#824 Visual editor n8n-parity push (phased): reliability, execution loop, canvas ops, expressions

Comprehensive review found major gaps vs n8n. Phased build (user approved all, in order): P1 reliability+errors (retry/timeout/trigger_rule/idempotency inspector + on_failure error-branch handle + join_mode/foreach-parallel/while-max_iterations/wait-timeout); P2 in-editor execution + per-node results overlay (poll /steps + /steps/logs); P3 canvas power-ops (multi/box-select, edge reconnect, copy/paste/duplicate, context menu, node disable, sticky notes, add-node-from-connection, auto-layout); P4 expression autocomplete/live-preview/nested-browser + repeating fields + re-add reflexive/agent operators. Ground truth: retry_policy={max_retries,delay(ISO8601 PT5S),backoff_factor}, timeout_policy={timeout(ISO8601),kill_on_timeout}, trigger_rule in {all_success,all_done,one_success,one_done,none_failed}, join_mode in {all_of,any_of,all_success,one_success}, on_failure_task_id honored (execution_handlers.py:341).