feat: prepare core hub platform onboarding

docs/evidence/core-hub-postgres-capacity-preflight-2026-08-20.md

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+# Core Hub PostgreSQL capacity preflight — 2026-08-20
+
+Workplan: `RPF-WP-0021-T02`
+
+Target: railiance01 `databases/platform-pg`
+
+Mode: live, read-only, non-secret
+
+## Purpose
+
+Record the current `platform-pg` resource posture before reviewing Core Hub as
+the fourth declaration on the cell. This is an admission preflight, not the
+controlled multi-consumer measurement required by `rapp-postgres` ADR-0004.
+
+## Observed baseline
+
+Collected through `ssh railiance01` using `kubectl top`, pod resource metadata,
+and read-only `pg_stat_activity` / database-size queries.
+
+| Signal | Observation |
+| --- | --- |
+| PostgreSQL pod CPU | 9m |
+| PostgreSQL pod memory | 362Mi |
+| CPU request / limit | 100m / 1 core |
+| Memory request / limit | 256Mi / 1Gi |
+| `max_connections` | 100 |
+| `shared_buffers` | 128MB |
+| `work_mem` | 4MB |
+| `maintenance_work_mem` | 64MB |
+
+Connection snapshot:
+
+| Database | Total | Active | Idle |
+| --- | ---: | ---: | ---: |
+| `audit_core` | 1 | 0 | 1 |
+| `postgres` | 2 | 1 | 1 |
+| no database | 6 | 0 | 0 |
+
+Database sizes were approximately 8MiB each for `audit_core`,
+`isolation_probe`, `platform_meta`, `postgres`, and `template1`.
+
+## Interpretation
+
+- The pod was using about 35% of its 1Gi memory limit during this quiet
+  snapshot. That is useful headroom evidence and not a peak or per-backend
+  measurement.
+- `tenant_engine` was not present in the database list, so this sample does
+  not exercise the declared second workload consumer.
+- Core Hub would reach the four-declaration ceiling after `audit-core`,
+  `tenant-engine`, and the counted isolation probe. It does not exceed the
+  ceiling if the stale, untracked Issue Core draft is removed as required by
+  `ISSUE-WP-0007`.
+- This snapshot does **not** close ADR-0004 section 5. Admission still needs a
+  coordinated measurement with the declared consumers active, including
+  connection/backend memory under representative load and a recorded peak.
+
+No PostgreSQL credential, query payload, tenant identifier, or secret value
+was read or recorded.