diff --git a/docs/04-api-reference.md b/docs/04-api-reference.md
index 34e5e2c..5b03436 100644
--- a/docs/04-api-reference.md
+++ b/docs/04-api-reference.md
@@ -19,6 +19,7 @@ and runnable examples are in [examples/](examples/).
 
 | Kind | Operation | Permission | Notes |
 |---|---|---|---|
+| query | `myOrganizations: [OrganizationChoice!]!` | (signed in) | Every lab the signed-in person can switch to (same email, active account), the current one included. |
 | query | `mySessions: [Session!]!` | (signed in) |  |
 | query | `permissions: [String!]!` | (signed in) | Every permission name the API checks. |
 | query | `roles: [Role!]!` | `role:read` |  |
@@ -38,6 +39,7 @@ and runnable examples are in [examples/](examples/).
 | mutation | `revokeSession(id: ID!): Boolean!` | (signed in) |  |
 | mutation | `setUserPassword(userId: ID!, newPassword: String!): Boolean!` | `user:update` |  |
 | mutation | `setUserRoles(userId: ID!, roles: [RoleAssignmentInput!]!): User!` | `user:update` |  |
+| mutation | `switchOrganization(orgCode: String!, device: DeviceInput): LoginResult!` | public | Moves this session to the signed-in person's account in another lab (same email, active there), without the password. This session ends; use the returned tokens. Send the same device as at login, or the session ends (INVALID_TOKEN). ORG_UNAVAILABLE when there is no such account, or it is the current lab. |
 | mutation | `upsertRole(input: RoleInput!): Role!` | `role:manage` |  |
 
 ## organization
diff --git a/docs/05-errors.md b/docs/05-errors.md
index abb1cfc..d1d4519 100644
--- a/docs/05-errors.md
+++ b/docs/05-errors.md
@@ -26,7 +26,8 @@ Every error in a response carries `extensions.code`. Clients switch on the code,
 | `INVALID_CREDENTIALS` | 401 | Wrong email, organisation or password (same answer for each) | "Email or password is wrong" |
 | `ACCOUNT_DISABLED` | 403 | The user is disabled | Contact an administrator |
 | `INVITE_PENDING` | 403 | The user has not set a password yet | Use the reset link |
-| `ORG_REQUIRED` | 400 | The email exists in more than one organisation | Ask for the organisation code |
+| `ORG_REQUIRED` | 400 | The email and password match accounts in more than one lab. `extensions.organizations` lists them (`code`, `name`) | Show the list; log in again with the picked `orgCode` |
+| `ORG_UNAVAILABLE` | 403 | `switchOrganization` to the current lab, an unknown code, or a lab without an active account for this person | Refresh `myOrganizations` |
 | `RATE_LIMITED` | 429 | Too many attempts; `extensions.retryAfterMs` says how long to wait | Wait, then retry |
 | `WEAK_PASSWORD` | 400 | The new password fails the policy | Show the message |
 | `INVALID_TOKEN` | 400 | A reset token is unknown, used or expired | Request a new link |
diff --git a/docs/06-auth-and-permissions.md b/docs/06-auth-and-permissions.md
index 18aa52c..5654960 100644
--- a/docs/06-auth-and-permissions.md
+++ b/docs/06-auth-and-permissions.md
@@ -90,6 +90,17 @@ value a client sent. A missing or malformed fingerprint is never an error. A cha
 session, whatever `DEVICE_BINDING` says: browser updates and TLS-inspecting networks change it too. It is
 not in the GraphQL schema; clients send nothing new.
 
+### One person, several labs
+
+The same email can have an account in several labs (one user each). When the email and password match more
+than one, `login` fails with `ORG_REQUIRED` and `extensions.organizations` (`[{ code, name }]`, only the labs
+whose account matched): show them and log in again with the picked `orgCode`. Once signed in,
+`myOrganizations` lists every lab the person can work in (`current` marks this session's), and
+`switchOrganization(orgCode, device)` moves the session there without the password. The old session ends,
+the same device rule as `refreshSession` applies, and auth-kit audits the switch in both labs
+(`auth.org_switch_out`, `auth.org_switch`). The lab code is a name, not an id: an unknown code and a lab
+without an account both answer `ORG_UNAVAILABLE`.
+
 ### Password reset
 
 `requestPasswordReset(email, orgCode?)` always returns `true`, whether or not the account exists, and
diff --git a/kits.json b/kits.json
index 020318a..0802fd0 100644
--- a/kits.json
+++ b/kits.json
@@ -19,7 +19,7 @@
     },
     {
       "name": "auth-kit",
-      "ref": "v1.4.0"
+      "ref": "v1.5.0"
     },
     {
       "name": "db-kit",
@@ -35,7 +35,7 @@
     },
     {
       "name": "client",
-      "ref": "v1.4.0"
+      "ref": "v1.5.0"
     },
     {
       "name": "invoice-kit",
diff --git a/llms-full.txt b/llms-full.txt
index b9838aa..09ca9f4 100644
--- a/llms-full.txt
+++ b/llms-full.txt
@@ -689,6 +689,7 @@ and runnable examples are in [examples/](examples/).
 
 | Kind | Operation | Permission | Notes |
 |---|---|---|---|
+| query | `myOrganizations: [OrganizationChoice!]!` | (signed in) | Every lab the signed-in person can switch to (same email, active account), the current one included. |
 | query | `mySessions: [Session!]!` | (signed in) |  |
 | query | `permissions: [String!]!` | (signed in) | Every permission name the API checks. |
 | query | `roles: [Role!]!` | `role:read` |  |
@@ -708,6 +709,7 @@ and runnable examples are in [examples/](examples/).
 | mutation | `revokeSession(id: ID!): Boolean!` | (signed in) |  |
 | mutation | `setUserPassword(userId: ID!, newPassword: String!): Boolean!` | `user:update` |  |
 | mutation | `setUserRoles(userId: ID!, roles: [RoleAssignmentInput!]!): User!` | `user:update` |  |
+| mutation | `switchOrganization(orgCode: String!, device: DeviceInput): LoginResult!` | public | Moves this session to the signed-in person's account in another lab (same email, active there), without the password. This session ends; use the returned tokens. Send the same device as at login, or the session ends (INVALID_TOKEN). ORG_UNAVAILABLE when there is no such account, or it is the current lab. |
 | mutation | `upsertRole(input: RoleInput!): Role!` | `role:manage` |  |
 
 ## organization
@@ -909,7 +911,8 @@ Every error in a response carries `extensions.code`. Clients switch on the code,
 | `INVALID_CREDENTIALS` | 401 | Wrong email, organisation or password (same answer for each) | "Email or password is wrong" |
 | `ACCOUNT_DISABLED` | 403 | The user is disabled | Contact an administrator |
 | `INVITE_PENDING` | 403 | The user has not set a password yet | Use the reset link |
-| `ORG_REQUIRED` | 400 | The email exists in more than one organisation | Ask for the organisation code |
+| `ORG_REQUIRED` | 400 | The email and password match accounts in more than one lab. `extensions.organizations` lists them (`code`, `name`) | Show the list; log in again with the picked `orgCode` |
+| `ORG_UNAVAILABLE` | 403 | `switchOrganization` to the current lab, an unknown code, or a lab without an active account for this person | Refresh `myOrganizations` |
 | `RATE_LIMITED` | 429 | Too many attempts; `extensions.retryAfterMs` says how long to wait | Wait, then retry |
 | `WEAK_PASSWORD` | 400 | The new password fails the policy | Show the message |
 | `INVALID_TOKEN` | 400 | A reset token is unknown, used or expired | Request a new link |
@@ -1039,6 +1042,17 @@ value a client sent. A missing or malformed fingerprint is never an error. A cha
 session, whatever `DEVICE_BINDING` says: browser updates and TLS-inspecting networks change it too. It is
 not in the GraphQL schema; clients send nothing new.
 
+### One person, several labs
+
+The same email can have an account in several labs (one user each). When the email and password match more
+than one, `login` fails with `ORG_REQUIRED` and `extensions.organizations` (`[{ code, name }]`, only the labs
+whose account matched): show them and log in again with the picked `orgCode`. Once signed in,
+`myOrganizations` lists every lab the person can work in (`current` marks this session's), and
+`switchOrganization(orgCode, device)` moves the session there without the password. The old session ends,
+the same device rule as `refreshSession` applies, and auth-kit audits the switch in both labs
+(`auth.org_switch_out`, `auth.org_switch`). The lab code is a name, not an id: an unknown code and a lab
+without an account both answer `ORG_UNAVAILABLE`.
+
 ### Password reset
 
 `requestPasswordReset(email, orgCode?)` always returns `true`, whether or not the account exists, and
@@ -2598,7 +2612,7 @@ flowchart TD
     },
     {
       "name": "auth-kit",
-      "ref": "v1.4.0"
+      "ref": "v1.5.0"
     },
     {
       "name": "db-kit",
@@ -2614,7 +2628,7 @@ flowchart TD
     },
     {
       "name": "client",
-      "ref": "v1.4.0"
+      "ref": "v1.5.0"
     },
     {
       "name": "invoice-kit",
@@ -2702,7 +2716,7 @@ Key facts for agents:
   },
   "dependencies": {
     "@graphql-tools/schema": "^10.1.5",
-    "@mgpl-diagnostics/auth-kit": "^1.4.0",
+    "@mgpl-diagnostics/auth-kit": "^1.5.0",
     "@mgpl-diagnostics/catalog-kit": "^1.0.0",
     "@mgpl-diagnostics/db-kit": "^2.1.1",
     "@mgpl-diagnostics/finance-kit": "^1.0.1",
@@ -2725,7 +2739,7 @@ Key facts for agents:
     "sequelize": "^6.37.8"
   },
   "devDependencies": {
-    "@mgpl-diagnostics/client": "^1.4.0",
+    "@mgpl-diagnostics/client": "^1.5.0",
     "@types/node": "^22.20.5",
     "embedded-postgres": "^18.4.0-beta.17",
     "ioredis-mock": "^8.13.1",
@@ -4016,6 +4030,13 @@ type Mutation {
   Renders a stored invoice or a booking's reports in the background; poll job(id) until completed or failed.
   """
   startDocumentJob(input: DocumentJobInput!): Job!
+
+  """
+  Moves this session to the signed-in person's account in another lab (same email, active there), without
+  the password. This session ends; use the returned tokens. Send the same device as at login, or the
+  session ends (INVALID_TOKEN). ORG_UNAVAILABLE when there is no such account, or it is the current lab.
+  """
+  switchOrganization(device: DeviceInput, orgCode: String!): LoginResult!
   updateBranch(id: ID!, input: BranchPatch!): Branch!
   updateCustomer(id: ID!, input: CustomerPatch!): Customer!
   updateDoctor(id: ID!, input: DoctorPatch!): Doctor!
@@ -4066,6 +4087,19 @@ type Organization {
   phone: String
 }
 
+"""
+A lab the signed-in person can work in: they have an active account there with the same email.
+Also listed in ORG_REQUIRED errors (extensions.organizations, without current) after a password matched.
+"""
+type OrganizationChoice {
+  """The lab code: pass it to login (orgCode) or switchOrganization."""
+  code: String!
+
+  """The lab of this session."""
+  current: Boolean!
+  name: String!
+}
+
 input OrganizationInput {
   address: AddressInput
   email: String
@@ -4356,6 +4390,11 @@ type Query {
   ledgers: [Ledger!]!
   letterhead(format: DocumentFormat = pdf): Document!
   lockDates: [PeriodLock!]!
+
+  """
+  Every lab the signed-in person can switch to (same email, active account), the current one included.
+  """
+  myOrganizations: [OrganizationChoice!]!
   mySessions: [Session!]!
   organization: Organization!
   outstandingReceivables(asOf: DateTime, branchId: ID): Outstanding!
@@ -5478,6 +5517,7 @@ import { deviceOf, type DeviceInput } from "../graphql/device";
 export const authController = withErrorCodes({
   Query: {
     viewer: (_: unknown, __: unknown, ctx: Ctx) => (ctx.viewer ? {} : null),
+    myOrganizations: (_: unknown, __: unknown, ctx: Ctx) => ctx.services.auth.organizations(actorOf(ctx)),
     mySessions: async (_: unknown, __: unknown, ctx: Ctx) => {
       const sessions = await ctx.services.auth.sessions(actorOf(ctx));
       return sessions.map((s) => ({ ...s, current: s.id === ctx.viewer!.sessionId, createdAt: new Date(s.createdAt), lastSeenAt: new Date(s.lastSeenAt), expiresAt: new Date(s.expiresAt), deviceId: s.device?.deviceId ?? null, deviceInfo: s.device?.info ?? null }));
@@ -5512,6 +5552,11 @@ export const authController = withErrorCodes({
       const r = await ctx.services.auth.login({ ...input, ip: ctx.ip, userAgent: ctx.userAgent, device: deviceOf(device), tlsFingerprint: ctx.tlsFingerprint });
       return { ...r, accessToken: r.token, accessExpiresAt: r.expiresAt };
     },
+    switchOrganization: async (_: unknown, a: { orgCode: string; device?: DeviceInput | null }, ctx: Ctx) => {
+      if (!ctx.token) throw unauthenticated();
+      const r = await ctx.services.auth.switchOrganization({ token: ctx.token, orgCode: a.orgCode, ip: ctx.ip, userAgent: ctx.userAgent, device: deviceOf(a.device), tlsFingerprint: ctx.tlsFingerprint });
+      return { ...r, accessToken: r.token, accessExpiresAt: r.expiresAt };
+    },
     refreshSession: (_: unknown, a: { refreshToken: string; device?: DeviceInput | null }, ctx: Ctx) =>
       ctx.services.auth.refresh({ refreshToken: a.refreshToken, ip: ctx.ip, userAgent: ctx.userAgent, device: deviceOf(a.device), tlsFingerprint: ctx.tlsFingerprint }),
     logout: async (_: unknown, a: { refreshToken?: string | null }, ctx: Ctx) => {
@@ -6434,6 +6479,7 @@ export const ERROR_CODES = [
   "PERIOD_LOCKED", "CREDIT_LIMIT_EXCEEDED",
   // auth-kit's own codes, passed through
   "INVALID_CREDENTIALS", "ACCOUNT_DISABLED", "INVITE_PENDING", "ORG_REQUIRED", "RATE_LIMITED", "WEAK_PASSWORD", "INVALID_TOKEN",
+  "ORG_UNAVAILABLE",
   // partner-lab imports (docs/18-imports.md)
   "UNSUPPORTED_REPORT", "REPORT_ALREADY_APPLIED", "BOOKING_PATIENT_MISMATCH", "FILE_TOO_LARGE",
 ] as const;
@@ -6452,7 +6498,13 @@ export const badInput = (message: string) => apiError("BAD_USER_INPUT", message,
 /** Domain errors from the kits → GraphQL errors with codes. Anything unknown is re-thrown (and masked by Yoga). */
 export function toGraphQLError(e: unknown): unknown {
   if (e instanceof GraphQLError) return e;
-  if (e instanceof AuthError) return apiError(e.code as ErrorCode, e.message, e.statusCode, e.details.retryAfterMs ? { retryAfterMs: e.details.retryAfterMs } : {});
+  if (e instanceof AuthError) {
+    const extra: Record<string, unknown> = {};
+    if (e.details.retryAfterMs) extra.retryAfterMs = e.details.retryAfterMs;
+    // ORG_REQUIRED: the labs whose account matched the password, for a pick list (ids stay on the server)
+    if (e.details.organizations?.length) extra.organizations = e.details.organizations.map((o) => ({ code: o.code, name: o.name }));
+    return apiError(e.code as ErrorCode, e.message, e.statusCode, extra);
+  }
   if (e instanceof ForbiddenError) return apiError("FORBIDDEN", e.message, 403);
   if (e instanceof UnsupportedReportError) return apiError("UNSUPPORTED_REPORT", e.message, 422);
   if (e instanceof FileTooLargeError) return apiError("FILE_TOO_LARGE", e.message, 413, { maxBytes: e.maxBytes });
@@ -7474,9 +7526,23 @@ export const authTypeDefs = /* GraphQL */ `
     expiresAt: DateTime! @deprecated(reason: "Use accessExpiresAt.")
   }
 
+  """
+  A lab the signed-in person can work in: they have an active account there with the same email.
+  Also listed in ORG_REQUIRED errors (extensions.organizations, without current) after a password matched.
+  """
+  type OrganizationChoice {
+    "The lab code: pass it to login (orgCode) or switchOrganization."
+    code: String!
+    name: String!
+    "The lab of this session."
+    current: Boolean!
+  }
+
   extend type Query {
     "null when not signed in."
     viewer: Viewer
+    "Every lab the signed-in person can switch to (same email, active account), the current one included."
+    myOrganizations: [OrganizationChoice!]!
     mySessions: [Session!]!
     users: [User!]!
     user(id: ID!): User
@@ -7498,6 +7564,12 @@ export const authTypeDefs = /* GraphQL */ `
     INVALID_TOKEN when it is unknown, spent or expired: sign in again.
     """
     refreshSession(refreshToken: String!, device: DeviceInput): LoginResult!
+    """
+    Moves this session to the signed-in person's account in another lab (same email, active there), without
+    the password. This session ends; use the returned tokens. Send the same device as at login, or the
+    session ends (INVALID_TOKEN). ORG_UNAVAILABLE when there is no such account, or it is the current lab.
+    """
+    switchOrganization(orgCode: String!, device: DeviceInput): LoginResult!
     "Ends this session: the bearer token (even an expired access token), or the refresh token when given."
     logout(refreshToken: String): Boolean!
     "Ends every other session of the signed-in user; returns how many."
@@ -8723,7 +8795,7 @@ export async function buildServer(container: Container): Promise<FastifyInstance
 ## File: src/services/auth.service.ts
 
 ```ts
-import { can, permissionMatches, PERMISSIONS, roleMap, SYSTEM_ROLES, type Auth, type DeviceSignals, type PublicUser } from "@mgpl-diagnostics/auth-kit";
+import { AuthError, can, permissionMatches, PERMISSIONS, roleMap, SYSTEM_ROLES, type Auth, type DeviceSignals, type PublicUser } from "@mgpl-diagnostics/auth-kit";
 import { ConflictError, createUser, NotFoundError, ValidationError, type Id, type Repositories, type Role, type RoleAssignment, type User } from "@mgpl-diagnostics/db-kit";
 import type { Actor } from "../graphql/context";
 import type { JobQueue } from "../jobs/types";
@@ -8750,6 +8822,20 @@ export class AuthService {
     return this.auth.login({ ...input, orgCode: input.orgCode ?? undefined });
   }
 
+  /** The labs the person can switch to (same email, active account), the current one marked. */
+  async organizations(actor: Actor): Promise<{ code: string; name: string; current: boolean }[]> {
+    return (await this.auth.organizationsOf(actor.userId)).map((o) => ({ code: o.code, name: o.name, current: o.orgId === actor.orgId }));
+  }
+
+  /** Moves the session to the person's account in the lab with this code (auth-kit checks it is theirs). */
+  async switchOrganization(input: { token: string; orgCode: string; ip?: string; userAgent?: string; device?: DeviceSignals; tlsFingerprint?: string }) {
+    const org = await this.repos.orgs.findOne({ code: input.orgCode.trim().toUpperCase() });
+    // an unknown code gets the same answer as a lab without an account, so codes cannot be probed
+    if (!org) throw new AuthError("ORG_UNAVAILABLE", "You can't switch to that organisation");
+    const { orgCode: _c, ...rest } = input;
+    return this.auth.switchOrganization({ ...rest, orgId: org.id });
+  }
+
   /** Spends a refresh token: a new access token and the next refresh token (rotation). */
   async refresh(input: { refreshToken: string; ip?: string; userAgent?: string; device?: DeviceSignals; tlsFingerprint?: string }) {
     const p = await this.auth.refresh(input);
@@ -11521,6 +11607,26 @@ async function suite(db: Db, tag: string) {
   ok(!!same?.refreshToken, `[${tag}] refresh on the same device (new fingerprint) works`);
   ok(code(await gql(null, "mutation($r: String!, $d: DeviceInput) { refreshSession(refreshToken: $r, device: $d) { refreshToken } }", { r: same.refreshToken, d: { deviceId: "dev-laptop-9999-zzzzzz" } })) === "INVALID_TOKEN" && code(await gql(bound.accessToken, "{ organization { id } }")) === "UNAUTHENTICATED", `[${tag}] refresh from another device → INVALID_TOKEN and the session ends`);
 
+  // ---------------------------------------------------------------- one person in two labs: pick list and switching
+  for (const [org, branch] of [[a.org.id, a.branch.id], [other.org.id, other.branch.id]] as const) {
+    await db.rawRepos.users.create({ orgId: org, name: "Two Labs", email: "two@labs.test", passwordHash: await hashPassword(pw), status: "active", roles: [{ role: "front_desk", branchId: branch }] });
+  }
+  const pick = await gql(null, 'mutation { login(input: { email: "two@labs.test", password: "Lab-Owner-2026!" }) { accessToken } }');
+  const choices = (pick.errors?.[0]?.extensions as { organizations?: { code: string; name: string }[] } | undefined)?.organizations;
+  ok(code(pick) === "ORG_REQUIRED" && choices?.map((o) => `${o.code}:${o.name}`).join() === "APL:API Lab,OTH:Other Lab" && !JSON.stringify(pick).includes(a.org.id), `[${tag}] ORG_REQUIRED lists the labs to pick from (code + name, no ids)`);
+  ok(!(await gql(null, 'mutation { login(input: { email: "two@labs.test", password: "wrong-password" }) { accessToken } }')).errors?.[0]?.extensions?.hasOwnProperty("organizations"), `[${tag}] a wrong password lists no labs`);
+  const solo = await login("x@oth.test");
+  const twoDev = { deviceId: "dev-two-labs-0001" };
+  const inApl = (await gql(null, 'mutation($d: DeviceInput) { login(input: { email: "two@labs.test", password: "Lab-Owner-2026!", orgCode: "apl", device: $d }) { accessToken refreshToken } }', { d: twoDev })).data?.login;
+  const mine = (await gql(inApl.accessToken, "{ myOrganizations { code name current } }")).data?.myOrganizations;
+  ok(mine?.map((o: any) => `${o.code}:${o.current}`).join() === "APL:true,OTH:false", `[${tag}] myOrganizations: both labs, the current one marked`);
+  ok((await gql(solo, "{ myOrganizations { code } }")).data?.myOrganizations.length === 1, `[${tag}] myOrganizations: one lab for a one-lab person`);
+  const moved = (await gql(inApl.accessToken, 'mutation($d: DeviceInput) { switchOrganization(orgCode: "OTH", device: $d) { accessToken refreshToken user { email } } }', { d: twoDev })).data?.switchOrganization;
+  ok((await gql(moved?.accessToken, "{ organization { code } }")).data?.organization.code === "OTH" && code(await gql(inApl.accessToken, "{ organization { code } }")) === "UNAUTHENTICATED", `[${tag}] switchOrganization: new tokens work in the other lab, the old session ends`);
+  ok(code(await gql(moved.accessToken, 'mutation { switchOrganization(orgCode: "OTH") { accessToken } }')) === "ORG_UNAVAILABLE" && code(await gql(moved.accessToken, 'mutation { switchOrganization(orgCode: "NOPE") { accessToken } }')) === "ORG_UNAVAILABLE" && code(await gql(solo, 'mutation { switchOrganization(orgCode: "OTH") { accessToken } }')) === "ORG_UNAVAILABLE", `[${tag}] switch to the current lab, an unknown code or a lab without an account → ORG_UNAVAILABLE`);
+  ok(code(await gql(null, 'mutation { switchOrganization(orgCode: "APL") { accessToken } }')) === "UNAUTHENTICATED", `[${tag}] switchOrganization needs a session`);
+  ok(code(await gql(moved.accessToken, 'mutation { switchOrganization(orgCode: "APL", device: { deviceId: "dev-elsewhere-0009" }) { accessToken } }')) === "INVALID_TOKEN" && code(await gql(moved.accessToken, "{ organization { code } }")) === "UNAUTHENTICATED", `[${tag}] switch from another device → INVALID_TOKEN and the session ends`);
+
   // ---------------------------------------------------------------- background documents (in-process queue here; BullMQ in [worker])
   const otherAgain = await login("x@oth.test");
   const owner2 = await login("owner@apl.test");
diff --git a/package-lock.json b/package-lock.json
index 74b096b..c3c0cbc 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -10,7 +10,7 @@
       "license": "SEE LICENSE IN LICENSE",
       "dependencies": {
         "@graphql-tools/schema": "^10.1.5",
-        "@mgpl-diagnostics/auth-kit": "^1.4.0",
+        "@mgpl-diagnostics/auth-kit": "^1.5.0",
         "@mgpl-diagnostics/catalog-kit": "^1.0.0",
         "@mgpl-diagnostics/db-kit": "^2.1.1",
         "@mgpl-diagnostics/finance-kit": "^1.0.1",
@@ -33,7 +33,7 @@
         "sequelize": "^6.37.8"
       },
       "devDependencies": {
-        "@mgpl-diagnostics/client": "^1.4.0",
+        "@mgpl-diagnostics/client": "^1.5.0",
         "@types/node": "^22.20.5",
         "embedded-postgres": "^18.4.0-beta.17",
         "ioredis-mock": "^8.13.1",
@@ -1025,7 +1025,7 @@
       }
     },
     "node_modules/@mgpl-diagnostics/auth-kit": {
-      "version": "1.4.0",
+      "version": "1.5.0",
       "license": "SEE LICENSE IN LICENSE",
       "engines": {
         "node": ">=20"
@@ -1044,7 +1044,7 @@
       }
     },
     "node_modules/@mgpl-diagnostics/client": {
-      "version": "1.4.0",
+      "version": "1.5.0",
       "dev": true,
       "license": "SEE LICENSE IN LICENSE",
       "engines": {
diff --git a/package.json b/package.json
index 7780dcf..f734460 100644
--- a/package.json
+++ b/package.json
@@ -24,7 +24,7 @@
   },
   "dependencies": {
     "@graphql-tools/schema": "^10.1.5",
-    "@mgpl-diagnostics/auth-kit": "^1.4.0",
+    "@mgpl-diagnostics/auth-kit": "^1.5.0",
     "@mgpl-diagnostics/catalog-kit": "^1.0.0",
     "@mgpl-diagnostics/db-kit": "^2.1.1",
     "@mgpl-diagnostics/finance-kit": "^1.0.1",
@@ -47,7 +47,7 @@
     "sequelize": "^6.37.8"
   },
   "devDependencies": {
-    "@mgpl-diagnostics/client": "^1.4.0",
+    "@mgpl-diagnostics/client": "^1.5.0",
     "@types/node": "^22.20.5",
     "embedded-postgres": "^18.4.0-beta.17",
     "ioredis-mock": "^8.13.1",
diff --git a/schema.graphql b/schema.graphql
index f7f043f..e093856 100644
--- a/schema.graphql
+++ b/schema.graphql
@@ -1267,6 +1267,13 @@ type Mutation {
   Renders a stored invoice or a booking's reports in the background; poll job(id) until completed or failed.
   """
   startDocumentJob(input: DocumentJobInput!): Job!
+
+  """
+  Moves this session to the signed-in person's account in another lab (same email, active there), without
+  the password. This session ends; use the returned tokens. Send the same device as at login, or the
+  session ends (INVALID_TOKEN). ORG_UNAVAILABLE when there is no such account, or it is the current lab.
+  """
+  switchOrganization(device: DeviceInput, orgCode: String!): LoginResult!
   updateBranch(id: ID!, input: BranchPatch!): Branch!
   updateCustomer(id: ID!, input: CustomerPatch!): Customer!
   updateDoctor(id: ID!, input: DoctorPatch!): Doctor!
@@ -1317,6 +1324,19 @@ type Organization {
   phone: String
 }
 
+"""
+A lab the signed-in person can work in: they have an active account there with the same email.
+Also listed in ORG_REQUIRED errors (extensions.organizations, without current) after a password matched.
+"""
+type OrganizationChoice {
+  """The lab code: pass it to login (orgCode) or switchOrganization."""
+  code: String!
+
+  """The lab of this session."""
+  current: Boolean!
+  name: String!
+}
+
 input OrganizationInput {
   address: AddressInput
   email: String
@@ -1607,6 +1627,11 @@ type Query {
   ledgers: [Ledger!]!
   letterhead(format: DocumentFormat = pdf): Document!
   lockDates: [PeriodLock!]!
+
+  """
+  Every lab the signed-in person can switch to (same email, active account), the current one included.
+  """
+  myOrganizations: [OrganizationChoice!]!
   mySessions: [Session!]!
   organization: Organization!
   outstandingReceivables(asOf: DateTime, branchId: ID): Outstanding!
diff --git a/src/controllers/auth.controller.ts b/src/controllers/auth.controller.ts
index e2fb3c8..4cccd59 100644
--- a/src/controllers/auth.controller.ts
+++ b/src/controllers/auth.controller.ts
@@ -8,6 +8,7 @@ import { deviceOf, type DeviceInput } from "../graphql/device";
 export const authController = withErrorCodes({
   Query: {
     viewer: (_: unknown, __: unknown, ctx: Ctx) => (ctx.viewer ? {} : null),
+    myOrganizations: (_: unknown, __: unknown, ctx: Ctx) => ctx.services.auth.organizations(actorOf(ctx)),
     mySessions: async (_: unknown, __: unknown, ctx: Ctx) => {
       const sessions = await ctx.services.auth.sessions(actorOf(ctx));
       return sessions.map((s) => ({ ...s, current: s.id === ctx.viewer!.sessionId, createdAt: new Date(s.createdAt), lastSeenAt: new Date(s.lastSeenAt), expiresAt: new Date(s.expiresAt), deviceId: s.device?.deviceId ?? null, deviceInfo: s.device?.info ?? null }));
@@ -42,6 +43,11 @@ export const authController = withErrorCodes({
       const r = await ctx.services.auth.login({ ...input, ip: ctx.ip, userAgent: ctx.userAgent, device: deviceOf(device), tlsFingerprint: ctx.tlsFingerprint });
       return { ...r, accessToken: r.token, accessExpiresAt: r.expiresAt };
     },
+    switchOrganization: async (_: unknown, a: { orgCode: string; device?: DeviceInput | null }, ctx: Ctx) => {
+      if (!ctx.token) throw unauthenticated();
+      const r = await ctx.services.auth.switchOrganization({ token: ctx.token, orgCode: a.orgCode, ip: ctx.ip, userAgent: ctx.userAgent, device: deviceOf(a.device), tlsFingerprint: ctx.tlsFingerprint });
+      return { ...r, accessToken: r.token, accessExpiresAt: r.expiresAt };
+    },
     refreshSession: (_: unknown, a: { refreshToken: string; device?: DeviceInput | null }, ctx: Ctx) =>
       ctx.services.auth.refresh({ refreshToken: a.refreshToken, ip: ctx.ip, userAgent: ctx.userAgent, device: deviceOf(a.device), tlsFingerprint: ctx.tlsFingerprint }),
     logout: async (_: unknown, a: { refreshToken?: string | null }, ctx: Ctx) => {
diff --git a/src/graphql/errors.ts b/src/graphql/errors.ts
index 98b1c5d..9ad4b16 100644
--- a/src/graphql/errors.ts
+++ b/src/graphql/errors.ts
@@ -15,6 +15,7 @@ export const ERROR_CODES = [
   "PERIOD_LOCKED", "CREDIT_LIMIT_EXCEEDED",
   // auth-kit's own codes, passed through
   "INVALID_CREDENTIALS", "ACCOUNT_DISABLED", "INVITE_PENDING", "ORG_REQUIRED", "RATE_LIMITED", "WEAK_PASSWORD", "INVALID_TOKEN",
+  "ORG_UNAVAILABLE",
   // partner-lab imports (docs/18-imports.md)
   "UNSUPPORTED_REPORT", "REPORT_ALREADY_APPLIED", "BOOKING_PATIENT_MISMATCH", "FILE_TOO_LARGE",
 ] as const;
@@ -33,7 +34,13 @@ export const badInput = (message: string) => apiError("BAD_USER_INPUT", message,
 /** Domain errors from the kits → GraphQL errors with codes. Anything unknown is re-thrown (and masked by Yoga). */
 export function toGraphQLError(e: unknown): unknown {
   if (e instanceof GraphQLError) return e;
-  if (e instanceof AuthError) return apiError(e.code as ErrorCode, e.message, e.statusCode, e.details.retryAfterMs ? { retryAfterMs: e.details.retryAfterMs } : {});
+  if (e instanceof AuthError) {
+    const extra: Record<string, unknown> = {};
+    if (e.details.retryAfterMs) extra.retryAfterMs = e.details.retryAfterMs;
+    // ORG_REQUIRED: the labs whose account matched the password, for a pick list (ids stay on the server)
+    if (e.details.organizations?.length) extra.organizations = e.details.organizations.map((o) => ({ code: o.code, name: o.name }));
+    return apiError(e.code as ErrorCode, e.message, e.statusCode, extra);
+  }
   if (e instanceof ForbiddenError) return apiError("FORBIDDEN", e.message, 403);
   if (e instanceof UnsupportedReportError) return apiError("UNSUPPORTED_REPORT", e.message, 422);
   if (e instanceof FileTooLargeError) return apiError("FILE_TOO_LARGE", e.message, 413, { maxBytes: e.maxBytes });
diff --git a/src/schema/auth.graphql.ts b/src/schema/auth.graphql.ts
index 804afe4..ddc0657 100644
--- a/src/schema/auth.graphql.ts
+++ b/src/schema/auth.graphql.ts
@@ -77,9 +77,23 @@ export const authTypeDefs = /* GraphQL */ `
     expiresAt: DateTime! @deprecated(reason: "Use accessExpiresAt.")
   }
 
+  """
+  A lab the signed-in person can work in: they have an active account there with the same email.
+  Also listed in ORG_REQUIRED errors (extensions.organizations, without current) after a password matched.
+  """
+  type OrganizationChoice {
+    "The lab code: pass it to login (orgCode) or switchOrganization."
+    code: String!
+    name: String!
+    "The lab of this session."
+    current: Boolean!
+  }
+
   extend type Query {
     "null when not signed in."
     viewer: Viewer
+    "Every lab the signed-in person can switch to (same email, active account), the current one included."
+    myOrganizations: [OrganizationChoice!]!
     mySessions: [Session!]!
     users: [User!]!
     user(id: ID!): User
@@ -101,6 +115,12 @@ export const authTypeDefs = /* GraphQL */ `
     INVALID_TOKEN when it is unknown, spent or expired: sign in again.
     """
     refreshSession(refreshToken: String!, device: DeviceInput): LoginResult!
+    """
+    Moves this session to the signed-in person's account in another lab (same email, active there), without
+    the password. This session ends; use the returned tokens. Send the same device as at login, or the
+    session ends (INVALID_TOKEN). ORG_UNAVAILABLE when there is no such account, or it is the current lab.
+    """
+    switchOrganization(orgCode: String!, device: DeviceInput): LoginResult!
     "Ends this session: the bearer token (even an expired access token), or the refresh token when given."
     logout(refreshToken: String): Boolean!
     "Ends every other session of the signed-in user; returns how many."
diff --git a/src/services/auth.service.ts b/src/services/auth.service.ts
index ec02a9d..7db1ade 100644
--- a/src/services/auth.service.ts
+++ b/src/services/auth.service.ts
@@ -1,4 +1,4 @@
-import { can, permissionMatches, PERMISSIONS, roleMap, SYSTEM_ROLES, type Auth, type DeviceSignals, type PublicUser } from "@mgpl-diagnostics/auth-kit";
+import { AuthError, can, permissionMatches, PERMISSIONS, roleMap, SYSTEM_ROLES, type Auth, type DeviceSignals, type PublicUser } from "@mgpl-diagnostics/auth-kit";
 import { ConflictError, createUser, NotFoundError, ValidationError, type Id, type Repositories, type Role, type RoleAssignment, type User } from "@mgpl-diagnostics/db-kit";
 import type { Actor } from "../graphql/context";
 import type { JobQueue } from "../jobs/types";
@@ -25,6 +25,20 @@ export class AuthService {
     return this.auth.login({ ...input, orgCode: input.orgCode ?? undefined });
   }
 
+  /** The labs the person can switch to (same email, active account), the current one marked. */
+  async organizations(actor: Actor): Promise<{ code: string; name: string; current: boolean }[]> {
+    return (await this.auth.organizationsOf(actor.userId)).map((o) => ({ code: o.code, name: o.name, current: o.orgId === actor.orgId }));
+  }
+
+  /** Moves the session to the person's account in the lab with this code (auth-kit checks it is theirs). */
+  async switchOrganization(input: { token: string; orgCode: string; ip?: string; userAgent?: string; device?: DeviceSignals; tlsFingerprint?: string }) {
+    const org = await this.repos.orgs.findOne({ code: input.orgCode.trim().toUpperCase() });
+    // an unknown code gets the same answer as a lab without an account, so codes cannot be probed
+    if (!org) throw new AuthError("ORG_UNAVAILABLE", "You can't switch to that organisation");
+    const { orgCode: _c, ...rest } = input;
+    return this.auth.switchOrganization({ ...rest, orgId: org.id });
+  }
+
   /** Spends a refresh token: a new access token and the next refresh token (rotation). */
   async refresh(input: { refreshToken: string; ip?: string; userAgent?: string; device?: DeviceSignals; tlsFingerprint?: string }) {
     const p = await this.auth.refresh(input);
diff --git a/test/run.ts b/test/run.ts
index aaa8b56..e9d9ef2 100644
--- a/test/run.ts
+++ b/test/run.ts
@@ -250,6 +250,26 @@ async function suite(db: Db, tag: string) {
   ok(!!same?.refreshToken, `[${tag}] refresh on the same device (new fingerprint) works`);
   ok(code(await gql(null, "mutation($r: String!, $d: DeviceInput) { refreshSession(refreshToken: $r, device: $d) { refreshToken } }", { r: same.refreshToken, d: { deviceId: "dev-laptop-9999-zzzzzz" } })) === "INVALID_TOKEN" && code(await gql(bound.accessToken, "{ organization { id } }")) === "UNAUTHENTICATED", `[${tag}] refresh from another device → INVALID_TOKEN and the session ends`);
 
+  // ---------------------------------------------------------------- one person in two labs: pick list and switching
+  for (const [org, branch] of [[a.org.id, a.branch.id], [other.org.id, other.branch.id]] as const) {
+    await db.rawRepos.users.create({ orgId: org, name: "Two Labs", email: "two@labs.test", passwordHash: await hashPassword(pw), status: "active", roles: [{ role: "front_desk", branchId: branch }] });
+  }
+  const pick = await gql(null, 'mutation { login(input: { email: "two@labs.test", password: "Lab-Owner-2026!" }) { accessToken } }');
+  const choices = (pick.errors?.[0]?.extensions as { organizations?: { code: string; name: string }[] } | undefined)?.organizations;
+  ok(code(pick) === "ORG_REQUIRED" && choices?.map((o) => `${o.code}:${o.name}`).join() === "APL:API Lab,OTH:Other Lab" && !JSON.stringify(pick).includes(a.org.id), `[${tag}] ORG_REQUIRED lists the labs to pick from (code + name, no ids)`);
+  ok(!(await gql(null, 'mutation { login(input: { email: "two@labs.test", password: "wrong-password" }) { accessToken } }')).errors?.[0]?.extensions?.hasOwnProperty("organizations"), `[${tag}] a wrong password lists no labs`);
+  const solo = await login("x@oth.test");
+  const twoDev = { deviceId: "dev-two-labs-0001" };
+  const inApl = (await gql(null, 'mutation($d: DeviceInput) { login(input: { email: "two@labs.test", password: "Lab-Owner-2026!", orgCode: "apl", device: $d }) { accessToken refreshToken } }', { d: twoDev })).data?.login;
+  const mine = (await gql(inApl.accessToken, "{ myOrganizations { code name current } }")).data?.myOrganizations;
+  ok(mine?.map((o: any) => `${o.code}:${o.current}`).join() === "APL:true,OTH:false", `[${tag}] myOrganizations: both labs, the current one marked`);
+  ok((await gql(solo, "{ myOrganizations { code } }")).data?.myOrganizations.length === 1, `[${tag}] myOrganizations: one lab for a one-lab person`);
+  const moved = (await gql(inApl.accessToken, 'mutation($d: DeviceInput) { switchOrganization(orgCode: "OTH", device: $d) { accessToken refreshToken user { email } } }', { d: twoDev })).data?.switchOrganization;
+  ok((await gql(moved?.accessToken, "{ organization { code } }")).data?.organization.code === "OTH" && code(await gql(inApl.accessToken, "{ organization { code } }")) === "UNAUTHENTICATED", `[${tag}] switchOrganization: new tokens work in the other lab, the old session ends`);
+  ok(code(await gql(moved.accessToken, 'mutation { switchOrganization(orgCode: "OTH") { accessToken } }')) === "ORG_UNAVAILABLE" && code(await gql(moved.accessToken, 'mutation { switchOrganization(orgCode: "NOPE") { accessToken } }')) === "ORG_UNAVAILABLE" && code(await gql(solo, 'mutation { switchOrganization(orgCode: "OTH") { accessToken } }')) === "ORG_UNAVAILABLE", `[${tag}] switch to the current lab, an unknown code or a lab without an account → ORG_UNAVAILABLE`);
+  ok(code(await gql(null, 'mutation { switchOrganization(orgCode: "APL") { accessToken } }')) === "UNAUTHENTICATED", `[${tag}] switchOrganization needs a session`);
+  ok(code(await gql(moved.accessToken, 'mutation { switchOrganization(orgCode: "APL", device: { deviceId: "dev-elsewhere-0009" }) { accessToken } }')) === "INVALID_TOKEN" && code(await gql(moved.accessToken, "{ organization { code } }")) === "UNAUTHENTICATED", `[${tag}] switch from another device → INVALID_TOKEN and the session ends`);
+
   // ---------------------------------------------------------------- background documents (in-process queue here; BullMQ in [worker])
   const otherAgain = await login("x@oth.test");
   const owner2 = await login("owner@apl.test");