* feat(core): share an instance runtime with CLI worker control
Add --shared-runtime to easytier-core and reuse --multi-thread-count.
Default shared workers to available CPUs while retaining dedicated
runtime defaults. Consume shared runtime flags at process scope so
config files remain writable and keep their own thread settings.
Share executor ownership across the factory and its instances, keeping
normal instance capabilities and independent shutdown paths. Cover
worker selection, instance deletion, hot addition, and final teardown.
* docs: document shared native runtime ownership
Describe the opt-in shared executor alongside the default per-instance model, including worker selection and last-owner shutdown semantics.
Restore per-instance Tokio executors for standard native instances,
honoring multi_thread and multi_thread_count with a two-worker minimum
in multi-thread mode. Preserve external execution for compact hosts.
Run construction, lifecycle operations, FFI data-plane tasks, and
hot-reloaded port forwards on the selected instance executor. Keep
shutdown cleanup running when its caller is cancelled, and release
owned executors without blocking their workers on runtime teardown.
Add runtime ownership, cancellation, cross-runtime connectivity, and
hot-reload regression coverage, and document the execution model.
Validation: all 45 PR checks passed, including linting, integration
tests, and cross-platform builds.
KKRainbow
fanyang