chore(automation): retire the workflow_rule authoring paradigm (ADR-0018 M5 dropped) (#1578)

ADR-0019 dropped the Workflow-Rule -> Flow compiler, but the `workflow_rule`
paradigm tag lingered in `ActionParadigmSchema` and on every built-in node
descriptor. With no declarative Workflow-Rule authoring view to feed, retire it:

- spec: `ActionParadigmSchema` -> `['flow','approval']`
- service-automation: `http` / `notify` / `connector_action` descriptors and the
  deprecated-alias fallback advertise `['flow','approval']`
- tests: builtin descriptor assertions + http-dispatcher `?paradigm` filter
  switched off the retired tag
- docs: ADR-0018 status + migration table -> M3 shipped, M4 framework-complete,
  M5 dropped (approval convergence delivered by the ADR-0019 approval node)

Co-authored-by: Jack Zhuang <277994282+os-zhuang@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: 3 people

.changeset/retire-workflow-rule-paradigm.md

@@ -0,0 +1,17 @@
+---
+'@objectstack/spec': patch
+'@objectstack/service-automation': patch
+---
+
+chore(automation): retire the `workflow_rule` authoring paradigm (ADR-0018 M5 dropped)
+
+ADR-0019 already removed the Workflow-Rule → Flow compiler (Workflow Rules were
+removed in #1398 and `workflow` was reclaimed for state machines), but the
+`workflow_rule` paradigm tag survived in `ActionParadigmSchema` and on every
+built-in node descriptor. There is no declarative Workflow-Rule authoring view
+to feed, so the tag is now retired: `ActionParadigmSchema` keeps `['flow',
+'approval']`, and the `http` / `notify` / `connector_action` descriptors (plus
+the deprecated-alias fallback) advertise `['flow', 'approval']`. Approval
+execution convergence is delivered by the ADR-0019 approval Flow node, not a
+compiler. ADR-0018's status and migration table are updated to mark M3 shipped,
+M4 framework-complete, and M5 dropped.

docs/adr/0018-unified-node-action-registry.md

@@ -1,6 +1,6 @@
 # ADR-0018: Unified Node/Action Registry across Flow, Workflow-Rule & Approval
 
-**Status**: Accepted (2026-05-31) — M1 + M2 implemented (built-in nodes folded into the core plugin; descriptor API + `GET /automation/actions` shipped). M3 (outbox-backed `http`/`notify`) next.
+**Status**: Accepted (2026-05-31) — M1–M3 implemented; M4 framework-side complete (designer config-forms tracked in `../objectui`); M5 **dropped** (Workflow-Rule→Flow compiler removed per [ADR-0019](./0019-approval-as-flow-node.md); approval execution converged via the approval Flow node, not a compiler). The `workflow_rule` authoring paradigm is retired.
 **Deciders**: ObjectStack Protocol Architects
 **Builds on**: [ADR-0005](./0005-metadata-customization-overlay.md) (one Zod source of truth per metadata type), [ADR-0012](./0012-notification-platform.md) (generalized outbox in `service-messaging`)
 **Consumers**: `@objectstack/spec` (`automation/`), `@objectstack/services/service-automation`, `@objectstack/plugins/plugin-approvals`, `@objectstack/plugins/plugin-webhooks` → `service-messaging`, every plugin that registers a node executor, `../objectui` (`plugin-workflow` designer)
@@ -168,9 +168,9 @@ No fourth engine. Workflow Rules stays a **simplified authoring view** for busin
 |:---|:---|:---|
 | M1 ✅ | Add canonical `ActionDescriptorSchema` (+ `defineActionDescriptor`) alongside the legacy `NodeExecutorDescriptor`; `FlowNodeSchema.type` → validated `string` (with `FlowNodeAction`/`FLOW_BUILTIN_NODE_TYPES` retained as the seed set); `registerFlow()` soft-validates node types against the live registry (warn, don't hard-fail). | **Shipped.** Existing flows keep validating (built-in types seed-registered); plugin-registered node types are now legal flow nodes. |
 | M2 (partial ✅) | Built-in nodes (logic/crud/http/screen) publish descriptors and are **folded into the core `AutomationServicePlugin`** (seeded via `installBuiltinNodes()`), so `automation` is a self-contained capability — no companion node-pack plugins, no `extras` in the capability loader. `connector_action` dropped from the baseline (an integration concern needing a connector registry the platform doesn't ship; left to the integration layer / marketplace plugins via the still-open `registerNodeExecutor()`). Descriptors tagged `source: 'builtin'` vs `'plugin'`. `AutomationEngine.getActionDescriptors()`/`getActionDescriptor()` + optional `IAutomationService.getActionDescriptors()`. `GET /api/v1/automation/actions` shipped via `HttpDispatcher.handleAutomation` (`?paradigm`/`?source`/`?category` filters; `AutomationActionsResponseSchema` in spec; declarative entry in `DEFAULT_AUTOMATION_ROUTES`). | Additive; built-in flows keep working from the core plugin alone. Hosts that hand-assembled the four `*NodesPlugin` classes drop them (the classes are gone). |
-| M3 | Introduce `http` + `notify` executors backed by `service-messaging`; register `http_request`/`http_call`/`webhook` as deprecated aliases | Old node types keep running via alias. |
-| M4 | Designer palette + config forms driven by the registry; remove hardcoded `FlowNodeType` | Designer-only; old saved graphs still load. |
-| M5 | Workflow-Rule → Flow compiler; `plugin-approvals` action executor delegates to the shared `http`/`notify` executors | Approval/Workflow-Rule definitions unchanged; execution path converges. |
+| M3 ✅ | Canonical `http` + `notify` executors backed by `service-messaging` (HTTP outbox `sys_http_delivery` / notification outbox); `http_request`/`http_call`/`webhook` registered as **deprecated aliases** (`registerNodeAlias`, `needsOutbox`). | **Shipped.** Old node types keep running via alias; degrade to inline when no outbox is wired. |
+| M4 (framework ✅) | Hardcoded `FlowNodeType` removed (M1 turned `FlowNodeSchema.type` into a validated string seeded from `FLOW_BUILTIN_NODE_TYPES`); `GET /automation/actions` drives the palette. Remaining: designer config-forms rendered from `descriptor.configSchema` — tracked in `../objectui`. | Framework carries no closed node enum; old saved graphs still load. |
+| ~~M5~~ **Dropped** | Workflow-Rule → Flow compiler **removed** — there is no declarative Workflow-Rule authoring type to compile (Workflow Rules removed in #1398; `workflow` reclaimed for state machines, ADR-0020). The `workflow_rule` paradigm tag is retired from `ActionParadigmSchema` and all descriptors. Approval execution convergence is delivered by [ADR-0019](./0019-approval-as-flow-node.md) (approval is a durable-pause Flow node; side-effects run on the shared `http`/`notify` executors), not a compiler. | No legacy to migrate (greenfield). |
 
 ---
 
@@ -231,6 +231,6 @@ Managed credentials/secret vault, OAuth2 token refresh, multi-tenant connection
 ### Implementation checklist
 
 - [x] `AutomationEngine`: connector registry (`registerConnector` / `unregisterConnector` / `resolveConnectorAction` / `getRegisteredConnectors`) + `ConnectorActionHandler` / `ConnectorActionContext` types.
-- [x] `builtin/connector-nodes.ts`: `connector_action` executor + descriptor (`category: 'io'`, `source: 'builtin'`, `paradigms: ['flow','workflow_rule','approval']`), wired into `installBuiltinNodes()`. The core plugin now seeds 11 baseline node types (was 10).
+- [x] `builtin/connector-nodes.ts`: `connector_action` executor + descriptor (`category: 'io'`, `source: 'builtin'`, `paradigms: ['flow','approval']`), wired into `installBuiltinNodes()`. The core plugin now seeds 11 baseline node types (was 10).
 - [x] First concrete plugin `@objectstack/connector-rest` (the reference connector) validating the registry — `request` action, static auth (`none`/`api-key`/`basic`/`bearer`), no OAuth2 refresh.
 - [x] Tests: baseline dispatch (fake connector) + REST plugin auth-header injection + end-to-end kernel boot (both plugins → `connector_action` flow → REST handler).

packages/runtime/src/http-dispatcher.test.ts

@@ -147,7 +147,7 @@ describe('HttpDispatcher', () => {
                 trigger: vi.fn().mockResolvedValue({ success: true }),
                 getActionDescriptors: vi.fn().mockReturnValue([
                     { type: 'decision', name: 'Decision', category: 'logic', paradigms: ['flow'], source: 'builtin' },
-                    { type: 'http_request', name: 'HTTP Request', category: 'io', paradigms: ['flow', 'workflow_rule'], source: 'builtin' },
+                    { type: 'http_request', name: 'HTTP Request', category: 'io', paradigms: ['flow', 'approval'], source: 'builtin' },
                     { type: 'send_sms', name: 'Send SMS', category: 'io', paradigms: ['flow'], source: 'plugin' },
                 ]),
                 getConnectorDescriptors: vi.fn().mockReturnValue([
@@ -270,7 +270,7 @@ describe('HttpDispatcher', () => {
         });
 
         it('should filter GET /actions by ?paradigm', async () => {
-            const result = await dispatcher.handleAutomation('actions', 'GET', {}, { request: {} }, { paradigm: 'workflow_rule' });
+            const result = await dispatcher.handleAutomation('actions', 'GET', {}, { request: {} }, { paradigm: 'approval' });
             expect(result.handled).toBe(true);
             expect(result.response?.body?.data?.total).toBe(1);
             expect(result.response?.body?.data?.actions[0].type).toBe('http_request');

packages/services/service-automation/src/builtin/connector-nodes.test.ts

@@ -51,7 +51,7 @@ describe('connector_action (baseline node)', () => {
         expect(descriptor?.source).toBe('builtin');
         expect(descriptor?.category).toBe('io');
         expect(descriptor?.paradigms).toEqual(
-            expect.arrayContaining(['flow', 'workflow_rule', 'approval']),
+            expect.arrayContaining(['flow', 'approval']),
         );
     });
 

packages/services/service-automation/src/builtin/connector-nodes.ts

@@ -32,8 +32,9 @@ export function registerConnectorNodes(engine: AutomationEngine, ctx: PluginCont
             category: 'io',
             source: 'builtin',
             supportsRetry: true,
-            // Present in all three authoring paradigms (ADR-0018 §registry table).
-            paradigms: ['flow', 'workflow_rule', 'approval'],
+            // Present in both authoring paradigms (ADR-0018 §registry table;
+            // workflow_rule retired per ADR-0019).
+            paradigms: ['flow', 'approval'],
             // Config contract — drives the Studio property form and flow validation.
             configSchema: {
                 type: 'object',

packages/services/service-automation/src/builtin/http-nodes.test.ts

@@ -58,7 +58,7 @@ describe('http (canonical node) + deprecated aliases', () => {
         expect(d?.source).toBe('builtin');
         expect(d?.category).toBe('io');
         expect(d?.needsOutbox).toBe(true);
-        expect(d?.paradigms).toEqual(expect.arrayContaining(['flow', 'workflow_rule', 'approval']));
+        expect(d?.paradigms).toEqual(expect.arrayContaining(['flow', 'approval']));
     });
 
     it('registers http_request/http_call/webhook as deprecated aliases of http', () => {

packages/services/service-automation/src/builtin/http-nodes.ts

@@ -73,7 +73,7 @@ export function registerHttpNodes(engine: AutomationEngine, ctx: PluginContext):
             // and the messaging HTTP outbox is wired).
             needsOutbox: true,
             supportsRetry: true,
-            paradigms: ['flow', 'workflow_rule', 'approval'],
+            paradigms: ['flow', 'approval'],
             configSchema: {
                 type: 'object',
                 required: ['url'],

packages/services/service-automation/src/builtin/notify-node.test.ts

@@ -72,7 +72,7 @@ describe('notify (baseline node)', () => {
         expect(descriptor?.source).toBe('builtin');
         expect(descriptor?.category).toBe('io');
         expect(descriptor?.paradigms).toEqual(
-            expect.arrayContaining(['flow', 'workflow_rule', 'approval']),
+            expect.arrayContaining(['flow', 'approval']),
         );
     });
 

packages/services/service-automation/src/builtin/notify-node.ts

@@ -67,7 +67,7 @@ export function registerNotifyNode(engine: AutomationEngine, ctx: PluginContext)
             // Delivery is outbox-backed inside the messaging service (ADR-0030
             // emit → sys_notification_delivery), so it inherits retry/dead-letter.
             needsOutbox: true,
-            paradigms: ['flow', 'workflow_rule', 'approval'],
+            paradigms: ['flow', 'approval'],
         }),
         async execute(node, variables, context) {
             const cfg = (node.config ?? {}) as Record<string, unknown>;

packages/services/service-automation/src/engine.ts

@@ -450,7 +450,7 @@ export class AutomationEngine implements IAutomationService {
                 description: `Deprecated alias of '${canonicalType}' (ADR-0018 M3). Author new flows with '${canonicalType}'.`,
                 category: meta?.category ?? 'io',
                 source: 'builtin',
-                paradigms: meta?.paradigms ?? ['flow', 'workflow_rule', 'approval'],
+                paradigms: meta?.paradigms ?? ['flow', 'approval'],
                 supportsRetry: true,
                 needsOutbox: meta?.needsOutbox ?? false,
                 deprecated: true,