feat(extensions): support multiple active catalogs simultaneously (#1720)

* Initial plan

* feat(extensions): implement multi-catalog stack support

- Add CatalogEntry dataclass to represent catalog entries
- Add get_active_catalogs() reading SPECKIT_CATALOG_URL, project config,
  user config, or built-in default stack (org-approved + community)
- Add _load_catalog_config() to parse .specify/extension-catalogs.yml
- Add _validate_catalog_url() HTTPS validation helper
- Add _fetch_single_catalog() with per-URL caching, backward-compat for DEFAULT_CATALOG_URL
- Add _get_merged_extensions() that merges all catalogs (priority wins on conflict)
- Update search() and get_extension_info() to use merged results
  annotated with _catalog_name and _install_allowed
- Update clear_cache() to also remove per-URL hash cache files
- Add extension_catalogs CLI command to list active catalogs
- Add catalog add/remove sub-commands for .specify/extension-catalogs.yml
- Update extension_add to enforce install_allowed=false policy
- Update extension_search to show source catalog per result
- Update extension_info to show source catalog with install_allowed status
- Add 13 new tests covering catalog stack, merge conflict resolution,
  install_allowed enforcement, and catalog metadata

Co-authored-by: mnriem <15701806+mnriem@users.noreply.github.com>

* docs: update RFC, user guide, and API reference for multi-catalog support

- RFC: replace FUTURE FEATURE section with full implementation docs,
  add catalog stack resolution order, config file examples, merge
  conflict resolution, and install_allowed behavior
- EXTENSION-USER-GUIDE.md: add multi-catalog section with CLI examples
  for catalogs/catalog-add/catalog-remove, update catalog config docs
- EXTENSION-API-REFERENCE.md: add CatalogEntry class docs, update
  ExtensionCatalog docs with new methods and result annotations,
  add catalog CLI commands (catalogs, catalog add, catalog remove)

Also fix extension_catalogs command to correctly show "Using built-in
default catalog stack" when config file exists but has empty catalogs

Co-authored-by: mnriem <15701806+mnriem@users.noreply.github.com>

* Potential fix for pull request finding 'Empty except'

Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

* fix: remove extraneous f-string prefixes (ruff F541)

Remove f-prefix from strings with no placeholders in catalog_remove
and extension_search commands.

Co-authored-by: mnriem <15701806+mnriem@users.noreply.github.com>

* fix: address PR review feedback for multi-catalog support

- Rename 'org-approved' catalog to 'default'
- Move 'catalogs' command to 'catalog list' for consistency
- Add 'description' field to CatalogEntry dataclass
- Add --description option to 'catalog add' CLI command
- Align install_allowed default to False in _load_catalog_config
- Add user-level config detection in catalog list footer
- Fix _load_catalog_config docstring (document ValidationError)
- Fix test isolation for test_search_by_tag, test_search_by_query,
  test_search_verified_only, test_get_extension_info
- Update version to 0.1.14 and CHANGELOG
- Update all docs (RFC, User Guide, API Reference)

* fix: wrap _load_catalog_config() calls in catalog_list with try/except

- Check SPECKIT_CATALOG_URL first (matching get_active_catalogs() resolution order)
- Wrap both _load_catalog_config() calls in try/except ValidationError so a
  malformed config file cannot crash `specify extension catalog list` after
  the active catalogs have already been printed successfully

Co-authored-by: mnriem <15701806+mnriem@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: mnriem <15701806+mnriem@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

CHANGELOG.md

@@ -12,6 +12,20 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - feat: add Tabnine CLI agent support
+- **Multi-Catalog Support (#1707)**: Extension catalog system now supports multiple active catalogs simultaneously via a catalog stack
+  - New `specify extension catalog list` command lists all active catalogs with name, URL, priority, and `install_allowed` status
+  - New `specify extension catalog add` and `specify extension catalog remove` commands for project-scoped catalog management
+  - Default built-in stack includes `catalog.json` (default, installable) and `catalog.community.json` (community, discovery only) — community extensions are now surfaced in search results out of the box
+  - `specify extension search` aggregates results across all active catalogs, annotating each result with source catalog
+  - `specify extension add` enforces `install_allowed` policy — extensions from discovery-only catalogs cannot be installed directly
+  - Project-level `.specify/extension-catalogs.yml` and user-level `~/.specify/extension-catalogs.yml` config files supported, with project-level taking precedence
+  - `SPECKIT_CATALOG_URL` environment variable still works for backward compatibility (replaces full stack with single catalog)
+  - All catalog URLs require HTTPS (HTTP allowed for localhost development)
+  - New `CatalogEntry` dataclass in `extensions.py` for catalog stack representation
+  - Per-URL hash-based caching for non-default catalogs; legacy cache preserved for default catalog
+  - Higher-priority catalogs win on merge conflicts (same extension id in multiple catalogs)
+  - 13 new tests covering catalog stack resolution, merge conflicts, URL validation, and `install_allowed` enforcement
+  - Updated RFC, Extension User Guide, and Extension API Reference documentation
 
 ## [0.1.13] - 2026-03-03