M5 — Runtime v1.0 core

[nficano]

Goal

Runtime v1.0 core.

Scope

• Add src/arcp/_runtime/session.py (SessionContext, _stamp_and_emit primitive, next_event_seq, resume)
• _runtime/job.py (Job state machine; emit_accepted / emit_event_kind / emit_result / emit_error; JobContext bar v1.1 surfaces)
• _runtime/lease.py (validate_lease_shape, validate_lease_op w/o constraints, is_lease_subset, canonicalize_target, compile_glob)
• _runtime/pending.py (salvage, rekey to envelope id)
• v1.0 state-machine tests

Spec §

§6.1–§6.3, §6.7, §7.1–§7.4, §8.1–§8.3, §9.1–§9.4, §10

Risk

M (cancellation channel)