Adds a push-to-origin workflow to the merge notice system, introducing a new `useMergeAdvanceNotice` hook, a `merge-advance-push-origin` route handler, and corresponding UI affordance in the `MergeAdvanceNotice` banner component. The engine gains TOCTOU and refusal audit assertions, and coverage exp
Fusion-Task-Id: FN-5359
Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>
Fusion-Task-Id: FN-5359
Fixes the main chat composer flex sizing so the input area properly expands (FN-5322), with regression guards in the autosize test suite and a new browser layout smoke script covering the composer expand behavior.
Fusion-Task-Id: FN-5322
Fixes completion handoff limbo by adding self-healing recovery paths and improves run context isolation in the executor, with corresponding reliability interaction tests covering the new error recovery flows.
Fusion-Task-Id: FN-4999
