v0.73.0

Added

• Made the Participant Fabric's session telemetry durable. A session's running operational
  metrics (turns, errors, abstentions, cumulative tokens, spend, latency, and the highest
  rate-limit utilisation) can now be recorded to the progress ledger as an opt-in
  session_metric note and read back across processes and sessions. emit_session_metric
  mirrors the usage-note bridge — it is opt-in, default off, skips an empty session, and never
  raises into the turn it observes — and run_session_metric_report /
  build_session_metric_report reduce those notes to the latest cumulative snapshot per
  session and total across sessions, rendering both human text and a stable JSON shape. The
  hub core remains a no-telemetry substrate: the snapshots ride the existing progress-ledger
  channel, introduce no new wire message or stored-event kind, and are descriptive evidence,
  not an enforcement gate.
• Added a routed, telemetered deliberation loop (orchestrate_session) that brings the
  Participant Fabric's Phase 5 pieces together at run time. It generalises a fixed-order
  conversation: each round the router picks which provider should answer now, the loop drives
  that participant, folds the result into the running session metrics, and reads the advisor's
  verdict. A turn's reported rate-limit utilisation is fed back before the next routing
  decision, so load steers away from a provider nearing its limit. The advisor stays advisory
  with one bounding exception that mirrors the existing budget guard — an over-budget signal
  halts the run — and, when a poster is supplied, each round persists a durable session_metric
  snapshot. The hub core is untouched.
• Bound the routed deliberation loop onto a live hub with BusOrchestration, the orchestration
  counterpart to BusConversation and BusConvocation. A connected bus identity publishes every
  routed turn to the room as a topic-stamped chat message; with emit_metrics enabled it also
  persists a durable session_metric snapshot to the hub after each round. Both emissions stay
  opt-in and default off, so the bus binding honours the no-telemetry stance.