[lifecycle-RSK] RSK-04: Add the run field, write helpers, and the projection #1794

Tracking

• Epic: [lifecycle-RSK] Run-state kernel #1790
• Size: 1 SP
• Blocked by: [lifecycle-RSK] RSK-01: Add the pure run-state kernel module #1791
• Design doc: docs/architecture/task-lifecycle-target-architecture.md (not yet on main)
• Ticket plan: docs/architecture/task-lifecycle-run-state-kernel-tickets.md (not yet on main)

Context

A direct swap is unsafe. The fields are read across src. The safe path runs the kernel beside the fields. The fields stay authoritative. This issue adds the parts that later issues use. It changes no behavior.

Developer Notes

• Add a run: RunState field to Task. It always runs. It is not gated.
• Add the write-helper pattern: one method per event that sets the old field and drives the event into nextRunState. Keep the field authoritative.
• If the kernel rejects an event that the code applies, keep the field write. Record the rejection for [lifecycle-RSK] RSK-05: Add the divergence comparison and a metric #1795.
• Add the projection: a pure function from the current field values to the expected RunState. [lifecycle-RSK] RSK-05: Add the divergence comparison and a metric #1795 compares against it.
• Do not read run for control flow.

Exit criteria: the helpers and the projection exist and are unit-tested. No write site uses them yet. Behavior is unchanged.

Reversibility: additive.