Memory provider discovery (discover_memory_providers, load_memory_provider)
only scanned the bundled plugins/memory/ directory. User-installed providers
at $HERMES_HOME/plugins/<name>/ were invisible, forcing users to symlink
into the repo source tree — which broke on hermes update and created a
dual-registration path causing duplicate tool names (400 errors on strict
providers like Xiaomi MiMo).
Changes:
- Add _get_user_plugins_dir(), _is_memory_provider_dir(), _iter_provider_dirs(),
and find_provider_dir() helpers to plugins/memory/__init__.py
- discover_memory_providers() now scans both bundled and user dirs
- load_memory_provider() uses find_provider_dir() (bundled-first)
- discover_plugin_cli_commands() uses find_provider_dir()
- _install_dependencies() in memory_setup.py uses find_provider_dir()
- User plugins use _hermes_user_memory namespace to avoid sys.modules collisions
- Non-memory user plugins filtered via source text heuristic
- Bundled providers always take precedence on name collisions
Fixes#4956, #9099. Supersedes #4987, #9123, #9130, #9132, #9982.