v1.2.21

• breaking: formalize qpipeline event-context state handling so context.runner.run_state is exposed directly as the live RunningState, while signal remains the default write-back channel
• feat: split qpipeline runner events into typed public/internal contexts under runner.events and add explicit contracts for validation, checkpoint, progress, and loss-computed payloads
• refactor: remove legacy EventContext / EventType plumbing, precompile event emitters at dispatcher init, and drop runtime frozen-state wrapping from the qpipeline event path
• docs: document qpipeline event context access rules, internal on_epoch_start_internal usage, and the intended freedom to mutate run_state and other payload objects when callers explicitly choose to
• test: add functional coverage for typed event contracts, live run_state behavior, pre-backward loss hooks, and updated lifecycle bridge semantics