ship-checklist - every write needs a read path an agent can find

The recurring miss in ax: we ship the write + an on-demand CLI read, and skip the proactive / agent-facing read. A signal only visible on a manual CLI run is invisible to the self-improvement loop. ax's whole thesis is that agents discover and act on signals - so a new write is not done until an agent can find it without being told.

Organizing rule: every write needs (B) an on-demand read AND (C) a proactive read AND an agent-facing surface (MCP/skill). Most features do A+B and stop.

Run this before opening the PR. Skipping a row is fine - but say so in the PR and why, don't skip silently.

A. Write

• Schema in schema.surql + registered in SCHEMA_TABLES (CI mirror guard)
• Ingest idempotent + incremental (since-aware) + deref-free denormalization for reads (no record derefs inside aggregates - they hang prod)
• Backfill: does history get the signal, or only new data? Note "dark until re-ingest" if so
• Stage deps = every producer of the input table