docs(adr): ADR-0002 — per-application environments via an env coordinate

Records the decision to extend the <app> join key with a second
coordinate <env>, governed by an elision rule (env=prod elides → every
existing app's derived names are byte-identical and its tofu plan is a
no-op; non-prod envs take the <app>-<env> suffix, with the Postgres
owner role staying snake-case <app>_<env>_role).

Motivated by the ERP's incoming write-capable AI-agent skill: it needs
an in-cluster sandbox instance (erp-sandbox) with a prod-like Dolibarr
API + isolated database to rehearse writes before a human promotes them
to prod. The ADR reconciles this against ADR-0001 honestly — ADR-0001
rejected an in-cluster sandbox for INFRA-change rehearsal (shared
fleet-wide control planes); ADR-0002 operates one layer up where the
agent's only reach is the app's HTTP API against an isolated DB, so the
fleet blast radius is not in scope. The two are complementary; ADR-0002
does not supersede ADR-0001.

Also:
- vibe/ADR/README.md: index row for 0002 + Last Updated 2026-06-25
- PRD safe-prod-like-environment README: bidirectional back-link to
  ADR-0002 on the Adjacent line + Last Updated 2026-06-25

Authored via the ADR Scribe persona, validated via the Continuity Warden
checklist (no-tombstone, breadcrumb, MADR-lite sections, dead-link scan,
bidirectional links).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

vibe/PRD/safe-prod-like-environment/README.md

@@ -3,9 +3,9 @@
 # Safe, production-like environment
 
 > **Status:** In design
-> **Last Updated:** 2026-06-23
+> **Last Updated:** 2026-06-25
 > **Design record:** [ADR 0001 — Safe, production-like environment](../../ADR/0001-safe-prod-like-environment.md)
-> **Adjacent:** [INV-001 — prod blast-radius couplings](../../investigations/INV-001-prod-blast-radius-couplings.md)
+> **Adjacent:** [INV-001 — prod blast-radius couplings](../../investigations/INV-001-prod-blast-radius-couplings.md) · [ADR 0002 — per-application environments](../../ADR/0002-per-application-environments.md) (the application-data-layer counterpart)
 > **Map:** [Lab ecosystem guidebook](../../guidebooks/lab-ecosystem/README.md)
 
 ## Problem