docs: revise RAMZ isolation decision to database-per-tenant

Schema-per-tenant was the original call, but falah-os-master's
infrastructure/postgres/init.sql already establishes database-per-service
as the platform convention (falahid, falahwallet, falahramz, falahmock,
falahistore). Database-per-tenant matches that pattern and is a stronger
isolation boundary than schemas would have been.

docs/architecture/ramz-tenant-isolation-decision.md

@@ -1,6 +1,6 @@
 # RAMZ Tenant Isolation — Decision
 
-**Status:** Resolved
+**Status:** Resolved (revised 2026-08-18 — see amendment below)
 **Blocks:** Phase 2 of the [moslem04 Sync API spec](./sync-api-spec.html) (admin console read view)
 **Originally flagged in:** Nur Falah Admin Console PRD review
 
@@ -17,10 +17,19 @@ Two options were on the table:
 
 ## Decision
 
-**Schema-per-tenant on a single shared Postgres cluster.**
+**Database-per-tenant on the shared Postgres instance.**
 
-Each tenant (EstateOS, Tanah Hidup, Cair) gets its own Postgres schema. Not a separate
+Each tenant (EstateOS, Tanah Hidup, Cair) gets its own Postgres *database* — `falahestateos`,
-server, not a shared table filtered by a `tenant_id` column.
+`falahtanahhidup`, `falahcair` — not a schema, not a shared table filtered by a `tenant_id`
+column.
+
+> **Amendment (2026-08-18):** this was originally decided as schema-per-tenant. Inspecting
+> `falah-os-master/infrastructure/postgres/init.sql` showed the codebase already has an
+> established convention — **database-per-service** (`falahid`, `falahwallet`, `falahramz`,
+> `falahmock`, `falahistore`, all separate databases in one Postgres instance, not schemas).
+> Database-per-tenant is a stronger isolation boundary than schema-per-tenant anyway, and it
+> keeps one consistent pattern across the platform instead of introducing a second, competing
+> one. Revised to match.
 
 ## Why
 
@@ -31,25 +40,25 @@ server, not a shared table filtered by a `tenant_id` column.
   boundary is something that can actually be demonstrated.
 - This was flagged as a trust/compliance blocker for the UK Innovator Visa pitch — the
   isolation model isn't just an engineering choice, it's part of the pitch.
-- Fully separate databases (or separate servers) solve the same trust problem but multiply
+- Separate databases on one Postgres instance is the platform's existing convention, not a
-  ops burden — separate backup policies, connection pools, migrations to run three times
+  new ops burden — `falah-os-master` already runs 5 databases this way. Adding 3 more
-  instead of once. Not justified at current scale.
+  follows the grain of the system instead of cutting against it.
-- Schema-per-tenant keeps one cluster, one backup policy, one connection pool — while still
-  giving each tenant a real, auditable namespace boundary.
 
 ## What RAMZ still does
 
-RAMZ doesn't disappear — it moves down a level. Within each tenant's schema, RAMZ handles
+RAMZ doesn't disappear — it moves down a level. Within each tenant's database, RAMZ handles
-the finer-grained access control that a schema boundary can't: which user or law firm
+the finer-grained access control that a database boundary can't: which user or law firm
 within EstateOS can see which case, which land officer within Tanah Hidup can see which
 lease. RAMZ was never going to be strong enough to be the *only* thing standing between
 tenants — now it doesn't have to be.
 
 ## Consequence for the sync API
 
-The `tenant_id` field in the [sync spec](./sync-api-spec.html) becomes a schema selector,
+The `tenant_id` field in the [sync spec](./sync-api-spec.html) becomes a database selector
-not a row filter. The admin console's `/v1/admin/metadata` endpoint queries across schemas
+(one connection pool per tenant), not a row filter. The `moslem-admin` service's
-explicitly, per-tenant — there is no accidental cross-tenant query path.
+`/v1/admin/metadata` endpoint holds one Postgres pool per tenant database — there is no
+shared table and no accidental cross-tenant query path, because a query issued against one
+pool cannot physically reach another tenant's rows.
 
 ## Still open