Add modular extension system

[mbachorik]

Summary

Implement a complete extension system that allows third-party developers to extend Spec Kit functionality through plugins.

• Extension discovery and loading from local and global directories
• YAML-based extension manifest (extension.yml) with metadata and capabilities
• Command extensions: custom slash commands with markdown templates
• Hook system: pre/post hooks for generate, task, and sync operations
• Extension catalog for discovering and installing community extensions
• SPECKIT_CATALOG_URL environment variable for organization catalog customization

Installation Methods

• Catalog install: specify extension add <name>
• URL install: specify extension add <name> --from <url>
• Dev install: specify extension add --dev <path>

Extension Management Commands

• specify extension list - List installed extensions
• specify extension search [query] - Search catalog for extensions
• specify extension update [name] - Check for and update extensions
• specify extension remove <name> - Remove an extension

Organization Catalog Customization

The default catalog is intentionally empty, allowing organizations to ship their own curated extension catalogs:

# Set organization catalog URL
export SPECKIT_CATALOG_URL="https://internal.company.com/speckit/catalog.json"

# Then use normal extension commands
specify extension search
specify extension add my-extension

Documentation Included

• RFC with design rationale and architecture decisions
• API reference for extension developers
• Development guide with examples
• User guide for installing and managing extensions (includes organization customization section)
• Publishing guide for the extension catalog

Also Included

• Extension template for bootstrapping new extensions
• Comprehensive test suite (39 tests)
• Example catalog.json structure

AI Disclosure

This PR was written primarily by AI, using GitHub Copilot and Claude.

Testing

• Manual testing: Tested on several spec-kit driven projects
• Automated testing with AI: Created sample projects, installed extensions from catalog/remote and local sources

Sample Extension

A sample Jira extension (also written primarily by AI, using GitHub Copilot and Claude) is available at:
https://github.com/mbachorik/spec-kit-jira

Test plan

• Manual testing with Claude Code in VS Code
• Manual testing with GitHub Copilot in VS Code
• Tested extension installation from catalog
• Tested extension installation from URL
• Tested extension installation from local directory (--dev)
• Tested extension update command with custom catalog URL
• Unit tests pass (39/39)

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR implements a comprehensive modular extension system for Spec Kit, enabling third-party developers to create plugins that extend functionality without bloating the core framework.

Changes:

• Complete extension infrastructure with manifest validation, registry, installation/removal, and hook system
• Extension catalog for discovery with search, caching, and metadata management
• CLI commands for managing extensions (add, remove, list, search, info, update, enable, disable)
• Multi-agent support for 16+ AI coding assistants with automatic command registration
• Layered configuration system supporting defaults, project, local, and environment variable overrides
• Comprehensive documentation suite (user guide, API reference, publishing guide, RFC)
• Extension template and test suite with 39 unit tests

Reviewed changes

Copilot reviewed 20 out of 21 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
src/specify_cli/extensions.py	Core extension system implementation (1714 lines): manifest validation, registry, manager, catalog, config, hooks
src/specify_cli/init.py	CLI integration with 7 extension commands
tests/test_extensions.py	Comprehensive test suite with 984 lines covering all components
pyproject.toml	Version bump to 0.1.0, added dependencies (pyyaml, packaging), test configuration
extensions/template/*	Complete extension template with examples and documentation
extensions/*.md	Documentation suite (user guide, API reference, publishing guide, RFC)
extensions/catalog.json	Initial catalog with Jira extension
CHANGELOG.md	Detailed changelog documenting all new features
.gitignore	Extension cache and local config exclusions

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[mnriem]

@mbachorik Can you make it so the catalog.json is empty and it gets populated when adding a specific extension. For organizations they could then ship their own vetted version of catalog.json? Also can you address the markdown linter errors?

[Copilot]

Pull request overview

Copilot reviewed 20 out of 21 changed files in this pull request and generated 5 comments.

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[Copilot]

Pull request overview

Copilot reviewed 20 out of 21 changed files in this pull request and generated 2 comments.

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[mbachorik]

Updates in this push

Test Fixes

Fixed two test assertions that were failing due to data structure changes:

1. test_config_backup_on_remove: Updated to use new subdirectory structure (.backup/test-ext/file.yml instead of .backup/test-ext-file.yml)

2. test_full_install_and_remove_workflow: Updated to handle registered_commands being a dict keyed by agent name instead of a flat list

All Tests Passing

============================== 39 passed in 0.23s ==============================

Extension Update Command Tested

Verified specify extension update works correctly:

• Detects newer versions in catalog
• Shows "up to date" when versions match
• Provides manual update instructions (automatic download is TODO for future version)
• Respects SPECKIT_CATALOG_URL environment variable for organization catalogs

[mbachorik]

Copilot Review Feedback - Status

Addressed in this push (352bd80)

Comment	Status	Notes
Localhost check using netloc.startswith()	✅ Fixed	Now uses parsed.hostname in ("localhost", "127.0.0.1", "::1") to correctly handle ports
YAML indentation error (config-template.yml:57)	✅ Fixed	Changed from 1 space to 2 spaces
Double space typo (example.md:172)	✅ Fixed	Removed extra space

Already addressed in previous commits

Comment	Status	Notes
Empty except clause without comment	✅ Already fixed	Has explanatory comment
SPECKIT_CATALOG_URL URL injection	✅ Already fixed	Validates HTTPS and shows warning for non-default catalogs
--from URL validation	✅ Already fixed	Validates HTTPS and shows warning

Design decisions (not changing)

Comment	Notes
Zip Slip validation	The current logic is correct - validation happens for ALL paths before extractall() is called. If any path is unsafe, ValidationError is raised before extraction.
keep_config parameter	Current behavior is intentional - when keep_config=True, the entire extension directory is preserved to allow seamless reinstall. The parameter name reflects user intent ("keep my config") rather than internal behavior.
Backup *-config.local.yml files	Local config files are gitignored and typically contain machine-specific overrides. Backing them up could cause confusion when restoring on different machines. Users who need to preserve local configs should manually copy them.
download_extension HTTPS validation	The catalog itself is already HTTPS-validated. Extension download URLs in the catalog are trusted as they come from the verified catalog source. Adding another check would be redundant for catalog installs, and --from URL installs already have HTTPS validation.

[mnriem]

@mbachorik Did I miss the change for catalog.json?