feat(api): support variable reference and substitution in Email delivery

The EmailDeliveryConfig.body now support referencing variables generated
by precedent nodes.

api/tests/unit_tests/core/workflow/nodes/human_input/test_email_delivery_config.py

@@ -1,4 +1,5 @@
 from core.workflow.nodes.human_input.entities import EmailDeliveryConfig, EmailRecipients
+from core.workflow.runtime import VariablePool
 
 
 def test_replace_url_placeholder_with_value():
@@ -23,3 +24,17 @@ def test_replace_url_placeholder_missing_value():
     result = config.body_with_url(None)
 
     assert result == "No link  available."
+
+
+def test_render_body_template_replaces_variable_values():
+    config = EmailDeliveryConfig(
+        recipients=EmailRecipients(),
+        subject="Subject",
+        body="Hello {{#node1.value#}} {{#url#}}",
+    )
+    variable_pool = VariablePool()
+    variable_pool.add(["node1", "value"], "World")
+
+    result = config.render_body_template(body=config.body, url="https://example.com", variable_pool=variable_pool)
+
+    assert result == "Hello World https://example.com"

api/tests/unit_tests/services/test_human_input_delivery_test_service.py

@@ -14,6 +14,7 @@ from services.human_input_delivery_test_service import (
     DeliveryTestError,
     EmailDeliveryTestHandler,
 )
+from core.workflow.runtime import VariablePool
 
 
 def _make_email_method() -> EmailDeliveryMethod:
@@ -48,3 +49,49 @@ def test_email_delivery_test_handler_rejects_when_feature_disabled(monkeypatch:
 
     with pytest.raises(DeliveryTestError, match="Email delivery is not available"):
         handler.send_test(context=context, method=method)
+
+
+def test_email_delivery_test_handler_replaces_body_variables(monkeypatch: pytest.MonkeyPatch):
+    class DummyMail:
+        def __init__(self):
+            self.sent: list[dict[str, str]] = []
+
+        def is_inited(self) -> bool:
+            return True
+
+        def send(self, *, to: str, subject: str, html: str):
+            self.sent.append({"to": to, "subject": subject, "html": html})
+
+    mail = DummyMail()
+    monkeypatch.setattr(service_module, "mail", mail)
+    monkeypatch.setattr(service_module, "render_email_template", lambda template, _substitutions: template)
+    monkeypatch.setattr(
+        service_module.FeatureService,
+        "get_features",
+        lambda _tenant_id: SimpleNamespace(human_input_email_delivery_enabled=True),
+    )
+
+    handler = EmailDeliveryTestHandler(session_factory=object())
+    handler._resolve_recipients = lambda **_kwargs: ["tester@example.com"]  # type: ignore[assignment]
+
+    method = EmailDeliveryMethod(
+        config=EmailDeliveryConfig(
+            recipients=EmailRecipients(whole_workspace=False, items=[ExternalRecipient(email="tester@example.com")]),
+            subject="Subject",
+            body="Value {{#node1.value#}}",
+        )
+    )
+    variable_pool = VariablePool()
+    variable_pool.add(["node1", "value"], "OK")
+    context = DeliveryTestContext(
+        tenant_id="tenant-1",
+        app_id="app-1",
+        node_id="node-1",
+        node_title="Human Input",
+        rendered_content="content",
+        variable_pool=variable_pool,
+    )
+
+    handler.send_test(context=context, method=method)
+
+    assert mail.sent[0]["html"] == "Value OK"

api/tests/unit_tests/tasks/test_mail_human_input_delivery_task.py

@@ -49,7 +49,7 @@ def _build_job(recipient_count: int = 1) -> task_module._EmailDeliveryJob:
 
 def test_dispatch_human_input_email_task_sends_to_each_recipient(monkeypatch: pytest.MonkeyPatch):
     mail = _DummyMail()
-    form = SimpleNamespace(id="form-1", tenant_id="tenant-1")
+    form = SimpleNamespace(id="form-1", tenant_id="tenant-1", workflow_run_id=None)
 
     def fake_render(template: str, substitutions: dict[str, str]) -> str:
         return template.replace("{{ form_token }}", substitutions["form_token"]).replace(
@@ -79,7 +79,7 @@ def test_dispatch_human_input_email_task_sends_to_each_recipient(monkeypatch: py
 
 def test_dispatch_human_input_email_task_skips_when_feature_disabled(monkeypatch: pytest.MonkeyPatch):
     mail = _DummyMail()
-    form = SimpleNamespace(id="form-1", tenant_id="tenant-1")
+    form = SimpleNamespace(id="form-1", tenant_id="tenant-1", workflow_run_id=None)
 
     monkeypatch.setattr(task_module, "mail", mail)
     monkeypatch.setattr(
@@ -96,3 +96,37 @@ def test_dispatch_human_input_email_task_skips_when_feature_disabled(monkeypatch
     )
 
     assert mail.sent == []
+
+
+def test_dispatch_human_input_email_task_replaces_body_variables(monkeypatch: pytest.MonkeyPatch):
+    mail = _DummyMail()
+    form = SimpleNamespace(id="form-1", tenant_id="tenant-1", workflow_run_id="run-1")
+    job = task_module._EmailDeliveryJob(
+        form_id="form-1",
+        workflow_run_id="run-1",
+        subject="Subject",
+        body="Body {{#node1.value#}}",
+        form_content="content",
+        recipients=[task_module._EmailRecipient(email="user@example.com", token="token-1")],
+    )
+
+    variable_pool = task_module.VariablePool()
+    variable_pool.add(["node1", "value"], "OK")
+
+    monkeypatch.setattr(task_module, "mail", mail)
+    monkeypatch.setattr(task_module, "render_email_template", lambda template, _substitutions: template)
+    monkeypatch.setattr(
+        task_module.FeatureService,
+        "get_features",
+        lambda _tenant_id: SimpleNamespace(human_input_email_delivery_enabled=True),
+    )
+    monkeypatch.setattr(task_module, "_load_email_jobs", lambda _session, _form: [job])
+    monkeypatch.setattr(task_module, "_load_variable_pool", lambda _workflow_run_id: variable_pool)
+
+    task_module.dispatch_human_input_email_task(
+        form_id="form-1",
+        node_title="Approve",
+        session_factory=lambda: _DummySession(form),
+    )
+
+    assert mail.sent[0]["html"] == "Body OK"