A subprocess step that reopens its parent's webform submission never resumes

Problem/Motivation

A webform that starts a workflow binds its submission to the instance it started. When a step of a subprocess reopens that submission, typically an editable review whose submission id variable is handed down to the child, the submit is saved but the step is not resumed. OrchestraInteractionHandler::postSave() looks for the step's token in the instance the submission is bound to (the parent), finds nothing because the token belongs to the child, and returns silently. The task stays open, the run never moves on, and the actor is not told.

Steps to reproduce

1. A workflow starts on a webform submission, stores its id, and hands it to a subprocess.
2. A step of that subprocess reopens the submission in editable mode.
3. Submit the form through the step: the step stays parked.

Proposed resolution

• On a bound re-edit, resume in the instance the binding handle names (the resolved continuation already carries it), when that instance is the bound one or one of its subprocesses, found by walking up the parent tokens. A submission still cannot resume a step in an unrelated instance, and the assigned-actor check is unchanged.
• When the handle names an unrelated instance, show the actor the existing "Your answers were saved, but this step was not completed" warning instead of returning silently.
• A kernel test: a parent starts the form, a child step reopens it, and the edit resumes the child's step.

Remaining tasks

A merge request with tests.

AI-Generated: Yes (Claude Code was used to help draft this issue summary, and is used to write the change and its tests, which I review.)