diff --git a/app/api/owner-auth.test.ts b/app/api/owner-auth.test.ts
index f3ab362..54ed842 100644
--- a/app/api/owner-auth.test.ts
+++ b/app/api/owner-auth.test.ts
@@ -118,9 +118,17 @@ async function setupWithSessions(db: ReturnType<typeof getDb>) {
   expect(bobResp.status).toBe(200);
   const bobCookie = extractCookie(bobResp.headers.get("set-cookie"));
 
-  // Capture Alice's userId from the users table (only Alice was first)
+  // Capture both userIds from the users table.
   const users = db.select({ id: schema.user.id, email: schema.user.email }).from(schema.user).all();
   const aliceRow = users.find((u) => u.email === "alice@example.com");
+  const bobRow = users.find((u) => u.email === "bob@example.com");
+
+  // Sign-up alone does not create a membership; acceptInvitation does. Insert Bob's member
+  // row directly to represent an accepted invite, so he is a real workspace member (which is
+  // what these IDOR tests intend). Without a membership row he is not an authorized actor.
+  db.insert(schema.member).values({
+    id: randomUUID(), organizationId: orgId, userId: bobRow!.id, role: "member", createdAt: new Date(),
+  }).run();
 
   return { aliceCookie: aliceCookie!, bobCookie: bobCookie!, aliceUserId: aliceRow!.id };
 }
@@ -475,6 +483,33 @@ describe("null-owner link — member blocked, admin allowed (fix 1)", () => {
   });
 });
 
+// ─────────────────────────────────────────────────────────────────────────────
+// Removing a member revokes their access at the endpoint layer
+// ─────────────────────────────────────────────────────────────────────────────
+
+describe("removed member loses endpoint access", () => {
+  it("a member's key goes from 403 (authed, not owner) to 401 (unauthed) after removal, in production", async () => {
+    vi.stubEnv("NODE_ENV", "production");
+    const { db, userB, keyB, ownedLinkId } = setupTwoActors();
+    const { GET: statsGet } = await import("@/app/api/stats/route");
+
+    // While a member, Bob is authenticated but not the owner of Alice's link → 403.
+    const before = await statsGet(new Request(`http://t/api/stats?id=${ownedLinkId}`, {
+      headers: { authorization: `Bearer ${keyB}` },
+    }));
+    expect(before.status).toBe(403);
+
+    // Admin removes Bob: delete his membership row (what removeMember does).
+    db.delete(schema.member).where(eq(schema.member.userId, userB)).run();
+
+    // Bob's key no longer resolves to an actor → requireOwner fails closed → 401.
+    const after = await statsGet(new Request(`http://t/api/stats?id=${ownedLinkId}`, {
+      headers: { authorization: `Bearer ${keyB}` },
+    }));
+    expect(after.status).toBe(401);
+  });
+});
+
 // ─────────────────────────────────────────────────────────────────────────────
 // Fix 2: API key creation endpoint round-trip
 // ─────────────────────────────────────────────────────────────────────────────
diff --git a/lib/auth-session.test.ts b/lib/auth-session.test.ts
index 16a935d..6d25ffd 100644
--- a/lib/auth-session.test.ts
+++ b/lib/auth-session.test.ts
@@ -3,10 +3,11 @@ import { mkdtempSync } from "node:fs";
 import { tmpdir } from "node:os";
 import path from "node:path";
 import { randomUUID, createHash } from "node:crypto";
+import { eq } from "drizzle-orm";
 import { migrate } from "drizzle-orm/better-sqlite3/migrator";
 import { getDb } from "@/lib/db/client";
 import { makeAuth } from "@/lib/auth";
-import { makeGetActor } from "@/lib/auth-session";
+import { makeGetActor, resolveMembership } from "@/lib/auth-session";
 import * as schema from "@/lib/db/schema";
 
 // better-auth requires BETTER_AUTH_SECRET.
@@ -161,4 +162,99 @@ describe("getActor", () => {
     );
     expect(actor).toBeNull();
   });
+
+  it("returns null for a valid API key whose user has no workspace membership", async () => {
+    // A user + key with NO member row (e.g. an orphaned invite: signed up but
+    // never accepted). The key is valid and enabled but must not authorize.
+    env.db.insert(schema.organization).values({
+      id: randomUUID(), name: "Workspace", slug: "workspace", createdAt: new Date(),
+    }).run();
+    const userId = randomUUID();
+    env.db.insert(schema.user).values({
+      id: userId, name: "Nomember", email: "nomember@example.com",
+      emailVerified: true, createdAt: new Date(), updatedAt: new Date(),
+    }).run();
+    const rawKey = "sentou_nomember_" + randomUUID().replace(/-/g, "");
+    env.db.insert(schema.apiKey).values({
+      id: randomUUID(), userId, name: "no-member key",
+      keyHash: createHash("sha256").update(rawKey).digest("hex"),
+      prefix: rawKey.slice(0, 8), createdAt: new Date(), enabled: true,
+    }).run();
+
+    const actor = await env.getActor(
+      new Request("http://t/api/publish", {
+        headers: { authorization: `Bearer ${rawKey}` },
+      }),
+    );
+    expect(actor).toBeNull();
+  });
+
+  it("stops authorizing an API key once the member's row is removed", async () => {
+    // Seed org + member + key, confirm the key authorizes, then delete the
+    // member row (what removeMember does) and confirm the key no longer does.
+    const orgId = randomUUID();
+    env.db.insert(schema.organization).values({
+      id: orgId, name: "Workspace", slug: "workspace", createdAt: new Date(),
+    }).run();
+    const userId = randomUUID();
+    env.db.insert(schema.user).values({
+      id: userId, name: "Bob", email: "bob@example.com",
+      emailVerified: true, createdAt: new Date(), updatedAt: new Date(),
+    }).run();
+    env.db.insert(schema.member).values({
+      id: randomUUID(), organizationId: orgId, userId, role: "member", createdAt: new Date(),
+    }).run();
+    const rawKey = "sentou_removed_" + randomUUID().replace(/-/g, "");
+    env.db.insert(schema.apiKey).values({
+      id: randomUUID(), userId, name: "bob key",
+      keyHash: createHash("sha256").update(rawKey).digest("hex"),
+      prefix: rawKey.slice(0, 8), createdAt: new Date(), enabled: true,
+    }).run();
+
+    const request = () =>
+      new Request("http://t/api/publish", { headers: { authorization: `Bearer ${rawKey}` } });
+
+    const before = await env.getActor(request());
+    expect(before?.role).toBe("member");
+
+    env.db.delete(schema.member).where(eq(schema.member.userId, userId)).run();
+
+    const after = await env.getActor(request());
+    expect(after).toBeNull();
+  });
+});
+
+describe("resolveMembership", () => {
+  let env: ReturnType<typeof makeTestEnv>;
+  beforeEach(() => {
+    env = makeTestEnv();
+  });
+
+  it("returns null when the user has no member row in the workspace org", () => {
+    env.db.insert(schema.organization).values({
+      id: randomUUID(), name: "Workspace", slug: "workspace", createdAt: new Date(),
+    }).run();
+    const userId = randomUUID();
+    env.db.insert(schema.user).values({
+      id: userId, name: "Nobody", email: "nobody@example.com",
+      emailVerified: true, createdAt: new Date(), updatedAt: new Date(),
+    }).run();
+    expect(resolveMembership(env.db, userId)).toBeNull();
+  });
+
+  it("returns the role when the user is a member of the workspace org", () => {
+    const orgId = randomUUID();
+    env.db.insert(schema.organization).values({
+      id: orgId, name: "Workspace", slug: "workspace", createdAt: new Date(),
+    }).run();
+    const userId = randomUUID();
+    env.db.insert(schema.user).values({
+      id: userId, name: "Owner", email: "owner@example.com",
+      emailVerified: true, createdAt: new Date(), updatedAt: new Date(),
+    }).run();
+    env.db.insert(schema.member).values({
+      id: randomUUID(), organizationId: orgId, userId, role: "owner", createdAt: new Date(),
+    }).run();
+    expect(resolveMembership(env.db, userId)).toBe("owner");
+  });
 });
diff --git a/lib/auth-session.ts b/lib/auth-session.ts
index 38b5d7d..7a9593a 100644
--- a/lib/auth-session.ts
+++ b/lib/auth-session.ts
@@ -28,14 +28,17 @@ export function isAdmin(actor: Actor): boolean {
   return actor.role === "owner" || actor.role === "admin";
 }
 
-// Resolves the actor's role, scoped to the workspace org (oldest by createdAt,
-// then id as tiebreaker). Defaults to "member" if the user has no membership.
-// Using the workspace org prevents a user from gaining elevated rights by
-// joining or creating a second org.
-export function resolveRole(
+// Resolves the user's membership role in the workspace org (oldest by createdAt,
+// then id as tiebreaker), or null when the user has no membership row there.
+// Scoping to the workspace org prevents a user from gaining elevated rights by
+// joining or creating a second org. null is the load-bearing signal for
+// authorization: a removed member, an orphaned invite (signed up but never
+// accepted), and a race-losing "second owner" all have no row here and so must
+// not resolve to an authorized actor.
+export function resolveMembership(
   db: BetterSQLite3Database<typeof schema>,
   userId: string,
-): string {
+): string | null {
   const workspaceOrg = db
     .select({ id: schema.organization.id })
     .from(schema.organization)
@@ -43,7 +46,7 @@ export function resolveRole(
     .limit(1)
     .get();
 
-  if (!workspaceOrg) return "member";
+  if (!workspaceOrg) return null;
 
   const memberRow = db
     .select({ role: schema.member.role })
@@ -56,7 +59,18 @@ export function resolveRole(
     )
     .get();
 
-  return memberRow?.role ?? "member";
+  return memberRow?.role ?? null;
+}
+
+// Back-compat helper for the dashboard pages that only need a role string to
+// compute isAdmin: a non-member reads as "member" (never elevated), which is
+// harmless there. Authorization decisions must use resolveMembership /
+// resolveActor, which fail closed on a missing membership.
+export function resolveRole(
+  db: BetterSQLite3Database<typeof schema>,
+  userId: string,
+): string {
+  return resolveMembership(db, userId) ?? "member";
 }
 
 // Internal implementation — shared between the factory (tests) and the
@@ -71,7 +85,11 @@ async function resolveActor(
   // signed session cookie and returns the user + session or null.
   const session = await authInst.api.getSession({ headers: req.headers });
   if (session?.user?.id) {
-    const role = resolveRole(db, session.user.id);
+    // Require a live workspace membership. A valid session for a removed member
+    // (or an account that signed up but never accepted its invite) must NOT be
+    // an authorized actor, so removing someone actually revokes their access.
+    const role = resolveMembership(db, session.user.id);
+    if (!role) return null;
     return { userId: session.user.id, role };
   }
 
@@ -99,7 +117,10 @@ async function resolveActor(
     .where(eq(schema.apiKey.id, keyRow.id))
     .run();
 
-  const role = resolveRole(db, keyRow.userId);
+  // Same membership requirement as the session path: a key belonging to a
+  // removed member resolves to no actor, so revoking membership revokes the key.
+  const role = resolveMembership(db, keyRow.userId);
+  if (!role) return null;
   return { userId: keyRow.userId, role };
 }