Let a human token carry the zone it is issued into, without relabelling anyone

KEY-WP-0013-T05's tenant blocker did not need the decision it was waiting on. The
two proposed resolutions differ in where a human's tenant comes from -- the
directory record, or the client registration -- and an implementation exists that
is correct under either, so the choice can be made later without another
migration.

A client registration may now declare a tenant. humanTenant() resolves it by four
rules: no declaration keeps the directory answer unchanged; a declared zone
applies where the directory has placed the user nowhere; agreement passes; and a
declared zone conflicting with a directory assignment refuses issuance rather
than relabelling the user.

The refusal is the design, not an edge case. A registration can bind a zone for
unplaced users and can never move a placed one, so this gets the approval chain
its tenant:platform without writing a general cross-tenant override into the
issuer. It fails closed rather than picking a winner, because either answer would
be a silent cross-tenant assertion, and it reports 403 with
error_type: tenant_binding so an operator can tell a misconfigured registration
from a rejected login. If the owners later populate directory tenants, the same
code stops supplying the zone and starts enforcing agreement with it.

Safe only because client registrations are static and deployment-owned. The
tenant contract records that this rule must be revisited if dynamic client
registration is ever admitted.

Tests cover all four rules; neutering the conflict check fails the relabel test
rather than passing silently.

T05 now waits on one thing only: the client_id and callback URI from
informed-decision once it has a deployed origin.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016uV8zoCKpA1WRAxsKRYbdH

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 1182213@bnt-lap001
Assistant-Session: 966597b9-ae61-46a4-8b9e-1594ab3ec4ad

docs/approval-engine-auth-contract.md

@@ -20,6 +20,12 @@ exact deployment-owned callback, `audience: approval-engine`,
 No callback is invented here. The ID token is for the login client; present the
 access token to approval-engine.
 
+That client must also declare `tenant: tenant:platform`. A human token's tenant
+comes from the directory record, which assigns none today, so without the
+declaration the token would carry `tenant:coulomb` and be refused here. See
+[the tenant contract](tenant-claim-contract.md) for the four resolution rules and
+for why a declared zone can never relabel a user the directory has placed.
+
 `approval:read` is present because approval-engine showed the surface cannot
 render a decision without it: `GET /v1/approvals/{id}` and `/claim` both require
 it, so the earlier `[openid, approval:approve]` would have let an approver submit

docs/approval-engine-provisioning-request.yaml

@@ -49,14 +49,18 @@ human_registration:
   client_type: public
   grant: authorization_code + S256 PKCE
   never: [approval:consume]
-  blocked_on_keycape_side: |
-    A human access token cannot carry tenant:platform today. The tenant claim on
-    a human token is resolved from the directory user (effectiveTenant in
-    src/internal/server/oidc/token.go), not from the client registration, and no
-    adapter populates User.Tenant -- so every human token defaults to
-    tenant:coulomb. approval-engine compares tenant by exact string equality and
-    refuses near-miss spellings, so an approver token would be rejected. This
-    must be resolved before the registration is issued, not after.
+  # Required. Without it the token carries tenant:coulomb from the directory
+  # default and approval-engine refuses it. See docs/tenant-claim-contract.md.
+  tenant: tenant:platform
+  keycape_side_resolved: |
+    2026-09-09: a human token can now carry tenant:platform. A client
+    registration may declare a tenant; humanTenant() supplies it when the
+    directory has not placed the user, requires agreement when it has, and
+    refuses issuance on conflict rather than relabelling. Safe only because
+    registrations are static and deployment-owned. Still outstanding from
+    elsewhere: the exact client_id and callback URI from informed-decision
+    (INFD-WP-0001-T07), and whether the owners prefer the directory-sourced
+    resolution instead, which this implementation degrades into cleanly.
 verification:
   # The first two lines are now one runnable command per client; see
   # docs/native-authentication.md, "Verifying a live registration". It writes

docs/tenant-claim-contract.md

@@ -84,6 +84,46 @@ KEY-WP-0013-T02; KeyCape changed no live registration or policy subject.
   drift or an alias reintroduced into `config/service-clients.example.yaml` fails
   the build.
 
+## How a human token's tenant is resolved (KEY-WP-0013-T05)
+
+A human's tenant is normally a property of the person, read from the directory
+record. That alone could not serve the approval chain: decision
+`5ed3fb35-eca9-413a-82b9-95171ba85bf6` binds it to the landlord zone,
+approval-engine compares the claim by exact string equality, and no adapter
+populates `domain.User.Tenant` — so every human token fell back to
+`tenant:coulomb` and an approver token would have been refused downstream. It
+would have presented as a failed approval rather than as a registration defect.
+
+A client registration may therefore declare a `tenant`, and `humanTenant` in
+`src/internal/server/oidc/token.go` resolves it by these four rules:
+
+| Client declares | Directory assigns | Result |
+| --- | --- | --- |
+| nothing | anything | the directory answer, or `tenant:coulomb` — unchanged |
+| a zone | nothing | the declared zone |
+| a zone | the same zone | that zone; client and directory agree |
+| a zone | a **different** zone | **issuance is refused** |
+
+The last row is the point. A registration can bind a zone for users the
+directory has not placed, and can never relabel a user it *has* placed. That
+case fails closed rather than picking a winner, because either answer would be a
+silent cross-tenant assertion. The refusal is a `403` with
+`error_type: tenant_binding`, distinct from an authentication failure, so an
+operator can tell a misconfigured registration from a rejected login.
+
+This also means the design survives the other resolution. If the directory later
+carries tenants, the same code stops supplying the zone and starts enforcing
+agreement with it — no second migration, and no window in which a stale
+registration silently wins.
+
+It is safe only because client registrations are static and deployment-owned.
+KeyCape excludes dynamic client registration by design; a self-service client
+able to name its users' tenant would be a straightforward escalation, and this
+rule must be revisited if that exclusion is ever lifted.
+
+Covered by `src/internal/server/oidc/human_tenant_test.go`, including the
+relabel refusal.
+
 These are local issuance proofs. They are not live-rollout evidence; see
 `docs/approval-engine-auth-contract.md` and KEY-WP-0013-T02 for the deployment
 boundary. No token or secret values appear in this document or in test output.