02 — Composer event wiring (migration 016 + runtime/260)

The 240x composer was a pure substrate — fn_iu_compose / add / remove / reorder emitted no events, so a composition change was invisible to the route / delivery / worker layers (240x open gap #1). This macro wires the composer onto the IU event bus.

Migration 016 — 016_composer_event_wiring.sql (+ rollback)

Additive only (CREATE OR REPLACE, no ALTER, no DROP, no data touched):

• fn_iu_emit_collection_event(event_type, collection_id, actor, payload) — the composer counterpart of fn_iu_emit_event. Fail-closed: RETURNS NULL unless the master gate (fn_iu_core_routes_enabled) is on AND the event type is registered + active. Writes a metadata-only event_outbox row with event_subject_table = 'iu_piece_collection'; event_stream / delivery_lane are sourced from event_type_registry (never hardcoded).
• fn_iu_collection_checkpoint(collection_id, event_type, actor, detail) — the gated emitter for the read-side checkpoint events. For a collection_validated checkpoint it runs the real fn_iu_collection _validate and folds the verdict into the payload.
• The four mutating composer functions (fn_iu_collection_create / _add_piece / _remove_piece / _reorder_piece) — CREATE OR REPLACEd with the byte-identical migration-015 body PLUS one PERFORM fn_iu_emit_collection_event(...). The migration-011 pattern. fn_iu_compose is unchanged — it emits via its sub-calls.
• 2 observability views: v_iu_composer_event_backlog, v_iu_collection_export_status.

The eight composer event types: collection_created, piece_added_to_collection, piece_removed_from_collection, piece_reordered (mutation half, auto-emitted by the 4 functions); collection_rendered, collection_validated, collection_exported, collection_import_proposed (checkpoint half, via fn_iu_collection _checkpoint).

Runtime 260 — 260_composer_event_family_register.sql (+ rollback)

Registers the 8 event types (event_stream='update', delivery_lane='immediate') + 8 outbound routes, every route enabled=true, dry_run=true. Idempotent. Modelled on runtime/160 + 190.

Emission is double-gated and safe

A composer event reaches the bus only when both composer_enabled=true and routes_master_enabled=true. The emit is best-effort; the op never fails because the bus is closed. Every composer route is dry_run=true — external delivery structurally impossible.

Evidence

sandbox/110 proves emission on the production schema BEGIN…ROLLBACK. Durable evidence is produced by runtime/270 on apply. No production mutation occurred this macro.

DOT

Migration 016 + runtime/260 grow the surface 84 → 104 (+2 functions, +2 views, +8 event types, +8 routes). runtime/110 bumped in the same commit.