diff --git a/CLAUDE.md b/CLAUDE.md
index 5e31526..9a5e06c 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -221,11 +221,21 @@ caller of ClickHouse/`rbacstore`, and (via a new
 its real result into the CRD — a real credential Secret, not the
 previous placeholder that authenticated against nothing, and status
 fields the reconciler derives `Phase`/`Ready` from instead of
-independently guessing "Active" the moment a Tenant object exists. What
-still keeps this phase from being done: ingest itself has no tenant
-concept for either storage engine (every record lands in the one shared
-ClickHouse database and Tantivy index no matter what — undesigned, not
-just unbuilt). Full accounting:
+independently guessing "Active" the moment a Tenant object exists. The
+tenant-picker's backend protocol is built too: an identity with more
+than one `tenant_memberships` row now gets a real `GET
+/auth/memberships`/`POST /auth/select-tenant` round trip (a short-lived
+pending-login token, distinct from a real session by both Go type and
+JWT claim name — a real token-confusion bug this design's own tests
+caught before it shipped) instead of the flat refusal Phase 4 shipped
+with earlier. What still keeps this phase from being done: the actual
+tenant-picker *page* doesn't exist (`web` has no session/cookie-handling
+code at all yet, and `enterprise-auth` has no CORS middleware for a
+cross-origin `fetch` with credentials — both real, separately-scoped
+frontend gaps), and ingest itself has no tenant concept for either
+storage engine (every record lands in the one shared ClickHouse database
+and Tantivy index no matter what — undesigned, not just unbuilt). Full
+accounting:
 `/docs/security/threat-model.md`; step-by-step verification procedure
 (not yet run against a live cluster in this environment):
 `/docs/phase-4-runbook.md`. The rest of this section describes the exit
diff --git a/docs/phase-4-runbook.md b/docs/phase-4-runbook.md
index 3e48e26..fe7d2b2 100644
--- a/docs/phase-4-runbook.md
+++ b/docs/phase-4-runbook.md
@@ -521,6 +521,39 @@ the full loop (does the operator's watch actually re-trigger a reconcile
 after `-provision-tenant`'s external status write the way controller-
 runtime's default predicate is expected to).
 
+## 12. Tenant-picker backend protocol (no frontend yet, no Docker needed)
+
+Like §9, this needs nothing but a local Go toolchain -- the real
+fake-IdP tests already exercise the full login → pending-login cookie →
+`GET /auth/memberships` → `POST /auth/select-tenant` → real session
+round trip:
+
+```sh
+cd enterprise
+go test ./internal/session/... -run PendingLogin -v
+# real JWT signing/verification: issues a pending-login token, validates
+# it, and proves the two negative regressions that matter most --
+# a real session token must not validate as a pending login (they share
+# a signing key but PendingLoginClaims uses a disjoint json field name,
+# see that type's doc comment for the bug this caught in its own tests),
+# and a pending-login token must not validate as a real session either.
+
+go test ./internal/loginhandler/... -run 'Memberships|SelectTenant|MultipleMemberships' -v
+# full round trip against the real fake OIDC/SAML IdPs: multi-membership
+# login sets a pending cookie and redirects (not a 501 anymore), GET
+# /auth/memberships lists the real tenant options with display names,
+# POST /auth/select-tenant re-derives role server-side and refuses a
+# tenant_id outside the identity's actual memberships.
+```
+
+**Not built, and explicitly not attempted here**: the frontend page.
+`web` has no session/cookie-handling code anywhere in it today (checked
+while designing this), and `enterprise-auth` has no CORS middleware at
+all -- a cross-origin `fetch` with credentials from `web`'s origin to
+`enterprise-auth`'s would need it, and doesn't work today. Building the
+actual picker UI is real, separately-scoped frontend work; this section
+only closes the backend half.
+
 ## Known gaps (do not treat this phase as done without reading these)
 
 Full accounting: `/docs/security/threat-model.md`. Headline items:
@@ -553,8 +586,13 @@ Full accounting: `/docs/security/threat-model.md`. Headline items:
 - **Human SSO login now works for both OIDC (§3a) and SAML (§3b)** --
   each verified with a real fake IdP (genuine cryptographic signing and
   verification), not yet a real external IdP or a running
-  `enterprise-auth` container. No tenant-picker UI for a multi-membership
-  identity either (refused outright) for either protocol.
+  `enterprise-auth` container. **The tenant-picker backend protocol is
+  now built too** (§12) -- `GET /auth/memberships`/
+  `POST /auth/select-tenant`, backed by a short-lived pending-login
+  token distinct from a real session -- but nothing in `web` calls it
+  yet, so a multi-membership identity still can't actually finish
+  logging in through a browser today, just through direct HTTP calls
+  (which is what §12's verification does).
 - No admin UI to create a `tenant_memberships` row, but §3a/§3b's manual
   SQL bootstrap is gone -- `enterprise-auth -create-tenant`/
   `-grant-membership-*`/`-revoke-membership-*`/`-list-memberships-tenant`
diff --git a/docs/security/threat-model.md b/docs/security/threat-model.md
index c613df3..c811143 100644
--- a/docs/security/threat-model.md
+++ b/docs/security/threat-model.md
@@ -176,11 +176,23 @@ container against a *real* external IdP (Google/Okta/etc.) — that needs
 real IdP credentials and a reachable callback/ACS URL neither of which
 this environment has; see `/docs/phase-4-runbook.md`.
 
-A user with zero or more than one `tenant_memberships` row is refused
-outright (403 / 501 respectively) rather than guessed at — a
-tenant-selection UI for the multi-membership case is real, undesigned
-future work, not silently approximated, for either protocol.
-`GET /auth/features` (`enterprise/internal/authhandler`) reports whether
+A user with zero `tenant_memberships` rows is refused outright (403).
+More than one no longer guesses or refuses: `finishLogin` issues a
+short-lived `session.Manager` "pending login" token (a distinct Go/JWT
+type from a real session, with its own disjoint claim name so a real
+session token can't double as one — a real bug this design's own test
+suite caught before it shipped, see `session.PendingLoginClaims`'s doc
+comment) and redirects to a not-yet-served URL instead, backed by two
+new endpoints (`GET /auth/memberships`, `POST /auth/select-tenant`) that
+list the identity's real tenant options and, on selection, re-derive the
+role for the chosen tenant server-side (never trusting a client-supplied
+role) before issuing the real session. This is the *backend protocol*
+for tenant selection, verified with the same real-fake-IdP tests as the
+rest of `internal/loginhandler` — the frontend page that would call it
+doesn't exist (`web` has no session/cookie-handling code at all today,
+and `enterprise-auth` has no CORS middleware for a cross-origin `fetch`
+with credentials to work), both real, separately-scoped gaps, not
+silently approximated. `GET /auth/features` (`enterprise/internal/authhandler`) reports whether
 OIDC/SAML are *configured*, for `/web`'s settings page to conditionally
 render — independent of whether a login button actually exists yet in
 the UI (it doesn't; only the HTTP endpoints do).
@@ -413,7 +425,7 @@ terms:
 | Deployment actually routing traffic to `enterprise-api` (docker-compose) | **Enforced** — `api`/`enterprise-api` are mutually exclusive via `COMPOSE_PROFILES`, same flag choice as Helm's `enterprise.enabled`; verified via `docker compose config`, not an actual `docker compose up` in this environment |
 | Human SSO login — OIDC | **Built, verified with a real fake IdP** (not yet tried against a real external IdP) |
 | Human SSO login — SAML | **Built, verified with a real fake IdP** (not yet tried against a real external IdP) |
-| Multi-tenant-membership login (tenant picker) | **Not implemented** — refused with a clear error, not guessed |
+| Multi-tenant-membership login (tenant picker) | **Backend protocol built and verified** (`GET /auth/memberships`, `POST /auth/select-tenant`, a pending-login token distinct from a real session) — no frontend page calls it yet |
 | Per-resource dashboard grants (`own/granted`) | **Built, unit-tested against a fake store; live-Postgres integration tests written, not run in this environment** (only when `enterprise-api` serves traffic — plain `api` falls back to own/Admin only) |
 | Query audit logging (routine queries) | **Enforced**, fail-open, and now wired to a real writer via `enterprise-api` (`audit.QueryAPILogger`) |
 | Audit log tamper detection (hash chain) | **Enforced**, verified live |
diff --git a/enterprise/README.md b/enterprise/README.md
index f48806d..48d6fb2 100644
--- a/enterprise/README.md
+++ b/enterprise/README.md
@@ -55,9 +55,12 @@ section for exactly what "not yet run" means here and why. Don't read
   -- the actual human login flow, previously entirely missing. Redirects
   to the configured IdP with CSRF-protection state in a short-lived
   cookie, exchanges the code, verifies the ID token via `internal/oidc`,
-  upserts a `users` row, resolves tenant/role from exactly one
-  `tenant_memberships` row (refuses with a clear error on zero or
-  multiple -- no tenant-picker UI yet), and issues a session cookie.
+  upserts a `users` row, resolves tenant/role from `tenant_memberships`
+  (refuses with a clear error on zero rows; more than one starts a real
+  tenant-selection round trip -- `GET /auth/memberships` +
+  `POST /auth/select-tenant`, backed by a short-lived
+  `session.Manager.IssuePendingLogin` token -- rather than guessing; see
+  "Tenant selection" below), and issues a session cookie.
   **This one genuinely is verified**, unlike the ClickHouse pieces above:
   `loginhandler_test.go` runs the full flow against a real fake IdP
   (`coreos/go-oidc`'s own `oidctest` package, real RS256 signing and
@@ -134,11 +137,51 @@ manage-grants regression); real integration tests exist in
 environment, same disclosed gap as the rest of this package's
 Postgres-backed pieces.
 
+## Tenant selection (multi-membership identities)
+
+The backend protocol for choosing a tenant is built and tested; the
+frontend page that would actually call it is deliberately not (see
+"Deliberately deferred" below). When `resolveIdentity` finds more than
+one `tenant_memberships` row for a logged-in identity, `finishLogin`
+issues a `session.Manager.IssuePendingLogin` token (a distinct Go/JWT
+type from a real session -- see that type's doc comment for a real bug
+this design caught in its own tests: a shared JSON key would have let a
+full session token double as a pending login) as a
+`sentry_pending_login` cookie (`Path=/auth`) and redirects to
+`SELECT_TENANT_REDIRECT_URL` (defaults to
+`{POST_LOGIN_REDIRECT_URL}/select-tenant`) instead of completing the
+login. From there:
+
+- `GET /auth/memberships` -- lists the pending identity's tenants
+  (`tenant_id`, `tenant_display_name`, `role`) to choose between.
+- `POST /auth/select-tenant` with `{"tenant_id": "..."}` -- re-derives
+  the role for that specific tenant server-side (never trusts a
+  client-supplied role, only checks the claimed `tenant_id` against the
+  identity's actual memberships, refusing with 403 otherwise), issues
+  the real session cookie, and responds with
+  `{"redirect_url": "..."}` for the caller to navigate to -- JSON, not a
+  redirect, since this is a POST/fetch call a frontend page should
+  control the navigation for itself.
+
+Verified with the same real-fake-IdP tests as the rest of this package
+(`loginhandler_test.go`/`saml_test.go`): the full login -> pending
+cookie -> `GET /auth/memberships` -> `POST /auth/select-tenant` -> real
+session round trip, plus negative paths (missing/expired/wrong-type
+pending cookie, a `tenant_id` outside the identity's actual
+memberships, a real session token rejected when presented as a pending
+login).
+
 **Deliberately deferred, not half-built** -- named explicitly rather than
 silently left out:
-- A tenant-picker UI/flow for an identity with more than one
-  `tenant_memberships` row -- `loginhandler` refuses these logins
-  outright rather than guessing (`ErrMultipleMemberships`).
+- **The actual tenant-picker page** -- nothing in `web/` calls the
+  endpoints above yet. Building it is genuinely different, larger scope
+  than the backend protocol: `web` has zero session/cookie-handling
+  code today (confirmed by reading it end to end while designing this),
+  so a real picker page means adding that from scratch, plus CORS
+  wiring (`enterprise-auth` has no CORS middleware at all right now --
+  a cross-origin `fetch` with credentials from `web`'s origin needs
+  it), neither of which is verifiable in this environment without a
+  live backend and a browser session to exercise.
 - **Ingest tenant-awareness, for either storage engine** -- `chrunner`/
   `searchclient` prove read isolation given tenant-scoped data exists,
   but nothing writes it: every record `ingest` produces still lands in
@@ -344,6 +387,7 @@ to, see `tenantprovision.ProvisionClickHouse`'s doc comment).
 | `SAML_IDP_METADATA_URL` | (empty — SAML disabled if unset; if set, fetched and parsed at startup via `samlsp.FetchMetadata`, same trust level as `OIDC_ISSUER_URL`'s discovery fetch) |
 | `ENTERPRISE_SESSION_SIGNING_KEY` | **required**, min 32 bytes |
 | `POST_LOGIN_REDIRECT_URL` | `http://localhost:3000` — where the browser lands after `internal/loginhandler` sets a session cookie |
+| `SELECT_TENANT_REDIRECT_URL` | `{POST_LOGIN_REDIRECT_URL}/select-tenant` — where the browser lands for a multi-membership identity instead; nothing serves this route yet, see "Tenant selection" above |
 
 ## Environment variables (`enterprise-api`)
 
diff --git a/enterprise/cmd/enterprise-auth/main.go b/enterprise/cmd/enterprise-auth/main.go
index 47c722a..52a4dbb 100644
--- a/enterprise/cmd/enterprise-auth/main.go
+++ b/enterprise/cmd/enterprise-auth/main.go
@@ -188,7 +188,7 @@ func main() {
 		SAMLEnabled: cfg.SAML.IDPMetadataURL != "",
 	}
 	authhandler.New(logger, sessionManager, features).RegisterRoutes(mux)
-	loginhandler.New(logger, oidcProvider, samlProvider, sessionManager, rbac, cfg.PostLoginRedirectURL).RegisterRoutes(mux)
+	loginhandler.New(logger, oidcProvider, samlProvider, sessionManager, rbac, cfg.PostLoginRedirectURL, cfg.SelectTenantRedirectURL).RegisterRoutes(mux)
 
 	srv := &http.Server{Addr: cfg.HTTPListenAddr, Handler: mux}
 
diff --git a/enterprise/internal/config/config.go b/enterprise/internal/config/config.go
index 0e1cd5c..4d0c3d2 100644
--- a/enterprise/internal/config/config.go
+++ b/enterprise/internal/config/config.go
@@ -17,6 +17,16 @@ type Config struct {
 	// internal/loginhandler sets a session cookie -- web's base URL in
 	// a real deployment.
 	PostLoginRedirectURL string
+	// SelectTenantRedirectURL is where the browser lands after a login
+	// resolves to more than one tenant_memberships row --
+	// internal/loginhandler issues a pending-login cookie and sends the
+	// browser here instead of straight to PostLoginRedirectURL. Nothing
+	// serves this route yet (a real tenant-picker page is undesigned
+	// frontend work -- see internal/loginhandler's package doc comment);
+	// the backend protocol (GET /auth/memberships, POST
+	// /auth/select-tenant) is complete and independently testable via
+	// HTTP regardless of what, if anything, is listening here today.
+	SelectTenantRedirectURL string
 }
 
 type PostgresConfig struct {
@@ -70,6 +80,12 @@ func Load() (Config, error) {
 		},
 		PostLoginRedirectURL: getenv("POST_LOGIN_REDIRECT_URL", "http://localhost:3000"),
 	}
+	// Defaults relative to PostLoginRedirectURL if not set explicitly --
+	// computed after cfg.PostLoginRedirectURL above so a caller
+	// overriding just POST_LOGIN_REDIRECT_URL still gets a sensible
+	// SelectTenantRedirectURL without also having to set the new
+	// variable.
+	cfg.SelectTenantRedirectURL = getenv("SELECT_TENANT_REDIRECT_URL", cfg.PostLoginRedirectURL+"/select-tenant")
 
 	// Required, unlike OIDC/SAML above: every enterprise-auth deployment
 	// issues and validates session/service tokens (internal/session),
diff --git a/enterprise/internal/loginhandler/loginhandler.go b/enterprise/internal/loginhandler/loginhandler.go
index 3b4da5e..797c4cf 100644
--- a/enterprise/internal/loginhandler/loginhandler.go
+++ b/enterprise/internal/loginhandler/loginhandler.go
@@ -12,13 +12,20 @@
 // gets verified differs.
 //
 // Multi-tenant users (one identity with memberships in more than one
-// tenant) are refused with a clear error rather than guessing which
-// tenant to log them into -- a tenant-selection step is real, undesigned
-// future work, not silently approximated.
+// tenant) get a real tenant-selection step, not a guess: finishLogin
+// issues a short-lived session.Manager "pending login" token (proves
+// who they are, commits to no tenant yet) and redirects to
+// selectTenantRedirectURL instead of issuing a session outright.
+// GET /auth/memberships and POST /auth/select-tenant complete the round
+// trip. The backend protocol is complete and independently testable via
+// HTTP; the frontend page that would actually call it doesn't exist yet
+// (a real tenant-picker UI is undesigned, separately-scoped frontend
+// work -- see config.SelectTenantRedirectURL's doc comment).
 package loginhandler
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"log/slog"
@@ -45,6 +52,12 @@ const oidcStateCookieName = "sentry_oidc_state"
 // response defense -- see saml.ServiceProvider.LoginURL's doc comment).
 const samlRequestCookieName = "sentry_saml_request"
 
+// pendingLoginCookieName carries a PendingLoginClaims token from
+// finishLogin's multi-membership branch through GET /auth/memberships
+// and POST /auth/select-tenant -- Path "/auth" (not "/") so it's never
+// sent on ordinary requests, only the two routes that need it.
+const pendingLoginCookieName = "sentry_pending_login"
+
 // loginCookieTTL bounds how long a user has to complete the IdP round
 // trip -- generous enough for a real login form, short enough that a
 // stale cookie isn't a long-lived CSRF token sitting in a browser.
@@ -57,6 +70,9 @@ const loginCookieTTL = 10 * time.Minute
 type userStore interface {
 	UpsertUserBySSO(ctx context.Context, ssoSubject, email, displayName string) (*rbacstore.User, error)
 	ListMembershipsForUser(ctx context.Context, userID string) ([]rbacstore.Membership, error)
+	// ListMembershipsWithTenantForUser backs GET /auth/memberships --
+	// the one caller that needs tenant display names, not just IDs/roles.
+	ListMembershipsWithTenantForUser(ctx context.Context, userID string) ([]rbacstore.MembershipWithTenant, error)
 }
 
 // oidcProvider is the narrow slice of *oidc.Provider Handler needs --
@@ -83,6 +99,10 @@ type Handler struct {
 	// postLoginRedirectURL is where the browser lands after a session
 	// cookie is set -- web's base URL in a real deployment.
 	postLoginRedirectURL string
+	// selectTenantRedirectURL is where the browser lands instead, when
+	// the identity has more than one tenant_memberships row -- see this
+	// package's doc comment.
+	selectTenantRedirectURL string
 }
 
 // New takes concrete *oidc.Provider/*saml.ServiceProvider (both
@@ -98,8 +118,8 @@ type Handler struct {
 // loginhandler_test.go's TestRegisterRoutesNoOpWithTypedNilProviderVariable
 // for the regression test that caught this the first time (OIDC; SAML
 // follows the same fix from day one).
-func New(logger *slog.Logger, oidcProvider *oidc.Provider, samlProvider *saml.ServiceProvider, sessionManager *session.Manager, users userStore, postLoginRedirectURL string) *Handler {
-	h := &Handler{logger: logger, session: sessionManager, users: users, postLoginRedirectURL: postLoginRedirectURL}
+func New(logger *slog.Logger, oidcProvider *oidc.Provider, samlProvider *saml.ServiceProvider, sessionManager *session.Manager, users userStore, postLoginRedirectURL, selectTenantRedirectURL string) *Handler {
+	h := &Handler{logger: logger, session: sessionManager, users: users, postLoginRedirectURL: postLoginRedirectURL, selectTenantRedirectURL: selectTenantRedirectURL}
 	if oidcProvider != nil {
 		h.oidc = oidcProvider
 	}
@@ -122,6 +142,10 @@ func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
 		mux.HandleFunc("GET /auth/saml/login", h.handleSAMLLogin)
 		mux.HandleFunc("POST /auth/saml/acs", h.handleSAMLACS)
 	}
+	if h.oidc != nil || h.saml != nil {
+		mux.HandleFunc("GET /auth/memberships", h.handleListMemberships)
+		mux.HandleFunc("POST /auth/select-tenant", h.handleSelectTenant)
+	}
 }
 
 func (h *Handler) handleOIDCLogin(w http.ResponseWriter, r *http.Request) {
@@ -248,17 +272,30 @@ func (h *Handler) handleSAMLACS(w http.ResponseWriter, r *http.Request) {
 }
 
 // finishLogin is the point both protocols converge on: a verified
-// (subject, email) pair, still needing tenant/role resolution and a
-// session cookie -- everything from here down is protocol-agnostic.
+// (subject, email) pair, still needing tenant/role resolution --
+// everything from here down is protocol-agnostic.
 func (h *Handler) finishLogin(w http.ResponseWriter, r *http.Request, subject, email string) {
-	identity, status, err := h.resolveIdentity(r.Context(), subject, email)
+	outcome, status, err := h.resolveIdentity(r.Context(), subject, email)
 	if err != nil {
 		h.logger.Error("resolving identity after login", "error", err, "email", email)
 		http.Error(w, err.Error(), status)
 		return
 	}
 
-	token, err := h.session.IssueUserSession(identity.tenantID, identity.userID, identity.role)
+	if outcome.ambiguous {
+		h.startTenantSelection(w, r, outcome.userID)
+		return
+	}
+	h.issueSessionAndRedirect(w, r, outcome.identity.tenantID, outcome.identity.userID, outcome.identity.role)
+}
+
+// issueSessionAndRedirect is finishLogin's single-membership path and
+// handleSelectTenant's success path converging on the same "issue a
+// real session, set the cookie, send the browser on" logic -- the only
+// difference between the two callers is how they got a
+// (tenantID, userID, role) tuple to issue a session for.
+func (h *Handler) issueSessionAndRedirect(w http.ResponseWriter, r *http.Request, tenantID, userID, role string) {
+	token, err := h.session.IssueUserSession(tenantID, userID, role)
 	if err != nil {
 		h.logger.Error("issuing session", "error", err)
 		http.Error(w, "internal error", http.StatusInternalServerError)
@@ -272,13 +309,142 @@ func (h *Handler) finishLogin(w http.ResponseWriter, r *http.Request, subject, e
 	http.Redirect(w, r, h.postLoginRedirectURL, http.StatusFound)
 }
 
+// startTenantSelection issues a pending-login token for an identity
+// with more than one tenant_memberships row and sends the browser to
+// selectTenantRedirectURL instead of completing the login -- the real
+// tenant-selection step named as a gap throughout Phase 4's docs, not a
+// refusal anymore (see this package's doc comment).
+func (h *Handler) startTenantSelection(w http.ResponseWriter, r *http.Request, userID string) {
+	token, err := h.session.IssuePendingLogin(userID)
+	if err != nil {
+		h.logger.Error("issuing pending login", "error", err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return
+	}
+	http.SetCookie(w, &http.Cookie{
+		Name: pendingLoginCookieName, Value: token, Path: "/auth",
+		HttpOnly: true, Secure: r.TLS != nil, SameSite: http.SameSiteLaxMode,
+		MaxAge: int(session.PendingLoginTTL.Seconds()),
+	})
+	http.Redirect(w, r, h.selectTenantRedirectURL, http.StatusFound)
+}
+
+// pendingUserID validates the pending-login cookie GET /auth/memberships
+// and POST /auth/select-tenant both require, writing an error response
+// and returning ok=false if it's missing, expired, or forged.
+func (h *Handler) pendingUserID(w http.ResponseWriter, r *http.Request) (userID string, ok bool) {
+	cookie, err := r.Cookie(pendingLoginCookieName)
+	if err != nil || cookie.Value == "" {
+		http.Error(w, "missing or expired pending login -- start over at /auth/oidc/login or /auth/saml/login", http.StatusBadRequest)
+		return "", false
+	}
+	userID, err = h.session.ValidatePendingLogin(cookie.Value)
+	if err != nil {
+		http.Error(w, "missing or expired pending login -- start over at /auth/oidc/login or /auth/saml/login", http.StatusUnauthorized)
+		return "", false
+	}
+	return userID, true
+}
+
+// membershipOption is one GET /auth/memberships response entry.
+type membershipOption struct {
+	TenantID          string `json:"tenant_id"`
+	TenantDisplayName string `json:"tenant_display_name"`
+	Role              string `json:"role"`
+}
+
+// handleListMemberships lists the pending login's tenants to choose
+// from -- a tenant-picker UI's first call, once one exists (see this
+// package's doc comment).
+func (h *Handler) handleListMemberships(w http.ResponseWriter, r *http.Request) {
+	userID, ok := h.pendingUserID(w, r)
+	if !ok {
+		return
+	}
+	memberships, err := h.users.ListMembershipsWithTenantForUser(r.Context(), userID)
+	if err != nil {
+		h.logger.Error("listing memberships with tenant", "error", err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return
+	}
+	options := make([]membershipOption, 0, len(memberships))
+	for _, m := range memberships {
+		options = append(options, membershipOption{TenantID: m.TenantID, TenantDisplayName: m.TenantDisplayName, Role: string(m.Role)})
+	}
+	w.Header().Set("Content-Type", "application/json")
+	_ = json.NewEncoder(w).Encode(options)
+}
+
+type selectTenantRequest struct {
+	TenantID string `json:"tenant_id"`
+}
+
+type selectTenantResponse struct {
+	RedirectURL string `json:"redirect_url"`
+}
+
+// handleSelectTenant completes the tenant-selection round trip: given a
+// still-valid pending login and a chosen tenant_id, re-derives the
+// membership/role for that specific tenant server-side (never trusting
+// a client-supplied role -- only which tenant they claim to want,
+// checked against their actual memberships) and issues the real
+// session. Responds with JSON, not a redirect: this is a POST a
+// tenant-picker page would call via fetch, which should decide for
+// itself how to navigate afterward, not have a redirect response
+// imposed on it the way the GET-based OIDC/SAML callbacks reasonably
+// can.
+func (h *Handler) handleSelectTenant(w http.ResponseWriter, r *http.Request) {
+	userID, ok := h.pendingUserID(w, r)
+	if !ok {
+		return
+	}
+	var body selectTenantRequest
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil || body.TenantID == "" {
+		http.Error(w, `invalid request body -- expected {"tenant_id": "..."}`, http.StatusBadRequest)
+		return
+	}
+
+	memberships, err := h.users.ListMembershipsForUser(r.Context(), userID)
+	if err != nil {
+		h.logger.Error("listing memberships", "error", err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return
+	}
+	var role string
+	found := false
+	for _, m := range memberships {
+		if m.TenantID == body.TenantID {
+			role = string(m.Role)
+			found = true
+			break
+		}
+	}
+	if !found {
+		http.Error(w, "no membership in the requested tenant", http.StatusForbidden)
+		return
+	}
+
+	clearCookie(w, r, pendingLoginCookieName, "/auth")
+	token, err := h.session.IssueUserSession(body.TenantID, userID, role)
+	if err != nil {
+		h.logger.Error("issuing session", "error", err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return
+	}
+	http.SetCookie(w, &http.Cookie{
+		Name: authhandler.SessionCookieName, Value: token, Path: "/",
+		HttpOnly: true, Secure: r.TLS != nil, SameSite: http.SameSiteLaxMode,
+		MaxAge: int(session.HumanSessionTTL.Seconds()),
+	})
+	w.Header().Set("Content-Type", "application/json")
+	_ = json.NewEncoder(w).Encode(selectTenantResponse{RedirectURL: h.postLoginRedirectURL})
+}
+
 var (
-	// ErrNoMembership and ErrMultipleMemberships are exported so tests
-	// (and any future caller that wants to distinguish these outcomes,
-	// e.g. to render a real tenant-picker UI instead of a flat error
-	// page) don't have to string-match the HTTP error body.
-	ErrNoMembership        = errors.New("loginhandler: this identity has no tenant membership -- contact your administrator")
-	ErrMultipleMemberships = errors.New("loginhandler: this identity belongs to multiple tenants -- tenant selection is not supported yet")
+	// ErrNoMembership is exported so tests (and any future caller that
+	// wants to distinguish this from other failures) don't have to
+	// string-match the HTTP error body.
+	ErrNoMembership = errors.New("loginhandler: this identity has no tenant membership -- contact your administrator")
 )
 
 type resolvedIdentity struct {
@@ -287,29 +453,40 @@ type resolvedIdentity struct {
 	role     string
 }
 
+// identityOutcome is resolveIdentity's result: exactly one membership
+// resolves identity directly; more than one sets ambiguous (userID is
+// always populated so the caller can start tenant selection without a
+// second lookup).
+type identityOutcome struct {
+	identity  resolvedIdentity
+	userID    string
+	ambiguous bool
+}
+
 // resolveIdentity is the policy decision this whole package exists to
 // make: given a verified external identity (subject, email -- OIDC's
 // "sub"/"email" claims or SAML's NameID/email attribute, already
 // protocol-normalized by the caller), which tenant/role does it map to.
-// Deliberately conservative -- exactly one tenant_memberships row is the
-// only case handled; zero or multiple both refuse rather than guess
-// (see this package's doc comment).
-func (h *Handler) resolveIdentity(ctx context.Context, subject, email string) (resolvedIdentity, int, error) {
+// Zero memberships refuses outright (ErrNoMembership) -- there's
+// nothing to choose between. More than one is no longer a refusal (see
+// this package's doc comment): finishLogin routes an ambiguous outcome
+// into tenant selection instead of erroring.
+func (h *Handler) resolveIdentity(ctx context.Context, subject, email string) (identityOutcome, int, error) {
 	user, err := h.users.UpsertUserBySSO(ctx, subject, email, email)
 	if err != nil {
-		return resolvedIdentity{}, http.StatusInternalServerError, fmt.Errorf("loginhandler: upserting user: %w", err)
+		return identityOutcome{}, http.StatusInternalServerError, fmt.Errorf("loginhandler: upserting user: %w", err)
 	}
 
 	memberships, err := h.users.ListMembershipsForUser(ctx, user.ID)
 	if err != nil {
-		return resolvedIdentity{}, http.StatusInternalServerError, fmt.Errorf("loginhandler: listing memberships: %w", err)
+		return identityOutcome{}, http.StatusInternalServerError, fmt.Errorf("loginhandler: listing memberships: %w", err)
 	}
 	switch len(memberships) {
 	case 0:
-		return resolvedIdentity{}, http.StatusForbidden, ErrNoMembership
+		return identityOutcome{}, http.StatusForbidden, ErrNoMembership
 	case 1:
-		return resolvedIdentity{tenantID: memberships[0].TenantID, userID: user.ID, role: string(memberships[0].Role)}, 0, nil
+		return identityOutcome{identity: resolvedIdentity{tenantID: memberships[0].TenantID, userID: user.ID, role: string(memberships[0].Role)}, userID: user.ID}, 0, nil
 	default:
-		return resolvedIdentity{}, http.StatusNotImplemented, ErrMultipleMemberships
+		return identityOutcome{userID: user.ID, ambiguous: true}, 0, nil
 	}
 }
diff --git a/enterprise/internal/loginhandler/loginhandler_test.go b/enterprise/internal/loginhandler/loginhandler_test.go
index 0d63cfb..9ef45df 100644
--- a/enterprise/internal/loginhandler/loginhandler_test.go
+++ b/enterprise/internal/loginhandler/loginhandler_test.go
@@ -17,6 +17,7 @@ import (
 	"log/slog"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
 	"time"
 
@@ -34,12 +35,17 @@ const testKeyID = "test-key-1"
 // SSO subject -- enough to drive resolveIdentity's logic without a real
 // Postgres.
 type fakeUserStore struct {
-	usersBySubject map[string]*rbacstore.User
-	memberships    map[string][]rbacstore.Membership // by user ID
+	usersBySubject     map[string]*rbacstore.User
+	memberships        map[string][]rbacstore.Membership // by user ID
+	tenantDisplayNames map[string]string                 // by tenant ID, defaults to the ID itself if unset
 }
 
 func newFakeUserStore() *fakeUserStore {
-	return &fakeUserStore{usersBySubject: map[string]*rbacstore.User{}, memberships: map[string][]rbacstore.Membership{}}
+	return &fakeUserStore{
+		usersBySubject:     map[string]*rbacstore.User{},
+		memberships:        map[string][]rbacstore.Membership{},
+		tenantDisplayNames: map[string]string{},
+	}
 }
 
 func (f *fakeUserStore) UpsertUserBySSO(_ context.Context, ssoSubject, email, displayName string) (*rbacstore.User, error) {
@@ -56,6 +62,19 @@ func (f *fakeUserStore) ListMembershipsForUser(_ context.Context, userID string)
 	return f.memberships[userID], nil
 }
 
+func (f *fakeUserStore) ListMembershipsWithTenantForUser(_ context.Context, userID string) ([]rbacstore.MembershipWithTenant, error) {
+	memberships := f.memberships[userID]
+	out := make([]rbacstore.MembershipWithTenant, 0, len(memberships))
+	for _, m := range memberships {
+		displayName := f.tenantDisplayNames[m.TenantID]
+		if displayName == "" {
+			displayName = m.TenantID
+		}
+		out = append(out, rbacstore.MembershipWithTenant{TenantID: m.TenantID, TenantDisplayName: displayName, Role: m.Role})
+	}
+	return out, nil
+}
+
 // testIdP bundles a real oidctest.Server (discovery + JWKS) with a local
 // /token handler, and knows how to mint a validly-signed ID token for a
 // given subject/email -- everything a test needs to drive a real login
@@ -128,7 +147,7 @@ func newTestSessionManager(t *testing.T) *session.Manager {
 
 func TestHandleLoginRedirectsAndSetsStateCookie(t *testing.T) {
 	idp := newTestIdP(t)
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 	mux := http.NewServeMux()
 	h.RegisterRoutes(mux)
 
@@ -188,7 +207,7 @@ func TestFullLoginFlowIssuesSessionForSingleMembership(t *testing.T) {
 	store := newFakeUserStore()
 	store.memberships["user-user-1"] = []rbacstore.Membership{{TenantID: "acme", UserID: "user-user-1", Role: rbacstore.RoleEditor}}
 	sessionManager := newTestSessionManager(t)
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, sessionManager, store, "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, sessionManager, store, "http://web/", "http://web/select-tenant")
 
 	idp.setNextIDToken(t, "user-1", "person@acme.example", true, time.Now().Add(time.Hour))
 	rec := fullLoginFlow(t, h, idp)
@@ -220,7 +239,7 @@ func TestFullLoginFlowIssuesSessionForSingleMembership(t *testing.T) {
 
 func TestFullLoginFlowRefusesNoMembership(t *testing.T) {
 	idp := newTestIdP(t)
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 
 	idp.setNextIDToken(t, "user-2", "nobody@acme.example", true, time.Now().Add(time.Hour))
 	rec := fullLoginFlow(t, h, idp)
@@ -230,26 +249,282 @@ func TestFullLoginFlowRefusesNoMembership(t *testing.T) {
 	}
 }
 
-func TestFullLoginFlowRefusesMultipleMemberships(t *testing.T) {
+// TestFullLoginFlowStartsTenantSelectionForMultipleMemberships is the
+// regression test for the real tenant-picker protocol (see this
+// package's doc comment): an identity with more than one
+// tenant_memberships row must get a pending-login cookie and a redirect
+// to selectTenantRedirectURL, not a flat refusal and not a session
+// cookie for either tenant guessed at.
+func TestFullLoginFlowStartsTenantSelectionForMultipleMemberships(t *testing.T) {
 	idp := newTestIdP(t)
 	store := newFakeUserStore()
 	store.memberships["user-user-3"] = []rbacstore.Membership{
 		{TenantID: "acme", UserID: "user-user-3", Role: rbacstore.RoleViewer},
 		{TenantID: "globex", UserID: "user-user-3", Role: rbacstore.RoleAdmin},
 	}
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), store, "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), store, "http://web/", "http://web/select-tenant")
 
 	idp.setNextIDToken(t, "user-3", "multi@example.com", true, time.Now().Add(time.Hour))
 	rec := fullLoginFlow(t, h, idp)
 
-	if rec.Code != http.StatusNotImplemented {
-		t.Fatalf("status = %d, want 501; body=%s", rec.Code, rec.Body.String())
+	if rec.Code != http.StatusFound {
+		t.Fatalf("status = %d, want 302; body=%s", rec.Code, rec.Body.String())
+	}
+	if loc := rec.Header().Get("Location"); loc != "http://web/select-tenant" {
+		t.Fatalf("Location = %q, want http://web/select-tenant", loc)
+	}
+	var pendingCookie, sessionCookie *http.Cookie
+	for _, c := range rec.Result().Cookies() {
+		switch c.Name {
+		case pendingLoginCookieName:
+			pendingCookie = c
+		case "sentry_session":
+			sessionCookie = c
+		}
+	}
+	if pendingCookie == nil || pendingCookie.Value == "" {
+		t.Fatal("expected a non-empty pending-login cookie")
+	}
+	if sessionCookie != nil {
+		t.Fatal("must not issue a real session cookie before a tenant is actually chosen")
+	}
+}
+
+// startTenantSelection drives a full OIDC login for an identity that
+// resolves to more than one membership, returning the mux (so callers
+// can drive GET /auth/memberships and POST /auth/select-tenant
+// afterward, exactly like a picker page would) and the pending-login
+// cookie the login flow set.
+func startTenantSelection(t *testing.T, h *Handler, idp *testIdP) (*http.ServeMux, *http.Cookie) {
+	t.Helper()
+	mux := http.NewServeMux()
+	h.RegisterRoutes(mux)
+
+	loginRec := httptest.NewRecorder()
+	mux.ServeHTTP(loginRec, httptest.NewRequest(http.MethodGet, "/auth/oidc/login", nil))
+	var stateCookie *http.Cookie
+	for _, c := range loginRec.Result().Cookies() {
+		if c.Name == oidcStateCookieName {
+			stateCookie = c
+		}
+	}
+	if stateCookie == nil {
+		t.Fatal("no state cookie from /auth/oidc/login")
+	}
+
+	callbackReq := httptest.NewRequest(http.MethodGet, "/auth/oidc/callback?state="+stateCookie.Value+"&code=test-code", nil)
+	callbackReq.AddCookie(stateCookie)
+	callbackRec := httptest.NewRecorder()
+	mux.ServeHTTP(callbackRec, callbackReq)
+	if callbackRec.Code != http.StatusFound {
+		t.Fatalf("callback status = %d, want 302; body=%s", callbackRec.Code, callbackRec.Body.String())
+	}
+	var pendingCookie *http.Cookie
+	for _, c := range callbackRec.Result().Cookies() {
+		if c.Name == pendingLoginCookieName {
+			pendingCookie = c
+		}
+	}
+	if pendingCookie == nil {
+		t.Fatal("expected a pending-login cookie")
+	}
+	return mux, pendingCookie
+}
+
+func newMultiMembershipStore() *fakeUserStore {
+	store := newFakeUserStore()
+	store.memberships["user-user-multi"] = []rbacstore.Membership{
+		{TenantID: "acme", UserID: "user-user-multi", Role: rbacstore.RoleViewer},
+		{TenantID: "globex", UserID: "user-user-multi", Role: rbacstore.RoleAdmin},
+	}
+	store.tenantDisplayNames["acme"] = "Acme Corp"
+	store.tenantDisplayNames["globex"] = "Globex Corporation"
+	return store
+}
+
+func TestListMembershipsReturnsTenantOptions(t *testing.T) {
+	idp := newTestIdP(t)
+	store := newMultiMembershipStore()
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), store, "http://web/", "http://web/select-tenant")
+	idp.setNextIDToken(t, "user-multi", "multi@example.com", true, time.Now().Add(time.Hour))
+	mux, pendingCookie := startTenantSelection(t, h, idp)
+
+	req := httptest.NewRequest(http.MethodGet, "/auth/memberships", nil)
+	req.AddCookie(pendingCookie)
+	rec := httptest.NewRecorder()
+	mux.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200; body=%s", rec.Code, rec.Body.String())
+	}
+	var options []membershipOption
+	if err := json.Unmarshal(rec.Body.Bytes(), &options); err != nil {
+		t.Fatalf("decoding response: %v", err)
+	}
+	if len(options) != 2 {
+		t.Fatalf("got %d options, want 2: %+v", len(options), options)
+	}
+	byTenant := map[string]membershipOption{}
+	for _, o := range options {
+		byTenant[o.TenantID] = o
+	}
+	if byTenant["acme"].TenantDisplayName != "Acme Corp" || byTenant["acme"].Role != "viewer" {
+		t.Fatalf("unexpected acme option: %+v", byTenant["acme"])
+	}
+	if byTenant["globex"].TenantDisplayName != "Globex Corporation" || byTenant["globex"].Role != "admin" {
+		t.Fatalf("unexpected globex option: %+v", byTenant["globex"])
+	}
+}
+
+func TestListMembershipsRejectsMissingPendingCookie(t *testing.T) {
+	idp := newTestIdP(t)
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
+	mux := http.NewServeMux()
+	h.RegisterRoutes(mux)
+
+	rec := httptest.NewRecorder()
+	mux.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, "/auth/memberships", nil))
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want 400", rec.Code)
+	}
+}
+
+func TestSelectTenantIssuesSessionForChosenTenant(t *testing.T) {
+	idp := newTestIdP(t)
+	store := newMultiMembershipStore()
+	sessionManager := newTestSessionManager(t)
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, sessionManager, store, "http://web/", "http://web/select-tenant")
+	idp.setNextIDToken(t, "user-multi", "multi@example.com", true, time.Now().Add(time.Hour))
+	mux, pendingCookie := startTenantSelection(t, h, idp)
+
+	req := httptest.NewRequest(http.MethodPost, "/auth/select-tenant", strings.NewReader(`{"tenant_id": "globex"}`))
+	req.AddCookie(pendingCookie)
+	rec := httptest.NewRecorder()
+	mux.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200; body=%s", rec.Code, rec.Body.String())
+	}
+	var sessionCookie, clearedPendingCookie *http.Cookie
+	for _, c := range rec.Result().Cookies() {
+		switch c.Name {
+		case "sentry_session":
+			sessionCookie = c
+		case pendingLoginCookieName:
+			clearedPendingCookie = c
+		}
+	}
+	if sessionCookie == nil || sessionCookie.Value == "" {
+		t.Fatal("expected a sentry_session cookie to be set")
+	}
+	if clearedPendingCookie == nil || clearedPendingCookie.MaxAge >= 0 {
+		t.Fatalf("expected the pending-login cookie to be cleared (MaxAge < 0), got %+v", clearedPendingCookie)
+	}
+	claims, err := sessionManager.Validate(sessionCookie.Value)
+	if err != nil {
+		t.Fatalf("validating issued session: %v", err)
+	}
+	if claims.TenantID != "globex" || claims.Role != "admin" || claims.UserID != "user-user-multi" {
+		t.Fatalf("unexpected session claims: %+v", claims)
+	}
+
+	var body selectTenantResponse
+	if err := json.Unmarshal(rec.Body.Bytes(), &body); err != nil {
+		t.Fatalf("decoding response: %v", err)
+	}
+	if body.RedirectURL != "http://web/" {
+		t.Fatalf("RedirectURL = %q, want http://web/", body.RedirectURL)
+	}
+}
+
+// TestSelectTenantRejectsTenantOutsideMembership is the regression test
+// for handleSelectTenant re-deriving role server-side rather than
+// trusting the request: a client claiming a tenant_id the pending
+// identity doesn't actually belong to must be refused, not silently
+// granted whatever role happened to be in the request.
+func TestSelectTenantRejectsTenantOutsideMembership(t *testing.T) {
+	idp := newTestIdP(t)
+	store := newMultiMembershipStore()
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), store, "http://web/", "http://web/select-tenant")
+	idp.setNextIDToken(t, "user-multi", "multi@example.com", true, time.Now().Add(time.Hour))
+	mux, pendingCookie := startTenantSelection(t, h, idp)
+
+	req := httptest.NewRequest(http.MethodPost, "/auth/select-tenant", strings.NewReader(`{"tenant_id": "not-a-real-membership"}`))
+	req.AddCookie(pendingCookie)
+	rec := httptest.NewRecorder()
+	mux.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusForbidden {
+		t.Fatalf("status = %d, want 403; body=%s", rec.Code, rec.Body.String())
+	}
+	for _, c := range rec.Result().Cookies() {
+		if c.Name == "sentry_session" {
+			t.Fatal("must not issue a session cookie for a tenant outside the identity's memberships")
+		}
+	}
+}
+
+func TestSelectTenantRejectsMissingBody(t *testing.T) {
+	idp := newTestIdP(t)
+	store := newMultiMembershipStore()
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), store, "http://web/", "http://web/select-tenant")
+	idp.setNextIDToken(t, "user-multi", "multi@example.com", true, time.Now().Add(time.Hour))
+	mux, pendingCookie := startTenantSelection(t, h, idp)
+
+	req := httptest.NewRequest(http.MethodPost, "/auth/select-tenant", strings.NewReader(`{}`))
+	req.AddCookie(pendingCookie)
+	rec := httptest.NewRecorder()
+	mux.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want 400", rec.Code)
+	}
+}
+
+func TestSelectTenantRejectsMissingPendingCookie(t *testing.T) {
+	idp := newTestIdP(t)
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
+	mux := http.NewServeMux()
+	h.RegisterRoutes(mux)
+
+	rec := httptest.NewRecorder()
+	mux.ServeHTTP(rec, httptest.NewRequest(http.MethodPost, "/auth/select-tenant", strings.NewReader(`{"tenant_id": "acme"}`)))
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want 400", rec.Code)
+	}
+}
+
+// TestSelectTenantRejectsSessionCookieAsPendingCookie is the regression
+// test for PendingLoginClaims being a distinct type from Claims: a real
+// session token must not work as a pending-login cookie, even though
+// both are signed by the same key.
+func TestSelectTenantRejectsSessionCookieAsPendingCookie(t *testing.T) {
+	idp := newTestIdP(t)
+	store := newFakeUserStore()
+	store.memberships["user-user-1"] = []rbacstore.Membership{{TenantID: "acme", UserID: "user-user-1", Role: rbacstore.RoleEditor}}
+	sessionManager := newTestSessionManager(t)
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, sessionManager, store, "http://web/", "http://web/select-tenant")
+
+	realSessionToken, err := sessionManager.IssueUserSession("acme", "user-user-1", "editor")
+	if err != nil {
+		t.Fatalf("IssueUserSession: %v", err)
+	}
+
+	mux := http.NewServeMux()
+	h.RegisterRoutes(mux)
+	req := httptest.NewRequest(http.MethodPost, "/auth/select-tenant", strings.NewReader(`{"tenant_id": "acme"}`))
+	req.AddCookie(&http.Cookie{Name: pendingLoginCookieName, Value: realSessionToken})
+	rec := httptest.NewRecorder()
+	mux.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusUnauthorized {
+		t.Fatalf("status = %d, want 401 (a real session token must not validate as a pending login)", rec.Code)
 	}
 }
 
 func TestCallbackRejectsStateMismatch(t *testing.T) {
 	idp := newTestIdP(t)
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 	mux := http.NewServeMux()
 	h.RegisterRoutes(mux)
 
@@ -265,7 +540,7 @@ func TestCallbackRejectsStateMismatch(t *testing.T) {
 
 func TestCallbackRejectsMissingStateCookie(t *testing.T) {
 	idp := newTestIdP(t)
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 	mux := http.NewServeMux()
 	h.RegisterRoutes(mux)
 
@@ -279,7 +554,7 @@ func TestCallbackRejectsMissingStateCookie(t *testing.T) {
 
 func TestCallbackRejectsExpiredIDToken(t *testing.T) {
 	idp := newTestIdP(t)
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), newTestOIDCProvider(t, idp), nil, newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 
 	idp.setNextIDToken(t, "user-4", "person@example.com", true, time.Now().Add(-time.Hour)) // already expired
 	rec := fullLoginFlow(t, h, idp)
@@ -290,7 +565,7 @@ func TestCallbackRejectsExpiredIDToken(t *testing.T) {
 }
 
 func TestRegisterRoutesNoOpWhenOIDCNotConfigured(t *testing.T) {
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 	mux := http.NewServeMux()
 	h.RegisterRoutes(mux)
 
@@ -314,7 +589,7 @@ func TestRegisterRoutesNoOpWhenOIDCNotConfigured(t *testing.T) {
 // the trap, only passing a nil-valued typed variable does.
 func TestRegisterRoutesNoOpWithTypedNilProviderVariable(t *testing.T) {
 	var provider *oidc.Provider // stays nil -- exactly main.go's shape when OIDC_ISSUER_URL is unset
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), provider, nil, newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), provider, nil, newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 	mux := http.NewServeMux()
 	h.RegisterRoutes(mux)
 
diff --git a/enterprise/internal/loginhandler/saml_test.go b/enterprise/internal/loginhandler/saml_test.go
index 563808b..59a0ac6 100644
--- a/enterprise/internal/loginhandler/saml_test.go
+++ b/enterprise/internal/loginhandler/saml_test.go
@@ -239,7 +239,7 @@ func fullSAMLLoginFlow(t *testing.T, h *Handler, idp *testSAMLIdP, nameID, email
 
 func TestHandleSAMLLoginRedirectsAndSetsRequestCookie(t *testing.T) {
 	idp := newTestSAMLIdP(t)
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 	mux := http.NewServeMux()
 	h.RegisterRoutes(mux)
 
@@ -274,7 +274,7 @@ func TestFullSAMLLoginFlowIssuesSessionForSingleMembership(t *testing.T) {
 	store := newFakeUserStore()
 	store.memberships["user-saml-user-1"] = []rbacstore.Membership{{TenantID: "acme", UserID: "user-saml-user-1", Role: rbacstore.RoleEditor}}
 	sessionManager := newTestSessionManager(t)
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), sessionManager, store, "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), sessionManager, store, "http://web/", "http://web/select-tenant")
 
 	rec := fullSAMLLoginFlow(t, h, idp, "saml-user-1", "person@acme.example")
 
@@ -305,7 +305,7 @@ func TestFullSAMLLoginFlowIssuesSessionForSingleMembership(t *testing.T) {
 
 func TestFullSAMLLoginFlowRefusesNoMembership(t *testing.T) {
 	idp := newTestSAMLIdP(t)
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 
 	rec := fullSAMLLoginFlow(t, h, idp, "saml-user-2", "nobody@acme.example")
 
@@ -314,25 +314,42 @@ func TestFullSAMLLoginFlowRefusesNoMembership(t *testing.T) {
 	}
 }
 
-func TestFullSAMLLoginFlowRefusesMultipleMemberships(t *testing.T) {
+// TestFullSAMLLoginFlowStartsTenantSelectionForMultipleMemberships is
+// SAML's side of the tenant-picker regression test -- see
+// loginhandler_test.go's OIDC equivalent for the full reasoning; both
+// protocols converge on the same finishLogin/resolveIdentity, so the
+// behavior must match exactly.
+func TestFullSAMLLoginFlowStartsTenantSelectionForMultipleMemberships(t *testing.T) {
 	idp := newTestSAMLIdP(t)
 	store := newFakeUserStore()
 	store.memberships["user-saml-user-3"] = []rbacstore.Membership{
 		{TenantID: "acme", UserID: "user-saml-user-3", Role: rbacstore.RoleViewer},
 		{TenantID: "globex", UserID: "user-saml-user-3", Role: rbacstore.RoleAdmin},
 	}
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), newTestSessionManager(t), store, "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), newTestSessionManager(t), store, "http://web/", "http://web/select-tenant")
 
 	rec := fullSAMLLoginFlow(t, h, idp, "saml-user-3", "multi@example.com")
 
-	if rec.Code != http.StatusNotImplemented {
-		t.Fatalf("status = %d, want 501; body=%s", rec.Code, rec.Body.String())
+	if rec.Code != http.StatusFound {
+		t.Fatalf("status = %d, want 302; body=%s", rec.Code, rec.Body.String())
+	}
+	if loc := rec.Header().Get("Location"); loc != "http://web/select-tenant" {
+		t.Fatalf("Location = %q, want http://web/select-tenant", loc)
+	}
+	var pendingCookie *http.Cookie
+	for _, c := range rec.Result().Cookies() {
+		if c.Name == pendingLoginCookieName {
+			pendingCookie = c
+		}
+	}
+	if pendingCookie == nil || pendingCookie.Value == "" {
+		t.Fatal("expected a non-empty pending-login cookie")
 	}
 }
 
 func TestFullSAMLLoginFlowRefusesMissingEmail(t *testing.T) {
 	idp := newTestSAMLIdP(t)
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 
 	rec := fullSAMLLoginFlow(t, h, idp, "saml-user-4", "") // no email attribute in the assertion
 
@@ -343,7 +360,7 @@ func TestFullSAMLLoginFlowRefusesMissingEmail(t *testing.T) {
 
 func TestSAMLACSRejectsMissingRequestCookie(t *testing.T) {
 	idp := newTestSAMLIdP(t)
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 	mux := http.NewServeMux()
 	h.RegisterRoutes(mux)
 
@@ -363,7 +380,7 @@ func TestSAMLACSRejectsMissingRequestCookie(t *testing.T) {
 
 func TestSAMLACSRejectsWrongRequestID(t *testing.T) {
 	idp := newTestSAMLIdP(t)
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, idp.serviceProvider(t), newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 	mux := http.NewServeMux()
 	h.RegisterRoutes(mux)
 
@@ -394,7 +411,7 @@ func TestSAMLACSRejectsWrongRequestID(t *testing.T) {
 }
 
 func TestRegisterRoutesNoOpWhenSAMLNotConfigured(t *testing.T) {
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 	mux := http.NewServeMux()
 	h.RegisterRoutes(mux)
 
@@ -411,7 +428,7 @@ func TestRegisterRoutesNoOpWhenSAMLNotConfigured(t *testing.T) {
 // typed-nil-interface trap this guards against.
 func TestRegisterRoutesNoOpWithTypedNilSAMLProviderVariable(t *testing.T) {
 	var provider *samlpkg.ServiceProvider // stays nil -- main.go's shape when SAML_IDP_METADATA_URL is unset
-	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, provider, newTestSessionManager(t), newFakeUserStore(), "http://web/")
+	h := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, provider, newTestSessionManager(t), newFakeUserStore(), "http://web/", "http://web/select-tenant")
 	mux := http.NewServeMux()
 	h.RegisterRoutes(mux)
 
diff --git a/enterprise/internal/rbacstore/rbacstore.go b/enterprise/internal/rbacstore/rbacstore.go
index eecf49e..cab8031 100644
--- a/enterprise/internal/rbacstore/rbacstore.go
+++ b/enterprise/internal/rbacstore/rbacstore.go
@@ -360,6 +360,46 @@ func (s *Store) ListMembershipsForUser(ctx context.Context, userID string) ([]Me
 	return out, rows.Err()
 }
 
+// MembershipWithTenant is ListMembershipsWithTenantForUser's result row
+// -- Membership plus the tenant's display name, the shape a
+// tenant-picker UI needs (a bare tenant_id/Role isn't enough to show a
+// human something recognizable to choose between).
+type MembershipWithTenant struct {
+	TenantID          string
+	TenantDisplayName string
+	Role              Role
+}
+
+// ListMembershipsWithTenantForUser is ListMembershipsForUser plus a join
+// against tenants -- used by loginhandler's multi-membership
+// tenant-selection step (GET /auth/memberships), which is the one
+// caller that actually needs to show a human "here are your tenants,"
+// not just resolve a single membership programmatically.
+func (s *Store) ListMembershipsWithTenantForUser(ctx context.Context, userID string) ([]MembershipWithTenant, error) {
+	rows, err := s.pool.Query(ctx, `
+		SELECT m.tenant_id, t.display_name, m.role
+		FROM tenant_memberships m
+		JOIN tenants t ON t.id = m.tenant_id
+		WHERE m.user_id = $1
+		ORDER BY t.display_name`, userID)
+	if err != nil {
+		return nil, fmt.Errorf("rbacstore: listing memberships with tenant: %w", err)
+	}
+	defer rows.Close()
+
+	var out []MembershipWithTenant
+	for rows.Next() {
+		var m MembershipWithTenant
+		var role string
+		if err := rows.Scan(&m.TenantID, &m.TenantDisplayName, &role); err != nil {
+			return nil, fmt.Errorf("rbacstore: scanning membership with tenant: %w", err)
+		}
+		m.Role = Role(role)
+		out = append(out, m)
+	}
+	return out, rows.Err()
+}
+
 // DataSource is one tenant's data-plane location -- today, exactly one
 // ClickHouse database + one Tantivy index per tenant (see
 // /docs/phase-4-rbac-design.md's "data_sources" extension-point
diff --git a/enterprise/internal/session/session.go b/enterprise/internal/session/session.go
index 5e95215..5d9f0c7 100644
--- a/enterprise/internal/session/session.go
+++ b/enterprise/internal/session/session.go
@@ -44,6 +44,12 @@ const (
 	// Rotation is by redeploying alerting with a freshly issued token,
 	// not automatic refresh.
 	ServiceTokenTTL = 24 * 365 * time.Hour
+	// PendingLoginTTL is intentionally short -- a pending login only
+	// bridges the gap between "the IdP round trip proved who you are"
+	// and "you picked which tenant to act as" for a multi-membership
+	// identity (see loginhandler's package doc comment), a single-page
+	// interaction, not a session lifetime.
+	PendingLoginTTL = 10 * time.Minute
 	// MinSigningKeyBytes: HS256 wants a key at least as long as its
 	// output (32 bytes/256 bits) to not weaken the MAC.
 	MinSigningKeyBytes = 32
@@ -115,6 +121,72 @@ func (m *Manager) IssueServiceToken(subject string) (string, error) {
 	return jwt.Signed(m.signer).Claims(claims).Serialize()
 }
 
+// PendingLoginClaims carries a proven-but-not-yet-tenant-scoped identity
+// through the multi-membership tenant-selection round trip -- see
+// loginhandler.startTenantSelection/handleSelectTenant. Deliberately a
+// different Go type from Claims, not the same struct with an empty
+// TenantID/Role: a pending token's JSON body never has those keys at
+// all, so there's no field a caller could mistake for a real session's
+// tenant/role, and no risk of this token type ever satisfying a
+// role-gated check by accident (see ValidatePendingLogin -- callers
+// that mistakenly feed a pending token to Validate instead just get a
+// Claims with an empty Role, which authz.Role.Satisfies already treats
+// as satisfying nothing).
+//
+// The json tag is deliberately "pending_user_id", not the "user_id" a
+// real Claims token also carries -- found while writing this package's
+// own test for "a real session token must not work as a pending
+// login": go-jose's Claims() unmarshal is happy to populate any struct
+// field whose json tag matches a key present in the token, key overlap
+// included, so reusing "user_id" would have let a full session token
+// parse successfully as a PendingLoginClaims too (extracting UserID
+// from the session's own user_id field) -- exactly the token-type
+// confusion this type's separate-Go-type design was supposed to
+// prevent. A disjoint field name closes that regardless of which
+// fields either struct happens to add later.
+type PendingLoginClaims struct {
+	UserID string `json:"pending_user_id"`
+	jwt.Claims
+}
+
+// IssuePendingLogin issues a short-lived token proving userID's identity
+// (already resolved by resolveIdentity's UpsertUserBySSO) without
+// committing to a tenant yet -- called only when that identity has more
+// than one tenant_memberships row.
+func (m *Manager) IssuePendingLogin(userID string) (string, error) {
+	now := time.Now()
+	claims := PendingLoginClaims{
+		UserID: userID,
+		Claims: jwt.Claims{
+			Subject:  userID,
+			IssuedAt: jwt.NewNumericDate(now),
+			Expiry:   jwt.NewNumericDate(now.Add(PendingLoginTTL)),
+		},
+	}
+	return jwt.Signed(m.signer).Claims(claims).Serialize()
+}
+
+// ValidatePendingLogin is IssuePendingLogin's counterpart -- same
+// signature/expiry checks as Validate, collapsed to ErrInvalidToken for
+// the same reasoning (see that method's doc comment).
+func (m *Manager) ValidatePendingLogin(token string) (userID string, err error) {
+	parsed, err := jwt.ParseSigned(token, []josev4.SignatureAlgorithm{josev4.HS256})
+	if err != nil {
+		return "", ErrInvalidToken
+	}
+	var claims PendingLoginClaims
+	if err := parsed.Claims(m.key, &claims); err != nil {
+		return "", ErrInvalidToken
+	}
+	if err := claims.Claims.Validate(jwt.Expected{}); err != nil {
+		return "", ErrInvalidToken
+	}
+	if claims.UserID == "" {
+		return "", ErrInvalidToken
+	}
+	return claims.UserID, nil
+}
+
 // Validate verifies signature and expiry and returns the token's claims.
 // Every failure mode collapses to ErrInvalidToken -- see its doc comment.
 func (m *Manager) Validate(token string) (Claims, error) {
diff --git a/enterprise/internal/session/session_test.go b/enterprise/internal/session/session_test.go
index 315559c..f4b3ed7 100644
--- a/enterprise/internal/session/session_test.go
+++ b/enterprise/internal/session/session_test.go
@@ -95,6 +95,107 @@ func TestValidateRejectsWrongKey(t *testing.T) {
 	}
 }
 
+func TestIssueAndValidatePendingLogin(t *testing.T) {
+	m, err := NewManager(testKey())
+	if err != nil {
+		t.Fatalf("NewManager: %v", err)
+	}
+	token, err := m.IssuePendingLogin("u1")
+	if err != nil {
+		t.Fatalf("IssuePendingLogin: %v", err)
+	}
+	userID, err := m.ValidatePendingLogin(token)
+	if err != nil {
+		t.Fatalf("ValidatePendingLogin: %v", err)
+	}
+	if userID != "u1" {
+		t.Fatalf("userID = %q, want u1", userID)
+	}
+}
+
+func TestValidatePendingLoginRejectsTamperedToken(t *testing.T) {
+	m, err := NewManager(testKey())
+	if err != nil {
+		t.Fatalf("NewManager: %v", err)
+	}
+	token, err := m.IssuePendingLogin("u1")
+	if err != nil {
+		t.Fatalf("IssuePendingLogin: %v", err)
+	}
+	parts := strings.Split(token, ".")
+	if len(parts) != 3 {
+		t.Fatalf("expected a 3-segment JWT, got %d segments", len(parts))
+	}
+	tampered := parts[0] + "." + parts[1] + "x" + "." + parts[2]
+	if _, err := m.ValidatePendingLogin(tampered); err != ErrInvalidToken {
+		t.Fatalf("ValidatePendingLogin(tampered) error = %v, want ErrInvalidToken", err)
+	}
+}
+
+// TestValidatePendingLoginRejectsRealSessionToken is the regression test
+// for PendingLoginClaims.UserID's "pending_user_id" json tag (see that
+// field's doc comment): a real user-session token must not parse as a
+// valid pending login just because both structs happen to be signed by
+// the same key.
+func TestValidatePendingLoginRejectsRealSessionToken(t *testing.T) {
+	m, err := NewManager(testKey())
+	if err != nil {
+		t.Fatalf("NewManager: %v", err)
+	}
+	sessionToken, err := m.IssueUserSession("acme", "u1", "editor")
+	if err != nil {
+		t.Fatalf("IssueUserSession: %v", err)
+	}
+	if _, err := m.ValidatePendingLogin(sessionToken); err != ErrInvalidToken {
+		t.Fatalf("ValidatePendingLogin(a real session token) error = %v, want ErrInvalidToken", err)
+	}
+}
+
+// TestValidateRejectsPendingLoginToken is the same regression in the
+// other direction: a pending-login token must not validate as a usable
+// session either (it carries no tenant_id/role at all, so it would be
+// inert even if it somehow parsed, but this proves that directly rather
+// than relying on downstream role checks alone).
+func TestValidateRejectsPendingLoginToken(t *testing.T) {
+	m, err := NewManager(testKey())
+	if err != nil {
+		t.Fatalf("NewManager: %v", err)
+	}
+	pendingToken, err := m.IssuePendingLogin("u1")
+	if err != nil {
+		t.Fatalf("IssuePendingLogin: %v", err)
+	}
+	claims, err := m.Validate(pendingToken)
+	if err != nil {
+		t.Fatalf("Validate(pending token): %v", err)
+	}
+	if claims.TenantID != "" || claims.UserID != "" || claims.Role != "" {
+		t.Fatalf("a pending-login token must not carry any tenant/user/role claims when read as a session, got %+v", claims)
+	}
+}
+
+func TestValidatePendingLoginRejectsExpiredToken(t *testing.T) {
+	m, err := NewManager(testKey())
+	if err != nil {
+		t.Fatalf("NewManager: %v", err)
+	}
+	now := time.Now()
+	claims := PendingLoginClaims{
+		UserID: "u1",
+		Claims: jwt.Claims{
+			IssuedAt: jwt.NewNumericDate(now.Add(-1 * time.Hour)),
+			Expiry:   jwt.NewNumericDate(now.Add(-30 * time.Minute)),
+		},
+	}
+	token, err := jwt.Signed(m.signer).Claims(claims).Serialize()
+	if err != nil {
+		t.Fatalf("building an already-expired pending token: %v", err)
+	}
+	if _, err := m.ValidatePendingLogin(token); err != ErrInvalidToken {
+		t.Fatalf("ValidatePendingLogin(expired) error = %v, want ErrInvalidToken", err)
+	}
+}
+
 func TestValidateRejectsExpiredToken(t *testing.T) {
 	m, err := NewManager(testKey())
 	if err != nil {