIQKxczTD/0s2CdEWHcb0eeJe6TFjxb+J5xgX7hScxqrGuyjmv4c1D4A/gelKfyox0gJJwIHF+fLjeaM8kQ==}
     engines: {node: '>=18'}
 
+  has-flag@4.0.0:
+    resolution: {integrity: sha512-EykJT/Q1KjTWctppgIAgfSO0tKVuZUjhgMr17kqTumMl6Afv3EISleU7qZUzoXDFTAHTDC4NOoG/ZxU3EvlMPQ==}
+    engines: {node: '>=8'}
+
   iconv-lite@0.4.24:
     resolution: {integrity: sha512-v3MXnZAcvnywkTUEZomIActle7RXXeedOR31wwl7VlyoXO4Qi9arvSenNQWne1TcRwhCL1HwLI21bEqdpj8/rA==}
     engines: {node: '>=0.10.0'}
@@ -605,6 +638,10 @@ packages:
     resolution: {integrity: sha512-mE00Gnza5EEB3Ds0HfMyllZzbBrmLOX3vfWoj9A9PEnTfratQ/BcaJOuMhnkhjXvb2+FkY3VuHqtAGpTPmglFQ==}
     engines: {node: '>=18'}
 
+  jest-diff@30.0.5:
+    resolution: {integrity: sha512-1UIqE9PoEKaHcIKvq2vbibrCog4Y8G0zmOxgQUVEiTqwR5hJVMCoDsN1vFvI5JvwD37hjueZ1C4l2FyGnfpE0A==}
+    engines: {node: ^18.14.0 || ^20.0.0 || ^22.0.0 || >=24.0.0}
+
   js-tokens@9.0.1:
     resolution: {integrity: sha512-mxa9E9ITFOt0ban3j6L5MpjwegGz6lBQmM1IJkWeBZGcMxto50+eWdjC/52xDbS2vy0k7vIMK0Fe2wfL9OQSpQ==}
 
@@ -668,6 +705,13 @@ packages:
     resolution: {integrity: sha512-3Ybi1tAuwAP9s0r1UQ2J4n5Y0G05bJkpUIO0/bI9MhwmD70S5aTWbXGBwxHrelT+XM1k6dM0pk+SwNkpTRN7Pg==}
     engines: {node: ^10 || ^12 || >=14}
 
+  pretty-format@30.0.5:
+    resolution: {integrity: sha512-D1tKtYvByrBkFLe2wHJl2bwMJIiT8rW+XA+TiataH79/FszLQMrpGEvzUVkzPau7OCO0Qnrhpe87PqtOAIB8Yw==}
+    engines: {node: ^18.14.0 || ^20.0.0 || ^22.0.0 || >=24.0.0}
+
+  react-is@18.3.1:
+    resolution: {integrity: sha512-/LLMVyas0ljjAtoYiPqYiL8VWXzUUdThrmU5+n20DZv+a+ClRoevUzw5JxU+Ieh5/c87ytoTBV9G1FiKfNJdmg==}
+
   restore-cursor@5.1.0:
     resolution: {integrity: sha512-oMA2dcrw6u0YfxJQXm342bFKX/E4sG9rbTzO9ptUcR/e8A33cHuvStiYOwH7fszkZlZ1z/ta9AAoPk2F4qIOHA==}
     engines: {node: '>=18'}
@@ -724,6 +768,10 @@ packages:
   strip-literal@3.0.0:
     resolution: {integrity: sha512-TcccoMhJOM3OebGhSBEmp3UZ2SfDMZUEBdRA/9ynfLi8yYajyWX3JiXArcJt4Umh4vISpspkQIY8ZZoCqjbviA==}
 
+  supports-color@7.2.0:
+    resolution: {integrity: sha512-qpCAvRl9stuOHveKsn7HncJRvv501qIacKzQlO/+Lwxc9+0q2wLyv4Dfvt80/DPn2pqOBsJdDiogXGR9+OvwRw==}
+    engines: {node: '>=8'}
+
   tinybench@2.9.0:
     resolution: {integrity: sha512-0+DUvqWMValLmha6lr4kD8iAMK1HzV0/aKnCtWb9v9641TnP/MFb7Pc2bxoxQjTXAErryXVgUOfv2YqNllqGeg==}
 
@@ -1048,6 +1096,14 @@ snapshots:
     optionalDependencies:
       '@types/node': 24.2.0
 
+  '@jest/diff-sequences@30.0.1': {}
+
+  '@jest/get-type@30.0.1': {}
+
+  '@jest/schemas@30.0.5':
+    dependencies:
+      '@sinclair/typebox': 0.34.38
+
   '@jridgewell/sourcemap-codec@1.5.4': {}
 
   '@polka/url@1.0.0-next.29': {}
@@ -1112,6 +1168,8 @@ snapshots:
   '@rollup/rollup-win32-x64-msvc@4.46.2':
     optional: true
 
+  '@sinclair/typebox@0.34.38': {}
+
   '@types/chai@5.2.2':
     dependencies:
       '@types/deep-eql': 4.0.2
@@ -1189,6 +1247,8 @@ snapshots:
     dependencies:
       color-convert: 2.0.1
 
+  ansi-styles@5.2.0: {}
+
   assertion-error@2.0.1: {}
 
   cac@6.7.14: {}
@@ -1201,6 +1261,11 @@ snapshots:
       loupe: 3.2.0
       pathval: 2.0.1
 
+  chalk@4.1.2:
+    dependencies:
+      ansi-styles: 4.3.0
+      supports-color: 7.2.0
+
   chalk@5.5.0: {}
 
   chardet@0.7.0: {}
@@ -1289,6 +1354,8 @@ snapshots:
 
   get-east-asian-width@1.3.0: {}
 
+  has-flag@4.0.0: {}
+
   iconv-lite@0.4.24:
     dependencies:
       safer-buffer: 2.1.2
@@ -1301,6 +1368,13 @@ snapshots:
 
   is-unicode-supported@2.1.0: {}
 
+  jest-diff@30.0.5:
+    dependencies:
+      '@jest/diff-sequences': 30.0.1
+      '@jest/get-type': 30.0.1
+      chalk: 4.1.2
+      pretty-format: 30.0.5
+
   js-tokens@9.0.1: {}
 
   log-symbols@6.0.0:
@@ -1356,6 +1430,14 @@ snapshots:
       picocolors: 1.1.1
       source-map-js: 1.2.1
 
+  pretty-format@30.0.5:
+    dependencies:
+      '@jest/schemas': 30.0.5
+      ansi-styles: 5.2.0
+      react-is: 18.3.1
+
+  react-is@18.3.1: {}
+
   restore-cursor@5.1.0:
     dependencies:
       onetime: 7.0.0
@@ -1431,6 +1513,10 @@ snapshots:
     dependencies:
       js-tokens: 9.0.1
 
+  supports-color@7.2.0:
+    dependencies:
+      has-flag: 4.0.0
+
   tinybench@2.9.0: {}
 
   tinyexec@0.3.2: {}

src/cli/index.ts

@@ -4,6 +4,9 @@ import path from 'path';
 import { promises as fs } from 'fs';
 import { InitCommand } from '../core/init.js';
 import { UpdateCommand } from '../core/update.js';
+import { DiffCommand } from '../core/diff.js';
+import { ListCommand } from '../core/list.js';
+import { ArchiveCommand } from '../core/archive.js';
 
 const program = new Command();
 
@@ -60,4 +63,47 @@ program
     }
   });
 
+program
+  .command('diff [change-name]')
+  .description('Show differences between proposed spec changes and current specs')
+  .action(async (changeName?: string) => {
+    try {
+      const diffCommand = new DiffCommand();
+      await diffCommand.execute(changeName);
+    } catch (error) {
+      console.log(); // Empty line for spacing
+      ora().fail(`Error: ${(error as Error).message}`);
+      process.exit(1);
+    }
+  });
+
+program
+  .command('list')
+  .description('List all active changes with their task status')
+  .action(async () => {
+    try {
+      const listCommand = new ListCommand();
+      await listCommand.execute();
+    } catch (error) {
+      console.log(); // Empty line for spacing
+      ora().fail(`Error: ${(error as Error).message}`);
+      process.exit(1);
+    }
+  });
+
+program
+  .command('archive [change-name]')
+  .description('Archive a completed change and update main specs')
+  .option('-y, --yes', 'Skip confirmation prompts')
+  .action(async (changeName?: string, options?: { yes?: boolean }) => {
+    try {
+      const archiveCommand = new ArchiveCommand();
+      await archiveCommand.execute(changeName, options);
+    } catch (error) {
+      console.log(); // Empty line for spacing
+      ora().fail(`Error: ${(error as Error).message}`);
+      process.exit(1);
+    }
+  });
+
 program.parse();

src/core/archive.ts

@@ -0,0 +1,224 @@
+import { promises as fs } from 'fs';
+import path from 'path';
+import { select, confirm } from '@inquirer/prompts';
+import { FileSystemUtils } from '../utils/file-system.js';
+
+interface SpecUpdate {
+  source: string;
+  target: string;
+  exists: boolean;
+}
+
+export class ArchiveCommand {
+  async execute(changeName?: string, options: { yes?: boolean } = {}): Promise<void> {
+    const targetPath = '.';
+    const changesDir = path.join(targetPath, 'openspec', 'changes');
+    const archiveDir = path.join(changesDir, 'archive');
+    const mainSpecsDir = path.join(targetPath, 'openspec', 'specs');
+
+    // Check if changes directory exists
+    try {
+      await fs.access(changesDir);
+    } catch {
+      throw new Error("No OpenSpec changes directory found. Run 'openspec init' first.");
+    }
+
+    // Get change name interactively if not provided
+    if (!changeName) {
+      const selectedChange = await this.selectChange(changesDir);
+      if (!selectedChange) {
+        console.log('No change selected. Aborting.');
+        return;
+      }
+      changeName = selectedChange;
+    }
+
+    const changeDir = path.join(changesDir, changeName);
+
+    // Verify change exists
+    try {
+      const stat = await fs.stat(changeDir);
+      if (!stat.isDirectory()) {
+        throw new Error(`Change '${changeName}' not found.`);
+      }
+    } catch {
+      throw new Error(`Change '${changeName}' not found.`);
+    }
+
+    // Check for incomplete tasks
+    const tasksPath = path.join(changeDir, 'tasks.md');
+    const incompleteTasks = await this.checkIncompleteTasks(tasksPath);
+    
+    if (incompleteTasks > 0) {
+      if (!options.yes) {
+        const proceed = await confirm({
+          message: `Warning: ${incompleteTasks} incomplete task(s) found. Continue?`,
+          default: false
+        });
+        if (!proceed) {
+          console.log('Archive cancelled.');
+          return;
+        }
+      } else {
+        console.log(`Warning: ${incompleteTasks} incomplete task(s) found. Continuing due to --yes flag.`);
+      }
+    }
+
+    // Find specs to update
+    const specUpdates = await this.findSpecUpdates(changeDir, mainSpecsDir);
+    
+    if (specUpdates.length > 0) {
+      console.log('\nSpecs to update:');
+      for (const update of specUpdates) {
+        const status = update.exists ? 'update' : 'create';
+        const capability = path.basename(path.dirname(update.target));
+        console.log(`  ${capability}: ${status}`);
+      }
+
+      if (!options.yes) {
+        const proceed = await confirm({
+          message: 'Proceed with spec updates?',
+          default: true
+        });
+        if (!proceed) {
+          console.log('Archive cancelled.');
+          return;
+        }
+      }
+
+      // Update specs
+      for (const update of specUpdates) {
+        await this.updateSpec(update);
+      }
+      console.log('Specs updated successfully.');
+    }
+
+    // Create archive directory with date prefix
+    const archiveName = `${this.getArchiveDate()}-${changeName}`;
+    const archivePath = path.join(archiveDir, archiveName);
+
+    // Check if archive already exists
+    try {
+      await fs.access(archivePath);
+      throw new Error(`Archive '${archiveName}' already exists.`);
+    } catch (error: any) {
+      if (error.code !== 'ENOENT') {
+        throw error;
+      }
+    }
+
+    // Create archive directory if needed
+    await fs.mkdir(archiveDir, { recursive: true });
+
+    // Move change to archive
+    await fs.rename(changeDir, archivePath);
+    
+    console.log(`Change '${changeName}' archived as '${archiveName}'.`);
+  }
+
+  private async selectChange(changesDir: string): Promise<string | null> {
+    // Get all directories in changes (excluding archive)
+    const entries = await fs.readdir(changesDir, { withFileTypes: true });
+    const changeDirs = entries
+      .filter(entry => entry.isDirectory() && entry.name !== 'archive')
+      .map(entry => entry.name)
+      .sort();
+
+    if (changeDirs.length === 0) {
+      console.log('No active changes found.');
+      return null;
+    }
+
+    console.log('Available changes:');
+    const choices = changeDirs.map(name => ({
+      name: name,
+      value: name
+    }));
+
+    try {
+      const answer = await select({
+        message: 'Select a change to archive',
+        choices
+      });
+      return answer;
+    } catch (error) {
+      // User cancelled (Ctrl+C)
+      return null;
+    }
+  }
+
+  private async checkIncompleteTasks(tasksPath: string): Promise<number> {
+    try {
+      const content = await fs.readFile(tasksPath, 'utf-8');
+      const lines = content.split('\n');
+      let incompleteTasks = 0;
+      
+      for (const line of lines) {
+        if (line.includes('- [ ]')) {
+          incompleteTasks++;
+        }
+      }
+      
+      return incompleteTasks;
+    } catch {
+      // No tasks.md file or error reading it
+      return 0;
+    }
+  }
+
+  private async findSpecUpdates(changeDir: string, mainSpecsDir: string): Promise<SpecUpdate[]> {
+    const updates: SpecUpdate[] = [];
+    const changeSpecsDir = path.join(changeDir, 'specs');
+
+    try {
+      const entries = await fs.readdir(changeSpecsDir, { withFileTypes: true });
+      
+      for (const entry of entries) {
+        if (entry.isDirectory()) {
+          const specFile = path.join(changeSpecsDir, entry.name, 'spec.md');
+          const targetFile = path.join(mainSpecsDir, entry.name, 'spec.md');
+          
+          try {
+            await fs.access(specFile);
+            
+            // Check if target exists
+            let exists = false;
+            try {
+              await fs.access(targetFile);
+              exists = true;
+            } catch {
+              exists = false;
+            }
+
+            updates.push({
+              source: specFile,
+              target: targetFile,
+              exists
+            });
+          } catch {
+            // Source spec doesn't exist, skip
+          }
+        }
+      }
+    } catch {
+      // No specs directory in change
+    }
+
+    return updates;
+  }
+
+  private async updateSpec(update: SpecUpdate): Promise<void> {
+    // Create target directory if needed
+    const targetDir = path.dirname(update.target);
+    await fs.mkdir(targetDir, { recursive: true });
+
+    // Copy spec file
+    const content = await fs.readFile(update.source, 'utf-8');
+    await fs.writeFile(update.target, content);
+  }
+
+  private getArchiveDate(): string {
+    // Returns date in YYYY-MM-DD format
+    return new Date().toISOString().split('T')[0];
+  }
+}

src/core/diff.ts

@@ -0,0 +1,179 @@
+import { promises as fs } from 'fs';
+import path from 'path';
+import chalk from 'chalk';
+import { diffStringsUnified } from 'jest-diff';
+import { select } from '@inquirer/prompts';
+
+// Constants
+const ARCHIVE_DIR = 'archive';
+const MARKDOWN_EXT = '.md';
+const OPENSPEC_DIR = 'openspec';
+const CHANGES_DIR = 'changes';
+const SPECS_DIR = 'specs';
+
+export class DiffCommand {
+  private filesChanged: number = 0;
+  private linesAdded: number = 0;
+  private linesRemoved: number = 0;
+
+  async execute(changeName?: string): Promise<void> {
+    const changesDir = path.join(process.cwd(), OPENSPEC_DIR, CHANGES_DIR);
+    
+    try {
+      await fs.access(changesDir);
+    } catch {
+      throw new Error('No OpenSpec changes directory found');
+    }
+
+    if (!changeName) {
+      changeName = await this.selectChange(changesDir);
+      if (!changeName) return;
+    }
+
+    const changeDir = path.join(changesDir, changeName);
+    
+    try {
+      await fs.access(changeDir);
+    } catch {
+      throw new Error(`Change '${changeName}' not found`);
+    }
+
+    const changeSpecsDir = path.join(changeDir, SPECS_DIR);
+    
+    try {
+      await fs.access(changeSpecsDir);
+    } catch {
+      console.log(`No spec changes found for '${changeName}'`);
+      return;
+    }
+
+    // Reset counters
+    this.filesChanged = 0;
+    this.linesAdded = 0;
+    this.linesRemoved = 0;
+
+    await this.showDiffs(changeSpecsDir);
+
+    // Show summary
+    if (this.filesChanged > 0) {
+      console.log(chalk.bold(`\n📊 Summary: ${this.filesChanged} file(s) changed, ${chalk.green(`+${this.linesAdded}`)} ${chalk.red(`-${this.linesRemoved}`)}`));
+    }
+  }
+
+  private async selectChange(changesDir: string): Promise<string | undefined> {
+    const entries = await fs.readdir(changesDir, { withFileTypes: true });
+    const changes = entries
+      .filter(entry => entry.isDirectory() && entry.name !== ARCHIVE_DIR)
+      .map(entry => entry.name);
+
+    if (changes.length === 0) {
+      console.log('No changes found');
+      return undefined;
+    }
+
+    console.log('Available changes:');
+    const choices = changes.map((name) => ({
+      name: name,
+      value: name
+    }));
+
+    const answer = await select({
+      message: 'Select a change',
+      choices
+    });
+
+    return answer as string;
+  }
+
+  private async showDiffs(changeSpecsDir: string): Promise<void> {
+    const currentSpecsDir = path.join(process.cwd(), OPENSPEC_DIR, SPECS_DIR);
+    await this.walkAndDiff(changeSpecsDir, currentSpecsDir, '');
+  }
+
+  private async walkAndDiff(changeDir: string, currentDir: string, relativePath: string): Promise<void> {
+    const entries = await fs.readdir(path.join(changeDir, relativePath), { withFileTypes: true });
+    
+    for (const entry of entries) {
+      const entryPath = path.join(relativePath, entry.name);
+      
+      if (entry.isDirectory()) {
+        await this.walkAndDiff(changeDir, currentDir, entryPath);
+      } else if (entry.isFile() && entry.name.endsWith(MARKDOWN_EXT)) {
+        await this.diffFile(
+          path.join(changeDir, entryPath),
+          path.join(currentDir, entryPath),
+          entryPath
+        );
+      }
+    }
+  }
+
+  private async diffFile(changePath: string, currentPath: string, displayPath: string): Promise<void> {
+    let changeContent = '';
+    let currentContent = '';
+    let isNewFile = false;
+    let isDeleted = false;
+    
+    try {
+      changeContent = await fs.readFile(changePath, 'utf-8');
+    } catch {
+      changeContent = '';
+    }
+    
+    try {
+      currentContent = await fs.readFile(currentPath, 'utf-8');
+    } catch {
+      currentContent = '';
+      isNewFile = true;
+    }
+
+    if (changeContent === currentContent) {
+      return;
+    }
+
+    if (changeContent === '' && currentContent !== '') {
+      isDeleted = true;
+    }
+
+    // Enhanced header with file status
+    console.log(chalk.bold.cyan(`\n${'═'.repeat(60)}`));
+    console.log(chalk.bold.cyan(`📄 ${displayPath}`));
+    
+    if (isNewFile) {
+      console.log(chalk.green(`   Status: NEW FILE`));
+    } else if (isDeleted) {
+      console.log(chalk.red(`   Status: DELETED`));
+    } else {
+      console.log(chalk.yellow(`   Status: MODIFIED`));
+    }
+    
+    // Use jest-diff for the actual diff with custom options
+    const diffOptions = {
+      aAnnotation: 'Current',
+      bAnnotation: 'Proposed',
+      aColor: chalk.red,
+      bColor: chalk.green,
+      commonColor: chalk.gray,
+      contextLines: 3,
+      expand: false,
+      includeChangeCounts: true,
+    };
+
+    const diff = diffStringsUnified(currentContent, changeContent, diffOptions);
+    
+    // Count lines for statistics (approximate)
+    const addedLines = (diff.match(/^\+[^+]/gm) || []).length;
+    const removedLines = (diff.match(/^-[^-]/gm) || []).length;
+    
+    console.log(chalk.gray(`   Lines: ${chalk.green(`+${addedLines}`)} ${chalk.red(`-${removedLines}`)}`));
+    console.log(chalk.bold.cyan(`${'─'.repeat(60)}\n`));
+    
+    // Display the diff
+    console.log(diff);
+    
+    // Update counters
+    this.filesChanged++;
+    this.linesAdded += addedLines;
+    this.linesRemoved += removedLines;
+  }
+}

src/core/init.ts

@@ -64,7 +64,7 @@ export class InitCommand {
       }))
     });
     
-    config.aiTools = [selectedTool];
+    config.aiTools = [selectedTool as string];
 
     return config;
   }

src/core/list.ts

@@ -0,0 +1,90 @@
+import { promises as fs } from 'fs';
+import path from 'path';
+
+interface ChangeInfo {
+  name: string;
+  completedTasks: number;
+  totalTasks: number;
+}
+
+export class ListCommand {
+  async execute(targetPath: string = '.'): Promise<void> {
+    const changesDir = path.join(targetPath, 'openspec', 'changes');
+    
+    // Check if changes directory exists
+    try {
+      await fs.access(changesDir);
+    } catch {
+      throw new Error("No OpenSpec changes directory found. Run 'openspec init' first.");
+    }
+
+    // Get all directories in changes (excluding archive)
+    const entries = await fs.readdir(changesDir, { withFileTypes: true });
+    const changeDirs = entries
+      .filter(entry => entry.isDirectory() && entry.name !== 'archive')
+      .map(entry => entry.name);
+
+    if (changeDirs.length === 0) {
+      console.log('No active changes found.');
+      return;
+    }
+
+    // Collect information about each change
+    const changes: ChangeInfo[] = [];
+    
+    for (const changeDir of changeDirs) {
+      const tasksPath = path.join(changesDir, changeDir, 'tasks.md');
+      let completedTasks = 0;
+      let incompleteTasks = 0;
+      
+      try {
+        const content = await fs.readFile(tasksPath, 'utf-8');
+        const lines = content.split('\n');
+        
+        for (const line of lines) {
+          if (line.includes('- [x]')) {
+            completedTasks++;
+          } else if (line.includes('- [ ]')) {
+            incompleteTasks++;
+          }
+        }
+      } catch {
+        // No tasks.md file
+        changes.push({
+          name: changeDir,
+          completedTasks: 0,
+          totalTasks: 0
+        });
+        continue;
+      }
+      
+      changes.push({
+        name: changeDir,
+        completedTasks,
+        totalTasks: completedTasks + incompleteTasks
+      });
+    }
+
+    // Sort alphabetically by name
+    changes.sort((a, b) => a.name.localeCompare(b.name));
+
+    // Display results
+    console.log('Changes:');
+    for (const change of changes) {
+      const padding = '  ';
+      const nameWidth = Math.max(...changes.map(c => c.name.length));
+      const paddedName = change.name.padEnd(nameWidth);
+      
+      let status: string;
+      if (change.totalTasks === 0) {
+        status = 'No tasks';
+      } else if (change.completedTasks === change.totalTasks) {
+        status = '✓ Complete';
+      } else {
+        status = `${change.completedTasks}/${change.totalTasks} tasks`;
+      }
+      
+      console.log(`${padding}${paddedName}     ${status}`);
+    }
+  }
+}

test/core/archive.test.ts

@@ -0,0 +1,269 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import { ArchiveCommand } from '../../src/core/archive.js';
+import { promises as fs } from 'fs';
+import path from 'path';
+import os from 'os';
+
+// Mock @inquirer/prompts
+vi.mock('@inquirer/prompts', () => ({
+  select: vi.fn(),
+  confirm: vi.fn()
+}));
+
+describe('ArchiveCommand', () => {
+  let tempDir: string;
+  let archiveCommand: ArchiveCommand;
+  const originalConsoleLog = console.log;
+
+  beforeEach(async () => {
+    // Create temp directory
+    tempDir = path.join(os.tmpdir(), `openspec-archive-test-${Date.now()}`);
+    await fs.mkdir(tempDir, { recursive: true });
+    
+    // Change to temp directory
+    process.chdir(tempDir);
+    
+    // Create OpenSpec structure
+    const openspecDir = path.join(tempDir, 'openspec');
+    await fs.mkdir(path.join(openspecDir, 'changes'), { recursive: true });
+    await fs.mkdir(path.join(openspecDir, 'specs'), { recursive: true });
+    await fs.mkdir(path.join(openspecDir, 'changes', 'archive'), { recursive: true });
+    
+    // Suppress console.log during tests
+    console.log = vi.fn();
+    
+    archiveCommand = new ArchiveCommand();
+  });
+
+  afterEach(async () => {
+    // Restore console.log
+    console.log = originalConsoleLog;
+    
+    // Clear mocks
+    vi.clearAllMocks();
+    
+    // Clean up temp directory
+    try {
+      await fs.rm(tempDir, { recursive: true, force: true });
+    } catch (error) {
+      // Ignore cleanup errors
+    }
+  });
+
+  describe('execute', () => {
+    it('should archive a change successfully', async () => {
+      // Create a test change
+      const changeName = 'test-feature';
+      const changeDir = path.join(tempDir, 'openspec', 'changes', changeName);
+      await fs.mkdir(changeDir, { recursive: true });
+      
+      // Create tasks.md with completed tasks
+      const tasksContent = '- [x] Task 1\n- [x] Task 2';
+      await fs.writeFile(path.join(changeDir, 'tasks.md'), tasksContent);
+      
+      // Execute archive with --yes flag
+      await archiveCommand.execute(changeName, { yes: true });
+      
+      // Check that change was moved to archive
+      const archiveDir = path.join(tempDir, 'openspec', 'changes', 'archive');
+      const archives = await fs.readdir(archiveDir);
+      
+      expect(archives.length).toBe(1);
+      expect(archives[0]).toMatch(new RegExp(`\\d{4}-\\d{2}-\\d{2}-${changeName}`));
+      
+      // Verify original change directory no longer exists
+      await expect(fs.access(changeDir)).rejects.toThrow();
+    });
+
+    it('should warn about incomplete tasks', async () => {
+      const changeName = 'incomplete-feature';
+      const changeDir = path.join(tempDir, 'openspec', 'changes', changeName);
+      await fs.mkdir(changeDir, { recursive: true });
+      
+      // Create tasks.md with incomplete tasks
+      const tasksContent = '- [x] Task 1\n- [ ] Task 2\n- [ ] Task 3';
+      await fs.writeFile(path.join(changeDir, 'tasks.md'), tasksContent);
+      
+      // Execute archive with --yes flag
+      await archiveCommand.execute(changeName, { yes: true });
+      
+      // Verify warning was logged
+      expect(console.log).toHaveBeenCalledWith(
+        expect.stringContaining('Warning: 2 incomplete task(s) found')
+      );
+    });
+
+    it('should update specs when archiving', async () => {
+      const changeName = 'spec-feature';
+      const changeDir = path.join(tempDir, 'openspec', 'changes', changeName);
+      const changeSpecDir = path.join(changeDir, 'specs', 'test-capability');
+      await fs.mkdir(changeSpecDir, { recursive: true });
+      
+      // Create spec in change
+      const specContent = '# Test Capability Spec\n\nTest content';
+      await fs.writeFile(path.join(changeSpecDir, 'spec.md'), specContent);
+      
+      // Execute archive with --yes flag
+      await archiveCommand.execute(changeName, { yes: true });
+      
+      // Verify spec was copied to main specs
+      const mainSpecPath = path.join(tempDir, 'openspec', 'specs', 'test-capability', 'spec.md');
+      const copiedContent = await fs.readFile(mainSpecPath, 'utf-8');
+      expect(copiedContent).toBe(specContent);
+    });
+
+    it('should throw error if change does not exist', async () => {
+      await expect(
+        archiveCommand.execute('non-existent-change', { yes: true })
+      ).rejects.toThrow("Change 'non-existent-change' not found.");
+    });
+
+    it('should throw error if archive already exists', async () => {
+      const changeName = 'duplicate-feature';
+      const changeDir = path.join(tempDir, 'openspec', 'changes', changeName);
+      await fs.mkdir(changeDir, { recursive: true });
+      
+      // Create existing archive with same date
+      const date = new Date().toISOString().split('T')[0];
+      const archivePath = path.join(tempDir, 'openspec', 'changes', 'archive', `${date}-${changeName}`);
+      await fs.mkdir(archivePath, { recursive: true });
+      
+      // Try to archive
+      await expect(
+        archiveCommand.execute(changeName, { yes: true })
+      ).rejects.toThrow(`Archive '${date}-${changeName}' already exists.`);
+    });
+
+    it('should handle changes without tasks.md', async () => {
+      const changeName = 'no-tasks-feature';
+      const changeDir = path.join(tempDir, 'openspec', 'changes', changeName);
+      await fs.mkdir(changeDir, { recursive: true });
+      
+      // Execute archive without tasks.md
+      await archiveCommand.execute(changeName, { yes: true });
+      
+      // Should complete without warnings
+      expect(console.log).not.toHaveBeenCalledWith(
+        expect.stringContaining('incomplete task(s)')
+      );
+      
+      // Verify change was archived
+      const archiveDir = path.join(tempDir, 'openspec', 'changes', 'archive');
+      const archives = await fs.readdir(archiveDir);
+      expect(archives.length).toBe(1);
+    });
+
+    it('should handle changes without specs', async () => {
+      const changeName = 'no-specs-feature';
+      const changeDir = path.join(tempDir, 'openspec', 'changes', changeName);
+      await fs.mkdir(changeDir, { recursive: true });
+      
+      // Execute archive without specs
+      await archiveCommand.execute(changeName, { yes: true });
+      
+      // Should complete without spec updates
+      expect(console.log).not.toHaveBeenCalledWith(
+        expect.stringContaining('Specs to update')
+      );
+      
+      // Verify change was archived
+      const archiveDir = path.join(tempDir, 'openspec', 'changes', 'archive');
+      const archives = await fs.readdir(archiveDir);
+      expect(archives.length).toBe(1);
+    });
+  });
+
+  describe('error handling', () => {
+    it('should throw error when openspec directory does not exist', async () => {
+      // Remove openspec directory
+      await fs.rm(path.join(tempDir, 'openspec'), { recursive: true });
+      
+      await expect(
+        archiveCommand.execute('any-change', { yes: true })
+      ).rejects.toThrow("No OpenSpec changes directory found. Run 'openspec init' first.");
+    });
+  });
+
+  describe('interactive mode', () => {
+    it('should use select prompt for change selection', async () => {
+      const { select } = await import('@inquirer/prompts');
+      const mockSelect = select as unknown as ReturnType<typeof vi.fn>;
+      
+      // Create test changes
+      const change1 = 'feature-a';
+      const change2 = 'feature-b';
+      await fs.mkdir(path.join(tempDir, 'openspec', 'changes', change1), { recursive: true });
+      await fs.mkdir(path.join(tempDir, 'openspec', 'changes', change2), { recursive: true });
+      
+      // Mock select to return first change
+      mockSelect.mockResolvedValueOnce(change1);
+      
+      // Execute without change name
+      await archiveCommand.execute(undefined, { yes: true });
+      
+      // Verify select was called with correct options
+      expect(mockSelect).toHaveBeenCalledWith({
+        message: 'Select a change to archive',
+        choices: [
+          { name: change1, value: change1 },
+          { name: change2, value: change2 }
+        ]
+      });
+      
+      // Verify the selected change was archived
+      const archiveDir = path.join(tempDir, 'openspec', 'changes', 'archive');
+      const archives = await fs.readdir(archiveDir);
+      expect(archives[0]).toContain(change1);
+    });
+
+    it('should use confirm prompt for task warnings', async () => {
+      const { confirm } = await import('@inquirer/prompts');
+      const mockConfirm = confirm as unknown as ReturnType<typeof vi.fn>;
+      
+      const changeName = 'incomplete-interactive';
+      const changeDir = path.join(tempDir, 'openspec', 'changes', changeName);
+      await fs.mkdir(changeDir, { recursive: true });
+      
+      // Create tasks.md with incomplete tasks
+      const tasksContent = '- [ ] Task 1';
+      await fs.writeFile(path.join(changeDir, 'tasks.md'), tasksContent);
+      
+      // Mock confirm to return true (proceed)
+      mockConfirm.mockResolvedValueOnce(true);
+      
+      // Execute without --yes flag
+      await archiveCommand.execute(changeName);
+      
+      // Verify confirm was called
+      expect(mockConfirm).toHaveBeenCalledWith({
+        message: 'Warning: 1 incomplete task(s) found. Continue?',
+        default: false
+      });
+    });
+
+    it('should cancel when user declines task warning', async () => {
+      const { confirm } = await import('@inquirer/prompts');
+      const mockConfirm = confirm as unknown as ReturnType<typeof vi.fn>;
+      
+      const changeName = 'cancel-test';
+      const changeDir = path.join(tempDir, 'openspec', 'changes', changeName);
+      await fs.mkdir(changeDir, { recursive: true });
+      
+      // Create tasks.md with incomplete tasks
+      const tasksContent = '- [ ] Task 1';
+      await fs.writeFile(path.join(changeDir, 'tasks.md'), tasksContent);
+      
+      // Mock confirm to return false (cancel)
+      mockConfirm.mockResolvedValueOnce(false);
+      
+      // Execute without --yes flag
+      await archiveCommand.execute(changeName);
+      
+      // Verify archive was cancelled
+      expect(console.log).toHaveBeenCalledWith('Archive cancelled.');
+      
+      // Verify change was not archived
+      await expect(fs.access(changeDir)).resolves.not.toThrow();
+    });
+  });
+});

test/core/list.test.ts

@@ -0,0 +1,165 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { promises as fs } from 'fs';
+import path from 'path';
+import os from 'os';
+import { ListCommand } from '../../src/core/list.js';
+
+describe('ListCommand', () => {
+  let tempDir: string;
+  let originalLog: typeof console.log;
+  let logOutput: string[] = [];
+
+  beforeEach(async () => {
+    // Create temp directory
+    tempDir = path.join(os.tmpdir(), `openspec-list-test-${Date.now()}`);
+    await fs.mkdir(tempDir, { recursive: true });
+
+    // Mock console.log to capture output
+    originalLog = console.log;
+    console.log = (...args: any[]) => {
+      logOutput.push(args.join(' '));
+    };
+    logOutput = [];
+  });
+
+  afterEach(async () => {
+    // Restore console.log
+    console.log = originalLog;
+
+    // Clean up temp directory
+    await fs.rm(tempDir, { recursive: true, force: true });
+  });
+
+  describe('execute', () => {
+    it('should handle missing openspec/changes directory', async () => {
+      const listCommand = new ListCommand();
+      
+      await expect(listCommand.execute(tempDir)).rejects.toThrow(
+        "No OpenSpec changes directory found. Run 'openspec init' first."
+      );
+    });
+
+    it('should handle empty changes directory', async () => {
+      const changesDir = path.join(tempDir, 'openspec', 'changes');
+      await fs.mkdir(changesDir, { recursive: true });
+
+      const listCommand = new ListCommand();
+      await listCommand.execute(tempDir);
+
+      expect(logOutput).toEqual(['No active changes found.']);
+    });
+
+    it('should exclude archive directory', async () => {
+      const changesDir = path.join(tempDir, 'openspec', 'changes');
+      await fs.mkdir(path.join(changesDir, 'archive'), { recursive: true });
+      await fs.mkdir(path.join(changesDir, 'my-change'), { recursive: true });
+      
+      // Create tasks.md with some tasks
+      await fs.writeFile(
+        path.join(changesDir, 'my-change', 'tasks.md'),
+        '- [x] Task 1\n- [ ] Task 2\n'
+      );
+
+      const listCommand = new ListCommand();
+      await listCommand.execute(tempDir);
+
+      expect(logOutput).toContain('Changes:');
+      expect(logOutput.some(line => line.includes('my-change'))).toBe(true);
+      expect(logOutput.some(line => line.includes('archive'))).toBe(false);
+    });
+
+    it('should count tasks correctly', async () => {
+      const changesDir = path.join(tempDir, 'openspec', 'changes');
+      await fs.mkdir(path.join(changesDir, 'test-change'), { recursive: true });
+      
+      await fs.writeFile(
+        path.join(changesDir, 'test-change', 'tasks.md'),
+        `# Tasks
+- [x] Completed task 1
+- [x] Completed task 2
+- [ ] Incomplete task 1
+- [ ] Incomplete task 2
+- [ ] Incomplete task 3
+Regular text that should be ignored
+`
+      );
+
+      const listCommand = new ListCommand();
+      await listCommand.execute(tempDir);
+
+      expect(logOutput.some(line => line.includes('2/5 tasks'))).toBe(true);
+    });
+
+    it('should show complete status for fully completed changes', async () => {
+      const changesDir = path.join(tempDir, 'openspec', 'changes');
+      await fs.mkdir(path.join(changesDir, 'completed-change'), { recursive: true });
+      
+      await fs.writeFile(
+        path.join(changesDir, 'completed-change', 'tasks.md'),
+        '- [x] Task 1\n- [x] Task 2\n- [x] Task 3\n'
+      );
+
+      const listCommand = new ListCommand();
+      await listCommand.execute(tempDir);
+
+      expect(logOutput.some(line => line.includes('✓ Complete'))).toBe(true);
+    });
+
+    it('should handle changes without tasks.md', async () => {
+      const changesDir = path.join(tempDir, 'openspec', 'changes');
+      await fs.mkdir(path.join(changesDir, 'no-tasks'), { recursive: true });
+
+      const listCommand = new ListCommand();
+      await listCommand.execute(tempDir);
+
+      expect(logOutput.some(line => line.includes('no-tasks') && line.includes('No tasks'))).toBe(true);
+    });
+
+    it('should sort changes alphabetically', async () => {
+      const changesDir = path.join(tempDir, 'openspec', 'changes');
+      await fs.mkdir(path.join(changesDir, 'zebra'), { recursive: true });
+      await fs.mkdir(path.join(changesDir, 'alpha'), { recursive: true });
+      await fs.mkdir(path.join(changesDir, 'middle'), { recursive: true });
+
+      const listCommand = new ListCommand();
+      await listCommand.execute(tempDir);
+
+      const changeLines = logOutput.filter(line => 
+        line.includes('alpha') || line.includes('middle') || line.includes('zebra')
+      );
+      
+      expect(changeLines[0]).toContain('alpha');
+      expect(changeLines[1]).toContain('middle');
+      expect(changeLines[2]).toContain('zebra');
+    });
+
+    it('should handle multiple changes with various states', async () => {
+      const changesDir = path.join(tempDir, 'openspec', 'changes');
+      
+      // Complete change
+      await fs.mkdir(path.join(changesDir, 'completed'), { recursive: true });
+      await fs.writeFile(
+        path.join(changesDir, 'completed', 'tasks.md'),
+        '- [x] Task 1\n- [x] Task 2\n'
+      );
+
+      // Partial change
+      await fs.mkdir(path.join(changesDir, 'partial'), { recursive: true });
+      await fs.writeFile(
+        path.join(changesDir, 'partial', 'tasks.md'),
+        '- [x] Done\n- [ ] Not done\n- [ ] Also not done\n'
+      );
+
+      // No tasks
+      await fs.mkdir(path.join(changesDir, 'no-tasks'), { recursive: true });
+
+      const listCommand = new ListCommand();
+      await listCommand.execute(tempDir);
+
+      expect(logOutput).toContain('Changes:');
+      expect(logOutput.some(line => line.includes('completed') && line.includes('✓ Complete'))).toBe(true);
+      expect(logOutput.some(line => line.includes('partial') && line.includes('1/3 tasks'))).toBe(true);
+      expect(logOutput.some(line => line.includes('no-tasks') && line.includes('No tasks'))).toBe(true);
+    });
+  });
+});