docs: define SaaS capacity controls

.scratch/saas-production-readiness/assets/tenant-auth-security-audit.md

@@ -29,8 +29,10 @@ The audit used these upstream requirements:
   run's project workspace.
 - ADR-0019: authorization is evaluated against principals resolved at request
   time so membership changes take effect immediately.
-- ADR-0021: customer Feishu and model-provider credentials are org-scoped
-  secrets, encrypted at rest, and accessed through a resolver.
+- ADR-0021: Feishu and model-provider credentials are org-scoped secrets,
+  encrypted at rest, and accessed through a resolver. Provider ownership may be
+  Organization-managed BYOK or a distinct platform-managed connection for that
+  Organization; neither mode permits a process-global shared key.
 
 ## Confirmed protections
 
@@ -130,10 +132,10 @@ encrypted credentials "deferred", although ADR-0021 says they **must** be
 org-scoped, encrypted at rest, and accessed through a resolver.
 
 `EnvRuntimeSettings.provider` similarly discards its `scope` argument and uses
-one global OpenRouter token for every project. This both leaks tenant ownership
-of credentials and makes the accepted "customers supply their own provider
-keys" accounting model false. The schema has no encrypted credential store,
-key version, rotation state, or resolver seam.
+one global OpenRouter token for every project. This erases the accepted
+per-Organization provider mode and makes both BYOK and platform-managed cost
+attribution false. The schema has no encrypted credential store, key version,
+rotation state, or resolver seam.
 
 This is also a product reachability blocker: one customer-owned Feishu app
 cannot receive bot/OAuth traffic for unrelated customer tenants under the
@@ -248,7 +250,9 @@ Production readiness requires automated proof of all of the following:
    organization, project, run, and pending action consistently.
 4. ACTIVE Organization status is enforced in the shared authorization seam.
 5. Feishu and provider credentials resolve by Organization, are encrypted at
-   rest with versioned keys, never enter logs/agent tools, and can rotate.
+   rest with versioned keys, never enter logs/agent tools, and can rotate;
+   provider resolution honors either Organization-managed BYOK or a distinct
+   platform-managed connection for that Organization.
 6. Cross-org HTTP and Prisma service tests remain green, while new negative
    tests cover every finding above.
 7. Production Node and Rust dependency audits pass with no ignored