feat: expose typed deployment capability receipts

docs/CONFIGURATION_PACKAGES.md

@@ -159,7 +159,36 @@ The initial implementation includes provider-neutral orchestration helpers:
 
 The first concrete provider is `govoplan_access.backend.configuration_provider`.
 It supports access-owned `roles`, `groups`, and `group_role_assignments`
-fragments and applies them idempotently.
+fragments and applies them idempotently. Mail and Files also register providers
+for deployment configuration: Mail owns receipt-bound SMTP profiles and Files
+validates the deployment-owned managed-storage binding.
+
+### Deployment capability receipt
+
+The installer mounts a bounded, non-secret infrastructure receipt at the path
+named by `GOVOPLAN_DEPLOYMENT_CAPABILITIES_PATH`. Core validates that document
+once for configuration-package context and exposes typed capability and
+post-install-task records to providers. Invalid receipts fail closed. Endpoint
+metadata is sanitized, and secret fields may cross this boundary only as
+`env:VARIABLE_NAME` references.
+
+Feature providers remain responsible for their own semantics:
+
+- Mail can derive host and port from `mail.smtp`, collect missing non-secret
+  transport fields, and bind an existing credential-envelope id. It never
+  accepts or exports a username, password, token, or decrypted credential.
+- Files compares `files.storage` with the effective runtime backend, endpoint,
+  trust marker, bucket, and presence of referenced environment secrets. Storage
+  remains deployment-owned, so the provider reports `skip` when they agree and
+  blocks drift instead of rewriting process environment or storage credentials.
+- A system-scoped Mail profile requires system configuration authority. Tenant
+  scope is the conservative default.
+- Existing Mail configuration is preserved unless a reviewed fragment
+  explicitly selects `on_conflict: update`. Reapplying an unchanged fragment is
+  a no-op.
+
+Ops projects the same Core-validated receipt. It must not maintain a second
+parser with different validation or secret-handling rules.
 
 The admin wizard backend starts with these routes: