Task: Implement Hotfix: the workflow deadline pass reads an entry it has freed

expire_overdue_steps() erases a step's awaiting entry only after it has read and stopped the run the entry names.

• No read through waiting happens after its entry is erased.
• An exception after the step is failed erases the entry once, through the handler, not twice.
• Valgrind reports no error on either deadline case, and the workflow suite passes.

Diagnosis: the loop binds const auto& waiting = it->second, fails the step, calls it = awaiting_.erase(it), and then reads waiting.instance_id to find the run. The node is freed by then. libstdc++ leaves the freed bytes in place, so Linux reads the right id by accident; on macOS the id reads back wrong, the run lookup returns nothing, the continue skips stop_on_failure, and the run keeps its state. That is every macOS symptom: the step is failed, the run is not, and a retry refuses a run that has not stopped.

A second fault sat beside it: if the run read or stop_on_failure threw, the handler erased it again, which by then pointed at the next entry or at end().

Fix: move the erase to the end of the expiry branch, after the run is read and stopped. The handler's erase is then the only one on that path.

Every number this task claims about a tree, with the command that produced it and the commit it was measured at. A number without both is not a measurement, because a clean-up record describes a tree and trunk moves under a branch: a consumer count, a gate's component count and a suite's size all change with no code changing, and the reader of a bare number cannot tell which tree it came from. Where the raw output matters, put it in an evidence/ file beside the task and name that file in the Command column.

Found from the macOS logs while fixing the marketdata timeout, captured as The workflow step-deadline tests fail on macOS.

Manual QA scenarios (scaffolded via compass add test_scenario) that verify this task. Link new ones here as they're created; the scenario doc itself links back via its "Verifies task" field.

The erase moved after the run is read and stopped. Valgrind went from one invalid read to none, and the workflow suite passes. macOS CI is the remaining check.