ADR: Domain term — ESIID vs service_point

[haydenk]

Decision needed

ESIID is an ERCOT-specific term (Electric Service Identifier). Other ISOs use:

• CAISO — Service Account ID (SAID) / Service Agreement
• PJM — Account Number / Service Point
• NYISO — ICAP ID / Premise ID
• MISO — Premise ID / Account ID
• ISO-NE — Account ID
• CENACE — RPU (Registro Único de Usuarios) / Punto de Carga

We need a generic term for "the thing we track per ISO." Candidates:

• service_point — neutral, used by some ISOs
• premise — used by NYISO, MISO
• account — too overloaded
• Keep esiid as the universal term — fastest, but locks the project to ERCOT vocabulary forever

Affected surfaces if we rename

• Table: esiids → service_points (or chosen term)
• Model: Esiid → ServicePoint
• API path: GET /esiid/{esiid} (Add GET /esiid/{esiid} direct lookup endpoint #14 if not yet implemented) → GET /service_points/{id} or GET /service_points/by_iso_id/{iso}/{id}
• API response field: esiid stays as the ERCOT-specific identifier on the record; the universal primary key is the surrogate id
• Crate names: esiid-* → handled separately in v0.4.0 crate rename
• README, CLAUDE.md, docs

Required output

ADR at docs/adr/0002-domain-term.md documenting the choice and rename plan.

Why now

This decision drives the v0.4.0 implementation work (crate rename, schema rename). Decide once, implement once.

Blocks

• v0.4.0 crate rename
• v0.4.0 schema implementation

Context

See docs/multi-iso-plan.md for the broader multi-ISO architectural plan.