feat(push): relay notifications as encrypted web push (#2906)

fluxer_api/src/api/instance/InstanceConfigRepository.test.ts

@@ -1,12 +1,21 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
+import {spawnSync} from 'node:child_process';
+import {createHash} from 'node:crypto';
+import {createServer} from 'node:net';
+import type {CassandraQueryExecutorForTesting} from '@app/api/database/CassandraQueryExecution';
 import {setCassandraQueryExecutorForTesting} from '@app/api/database/CassandraQueryExecution';
 import type {PreparedQuery} from '@app/api/database/CassandraTypes';
+import {ensurePostgresKvSchema, PostgresKvQueryExecutor} from '@app/api/database/PostgresKvQueryExecutor';
 import {
 	INSTANCE_CONFIG_REFRESH_CHANNEL,
+	INSTANCE_CONFIG_WRITE_ATTEMPTS,
 	InstanceConfigRepository,
+	InstanceConfigWriteConflictError,
 	type InstanceRegistrationConfig,
 } from '@app/api/instance/InstanceConfigRepository';
+import {InstanceConfigWriteRaceExecutor} from '@app/api/instance/tests/InstanceConfigWriteRaceExecutor';
+import {startDockerContainer} from '@app/api/test/DockerTestContainer';
 import {InMemoryCassandraQueryExecutor} from '@app/api/test/InMemoryCassandraQueryExecutor';
 import {MockKVProvider} from '@app/api/test/mocks/MockKVProvider';
 import {
@@ -21,7 +30,13 @@ import {
 	DEFAULT_EXPERIMENT_DELIVERY_CONFIG,
 	type ExperimentDeliveryConfig,
 } from '@fluxer/schema/src/domains/experiment/ExperimentSchemas';
-import {afterEach, describe, expect, it, vi} from 'vitest';
+import {
+	getDefaultPostgresClient,
+	type IPostgresClient,
+	initPostgres,
+	shutdownPostgres,
+} from '@pkgs/postgres/src/Client';
+import {afterAll, afterEach, beforeAll, beforeEach, describe, expect, it, vi} from 'vitest';
 
 const VOICE_NOISE_SUPPRESSION_CONFIG_KEY = 'voice_noise_suppression_config';
 const SCREEN_SHARE_DELIVERY_CONFIG_KEY = 'screen_share_delivery_config';
@@ -29,6 +44,12 @@ const EXPERIMENT_DELIVERY_CONFIG_KEY = 'experiment_delivery_config';
 const APP_PUBLIC_CONFIG_KEY = 'app_public_config';
 const INSTANCE_POLICY_CONFIG_KEY = 'instance_policy_config';
 const INSTANCE_INTEGRATIONS_CONFIG_KEY = 'instance_integrations_config';
+const REGISTRATION_CONFIG_KEY = 'registration_config';
+const REGISTRATION_URLS_KEY = 'registration_urls';
+const REGISTRATION_PENDING_APPROVALS_KEY = 'registration_pending_approvals';
+const POSTGRES_KV_TABLE = 'kv_instance_config_races';
+const POSTGRES_CONTAINER = `fluxer-instance-config-races-${process.pid.toString(36)}-${Date.now().toString(36)}`;
+const dockerAvailable = spawnSync('docker', ['version'], {stdio: 'ignore'}).status === 0;
 
 class CountingInMemoryCassandraQueryExecutor extends InMemoryCassandraQueryExecutor {
 	instanceConfigSelects = 0;
@@ -512,3 +533,466 @@ describe('InstanceConfigRepository', () => {
 		});
 	});
 });
+
+async function sleep(ms: number): Promise<void> {
+	await new Promise((resolve) => setTimeout(resolve, ms));
+}
+
+async function freePort(): Promise<number> {
+	return new Promise((resolve, reject) => {
+		const server = createServer();
+		server.on('error', reject);
+		server.listen(0, '127.0.0.1', () => {
+			const address = server.address();
+			if (typeof address === 'string' || address === null) {
+				reject(new Error('no port'));
+				return;
+			}
+			server.close(() => resolve(address.port));
+		});
+	});
+}
+
+function describeConcurrentInstanceConfigWrites(prepareBase: () => Promise<CassandraQueryExecutorForTesting>): void {
+	const pods: Array<InstanceConfigRepository> = [];
+	let executor: InstanceConfigWriteRaceExecutor;
+
+	beforeEach(async () => {
+		executor = new InstanceConfigWriteRaceExecutor(await prepareBase());
+		setCassandraQueryExecutorForTesting(executor);
+	});
+
+	afterEach(async () => {
+		await Promise.all(pods.map((pod) => pod.shutdown()));
+		pods.length = 0;
+	});
+
+	function createPod(): InstanceConfigRepository {
+		const pod = new InstanceConfigRepository(new MockKVProvider());
+		pods.push(pod);
+		return pod;
+	}
+
+	async function readStoredRegistrationConfig(): Promise<unknown> {
+		const raw = await executor.readDirectly(REGISTRATION_CONFIG_KEY);
+		return raw === null ? null : JSON.parse(raw);
+	}
+
+	it('applies two concurrent patches on top of each other instead of dropping one', async () => {
+		const first = createPod();
+		const second = createPod();
+		await first.setRegistrationConfig({mode: 'open', admin_registration_urls_enabled: true});
+		await second.getRegistrationConfig();
+		executor.watch(REGISTRATION_CONFIG_KEY);
+		executor.pauseWritesUntil(2);
+
+		await Promise.all([
+			first.setRegistrationConfig({mode: 'closed'}),
+			second.setRegistrationConfig({admin_registration_urls_enabled: false}),
+		]);
+
+		expect(executor.events.filter((event) => event === 'write rejected')).toHaveLength(1);
+		expect(executor.events.filter((event) => event === 'write')).toHaveLength(2);
+		expect(await readStoredRegistrationConfig()).toEqual({mode: 'closed', admin_registration_urls_enabled: false});
+	});
+
+	it('lets one of two concurrent first writes create the config and applies the other on top', async () => {
+		const first = createPod();
+		const second = createPod();
+		await first.getRegistrationConfig();
+		await second.getRegistrationConfig();
+		executor.watch(REGISTRATION_CONFIG_KEY);
+		executor.pauseWritesUntil(2);
+
+		await Promise.all([
+			first.setRegistrationConfig({mode: 'closed'}),
+			second.setRegistrationConfig({admin_registration_urls_enabled: false}),
+		]);
+
+		expect(executor.events.filter((event) => event === 'write rejected')).toHaveLength(1);
+		expect(executor.events.filter((event) => event === 'write')).toHaveLength(2);
+		expect(await readStoredRegistrationConfig()).toEqual({mode: 'closed', admin_registration_urls_enabled: false});
+	});
+
+	it('re-reads the database, not its stale cache, when a concurrent write lands between its read and its write', async () => {
+		const stale = createPod();
+		const other = createPod();
+		await stale.setRegistrationConfig({mode: 'open', admin_registration_urls_enabled: true});
+		await stale.getRegistrationConfig();
+		await other.setRegistrationConfig({mode: 'approval'});
+		expect(await stale.getRegistrationConfig()).toEqual({mode: 'open', admin_registration_urls_enabled: true});
+		executor.watch(REGISTRATION_CONFIG_KEY);
+		let competed = false;
+		executor.competeBeforeEachWrite(async () => {
+			if (competed) return;
+			competed = true;
+			await executor.writeDirectly(
+				REGISTRATION_CONFIG_KEY,
+				JSON.stringify({mode: 'approval', admin_registration_urls_enabled: false}),
+			);
+		});
+
+		await stale.setRegistrationConfig({mode: 'closed'});
+
+		expect(executor.events).toEqual(['read', 'write rejected', 'read', 'write']);
+		expect(await readStoredRegistrationConfig()).toEqual({mode: 'closed', admin_registration_urls_enabled: false});
+	});
+
+	it('fails loudly and writes nothing once every attempt has lost the race', async () => {
+		const pod = createPod();
+		await pod.setRegistrationConfig({mode: 'open', admin_registration_urls_enabled: true});
+		executor.watch(REGISTRATION_CONFIG_KEY);
+		let competingWrites = 0;
+		executor.competeBeforeEachWrite(async () => {
+			competingWrites++;
+			await executor.writeDirectly(
+				REGISTRATION_CONFIG_KEY,
+				JSON.stringify({mode: 'approval', admin_registration_urls_enabled: competingWrites % 2 === 0}),
+			);
+		});
+
+		const write = pod.setRegistrationConfig({mode: 'closed'});
+
+		await expect(write).rejects.toBeInstanceOf(InstanceConfigWriteConflictError);
+		await expect(write).rejects.toMatchObject({
+			status: 409,
+			code: 'CONFLICT',
+			message: expect.stringContaining(REGISTRATION_CONFIG_KEY),
+		});
+		expect(executor.events.filter((event) => event === 'write rejected')).toHaveLength(INSTANCE_CONFIG_WRITE_ATTEMPTS);
+		expect(executor.events).not.toContain('write');
+		expect(await readStoredRegistrationConfig()).toEqual({
+			mode: 'approval',
+			admin_registration_urls_enabled: INSTANCE_CONFIG_WRITE_ATTEMPTS % 2 === 0,
+		});
+	});
+
+	it('keeps a pending registration another pod added while this pod held a stale list', async () => {
+		const first = createPod();
+		const second = createPod();
+		await first.getPendingRegistrations();
+		await second.getPendingRegistrations();
+
+		await first.addPendingRegistration(pendingRegistration('1400000000000000011'));
+		await second.addPendingRegistration(pendingRegistration('1400000000000000012'));
+
+		const listed = await createPod().getPendingRegistrations();
+		expect(listed.map((entry) => entry.user_id)).toEqual(['1400000000000000011', '1400000000000000012']);
+	});
+
+	it('keeps a pending registration another pod stored and removes it once decided', async () => {
+		const pod = createPod();
+		await executor.writeDirectly(
+			REGISTRATION_PENDING_APPROVALS_KEY,
+			JSON.stringify([pendingRegistration('1400000000000000021')]),
+		);
+		await pod.addPendingRegistration(pendingRegistration('1400000000000000022'));
+
+		expect((await createPod().getPendingRegistrations()).map((entry) => entry.user_id)).toEqual([
+			'1400000000000000021',
+			'1400000000000000022',
+		]);
+
+		await pod.removePendingRegistration('1400000000000000021');
+		await pod.removePendingRegistration('1400000000000000022');
+
+		expect(await createPod().getPendingRegistrations()).toEqual([]);
+		expect(await executor.readDirectly(REGISTRATION_PENDING_APPROVALS_KEY)).toBe('[]');
+	});
+
+	it('keeps a registration URL another pod created while this pod held a stale list', async () => {
+		const first = createPod();
+		const second = createPod();
+		await first.getRegistrationUrls();
+		await second.getRegistrationUrls();
+
+		const created = [
+			await first.createRegistrationUrl(registrationUrlParams(null)),
+			await second.createRegistrationUrl(registrationUrlParams(null)),
+		];
+
+		const listed = await createPod().getRegistrationUrlsForAdmin();
+		expect(listed.map((url) => url.id).toSorted()).toEqual(created.map((entry) => entry.registrationUrl.id).toSorted());
+	});
+
+	it('refuses a registration URL another pod revoked while this pod held a stale list', async () => {
+		const admin = createPod();
+		const signup = createPod();
+		const {code, registrationUrl} = await admin.createRegistrationUrl(registrationUrlParams(null));
+		expect(await signup.resolveRegistrationUrlCode(code)).not.toBeNull();
+
+		await admin.revokeRegistrationUrl(registrationUrl.id);
+
+		await expect(signup.resolveRegistrationUrlCode(code)).resolves.toBeNull();
+		await expect(signup.claimRegistrationUrlUse(registrationUrl.id, '1400000000000000501')).resolves.toBeNull();
+		const [listed] = await createPod().getRegistrationUrlsForAdmin();
+		expect(listed?.use_count).toBe(0);
+	});
+
+	it('admits a registration URL another pod created while this pod held a stale list', async () => {
+		const admin = createPod();
+		const signup = createPod();
+		await signup.getRegistrationUrls();
+
+		const {code, registrationUrl} = await admin.createRegistrationUrl(registrationUrlParams(1));
+
+		await expect(signup.resolveRegistrationUrlCode(code)).resolves.toMatchObject({
+			id: registrationUrl.id,
+			approval_required: false,
+		});
+		await expect(signup.claimRegistrationUrlUse(registrationUrl.id, '1400000000000000601')).resolves.not.toBeNull();
+		const [listed] = await createPod().getRegistrationUrlsForAdmin();
+		expect(listed?.use_count).toBe(1);
+	});
+
+	it('never seats more signups than max_uses when pods claim the same registration URL at once', async () => {
+		const pods = [createPod(), createPod(), createPod()];
+		const {code} = await pods[0]!.createRegistrationUrl(registrationUrlParams(2));
+		const registrationUrl = await pods[0]!.resolveRegistrationUrlCode(code);
+		if (registrationUrl === null) throw new Error('registration URL did not resolve');
+
+		const claims = await Promise.all(
+			Array.from({length: 6}, (_, index) =>
+				pods[index % pods.length]!.claimRegistrationUrlUse(registrationUrl.id, `14000000000000001${index}0`),
+			),
+		);
+
+		expect(claims.filter((claim) => claim !== null)).toHaveLength(2);
+		const [listed] = await createPod().getRegistrationUrlsForAdmin();
+		expect(listed?.use_count).toBe(2);
+		await expect(createPod().resolveRegistrationUrlCode(code)).resolves.toBeNull();
+	});
+
+	it('refuses a claim whose retry finds the registration URL exhausted, rather than reporting the lost attempt', async () => {
+		const pod = createPod();
+		const {code, registrationUrl} = await pod.createRegistrationUrl(registrationUrlParams(1));
+		expect(await pod.resolveRegistrationUrlCode(code)).not.toBeNull();
+		executor.watch(REGISTRATION_URLS_KEY);
+		let competed = false;
+		executor.competeBeforeEachWrite(async () => {
+			if (competed) return;
+			competed = true;
+			const stored = JSON.parse((await executor.readDirectly(REGISTRATION_URLS_KEY)) ?? 'null') as Array<
+				Record<string, unknown>
+			>;
+			await executor.writeDirectly(
+				REGISTRATION_URLS_KEY,
+				JSON.stringify(
+					stored.map((entry) => ({
+						...entry,
+						use_count: 1,
+						last_used_at: '2026-09-20T00:00:00.000Z',
+						last_used_by_user_id: '1400000000000000901',
+					})),
+				),
+			);
+		});
+
+		await expect(pod.claimRegistrationUrlUse(registrationUrl.id, '1400000000000000902')).resolves.toBeNull();
+
+		expect(executor.events).toEqual(['read', 'write rejected', 'read']);
+		const [listed] = await createPod().getRegistrationUrlsForAdmin();
+		expect(listed).toMatchObject({use_count: 1, last_used_by_user_id: '1400000000000000901'});
+	});
+
+	it('counts concurrent uses of an uncapped registration URL without ever refusing one', async () => {
+		const pods = [createPod(), createPod()];
+		const {code} = await pods[0]!.createRegistrationUrl(registrationUrlParams(null));
+		const registrationUrl = await pods[0]!.resolveRegistrationUrlCode(code);
+		if (registrationUrl === null) throw new Error('registration URL did not resolve');
+
+		const claims = await Promise.all(
+			Array.from({length: 5}, (_, index) =>
+				pods[index % pods.length]!.claimRegistrationUrlUse(registrationUrl.id, `14000000000000002${index}0`),
+			),
+		);
+
+		expect(claims.every((claim) => claim !== null)).toBe(true);
+		const [listed] = await createPod().getRegistrationUrlsForAdmin();
+		expect(listed?.use_count).toBe(5);
+	});
+
+	it('frees a released seat for the next signup', async () => {
+		const pod = createPod();
+		const {code} = await pod.createRegistrationUrl(registrationUrlParams(1));
+		const registrationUrl = await pod.resolveRegistrationUrlCode(code);
+		if (registrationUrl === null) throw new Error('registration URL did not resolve');
+
+		const failedSignup = await pod.claimRegistrationUrlUse(registrationUrl.id, '1400000000000000301');
+		if (failedSignup === null) throw new Error('the first claim was refused');
+		await expect(pod.claimRegistrationUrlUse(registrationUrl.id, '1400000000000000302')).resolves.toBeNull();
+		await pod.releaseRegistrationUrlUse(failedSignup);
+
+		await expect(pod.claimRegistrationUrlUse(registrationUrl.id, '1400000000000000303')).resolves.not.toBeNull();
+		const [listed] = await createPod().getRegistrationUrlsForAdmin();
+		expect(listed).toMatchObject({use_count: 1, last_used_by_user_id: '1400000000000000303'});
+	});
+
+	it('enforces max_uses against the use count already stored in the blob', async () => {
+		const pod = createPod();
+		const id = 'b3c4f0b2-8a6e-4c41-9f55-3f0c2a7d1e91';
+		await executor.writeDirectly(
+			REGISTRATION_URLS_KEY,
+			JSON.stringify([
+				{
+					id,
+					label: 'Issued earlier',
+					code_hash: createHash('sha256').update(id).digest('hex'),
+					created_by_user_id: '1400000000000000001',
+					created_at: '2026-09-01T00:00:00.000Z',
+					expires_at: null,
+					max_uses: 3,
+					use_count: 2,
+					revoked_at: null,
+					approval_required: true,
+					last_used_at: '2026-09-02T00:00:00.000Z',
+					last_used_by_user_id: '1400000000000000002',
+				},
+			]),
+		);
+
+		expect(await pod.getRegistrationUrlsForAdmin()).toEqual([
+			expect.objectContaining({
+				id,
+				use_count: 2,
+				max_uses: 3,
+				approval_required: true,
+				last_used_at: '2026-09-02T00:00:00.000Z',
+				last_used_by_user_id: '1400000000000000002',
+			}),
+		]);
+		const registrationUrl = await pod.resolveRegistrationUrlCode(id);
+		if (registrationUrl === null) throw new Error('stored registration URL did not resolve');
+		expect(registrationUrl).toMatchObject({id, approval_required: true});
+
+		await expect(pod.claimRegistrationUrlUse(registrationUrl.id, '1400000000000000401')).resolves.not.toBeNull();
+		await expect(pod.claimRegistrationUrlUse(registrationUrl.id, '1400000000000000402')).resolves.toBeNull();
+
+		const [listed] = await createPod().getRegistrationUrlsForAdmin();
+		expect(listed).toMatchObject({use_count: 3, max_uses: 3, last_used_by_user_id: '1400000000000000401'});
+		await expect(pod.resolveRegistrationUrlCode(id)).resolves.toBeNull();
+		expect(JSON.parse((await executor.readDirectly(REGISTRATION_URLS_KEY)) ?? 'null')[0]).toMatchObject({
+			use_count: 3,
+			max_uses: 3,
+		});
+	});
+
+	it('keeps an SSO field another pod changed while this pod held a stale snapshot', async () => {
+		const first = createPod();
+		const second = createPod();
+		await first.getSsoConfig();
+		await second.getSsoConfig();
+
+		await first.setSsoConfig({displayName: 'Set by the first pod'});
+		await second.setSsoConfig({clientId: 'set-by-the-second-pod'});
+
+		expect(await createPod().getSsoConfig()).toMatchObject({
+			displayName: 'Set by the first pod',
+			clientId: 'set-by-the-second-pod',
+		});
+	});
+
+	it('leaves an SSO row alone when another pod wrote it between this pod reading and writing it', async () => {
+		const pod = createPod();
+		await pod.getSsoConfig();
+		executor.watch('sso_enforced');
+		let competed = false;
+		executor.competeBeforeEachWrite(async () => {
+			if (competed) return;
+			competed = true;
+			await executor.writeDirectly('sso_enforced', 'true');
+		});
+
+		await pod.setSsoConfig({displayName: 'Only the display name'});
+
+		expect(await executor.readDirectly('sso_enforced')).toBe('true');
+		expect(await executor.readDirectly('sso_display_name')).toBe('Only the display name');
+	});
+}
+
+function pendingRegistration(userId: string) {
+	return {
+		user_id: userId,
+		username: `pending_${userId.slice(-3)}`,
+		discriminator: 1,
+		global_name: null,
+		email: `${userId}@example.com`,
+		requested_at: `2026-09-01T00:00:${userId.slice(-2)}.000Z`,
+		registration_url_id: null,
+		client_ip: '127.0.0.1',
+	};
+}
+
+function registrationUrlParams(maxUses: number | null) {
+	return {
+		label: maxUses === null ? 'Uncapped' : `Capped at ${maxUses}`,
+		createdByUserId: '1400000000000000001',
+		expiresAt: null,
+		maxUses,
+		approvalRequired: false,
+	};
+}
+
+describe('InstanceConfigRepository concurrent writes', () => {
+	describe('in memory', () => {
+		describeConcurrentInstanceConfigWrites(async () => new InMemoryCassandraQueryExecutor());
+	});
+
+	describe.skipIf(!dockerAvailable)('on postgres', () => {
+		let client: IPostgresClient;
+
+		beforeAll(async () => {
+			const port = await freePort();
+			startDockerContainer([
+				'run',
+				'-d',
+				'--name',
+				POSTGRES_CONTAINER,
+				'-e',
+				'POSTGRES_USER=fluxer',
+				'-e',
+				'POSTGRES_PASSWORD=fluxer',
+				'-e',
+				'POSTGRES_DB=fluxer',
+				'-p',
+				`127.0.0.1:${port}:5432`,
+				'postgres:16-alpine',
+				'-c',
+				'fsync=off',
+			]);
+			let ready = false;
+			for (let attempt = 0; attempt < 180 && !ready; attempt += 1) {
+				await sleep(500);
+				const probe = spawnSync('docker', ['exec', POSTGRES_CONTAINER, 'pg_isready', '-U', 'fluxer', '-d', 'fluxer'], {
+					stdio: 'ignore',
+				});
+				if (probe.status !== 0) continue;
+				try {
+					await initPostgres({
+						url: `postgres://fluxer:[email protected]:${port}/fluxer`,
+						maxConnections: 4,
+						kvTable: POSTGRES_KV_TABLE,
+					});
+					await getDefaultPostgresClient().query('SELECT 1');
+					ready = true;
+				} catch {
+					await shutdownPostgres().catch(() => {});
+				}
+			}
+			if (!ready) throw new Error('postgres never came up');
+			client = getDefaultPostgresClient();
+			await ensurePostgresKvSchema(client);
+		}, 900_000);
+
+		afterAll(async () => {
+			setCassandraQueryExecutorForTesting(new InMemoryCassandraQueryExecutor());
+			await shutdownPostgres().catch(() => {});
+			spawnSync('docker', ['rm', '-f', POSTGRES_CONTAINER], {stdio: 'ignore'});
+		});
+
+		describeConcurrentInstanceConfigWrites(async () => {
+			await client.query(`DELETE FROM ${POSTGRES_KV_TABLE}`);
+			return new PostgresKvQueryExecutor(client);
+		});
+	});
+});

fluxer_api/src/api/instance/InstanceConfigRepository.ts

@@ -3,7 +3,8 @@
 import crypto from 'node:crypto';
 import {Config} from '@app/api/Config';
 import type {APIConfig, BlueskyOAuthConfig, BlueskyOAuthKeyConfig} from '@app/api/config/APIConfig';
-import {fetchMany, fetchOne, upsertOne} from '@app/api/database/CassandraQueryExecution';
+import {executeConditional, fetchMany, fetchOne, upsertOne} from '@app/api/database/CassandraQueryExecution';
+import {Db, type PreparedQuery} from '@app/api/database/CassandraTypes';
 import type {InstanceConfigurationRow} from '@app/api/database/types/InstanceConfigTypes';
 import {
 	getDefaultDateOfBirthCollection,
@@ -17,6 +18,9 @@ import {resolveDeferredPhoneGateEnabled, setCachedDeferredPhoneGateEnabled} from
 import {InstanceConfiguration} from '@app/api/Tables';
 import {DEFAULT_DECAY_CONSTANTS, DEFAULT_RENEWAL_CONSTANTS} from '@app/api/utils/AttachmentDecay';
 import {isJsonRecord} from '@app/api/utils/JsonBoundaryUtils';
+import {APIErrorCodes} from '@fluxer/constants/src/ApiErrorCodes';
+import {ConflictError} from '@fluxer/errors/src/domains/core/ConflictError';
+import {ServiceUnavailableError} from '@fluxer/errors/src/domains/core/ServiceUnavailableError';
 import type {LimitConfigSnapshot} from '@fluxer/limits/src/LimitTypes';
 import {
 	InstanceConfigResponse,
@@ -28,6 +32,10 @@ import {
 	type GatewayRolloutConfig,
 	GatewayRolloutConfigSchema,
 } from '@fluxer/schema/src/domains/admin/GatewayRolloutSchemas';
+import {
+	type PushServiceDeliveryConfig,
+	PushServiceDeliveryConfigSchema,
+} from '@fluxer/schema/src/domains/admin/PushServiceDeliverySchemas';
 import {
 	type ScreenShareDeliveryConfig,
 	ScreenShareDeliveryConfigSchema,
@@ -59,6 +67,7 @@ import {z} from 'zod';
 const GATEWAY_ROLLOUT_CONFIG_KEY = 'gateway_rollout_config';
 const VOICE_NOISE_SUPPRESSION_CONFIG_KEY = 'voice_noise_suppression_config';
 const SCREEN_SHARE_DELIVERY_CONFIG_KEY = 'screen_share_delivery_config';
+const PUSH_SERVICE_DELIVERY_CONFIG_KEY = 'push_service_delivery_config';
 const EXPERIMENT_DELIVERY_CONFIG_KEY = 'experiment_delivery_config';
 const REGISTRATION_CONFIG_KEY = 'registration_config';
 const REGISTRATION_URLS_KEY = 'registration_urls';
@@ -72,6 +81,22 @@ const INSTANCE_MEDIA_CONFIG_KEY = 'instance_media_config';
 export const INSTANCE_CONFIG_REFRESH_CHANNEL = 'instance-config-refresh';
 export const REGISTRATION_PENDING_APPROVAL_TRAIT = 'registration_pending_approval';
 export const REGISTRATION_REJECTED_TRAIT = 'registration_rejected';
+export const INSTANCE_CONFIG_WRITE_ATTEMPTS = 5;
+
+export class InstanceConfigWriteConflictError extends ConflictError {
+	constructor(key: string) {
+		super({
+			code: APIErrorCodes.CONFLICT,
+			message: `Instance config "${key}" changed concurrently on all ${INSTANCE_CONFIG_WRITE_ATTEMPTS} write attempts. Nothing was written. Retry the change.`,
+		});
+		this.name = 'InstanceConfigWriteConflictError';
+	}
+}
+
+interface StoredValueUpdate<T> {
+	value: string | null;
+	result: T;
+}
 
 export type InstanceRegistrationConfig = InstanceRegistration;
 
@@ -277,6 +302,11 @@ export interface InstanceRegistrationUrl extends RegistrationUrlResponse {
 type InstanceRegistrationUrlPublic = RegistrationUrlResponse;
 type InstancePendingRegistration = PendingRegistrationResponse;
 
+export interface RegistrationUrlClaim {
+	registration_url_id: string;
+	user_id: string;
+}
+
 const DEFAULT_REGISTRATION_CONFIG: InstanceRegistrationConfig = {
 	mode: 'open',
 	admin_registration_urls_enabled: true,
@@ -345,6 +375,7 @@ type StoredConfigSection =
 	| 'gateway rollout'
 	| 'voice noise suppression'
 	| 'screen share delivery'
+	| 'push service delivery'
 	| 'experiment delivery'
 	| 'instance policy'
 	| 'integrations'
@@ -487,6 +518,10 @@ function parseStoredScreenShareDeliveryConfig(raw: string | null): ScreenShareDe
 	return parseStoredConfigOrDefault(ScreenShareDeliveryConfigSchema, raw, 'screen share delivery');
 }
 
+function parseStoredPushServiceDeliveryConfig(raw: string | null): PushServiceDeliveryConfig {
+	return parseStoredConfigOrDefault(PushServiceDeliveryConfigSchema, raw, 'push service delivery');
+}
+
 function parseStoredExperimentDeliveryConfig(raw: string | null): ExperimentDeliveryConfig {
 	return parseStoredConfigOrDefault(ExperimentDeliveryConfigSchema, raw, 'experiment delivery');
 }
@@ -910,6 +945,75 @@ function parseStoredSsoAllowedEmailDomains(raw: string | undefined, log = false)
 	return Array.from(domains).slice(0, MAX_SSO_ALLOWED_DOMAINS);
 }
 
+function readStoredSsoConfig(
+	configs: ReadonlyMap<string, string>,
+	options?: {includeSecret?: boolean},
+): InstanceSsoConfig {
+	const flags = readStoredSsoFlags(configs);
+	const read = (key: string): string | null => {
+		const v = configs.get(key);
+		if (!v) return null;
+		const trimmed = v.trim();
+		return trimmed.length === 0 ? null : trimmed;
+	};
+	const allowedDomains = parseStoredSsoAllowedEmailDomains(configs.get('sso_allowed_domains'));
+	const clientSecret = read('sso_client_secret');
+	return {
+		...flags,
+		displayName: read('sso_display_name'),
+		issuer: read('sso_issuer'),
+		authorizationUrl: read('sso_authorization_url'),
+		tokenUrl: read('sso_token_url'),
+		userInfoUrl: read('sso_userinfo_url'),
+		jwksUrl: read('sso_jwks_url'),
+		clientId: read('sso_client_id'),
+		clientSecret: options?.includeSecret ? clientSecret : undefined,
+		clientSecretSet: Boolean(clientSecret),
+		scope: read('sso_scope'),
+		allowedEmailDomains: allowedDomains,
+		redirectUri: null,
+	};
+}
+
+interface SsoRowWrite {
+	key: string;
+	value: string | undefined;
+	unset: string;
+}
+
+function ssoRow<T>(key: string, value: T | undefined, current: T, format: (value: T) => string): SsoRowWrite {
+	return {key, value: value === undefined ? undefined : format(value), unset: format(current)};
+}
+
+function nextSsoRowValue(row: SsoRowWrite, raw: string | null): string | null {
+	const value = row.value ?? raw ?? row.unset;
+	return value === raw ? null : value;
+}
+
+function formatSsoBoolean(value: boolean): string {
+	return value ? 'true' : 'false';
+}
+
+function formatSsoString(value: string | null): string {
+	return value ?? '';
+}
+
+function formatSsoDomains(value: Array<string>): string {
+	return JSON.stringify(value);
+}
+
+function normalizeSsoAllowedEmailDomainsForWrite(domains: Array<string>, enabled: boolean): Array<string> {
+	try {
+		return normalizeSsoAllowedEmailDomains(domains);
+	} catch (error) {
+		if (enabled) {
+			throw error;
+		}
+		Logger.warn({error}, 'Clearing invalid SSO allowed domain config while SSO is disabled');
+		return [];
+	}
+}
+
 export class InstanceConfigRepository {
 	private readonly kvClient: IKVProvider | null;
 	private configCache: InstanceConfigCache;
@@ -993,6 +1097,57 @@ export class InstanceConfigRepository {
 		);
 	}
 
+	private async updateStoredConfig<T>(key: string, next: (raw: string | null) => T): Promise<T> {
+		const cache = this.configCache;
+		const {result} = await this.compareAndSetStoredValue(cache, key, (raw) => {
+			const config = next(raw);
+			return {value: JSON.stringify(config), result: config};
+		});
+		await this.publishRefresh(cache.sourceId);
+		return result;
+	}
+
+	private async compareAndSetStoredValue<T>(
+		cache: InstanceConfigCache,
+		key: string,
+		next: (raw: string | null) => StoredValueUpdate<T>,
+	): Promise<{result: T; written: boolean}> {
+		await cache.getSnapshot();
+		for (let attempt = 0; attempt < INSTANCE_CONFIG_WRITE_ATTEMPTS; attempt++) {
+			cache.assertActive();
+			const current = await this.fetchConfigForWrite(key);
+			cache.assertActive();
+			const {value, result} = next(current);
+			if (value === null) return {result, written: false};
+			if (await executeConditional(this.compareAndSetConfig(key, current, value))) {
+				cache.update(key, value);
+				return {result, written: true};
+			}
+		}
+		Logger.error(
+			{key, attempts: INSTANCE_CONFIG_WRITE_ATTEMPTS},
+			'Instance config write lost to a concurrent write on every attempt',
+		);
+		throw new InstanceConfigWriteConflictError(key);
+	}
+
+	private compareAndSetConfig(key: string, current: string | null, value: string): PreparedQuery {
+		const updatedAt = new Date();
+		if (current === null) {
+			return InstanceConfiguration.insertIfNotExists({key, value, updated_at: updatedAt});
+		}
+		return InstanceConfiguration.conditionalPatchByPk(
+			{key},
+			{value: Db.set(value), updated_at: Db.set(updatedAt)},
+			{value: current},
+		);
+	}
+
+	private async fetchConfigForWrite(key: string): Promise<string | null> {
+		const [row] = await fetchMany<InstanceConfigurationRow>(FETCH_CONFIG_QUERY, {key}, {consistency: 'serial'});
+		return row?.value ?? null;
+	}
+
 	private async fetchConfigFromDatabase(key: string): Promise<string | null> {
 		const row = await fetchOne<InstanceConfigurationRow>(FETCH_CONFIG_QUERY, {key});
 		return row?.value ?? null;
@@ -1015,6 +1170,7 @@ export class InstanceConfigRepository {
 		);
 		parseStoredVoiceNoiseSuppressionConfig(snapshot.get(VOICE_NOISE_SUPPRESSION_CONFIG_KEY) ?? null);
 		parseStoredScreenShareDeliveryConfig(snapshot.get(SCREEN_SHARE_DELIVERY_CONFIG_KEY) ?? null);
+		parseStoredPushServiceDeliveryConfig(snapshot.get(PUSH_SERVICE_DELIVERY_CONFIG_KEY) ?? null);
 		parseStoredExperimentDeliveryConfig(snapshot.get(EXPERIMENT_DELIVERY_CONFIG_KEY) ?? null);
 		const policy = parseStoredInstancePolicyConfig(snapshot.get(INSTANCE_POLICY_CONFIG_KEY) ?? null);
 		checkStoredConfig('registration', () =>
@@ -1082,8 +1238,12 @@ export class InstanceConfigRepository {
 		return parseStoredGatewayRolloutConfig(raw);
 	}
 
-	async setGatewayRolloutConfig(config: GatewayRolloutConfig): Promise<void> {
-		await this.setConfig(GATEWAY_ROLLOUT_CONFIG_KEY, JSON.stringify(decodeGatewayRolloutConfig(config)));
+	updateGatewayRolloutConfig(
+		update: (current: GatewayRolloutConfig) => GatewayRolloutConfig,
+	): Promise<GatewayRolloutConfig> {
+		return this.updateStoredConfig(GATEWAY_ROLLOUT_CONFIG_KEY, (raw) =>
+			decodeGatewayRolloutConfig(update(parseStoredGatewayRolloutConfig(raw))),
+		);
 	}
 
 	async getVoiceNoiseSuppressionConfig(): Promise<VoiceNoiseSuppressionConfig> {
@@ -1092,8 +1252,19 @@ export class InstanceConfigRepository {
 	}
 
 	async setVoiceNoiseSuppressionConfig(config: VoiceNoiseSuppressionConfig): Promise<void> {
-		const validated = validateStoredConfig(VoiceNoiseSuppressionConfigSchema, config, 'voice noise suppression');
-		await this.setConfig(VOICE_NOISE_SUPPRESSION_CONFIG_KEY, JSON.stringify(validated));
+		await this.updateVoiceNoiseSuppressionConfig(() => config);
+	}
+
+	updateVoiceNoiseSuppressionConfig(
+		update: (current: VoiceNoiseSuppressionConfig) => VoiceNoiseSuppressionConfig,
+	): Promise<VoiceNoiseSuppressionConfig> {
+		return this.updateStoredConfig(VOICE_NOISE_SUPPRESSION_CONFIG_KEY, (raw) =>
+			validateStoredConfig(
+				VoiceNoiseSuppressionConfigSchema,
+				update(parseStoredVoiceNoiseSuppressionConfig(raw)),
+				'voice noise suppression',
+			),
+		);
 	}
 
 	async getScreenShareDeliveryConfig(): Promise<ScreenShareDeliveryConfig> {
@@ -1102,8 +1273,36 @@ export class InstanceConfigRepository {
 	}
 
 	async setScreenShareDeliveryConfig(config: ScreenShareDeliveryConfig): Promise<void> {
-		const validated = validateStoredConfig(ScreenShareDeliveryConfigSchema, config, 'screen share delivery');
-		await this.setConfig(SCREEN_SHARE_DELIVERY_CONFIG_KEY, JSON.stringify(validated));
+		await this.updateScreenShareDeliveryConfig(() => config);
+	}
+
+	updateScreenShareDeliveryConfig(
+		update: (current: ScreenShareDeliveryConfig) => ScreenShareDeliveryConfig,
+	): Promise<ScreenShareDeliveryConfig> {
+		return this.updateStoredConfig(SCREEN_SHARE_DELIVERY_CONFIG_KEY, (raw) =>
+			validateStoredConfig(
+				ScreenShareDeliveryConfigSchema,
+				update(parseStoredScreenShareDeliveryConfig(raw)),
+				'screen share delivery',
+			),
+		);
+	}
+
+	async getPushServiceDeliveryConfig(): Promise<PushServiceDeliveryConfig> {
+		const raw = await this.getConfig(PUSH_SERVICE_DELIVERY_CONFIG_KEY);
+		return parseStoredPushServiceDeliveryConfig(raw);
+	}
+
+	updatePushServiceDeliveryConfig(
+		update: (current: PushServiceDeliveryConfig) => PushServiceDeliveryConfig,
+	): Promise<PushServiceDeliveryConfig> {
+		return this.updateStoredConfig(PUSH_SERVICE_DELIVERY_CONFIG_KEY, (raw) =>
+			validateStoredConfig(
+				PushServiceDeliveryConfigSchema,
+				update(parseStoredPushServiceDeliveryConfig(raw)),
+				'push service delivery',
+			),
+		);
 	}
 
 	async getExperimentDeliveryConfig(): Promise<ExperimentDeliveryConfig> {
@@ -1112,8 +1311,19 @@ export class InstanceConfigRepository {
 	}
 
 	async setExperimentDeliveryConfig(config: ExperimentDeliveryConfig): Promise<void> {
-		const validated = validateStoredConfig(ExperimentDeliveryConfigSchema, config, 'experiment delivery');
-		await this.setConfig(EXPERIMENT_DELIVERY_CONFIG_KEY, JSON.stringify(validated));
+		await this.updateExperimentDeliveryConfig(() => config);
+	}
+
+	updateExperimentDeliveryConfig(
+		update: (current: ExperimentDeliveryConfig) => ExperimentDeliveryConfig,
+	): Promise<ExperimentDeliveryConfig> {
+		return this.updateStoredConfig(EXPERIMENT_DELIVERY_CONFIG_KEY, (raw) =>
+			validateStoredConfig(
+				ExperimentDeliveryConfigSchema,
+				update(parseStoredExperimentDeliveryConfig(raw)),
+				'experiment delivery',
+			),
+		);
 	}
 
 	async readLimitConfigInputs(): Promise<LimitConfigInputs> {
@@ -1149,26 +1359,27 @@ export class InstanceConfigRepository {
 		legal?: Partial<InstanceAppPublicConfig['legal']>;
 		registration?: Partial<InstanceAppPublicConfig['registration']>;
 	}): Promise<InstanceAppPublicConfig> {
-		const current = await this.getAppPublicConfig();
-		const next = decodeAppPublicConfig({
-			branding: {
-				...current.branding,
-				...(config.branding ?? {}),
-			},
-			setup: {
-				...current.setup,
-				...(config.setup ?? {}),
-			},
-			legal: {
-				...current.legal,
-				...(config.legal ?? {}),
-			},
-			registration: {
-				...current.registration,
-				...(config.registration ?? {}),
-			},
+		const next = await this.updateStoredConfig(APP_PUBLIC_CONFIG_KEY, (raw) => {
+			const current = parseStoredAppPublicConfig(raw);
+			return decodeAppPublicConfig({
+				branding: {
+					...current.branding,
+					...(config.branding ?? {}),
+				},
+				setup: {
+					...current.setup,
+					...(config.setup ?? {}),
+				},
+				legal: {
+					...current.legal,
+					...(config.legal ?? {}),
+				},
+				registration: {
+					...current.registration,
+					...(config.registration ?? {}),
+				},
+			});
 		});
-		await this.setConfig(APP_PUBLIC_CONFIG_KEY, JSON.stringify(next));
 		setCachedDateOfBirthCollection(next.registration.collect_date_of_birth);
 		return next;
 	}
@@ -1188,10 +1399,21 @@ export class InstanceConfigRepository {
 		return parseStoredInstancePolicyConfig(raw);
 	}
 
-	async setInstancePolicyConfig(config: Partial<InstancePolicyConfig>): Promise<InstancePolicyConfig> {
-		const current = await this.readStoredInstancePolicyConfig();
-		const next = decodeInstancePolicyConfig({...current, ...config});
-		await this.setConfig(INSTANCE_POLICY_CONFIG_KEY, JSON.stringify(next));
+	setInstancePolicyConfig(config: Partial<InstancePolicyConfig>): Promise<InstancePolicyConfig> {
+		return this.updateInstancePolicyConfig(() => config);
+	}
+
+	async updateInstancePolicyConfig(
+		plan: (current: InstancePolicyConfig) => Partial<InstancePolicyConfig>,
+	): Promise<InstancePolicyConfig> {
+		const cache = this.configCache;
+		const {result: next, written} = await this.compareAndSetStoredValue(cache, INSTANCE_POLICY_CONFIG_KEY, (raw) => {
+			const current = parseStoredInstancePolicyConfig(raw);
+			const patch = plan(current);
+			const config = decodeInstancePolicyConfig({...current, ...patch});
+			return {value: Object.keys(patch).length === 0 ? null : JSON.stringify(config), result: config};
+		});
+		if (written) await this.publishRefresh(cache.sourceId);
 		setCachedDeferredPhoneGateEnabled(resolveDeferredPhoneGateEnabled(next));
 		return next;
 	}
@@ -1201,37 +1423,37 @@ export class InstanceConfigRepository {
 		return parseStoredInstanceIntegrationsConfig(raw);
 	}
 
-	async setInstanceIntegrationsConfig(config: InstanceIntegrationsConfigPatch): Promise<InstanceIntegrationsConfig> {
-		const current = await this.getInstanceIntegrationsConfig();
-		const next = decodeInstanceIntegrationsConfig({
-			gif: {
-				...current.gif,
-				...(config.gif ?? {}),
-			},
-			youtube: {
-				...current.youtube,
-				...(config.youtube ?? {}),
-			},
-			captcha: {
-				...current.captcha,
-				...(config.captcha ?? {}),
-			},
-			email: {
-				...current.email,
-				...(config.email ?? {}),
-				smtp: {
-					...current.email.smtp,
-					...(config.email?.smtp ?? {}),
+	setInstanceIntegrationsConfig(config: InstanceIntegrationsConfigPatch): Promise<InstanceIntegrationsConfig> {
+		return this.updateStoredConfig(INSTANCE_INTEGRATIONS_CONFIG_KEY, (raw) => {
+			const current = parseStoredInstanceIntegrationsConfig(raw);
+			return decodeInstanceIntegrationsConfig({
+				gif: {
+					...current.gif,
+					...(config.gif ?? {}),
 				},
-			},
-			bluesky: {
-				...current.bluesky,
-				...(config.bluesky ?? {}),
-				keys: config.bluesky?.keys ?? current.bluesky.keys,
-			},
+				youtube: {
+					...current.youtube,
+					...(config.youtube ?? {}),
+				},
+				captcha: {
+					...current.captcha,
+					...(config.captcha ?? {}),
+				},
+				email: {
+					...current.email,
+					...(config.email ?? {}),
+					smtp: {
+						...current.email.smtp,
+						...(config.email?.smtp ?? {}),
+					},
+				},
+				bluesky: {
+					...current.bluesky,
+					...(config.bluesky ?? {}),
+					keys: config.bluesky?.keys ?? current.bluesky.keys,
+				},
+			});
 		});
-		await this.setConfig(INSTANCE_INTEGRATIONS_CONFIG_KEY, JSON.stringify(next));
-		return next;
 	}
 
 	async getInstanceMediaConfig(): Promise<InstanceMediaConfig> {
@@ -1239,16 +1461,16 @@ export class InstanceConfigRepository {
 		return parseStoredInstanceMediaConfig(raw);
 	}
 
-	async setInstanceMediaConfig(config: InstanceMediaConfigPatch): Promise<InstanceMediaConfig> {
-		const current = await this.getInstanceMediaConfig();
-		const next = decodeInstanceMediaConfig({
-			attachment_decay: {
-				...current.attachment_decay,
-				...(config.attachment_decay ?? {}),
-			},
+	setInstanceMediaConfig(config: InstanceMediaConfigPatch): Promise<InstanceMediaConfig> {
+		return this.updateStoredConfig(INSTANCE_MEDIA_CONFIG_KEY, (raw) => {
+			const current = parseStoredInstanceMediaConfig(raw);
+			return decodeInstanceMediaConfig({
+				attachment_decay: {
+					...current.attachment_decay,
+					...(config.attachment_decay ?? {}),
+				},
+			});
 		});
-		await this.setConfig(INSTANCE_MEDIA_CONFIG_KEY, JSON.stringify(next));
-		return next;
 	}
 
 	async getEffectiveAttachmentDecayConfig(): Promise<InstanceAttachmentDecayEffectiveConfig> {
@@ -1485,15 +1707,15 @@ export class InstanceConfigRepository {
 		return parseStoredRegistrationConfig(raw);
 	}
 
-	async setRegistrationConfig(config: Partial<InstanceRegistrationConfig>): Promise<InstanceRegistrationConfig> {
-		const current = await this.getRegistrationConfig();
-		const next = decodeRegistrationConfig({
-			mode: config.mode ?? current.mode,
-			admin_registration_urls_enabled:
-				config.admin_registration_urls_enabled ?? current.admin_registration_urls_enabled,
+	setRegistrationConfig(config: Partial<InstanceRegistrationConfig>): Promise<InstanceRegistrationConfig> {
+		return this.updateStoredConfig(REGISTRATION_CONFIG_KEY, (raw) => {
+			const current = parseStoredRegistrationConfig(raw);
+			return decodeRegistrationConfig({
+				mode: config.mode ?? current.mode,
+				admin_registration_urls_enabled:
+					config.admin_registration_urls_enabled ?? current.admin_registration_urls_enabled,
+			});
 		});
-		await this.setConfig(REGISTRATION_CONFIG_KEY, JSON.stringify(next));
-		return next;
 	}
 
 	async getRegistrationPublicConfig(): Promise<InstanceRegistrationConfig> {
@@ -1534,16 +1756,20 @@ export class InstanceConfigRepository {
 			last_used_at: null,
 			last_used_by_user_id: null,
 		};
-		const registrationUrls = await this.getRegistrationUrls();
-		await this.setRegistrationUrls([registrationUrl, ...registrationUrls]);
+		await this.updateStoredConfig(REGISTRATION_URLS_KEY, (raw) =>
+			validateStoredCollection(
+				StoredRegistrationUrlSchema,
+				[registrationUrl, ...parseStoredCollection(StoredRegistrationUrlSchema, raw, 'registration URLs')],
+				'registration URLs',
+			),
+		);
 		return {registrationUrl: redactRegistrationUrl(registrationUrl), code};
 	}
 
 	async revokeRegistrationUrl(id: string): Promise<void> {
 		const now = new Date().toISOString();
-		const registrationUrls = await this.getRegistrationUrls();
-		await this.setRegistrationUrls(
-			registrationUrls.map((registrationUrl) =>
+		await this.updateStoredConfig(REGISTRATION_URLS_KEY, (raw) =>
+			parseStoredCollection(StoredRegistrationUrlSchema, raw, 'registration URLs').map((registrationUrl) =>
 				registrationUrl.id === id && !registrationUrl.revoked_at
 					? {...registrationUrl, revoked_at: now}
 					: registrationUrl,
@@ -1556,9 +1782,8 @@ export class InstanceConfigRepository {
 		if (!normalizedCode) return null;
 		const hash = this.hashRegistrationUrlCode(normalizedCode);
 		const now = new Date();
-		const registrationUrls = await this.getRegistrationUrls();
 		return (
-			registrationUrls.find(
+			(await this.fetchRegistrationUrlDefinitions()).find(
 				(registrationUrl) =>
 					(registrationUrl.id === normalizedCode || registrationUrl.code_hash === hash) &&
 					isRegistrationUrlUsable(registrationUrl, now),
@@ -1566,21 +1791,68 @@ export class InstanceConfigRepository {
 		);
 	}
 
-	async recordRegistrationUrlUse(id: string, userId: string): Promise<void> {
-		const now = new Date().toISOString();
-		const registrationUrls = await this.getRegistrationUrls();
-		await this.setRegistrationUrls(
-			registrationUrls.map((registrationUrl) =>
-				registrationUrl.id === id
-					? {
-							...registrationUrl,
-							use_count: registrationUrl.use_count + 1,
-							last_used_at: now,
-							last_used_by_user_id: userId,
-						}
-					: registrationUrl,
-			),
-		);
+	async claimRegistrationUrlUse(registrationUrlId: string, userId: string): Promise<RegistrationUrlClaim | null> {
+		const cache = this.configCache;
+		let claimed: {result: RegistrationUrlClaim | null; written: boolean};
+		try {
+			claimed = await this.compareAndSetStoredValue<RegistrationUrlClaim | null>(
+				cache,
+				REGISTRATION_URLS_KEY,
+				(raw) => {
+					const registrationUrls = parseStoredCollection(StoredRegistrationUrlSchema, raw, 'registration URLs');
+					const now = new Date();
+					const claimable = registrationUrls.find(
+						(registrationUrl) =>
+							registrationUrl.id === registrationUrlId && isRegistrationUrlUsable(registrationUrl, now),
+					);
+					if (!claimable) return {value: null, result: null};
+					const next = registrationUrls.map((registrationUrl) =>
+						registrationUrl === claimable
+							? {
+									...registrationUrl,
+									use_count: registrationUrl.use_count + 1,
+									last_used_at: now.toISOString(),
+									last_used_by_user_id: userId,
+								}
+							: registrationUrl,
+					);
+					return {
+						value: JSON.stringify(validateStoredCollection(StoredRegistrationUrlSchema, next, 'registration URLs')),
+						result: {registration_url_id: registrationUrlId, user_id: userId},
+					};
+				},
+			);
+		} catch (error) {
+			if (error instanceof InstanceConfigWriteConflictError) throw new ServiceUnavailableError();
+			throw error;
+		}
+		if (claimed.written) await this.publishRefresh(cache.sourceId);
+		return claimed.result;
+	}
+
+	async releaseRegistrationUrlUse(claim: RegistrationUrlClaim): Promise<void> {
+		const cache = this.configCache;
+		try {
+			const {written} = await this.compareAndSetStoredValue<null>(cache, REGISTRATION_URLS_KEY, (raw) => {
+				const registrationUrls = parseStoredCollection(StoredRegistrationUrlSchema, raw, 'registration URLs');
+				const released = registrationUrls.find(
+					(registrationUrl) => registrationUrl.id === claim.registration_url_id && registrationUrl.use_count > 0,
+				);
+				if (!released) return {value: null, result: null};
+				const next = registrationUrls.map((registrationUrl) =>
+					registrationUrl === released
+						? {...registrationUrl, use_count: registrationUrl.use_count - 1}
+						: registrationUrl,
+				);
+				return {value: JSON.stringify(next), result: null};
+			});
+			if (written) await this.publishRefresh(cache.sourceId);
+		} catch (error) {
+			Logger.warn(
+				{registrationUrlId: claim.registration_url_id, userId: claim.user_id, error},
+				'Releasing a registration URL use failed',
+			);
+		}
 	}
 
 	async getPendingRegistrations(): Promise<Array<InstancePendingRegistration>> {
@@ -1591,104 +1863,82 @@ export class InstanceConfigRepository {
 	}
 
 	async addPendingRegistration(pendingRegistration: InstancePendingRegistration): Promise<void> {
-		const pendingRegistrations = await this.getPendingRegistrations();
-		const next = [
-			pendingRegistration,
-			...pendingRegistrations.filter((entry) => entry.user_id !== pendingRegistration.user_id),
-		];
-		await this.setPendingRegistrations(next);
+		await this.updateStoredConfig(REGISTRATION_PENDING_APPROVALS_KEY, (raw) =>
+			validateStoredCollection(
+				StoredPendingRegistrationSchema,
+				[
+					pendingRegistration,
+					...parseStoredCollection(StoredPendingRegistrationSchema, raw, 'pending registrations').filter(
+						(entry) => entry.user_id !== pendingRegistration.user_id,
+					),
+				],
+				'pending registrations',
+			),
+		);
 	}
 
 	async removePendingRegistration(userId: string): Promise<void> {
-		const pendingRegistrations = await this.getPendingRegistrations();
-		await this.setPendingRegistrations(pendingRegistrations.filter((entry) => entry.user_id !== userId));
+		await this.updateStoredConfig(REGISTRATION_PENDING_APPROVALS_KEY, (raw) =>
+			parseStoredCollection(StoredPendingRegistrationSchema, raw, 'pending registrations').filter(
+				(entry) => entry.user_id !== userId,
+			),
+		);
 	}
 
 	async getSsoConfig(options?: {includeSecret?: boolean}): Promise<InstanceSsoConfig> {
-		const configs = await this.getAllConfigs();
-		const flags = readStoredSsoFlags(configs);
-		const read = (key: string): string | null => {
-			const v = configs.get(key);
-			if (!v) return null;
-			const trimmed = v.trim();
-			return trimmed.length === 0 ? null : trimmed;
-		};
-		const allowedDomains = parseStoredSsoAllowedEmailDomains(configs.get('sso_allowed_domains'));
-		const clientSecret = read('sso_client_secret');
-		return {
-			...flags,
-			displayName: read('sso_display_name'),
-			issuer: read('sso_issuer'),
-			authorizationUrl: read('sso_authorization_url'),
-			tokenUrl: read('sso_token_url'),
-			userInfoUrl: read('sso_userinfo_url'),
-			jwksUrl: read('sso_jwks_url'),
-			clientId: read('sso_client_id'),
-			clientSecret: options?.includeSecret ? clientSecret : undefined,
-			clientSecretSet: Boolean(clientSecret),
-			scope: read('sso_scope'),
-			allowedEmailDomains: allowedDomains,
-			redirectUri: null,
-		};
+		return readStoredSsoConfig(await this.getAllConfigs(), options);
 	}
 
 	async setSsoConfig(config: Partial<InstanceSsoConfig>): Promise<InstanceSsoConfig> {
-		const current = await this.getSsoConfig({includeSecret: true});
-		const definedConfig = Object.fromEntries(
-			Object.entries(config).filter(([, value]) => value !== undefined),
-		) as Partial<InstanceSsoConfig>;
-		const next: InstanceSsoConfig = {
-			...current,
-			...definedConfig,
-			clientSecret: config.clientSecret !== undefined ? config.clientSecret : current.clientSecret,
-		};
-		if (config.enabled === true && config.enforced === undefined && !current.enabled) {
-			next.enforced = true;
-		}
-		let allowedEmailDomains: Array<string>;
-		try {
-			allowedEmailDomains = normalizeSsoAllowedEmailDomains(next.allowedEmailDomains);
-		} catch (error) {
-			if (next.enabled) {
-				throw error;
-			}
-			Logger.warn({error}, 'Clearing invalid SSO allowed domain config while SSO is disabled');
-			allowedEmailDomains = [];
-		}
-		const entries: Array<[string, string]> = [
-			['sso_enabled', next.enabled ? 'true' : 'false'],
-			['sso_enforced', next.enforced ? 'true' : 'false'],
-			['sso_display_name', next.displayName ?? ''],
-			['sso_issuer', next.issuer ?? ''],
-			['sso_authorization_url', next.authorizationUrl ?? ''],
-			['sso_token_url', next.tokenUrl ?? ''],
-			['sso_userinfo_url', next.userInfoUrl ?? ''],
-			['sso_jwks_url', next.jwksUrl ?? ''],
-			['sso_client_id', next.clientId ?? ''],
-			['sso_scope', next.scope ?? ''],
-			['sso_allowed_domains', JSON.stringify(allowedEmailDomains)],
-			['sso_auto_provision', next.autoProvision ? 'true' : 'false'],
-			['sso_redirect_uri', ''],
+		const configs = await this.getAllConfigs();
+		const current = readStoredSsoConfig(configs, {includeSecret: true});
+		const enabled = config.enabled ?? current.enabled;
+		const allowedEmailDomains =
+			config.allowedEmailDomains === undefined
+				? undefined
+				: normalizeSsoAllowedEmailDomainsForWrite(config.allowedEmailDomains, enabled);
+		const rows: Array<SsoRowWrite> = [
+			ssoRow('sso_enabled', config.enabled, current.enabled, formatSsoBoolean),
+			ssoRow('sso_enforced', config.enforced, current.enforced, formatSsoBoolean),
+			ssoRow('sso_display_name', config.displayName, current.displayName, formatSsoString),
+			ssoRow('sso_issuer', config.issuer, current.issuer, formatSsoString),
+			ssoRow('sso_authorization_url', config.authorizationUrl, current.authorizationUrl, formatSsoString),
+			ssoRow('sso_token_url', config.tokenUrl, current.tokenUrl, formatSsoString),
+			ssoRow('sso_userinfo_url', config.userInfoUrl, current.userInfoUrl, formatSsoString),
+			ssoRow('sso_jwks_url', config.jwksUrl, current.jwksUrl, formatSsoString),
+			ssoRow('sso_client_id', config.clientId, current.clientId, formatSsoString),
+			ssoRow('sso_scope', config.scope, current.scope, formatSsoString),
+			ssoRow('sso_allowed_domains', allowedEmailDomains, current.allowedEmailDomains, formatSsoDomains),
+			ssoRow('sso_auto_provision', config.autoProvision, current.autoProvision, formatSsoBoolean),
+			ssoRow('sso_redirect_uri', undefined, null, formatSsoString),
 		];
 		if (config.clientSecret !== undefined) {
-			entries.push(['sso_client_secret', config.clientSecret ?? '']);
+			rows.push(ssoRow('sso_client_secret', config.clientSecret, current.clientSecret ?? null, formatSsoString));
 		}
-		await this.setConfigs(entries);
+		const cache = this.configCache;
+		const results = await Promise.allSettled(
+			rows
+				.filter((row) => row.value !== undefined || !configs.has(row.key))
+				.map((row) =>
+					this.compareAndSetStoredValue(cache, row.key, (raw) => ({value: nextSsoRowValue(row, raw), result: null})),
+				),
+		);
+		const errors: Array<unknown> = results.flatMap((result) => (result.status === 'rejected' ? [result.reason] : []));
+		if (results.some((result) => result.status === 'fulfilled' && result.value.written)) {
+			try {
+				await this.publishRefresh(cache.sourceId);
+			} catch (error) {
+				errors.push(error);
+			}
+		}
+		if (errors.length === 1) throw errors[0];
+		if (errors.length > 1) throw new AggregateError(errors, 'Failed to write or publish the SSO config');
 		return this.getSsoConfig({includeSecret: true});
 	}
 
-	private async setRegistrationUrls(registrationUrls: Array<InstanceRegistrationUrl>): Promise<void> {
-		const validated = validateStoredCollection(StoredRegistrationUrlSchema, registrationUrls, 'registration URLs');
-		await this.setConfig(REGISTRATION_URLS_KEY, JSON.stringify(validated));
-	}
-
-	private async setPendingRegistrations(pendingRegistrations: Array<InstancePendingRegistration>): Promise<void> {
-		const validated = validateStoredCollection(
-			StoredPendingRegistrationSchema,
-			pendingRegistrations,
-			'pending registrations',
-		);
-		await this.setConfig(REGISTRATION_PENDING_APPROVALS_KEY, JSON.stringify(validated));
+	private async fetchRegistrationUrlDefinitions(): Promise<Array<InstanceRegistrationUrl>> {
+		const raw = await this.fetchConfigFromDatabase(REGISTRATION_URLS_KEY);
+		return parseStoredCollection(StoredRegistrationUrlSchema, raw, 'registration URLs');
 	}
 
 	private hashRegistrationUrlCode(code: string): string {

fluxer_api/src/api/instance/PushServiceDeliveryConfigPublisher.ts

@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import type {PushServiceDeliveryConfig} from '@fluxer/schema/src/domains/admin/PushServiceDeliverySchemas';
+import type {INatsConnectionManager} from '@pkgs/nats/src/INatsConnectionManager';
+
+const textEncoder = new TextEncoder();
+
+export const PUSH_SERVICE_DELIVERY_CONFIG_NATS_SUBJECT = 'config.push.delivery';
+
+interface PushServiceDeliveryConfigNatsMessage {
+	type: 'push_service_delivery_config';
+	config: PushServiceDeliveryConfig;
+}
+
+export class PushServiceDeliveryConfigPublisher {
+	constructor(private readonly connectionManager: INatsConnectionManager) {}
+
+	async publish(config: PushServiceDeliveryConfig): Promise<void> {
+		if (this.connectionManager.isClosed()) {
+			await this.connectionManager.connect();
+		}
+		const connection = this.connectionManager.getConnection();
+		const message: PushServiceDeliveryConfigNatsMessage = {
+			type: 'push_service_delivery_config',
+			config,
+		};
+		connection.publish(PUSH_SERVICE_DELIVERY_CONFIG_NATS_SUBJECT, textEncoder.encode(JSON.stringify(message)));
+		await connection.flush();
+	}
+}

fluxer_api/src/api/instance/tests/InstanceConfigWriteRaceExecutor.ts

@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import {getKvMeta} from '@app/api/database/CassandraMetaRegistry';
+import type {CassandraQueryExecutorForTesting} from '@app/api/database/CassandraQueryExecution';
+import type {CassandraParams, KvQueryMeta, PreparedQuery} from '@app/api/database/CassandraTypes';
+import type {InstanceConfigurationRow} from '@app/api/database/types/InstanceConfigTypes';
+import {InstanceConfiguration} from '@app/api/Tables';
+
+type InstanceConfigWriteEvent = 'read' | 'write' | 'write rejected';
+
+interface WriteGate {
+	size: number;
+	paused: Array<() => void>;
+}
+
+const FETCH_ROW_QUERY = InstanceConfiguration.selectCql({
+	where: InstanceConfiguration.where.eq('key'),
+	limit: 1,
+});
+
+export class InstanceConfigWriteRaceExecutor implements CassandraQueryExecutorForTesting {
+	readonly events: Array<InstanceConfigWriteEvent> = [];
+	private watchedKey: string | null = null;
+	private gate: WriteGate | null = null;
+	private beforeEachWrite: (() => Promise<void>) | null = null;
+
+	constructor(private readonly base: CassandraQueryExecutorForTesting) {}
+
+	watch(key: string): void {
+		this.watchedKey = key;
+		this.events.length = 0;
+	}
+
+	pauseWritesUntil(size: number): void {
+		this.gate = {size, paused: []};
+	}
+
+	competeBeforeEachWrite(write: () => Promise<void>): void {
+		this.beforeEachWrite = write;
+	}
+
+	async writeDirectly(key: string, value: string): Promise<void> {
+		await this.base.executeQuery(InstanceConfiguration.upsertAll({key, value, updated_at: new Date()}));
+	}
+
+	async readDirectly(key: string): Promise<string | null> {
+		const [row] = await this.base.executeQuery<InstanceConfigurationRow>({cql: FETCH_ROW_QUERY, params: {key}});
+		return row?.value ?? null;
+	}
+
+	async executeQuery<T = Record<string, unknown>, P extends CassandraParams = CassandraParams>(
+		query: PreparedQuery<P>,
+	): Promise<Array<T>> {
+		const meta = query.kvMeta ?? getKvMeta(query.cql);
+		if (this.watchedKey === null || !this.isWatched(meta, query.params)) {
+			return this.base.executeQuery<T, P>(query);
+		}
+		if (meta?.action === 'select') {
+			this.events.push('read');
+			return this.base.executeQuery<T, P>(query);
+		}
+		await this.passGate();
+		await this.beforeEachWrite?.();
+		const rows = await this.base.executeQuery<T, P>(query);
+		const applied = (rows[0] as {'[applied]'?: unknown} | undefined)?.['[applied]'];
+		this.events.push(applied === false ? 'write rejected' : 'write');
+		return rows;
+	}
+
+	executeBatch(queries: Array<{query: string; params: object; meta?: KvQueryMeta}>, atomic?: boolean): Promise<void> {
+		return this.base.executeBatch(queries, atomic);
+	}
+
+	reset(): void {
+		this.base.reset?.();
+		this.watchedKey = null;
+		this.gate = null;
+		this.beforeEachWrite = null;
+		this.events.length = 0;
+	}
+
+	async shutdown(): Promise<void> {
+		await this.base.shutdown?.();
+	}
+
+	private isWatched(meta: KvQueryMeta | null | undefined, params: CassandraParams): boolean {
+		return meta?.table.name === InstanceConfiguration.name && params.key === this.watchedKey;
+	}
+
+	private async passGate(): Promise<void> {
+		const gate = this.gate;
+		if (gate === null) return;
+		await new Promise<void>((release) => {
+			gate.paused.push(release);
+			if (gate.paused.length < gate.size) return;
+			this.gate = null;
+			for (const release of gate.paused) release();
+		});
+	}
+}