Overview

This adds an owned Python binding for explicit native and worker dynamic-plugin activation. It is stacked on #364; once that PR lands, this diff reduces to the Python binding and its tests.

Static-only harness-native applications keep using plugin.initialize() / plugin.clear(). activate_dynamic_plugins(...) requires at least one dynamic specification; its base config may also contain static components, which initialize before components appended by the dynamic plugins.

• I confirm this contribution is my own work, or I have the right to submit it under this project's license.
• I searched existing issues and open pull requests, and this does not duplicate existing work.

Details

• Add DynamicPluginActivationSpec and async activate_dynamic_plugins(...) to nemo_relay.plugin.
• Return an owned PluginHostActivation with the successful validation report and active-state inspection.
• Support async close(), async with, and best-effort finalization without blocking the Python finalizer or holding the GIL during teardown.
• Share one cancellation-resistant close operation across repeated or concurrent callers; every caller observes the same cached result.
• Preserve nested Python None values as JSON null in plugin configuration while still omitting optional top-level specification fields.
• Preserve the existing static plugin.initialize() and plugin.clear() APIs. Empty dynamic activation is rejected without claiming process ownership, so static initialization remains available.
• Map invalid config, missing manifests, ownership conflicts, registration failures, and teardown failures to ordinary Python exceptions.
• Add neutral native and worker fixture coverage for callbacks, mixed static/dynamic configuration, conflicts, partial-load rollback, explicit close, context cleanup, concurrent close, cancellation, and finalization.

Where should the reviewer start?

Start with python/nemo_relay/plugin.py for the public API and crates/python/src/py_plugin.rs for shared ownership, cancellation-resistant cleanup, and exception translation. End-to-end fixture cases are in python/tests/test_dynamic_plugin_host.py.

Validation

• python/tests/test_dynamic_plugin_host.py — 10 passed
• cargo fmt --all -- --check
• cargo clippy -p nemo-relay-python --all-targets -- -D warnings
• Ruff check and format passed
• The earlier full non-integration Python suite passed (505 tests)
• git diff --check

Related Issues: (use one of the action keywords Closes / Fixes / Resolves / Relates to)

Relates to #364.