diff --git a/‎.changeset/client-get-active-member-names-the-organisation.md‎
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diff --git a/‎packages/client/src/index.ts‎
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@@ -0,0 +1,33 @@
+---
+"@objectstack/client": minor
+---
+
+fix(client): `organizations.getActiveMember(organizationId)` answers the organisation the caller NAMES, not whichever one the session has active (#16568)
+
+**BREAKING** — the answer this published method gives moves for existing inputs. The signature, the declared return type and the export are byte-identical; what changes is the response an existing call observes, stated below as a before/after pair per input.
+
+The method built `GET /organization/get-active-member?organizationId=…`, and better-auth 1.7.2's handler for that path reads `session.session.activeOrganizationId` and never looks at `ctx.query`. The query string was dead on arrival: a client doing a permission check for organisation B while A was active got **A's** membership row back, with a 200 and no diagnostic — the wrong-but-plausible answer, silently. The SDK's own JSDoc promised "the calling user's membership row in the given organisation", so this was a declared capability the runtime did not deliver.
+
+It now asks the question honestly, in two requests:
+
+1. `GET /get-session` — the caller's own user id;
+2. `GET /organization/list-members?organizationId=…&filterField=userId&filterValue=<the caller>&limit=1` — the row, unwrapped from the one-entry page.
+
+`list-members` reads `ctx.query.organizationId`, and its rows carry the identical shape (`OrganizationMemberWithUserWire`, user projection included), so the signature and the declared return type are unchanged and no caller's types move.
+
+## What an existing call observes, before and after
+
+Everything here is measured against a real `AuthManager` (better-auth 1.7.2, organization plugin) over a real `SqlDriver`. Each bullet is one input, with the response it drew before and the response it draws now.
+
+- **An organisation id other than the session's active one.** Before: a 200 carrying the **active** organisation's membership row, whatever id was named. After: a 200 carrying the **named** organisation's row. An input that named the active organisation's own id drew that organisation's row before and draws the same row after — `auth.me()` is where that id is readable, on `session.activeOrganizationId`.
+- **An organisation the caller is not a member of.** Before: the named organisation was never consulted, so the answer was about the **active** one — a 200 carrying the active organisation's row, or `400 MEMBER_NOT_FOUND` when the caller had no row there either. After: `403 YOU_ARE_NOT_A_MEMBER_OF_THIS_ORGANIZATION`, the server's own refusal, about the organisation that was actually named.
+- **Any id, on a session with no active organisation.** Before: `400 NO_ACTIVE_ORGANIZATION`. After: a 200 carrying the caller's row in the named organisation. `setActive` has stopped being a precondition, which is the point of naming the organisation.
+- **An empty `organizationId`.** Before: a 200 carrying the **active** organisation's row — better-auth resolves `ctx.query.organizationId || session.activeOrganizationId`, so an empty string fell through to session state and the wrong-but-plausible answer survived on that one input. After: the SDK refuses it before the wire, with a thrown `[ObjectStack] organizations.getActiveMember: organizationId is required`.
+
+Two things do not move: an anonymous caller still draws `401 UNAUTHORIZED`, thrown by the same session middleware that guarded the old route; and the row's shape is the same on both sides. The method now makes two HTTP requests where it made one.
+
+Graded `minor` rather than `patch`: the method's published behaviour moves for existing callers, which is the same clause-② judgement this PR declares, and the maintainer's ruling of 2026-09-04 (decision batch #35) holds that a change to a published package's public surface takes at least `minor` — a commit type may raise a bump, never lower it below what the act requires. The banner above carries the breaking-ness that the level cannot, per the ruling recorded on #16568 on 2026-09-08.
+
+The auth route ledger's `GET /api/v1/auth/organization/get-active-member` row is rebooked from `sdk` to `server-only` in the same change: `sdk` means "expressed by the SDK", and no SDK method builds that URL any more. The `get-session` and `list-members` rows gain the method in their notes, since it now builds both. Ledger-internal, nothing published moves with it.
+
+<!-- adr-0087: not-required (no-migration-prescription) SDK call-site change, no metadata conversion -->
@@ -3426,25 +3426,93 @@ export class ObjectStackClient {
     },
 
     /**
-     * Look up the calling user's membership row in the ACTIVE organisation.
+     * Look up the calling user's membership row in the GIVEN organisation.
      * Useful for permission checks on the client without having to scan the
      * full member list.
      *
-     * better-auth: GET /organization/get-active-member?organizationId=…
+     * Two requests, because no single better-auth route answers this question:
      *
-     * ⚠️ The server reads only the session's `activeOrganizationId` and
-     * ignores the `organizationId` query this method sends (measured: a query
-     * naming another organization answered the active one's row). Call
-     * `setActive` first if the organisation you mean is not the active one;
-     * with no active organisation the route is a thrown 400
-     * `NO_ACTIVE_ORGANIZATION`.
+     *   1. `GET /get-session` — who is calling. The body is the bare
+     *      `{ user, session }` envelope for a signed-in caller and the literal
+     *      `null` for an anonymous one (measured).
+     *   2. `GET /organization/list-members?organizationId=…&filterField=userId`
+     *      `&filterValue=<the caller>&limit=1` — the row, unwrapped from the
+     *      one-entry page.
+     *
+     * ⚠️ It is deliberately NOT `GET /organization/get-active-member`, which
+     * this method used to call. That handler reads only the session's
+     * `activeOrganizationId` and never looks at `ctx.query`, so it answered the
+     * ACTIVE organisation's row whatever id the caller named — the
+     * wrong-but-plausible answer, silently. `list-members` reads
+     * `ctx.query.organizationId` and its rows carry the identical shape
+     * ({@link OrganizationMemberWithUserWire}), so only the addressing moved.
+     * Measured against better-auth 1.7.2 over a real `AuthManager` + `SqlDriver`.
+     *
+     * What an existing caller sees change, all of it measured on the same drive:
+     *
+     *   - naming a NON-active organisation now answers THAT organisation's row
+     *     instead of the active one's — the defect this method carried;
+     *   - a caller who is not a member of `organizationId` is refused
+     *     `403 YOU_ARE_NOT_A_MEMBER_OF_THIS_ORGANIZATION`. Before, the named
+     *     organisation was never consulted, so the answer was about the
+     *     ACTIVE one: a 200 carrying the active organisation's row, or
+     *     `400 MEMBER_NOT_FOUND` when the caller had no row there either;
+     *   - a caller with no active organisation gets their row rather than
+     *     `400 NO_ACTIVE_ORGANIZATION` — `setActive` is no longer a
+     *     precondition, which is the point of naming the organisation;
+     *   - an anonymous caller still gets `401 UNAUTHORIZED`, thrown from the
+     *     `list-members` request by the same session middleware that guarded
+     *     `get-active-member`;
+     *   - a FALSY `organizationId` is refused here, before the wire. It used to
+     *     answer the ACTIVE organisation's row at 200: better-auth resolves
+     *     `ctx.query.organizationId || session.activeOrganizationId`, so an
+     *     empty string fell through to session state — the same
+     *     wrong-but-plausible answer this method was fixed to stop giving,
+     *     surviving on one input while the contract above says "the GIVEN
+     *     organisation". Naming the active organisation explicitly asks that
+     *     question honestly; `auth.me()` carries the id, on
+     *     `session.activeOrganizationId`.
+     *
+     * @param organizationId the organisation to ask about. Required and
+     *   non-empty; there is no "whichever one is active" spelling, deliberately.
+     * @throws if `organizationId` is falsy, or if the server answers 200 with no
+     *   membership row for the caller.
      */
     getActiveMember: async (organizationId: string): Promise<OrganizationMemberWithUserWire> => {
+      // A falsy id is not "the active organisation", it is a caller bug: the
+      // route would silently substitute session state for the question asked.
+      // Loud beats a plausible answer about the wrong organisation (#16568).
+      if (!organizationId) {
+        throw new Error('[ObjectStack] organizations.getActiveMember: organizationId is required');
+      }
       const route = this.getRoute('auth');
+      // Step 1 — the caller's own user id. Typed to the shape the route really
+      // serves rather than to `SessionResponse`, which declares the REST
+      // `{ success, data }` envelope this better-auth route does not use.
+      const sessionRes = await this.fetch(`${this.baseUrl}${route}/get-session`, {
+        headers: { Origin: this.baseUrl },
+      });
+      const session = (await sessionRes.json()) as { user?: { id?: string } } | null;
+      // Anonymous → `null`, and the request below is then refused 401 by the
+      // session middleware before the filter is ever read. The refusal stays
+      // the SERVER's; nothing is invented here to stand in for it.
+      const userId = session?.user?.id ?? '';
       const res = await this.fetch(
-        `${this.baseUrl}${route}/organization/get-active-member?organizationId=${encodeURIComponent(organizationId)}`,
+        `${this.baseUrl}${route}/organization/list-members`
+          + `?organizationId=${encodeURIComponent(organizationId)}`
+          + `&filterField=userId&filterValue=${encodeURIComponent(userId)}&limit=1`,
       );
-      return res.json();
+      const page = (await res.json()) as OrganizationMembersPage;
+      const [member] = page.members;
+      if (!member) {
+        // Unreachable through the route's own gate — `list-members` refuses a
+        // non-member 403 before it filters, so a 200 with no row means the
+        // membership vanished between the two requests. Loud beats a cast.
+        throw new Error(
+          `[ObjectStack] organizations.getActiveMember: no membership row for the calling user in organization "${organizationId}"`,
+        );
+      }
+      return member;
     },
 
     /**