## Summary
Records the per-environment config strategy for both apps. ADR-only — no code changes; the implementation is anchored in §Confirmation against the next feature work that touches per-environment values.
## What lands
[**ADR-0018 — Environment configuration**](docs/decisions/0018-environment-configuration-strategy.md):
- **SPA**: Angular `environment.ts` + project.json `fileReplacements`. Build-time substitution; no runtime config fetch (rejected for the LCP/TTFB cost it would add and the deploy-time HTML rewrite that the alternatives need). Concretely cleans up the hard-coded URLs we left in `observability/tracing.ts` and `home-status.service.ts` ("hard-coded for v1 — env-config when it lands" comments).
- **BFF**: keep `process.env` + small per-key boot-time validators (the shape `apps/portal-bff/src/config/check-database-url.ts` already follows). `@nestjs/config` rejected as too heavy for the current key count; `zod` not justified yet.
- **Audit log connection**: formalises the `AUDIT_DATABASE_URL` split that ADR-0013 §"Wired as features land" already pointed at. When set, the `AuditModule` instantiates a second Prisma client with `audit_writer`-only credentials (defense in depth); when unset, the dev fallback (shared pool + `SET LOCAL ROLE audit_writer` per transaction) keeps working. A boot-time `UPDATE`-rejection self-test runs against the dedicated pool when configured — refuses to start if the pool can mutate the audit table.
The §Confirmation block cross-references the env-var-as-boot-gate items already pre-figured in ADR-0009 / ADR-0010 / ADR-0012 / ADR-0013 / ADR-0014, so the validator pattern is the single landing place when those features ship.
## What does NOT change in this PR
- No `apps/portal-shell/src/environments/*.ts` files yet — landed alongside the next feature that actually needs per-environment values.
- No `AUDIT_DATABASE_URL` validator in BFF — same; lands when the second pool is wired.
- No CLAUDE.md restructuring; just one extra bullet under the Architecture summary referencing ADR-0018.
## Doc updates
- `docs/decisions/README.md` index — new row for ADR-0018.
- `CLAUDE.md` Architecture summary — one-line reference to ADR-0018 between the perf-budget and local-quality-gates entries.
## Test plan
- [ ] CI green on this PR (`format:check`).
- [ ] ADR-0018 renders in the doc index with the right tags (`frontend`, `backend`, `infrastructure`, `process`) and 2026-05-10 date.
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Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #80
