18000x · 08 — Auto-Instantiate-From-Event Proof

Goal

Demonstrate the "event arrives → compose instance" flow as a sandbox BEGIN/ROLLBACK with no daemon, no cron, no worker — purely the in-TX simulation the macro explicitly authorises.

Design

1. A _simulated_event TEMP table represents the event queue. Each row carries (template_collection_id, instance_key_suffix) — the minimum a consumer needs.
2. A DO block walks the queue:
   • fetches v2 template piece iu_ids from iu_piece_membership
   • builds a pieces_json reusing all 5
   • calls fn_iu_compose to mint the instance
   • calls fn_iu_collection_record_template_instance for lineage
3. The composer gate is opened inside the TX and closed before ROLLBACK — gate-toggle reversibility pattern.

Live transcript

-- simulated event
template_collection_id               | instance_key_suffix
1cd4f881-0e7f-4f7a-9133-07ce7e726d8d | auto-event-2026-05-25-001

NOTICE: composed instance 8f4724e9-1624-4344-87ab-e800b10d220b
        from template 1cd4f881-…  (minted=0, attached=5)
NOTICE: lineage recorded: digest_matches=true

             instance_collection_key              | template_collection_key | digest_matches_template |      instantiated_by
--------------------------------------------------+-------------------------+-------------------------+---------------------------
 tpl-inst:wf:onboarding/auto-event-2026-05-25-001 | tpl:wf:onboarding/v2    | t                       | iu-core-18000x-auto-event

ROLLBACK

-- post-rollback
auto_event_rows_post = 0
iu_core.composer_enabled = false

Productization path to a durable auto-instantiate

The sandbox proves the mechanism. To productize this as a real "subscribe to template.published → spawn instance" worker:

1. Define a new event_type template.published (event_domain=template or repurpose iu domain — open question) with event_type_registry row + corresponding event_outbox CHECK constraint update (per [[feedback-event-outbox-check-vs-registry-drift]]).
2. Emit template.published from fn_iu_collection_register_template_version (one-line hook into the existing function).
3. Consumer: a new function fn_iu_template_auto_instantiate(p_template_id, p_instance_key_suffix, p_actor) that does the DO-block work (refactor of the sandbox).
4. Route + worker registration in iu_outbound_route so the existing 014 route worker drives the consumer (route is internal-only — no external HTTP).
5. Gate: a new iu_core.template_auto_instantiate_enabled config defaulting to false — durable opt-in.

None of steps 1–5 are authored in 18000x — they are listed here as the exact next-step package for ≥19000x.

Why no productization in 18000x

The sandbox PROVES the mechanism works. The constitution requires:

• No daemon
• No cron
• Reversible by default
• Discover-first before create

Productization steps 1–5 above add 1 event_type + 1 fn + 1 route + 1 gate to the surface and would push the D9 inventory higher. The sandbox proof is the discover-first deliverable; the productization itself is a separate, smaller macro.