fix(auth): atomic last-admin guards on role-change and delete

src/data/users.test.ts

@@ -122,4 +122,65 @@ describe("UserStore", () => {
     expect(alice.role).toBe("admin");
     expect(bob.role).toBe("member");
   });
+
+  it("setRoleIfNotLastAdmin returns 'would_orphan' for the only admin being demoted", async () => {
+    const alice = await users.createUser("alice", "pw-alice", "admin");
+    expect(users.setRoleIfNotLastAdmin(alice.id, "member")).toBe("would_orphan");
+    expect(users.findById(alice.id)!.role).toBe("admin"); // unchanged
+  });
+
+  it("setRoleIfNotLastAdmin allows demotion when another admin exists", async () => {
+    const alice = await users.createUser("alice", "pw-alice", "admin");
+    await users.createUser("bob", "pw-bob-bob", "admin");
+    expect(users.setRoleIfNotLastAdmin(alice.id, "member")).toBe("ok");
+    expect(users.findById(alice.id)!.role).toBe("member");
+  });
+
+  it("setRoleIfNotLastAdmin returns 'not_found' for unknown id", () => {
+    expect(users.setRoleIfNotLastAdmin("not-a-real-id", "member")).toBe("not_found");
+  });
+
+  it("setRoleIfNotLastAdmin: concurrent demotions of two admins keep one admin", async () => {
+    const alice = await users.createUser("alice", "pw-alice", "admin");
+    const bob = await users.createUser("bob", "pw-bob-bob", "admin");
+    // Concurrent demotion of both
+    const [r1, r2] = await Promise.all([
+      Promise.resolve(users.setRoleIfNotLastAdmin(alice.id, "member")),
+      Promise.resolve(users.setRoleIfNotLastAdmin(bob.id, "member")),
+    ]);
+    // Exactly one should succeed; the other gets "would_orphan"
+    const oks = [r1, r2].filter((r) => r === "ok").length;
+    const orphans = [r1, r2].filter((r) => r === "would_orphan").length;
+    expect(oks).toBe(1);
+    expect(orphans).toBe(1);
+    // System retains at least one admin
+    expect(users.countAdmins()).toBe(1);
+  });
+
+  it("deleteUserIfNotLastAdmin returns 'would_orphan' for the only admin", async () => {
+    const alice = await users.createUser("alice", "pw-alice", "admin");
+    expect(users.deleteUserIfNotLastAdmin(alice.id)).toBe("would_orphan");
+    expect(users.findById(alice.id)).not.toBeNull();
+  });
+
+  it("deleteUserIfNotLastAdmin allows deleting a member at any count", async () => {
+    await users.createUser("alice", "pw-alice", "admin");
+    const bob = await users.createUser("bob", "pw-bob-bob", "member");
+    expect(users.deleteUserIfNotLastAdmin(bob.id)).toBe("ok");
+    expect(users.findById(bob.id)).toBeNull();
+  });
+
+  it("deleteUserIfNotLastAdmin: concurrent deletes of two admins keep one admin", async () => {
+    const alice = await users.createUser("alice", "pw-alice", "admin");
+    const bob = await users.createUser("bob", "pw-bob-bob", "admin");
+    const [r1, r2] = await Promise.all([
+      Promise.resolve(users.deleteUserIfNotLastAdmin(alice.id)),
+      Promise.resolve(users.deleteUserIfNotLastAdmin(bob.id)),
+    ]);
+    const oks = [r1, r2].filter((r) => r === "ok").length;
+    const orphans = [r1, r2].filter((r) => r === "would_orphan").length;
+    expect(oks).toBe(1);
+    expect(orphans).toBe(1);
+    expect(users.countAdmins()).toBe(1);
+  });
 });

src/data/users.ts

@@ -25,7 +25,9 @@ export interface UserStore {
   verifyPassword(plain: string, hash: string): Promise<boolean>;
   changePassword(userId: string, newPassword: string): Promise<void>;
   setRole(userId: string, role: UserRole): boolean;
+  setRoleIfNotLastAdmin(id: string, newRole: UserRole): "ok" | "not_found" | "would_orphan";
   deleteUser(id: string): boolean;
+  deleteUserIfNotLastAdmin(id: string): "ok" | "not_found" | "would_orphan";
   listUsers(): Array<{ id: string; username: string; createdAt: number; role: UserRole }>;
 }
 
@@ -125,6 +127,21 @@ export function createUserStore(db: Database.Database): UserStore {
       return result.changes > 0;
     },
 
+    setRoleIfNotLastAdmin(id, newRole) {
+      const tx = db.transaction(() => {
+        const row = findByIdStmt.get(id) as UserRow | undefined;
+        if (!row) return "not_found" as const;
+        if (row.role === newRole) return "ok" as const; // no-op
+        if (row.role === "admin" && newRole === "member") {
+          const adminCount = (countAdminsStmt.get() as { n: number }).n;
+          if (adminCount <= 1) return "would_orphan" as const;
+        }
+        updateRoleStmt.run(newRole, Date.now(), id);
+        return "ok" as const;
+      });
+      return tx();
+    },
+
     listUsers() {
       return listUsersStmt.all() as Array<{ id: string; username: string; createdAt: number; role: UserRole }>;
     },
@@ -133,5 +150,19 @@ export function createUserStore(db: Database.Database): UserStore {
       const result = deleteUserStmt.run(id);
       return result.changes > 0;
     },
+
+    deleteUserIfNotLastAdmin(id) {
+      const tx = db.transaction(() => {
+        const row = findByIdStmt.get(id) as UserRow | undefined;
+        if (!row) return "not_found" as const;
+        if (row.role === "admin") {
+          const adminCount = (countAdminsStmt.get() as { n: number }).n;
+          if (adminCount <= 1) return "would_orphan" as const;
+        }
+        deleteUserStmt.run(id);
+        return "ok" as const;
+      });
+      return tx();
+    },
   };
 }