diff --git a/packages/plugins/plugin-auth/src/auth-manager-membership-admission.ts b/packages/plugins/plugin-auth/src/auth-manager-membership-admission.ts
index e064d46a794..1be746b5352 100644
--- a/packages/plugins/plugin-auth/src/auth-manager-membership-admission.ts
+++ b/packages/plugins/plugin-auth/src/auth-manager-membership-admission.ts
@@ -45,6 +45,12 @@
  * while they are first evaluated: this module's top level is imports, an
  * interface and function declarations.
  *
+ * `settleMembership` below is governed by ADR-0093 D2: the membership
+ * reconciler is the single owner of the "every user gets a membership"
+ * invariant, and this is the manager's single assembly of its inputs, which
+ * both creation seams call. `scripts/adr-anchors/` carries the invariant for
+ * this file, as it does for `auth-manager.ts`.
+ *
  * Nothing re-exports this module, so the published surface does not move.
  */
 
diff --git a/packages/plugins/plugin-auth/src/auth-manager-password-hasher.ts b/packages/plugins/plugin-auth/src/auth-manager-password-hasher.ts
new file mode 100644
index 00000000000..356d30afb76
--- /dev/null
+++ b/packages/plugins/plugin-auth/src/auth-manager-password-hasher.ts
@@ -0,0 +1,75 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#25224 cut 11] The WebContainer password hasher of `AuthManager` — the
+ * pure-JS scrypt hasher handed to better-auth when the runtime is StackBlitz's
+ * WebContainer, whose `node:crypto.scrypt` polyfill fails sign-up — moved out
+ * of `auth-manager.ts` whole.
+ *
+ * A MOVE, not a redesign. The function below is the body of the
+ * `AuthManager` method of the same name as it stood, re-indented one level
+ * and otherwise unedited: the same runtime test, the same scrypt parameters
+ * and `{saltHex}:{keyHex}` storage format, the same lazy load of
+ * `@noble/hashes` (only inside WebContainer), and the same warning and
+ * fallback when that load fails.
+ *
+ * ## How the moved body reaches the class
+ *
+ * The shape #23050 set for `rest-server.ts` (its `data-action-routes.ts`
+ * header carries the full reasoning), which the ten `auth-manager-*.ts`
+ * modules split out before this one follow. The class keeps the method — the
+ * published `dist/*.d.ts` lists it — and its body is a plain call: it reads
+ * no member of the class, so it is handed none, and there is no host type.
+ * It is no longer `async`: it returns the moved function's own promise, so a
+ * caller awaits the same promise the body settles, with no extra wrapper.
+ *
+ * `isWebContainerRuntime` stays: the request-state polyfill in
+ * `auth-manager.ts`, which the constructor installs, reads it too. So that
+ * file exports it and this module imports it by VALUE, for one read inside
+ * `resolvePasswordHasher`, when the better-auth instance is built.
+ * `index.ts` lists `auth-manager.ts`'s published names one by one, so that
+ * export is not published. The two modules import each other, and that is
+ * safe because nothing reads the binding while they are first evaluated: this
+ * module's top level is one import and one function declaration.
+ *
+ * Nothing re-exports this module, so the published surface does not move.
+ */
+
+import { isWebContainerRuntime } from './auth-manager.js';
+
+/** The body of `AuthManager#resolvePasswordHasher`; the method's docblock there is its contract. */
+export async function resolvePasswordHasher(): Promise<
+  { hash: (password: string) => Promise<string>; verify: (args: { hash: string; password: string }) => Promise<boolean> } | undefined
+> {
+  if (!isWebContainerRuntime()) return undefined;
+  try {
+    const { scryptAsync } = await import('@noble/hashes/scrypt.js');
+    const PARAMS = { N: 16384, r: 16, p: 1, dkLen: 64, maxmem: 128 * 16384 * 16 * 2 } as const;
+    const toHex = (b: Uint8Array): string => {
+      let s = '';
+      for (let i = 0; i < b.length; i++) s += b[i]!.toString(16).padStart(2, '0');
+      return s;
+    };
+    const generateKey = (password: string, saltHex: string): Promise<Uint8Array> =>
+      scryptAsync(password.normalize('NFKC'), saltHex, PARAMS);
+    return {
+      hash: async (password: string) => {
+        const saltBytes = (globalThis as any).crypto.getRandomValues(new Uint8Array(16));
+        const saltHex = toHex(saltBytes);
+        const key = await generateKey(password, saltHex);
+        return `${saltHex}:${toHex(key)}`;
+      },
+      verify: async ({ hash, password }) => {
+        const [saltHex, keyHex] = hash.split(':');
+        if (!saltHex || !keyHex) throw new Error('Invalid password hash');
+        const target = await generateKey(password, saltHex);
+        return toHex(target) === keyHex;
+      },
+    };
+  } catch (err: any) {
+    console.warn(
+      `[AuthManager] WebContainer detected but pure-JS scrypt unavailable: ${err?.message ?? err}. Falling back to default.`,
+    );
+    return undefined;
+  }
+}
diff --git a/packages/plugins/plugin-auth/src/auth-manager.ts b/packages/plugins/plugin-auth/src/auth-manager.ts
index 380ddd3f482..a23c06231ad 100644
--- a/packages/plugins/plugin-auth/src/auth-manager.ts
+++ b/packages/plugins/plugin-auth/src/auth-manager.ts
@@ -249,6 +249,10 @@ import {
   ownsRoute,
   type RequestRoutingHost,
 } from './auth-manager-request-routing.js';
+// [#25224 cut 11] The WebContainer password hasher; the method of the same
+// name below calls it, and hands it nothing, because it reads no member of
+// this class.
+import { resolvePasswordHasher } from './auth-manager-password-hasher.js';
 
 /**
  * Detect WebContainer (StackBlitz) environment.
@@ -259,7 +263,7 @@ import {
  * propagate the store across `await` boundaries the way Node's native
  * implementation does.
  */
-function isWebContainerRuntime(): boolean {
+export function isWebContainerRuntime(): boolean {
   if (typeof globalThis === 'undefined') return false;
   const proc = (globalThis as any).process;
   return (
@@ -3157,40 +3161,11 @@ export class AuthManager {
    * Returns `undefined` outside WebContainer so production deployments keep
    * the native (fast) hasher and never load `@noble/hashes`.
    */
-  private async resolvePasswordHasher(): Promise<
+  private resolvePasswordHasher(): Promise<
     { hash: (password: string) => Promise<string>; verify: (args: { hash: string; password: string }) => Promise<boolean> } | undefined
   > {
-    if (!isWebContainerRuntime()) return undefined;
-    try {
-      const { scryptAsync } = await import('@noble/hashes/scrypt.js');
-      const PARAMS = { N: 16384, r: 16, p: 1, dkLen: 64, maxmem: 128 * 16384 * 16 * 2 } as const;
-      const toHex = (b: Uint8Array): string => {
-        let s = '';
-        for (let i = 0; i < b.length; i++) s += b[i]!.toString(16).padStart(2, '0');
-        return s;
-      };
-      const generateKey = (password: string, saltHex: string): Promise<Uint8Array> =>
-        scryptAsync(password.normalize('NFKC'), saltHex, PARAMS);
-      return {
-        hash: async (password: string) => {
-          const saltBytes = (globalThis as any).crypto.getRandomValues(new Uint8Array(16));
-          const saltHex = toHex(saltBytes);
-          const key = await generateKey(password, saltHex);
-          return `${saltHex}:${toHex(key)}`;
-        },
-        verify: async ({ hash, password }) => {
-          const [saltHex, keyHex] = hash.split(':');
-          if (!saltHex || !keyHex) throw new Error('Invalid password hash');
-          const target = await generateKey(password, saltHex);
-          return toHex(target) === keyHex;
-        },
-      };
-    } catch (err: any) {
-      console.warn(
-        `[AuthManager] WebContainer detected but pure-JS scrypt unavailable: ${err?.message ?? err}. Falling back to default.`,
-      );
-      return undefined;
-    }
+    // [#25224 cut 11] The body moved to `auth-manager-password-hasher.ts`; it reads no member of this class.
+    return resolvePasswordHasher();
   }
 
   /**
diff --git a/scripts/adr-anchors/packages__plugins__plugin-auth__src__auth-manager-membership-admission.ts.json b/scripts/adr-anchors/packages__plugins__plugin-auth__src__auth-manager-membership-admission.ts.json
new file mode 100644
index 00000000000..e176690d07f
--- /dev/null
+++ b/scripts/adr-anchors/packages__plugins__plugin-auth__src__auth-manager-membership-admission.ts.json
@@ -0,0 +1,7 @@
+{
+  "file": "packages/plugins/plugin-auth/src/auth-manager-membership-admission.ts",
+  "adrs": [
+    "ADR-0093"
+  ],
+  "invariant": "ADR-0093 D2 — the membership reconciler is the SINGLE owner of the \"every user gets a membership\" invariant, and `settleMembership` is this manager's single assembly of its inputs. TWO seams call it and must never disagree: `user.create.after` (the creation seam every path flows through — email signup, admin create-user, bulk import, SSO JIT, none of which need a session) and `session.create.before` (which settles BEFORE resolving the session's active organization, so a user's first session is not minted tenant-less — #8245). Assembling the deps per call site would let them drift on the policy, which is a live platform setting read through `getMembershipPolicy()` (#5152): a captured option leaves one seam auto-binding after an admin switched the deployment to `invite-only`. The session-seam call must also stay a pure ORDERING change — same reconciler, same policy, same target-org resolution — so `invite-only` and multi-org still bind nobody and those sessions still mint with no active organization, which is the legal state the #8247 ruling declares."
+}