Task: Add the process run record

One run of a process is a record with its own identity, the process it is a run of, the time it ran and the states it moved through.

• The process enumeration is seeded, so a run names which process ran.
• A run has an identity and a state machine over its evolution.
• The state machine refuses a transition the process does not allow; a pgTAP test walks a run through its states.
• The run records the process it is a run of with an enforced foreign key, and no run exists without one.

(Implementation strategy. Written when work starts; key decisions are distilled into the parent story's * Decisions at close, but the plan itself stays — it is the historical record of what we did.)

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.

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.