SEP-1818: Warn when the chosen executor node is not the node hosting the target service (#1399)

## Summary

Added an advisory executor-host mismatch warning so SEP task forms can
surface when the selected executor runs on a different node than the
selected service, without changing submission or cascade behavior.

- `app/sep/apps/framework/form_dsl/markers.py`,
`app/sep/apps/framework/form_dsl/derivation.py`,
`app/sep/apps/framework/schema.py`,
`app/sep/apps/framework/form_dsl/model.py`,
`app/sep/apps/alters/models.py`: added the new `target_service`
form-DSL/schema contract, derived it onto host fields, and declared
`service_id` as the target service for executor host fields.
-
`frontend/packages/framework/src/components/HostSelector/HostSelector.tsx`,
`frontend/packages/framework/src/components/HostSelector/isHostMismatch.ts`,
`frontend/packages/framework/src/components/SchemaFormRenderer/fields/HostField.tsx`,
`frontend/packages/api/src/types/app-schema.ts`: added address-based
mismatch detection, rendered a non-blocking warning in the single host
selector, and threaded the new schema field through the frontend types
and renderer.
- `frontend/packages/api/specs/sep.json`,
`frontend/packages/api/src/generated/sep.ts`,
`tests/app/sep/snapshots/openapi/*.json`,
`tests/app/sep/snapshots/schema/*.json`: regenerated the OpenAPI spec,
generated TypeScript client, and schema/openapi snapshots for the
additive `target_service` contract.
- `tests/app/sep/apps/framework/test_form_dsl.py`,
`tests/app/sep/apps/framework/test_task_form_model.py`,
`frontend/packages/framework/src/components/HostSelector/isHostMismatch.test.ts`,
`frontend/packages/framework/src/components/HostSelector/HostSelector.test.tsx`:
added backend/frontend coverage for derivation rules, task-form
propagation, mismatch comparison, warning rendering, and silence states.
- Test files: updated focused backend and frontend tests to cover the
new warning behavior and preserve existing host selector behavior.
## Tested

- [x] Show a warning when the host and service are on different nodes,
and hide it when they match.
- [x] Do not show the warning when the service is missing or the check
cannot run.
- [x] Keep MongoDB Backup cascade working, and warn only if the user
picks a different host.
## Checklist

<!-- Check items that apply. Leave unchecked items visible — reviewers
use this too. -->

- [x] New/modified functions have type hints and rST docstrings
- [x] New tests added for new features or bug fixes
- [x] All tests pass locally (`make test`)
- [x] Pre-commit hooks pass (`make run-pre-commit`)
- [ ] Database migrations generated if models changed (`make
makemigrations`)
- [ ] User-facing changes documented (README, inline help, UI text)
- [ ] Configuration changes documented with examples
- [ ] Changelog fragment added under `changelog.d/` if the change is
user-facing (`make changelog-add`), or confirmed N/A (internal-only
change, or a same-release-cycle fix for an unreleased sibling ticket)

---------

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: peter-o-addo

app/sep/apps/alters/models.py

@@ -128,7 +128,9 @@ def _default_dsn_table_for_dsn_recursion(cls, data: Any) -> Any:
 
     task_name: Annotated[NonEmptyStr, Ui(label="Task Name", section="Task")]
     hostname: Annotated[
-        NonEmptyStr, HostRef(), Ui(label=EXECUTION_HOST_LABEL, section="Task")
+        NonEmptyStr,
+        HostRef(target_service="service_id"),
+        Ui(label=EXECUTION_HOST_LABEL, section="Task"),
     ]
     service_id: Annotated[
         int,

app/sep/apps/framework/form_dsl/derivation.py

@@ -462,7 +462,12 @@ def _build_ref_field(
         # MultiHostField may carry the key for wire uniformity, but only the
         # single-value HostField renderer honours it today.
         return field_class(
-            **common, allow_custom=allow_custom, depends_on=ui.depends_on
+            **common,
+            allow_custom=allow_custom,
+            depends_on=ui.depends_on,
+            target_service=(
+                ref.target_service if ref.target_service is not None else ui.depends_on
+            ),
         )
     return field_class(**common, allow_custom=allow_custom)
 

app/sep/apps/framework/form_dsl/markers.py

@@ -312,15 +312,26 @@ class HostRef:
     (``multiple=True``) may still emit ``depends_on`` on ``MultiHostField``,
     but cascade auto-select is single-host only today.
 
+    ``target_service`` is independent of ``Ui(depends_on=...)``: setting it does
+    not turn on cascade auto-select. It names the service field whose node
+    address the renderer compares against the selected host for a non-blocking
+    co-location warning. When it is omitted, derivation falls back to
+    ``Ui(depends_on=...)`` when that is set, so a form that already declares a
+    service-driven cascade gets the warning with no new declaration.
+
     :param allow_custom: When ``True``, the field also accepts a free-typed
         value and emits ``allow_custom`` on the wire. Defaults to ``False``.
     :param multiple: When ``True``, the field is a multi-value selector backed by
         a ``list[...]`` / ``set[...]`` annotation and derives a
         ``MultiHostField``. Defaults to ``False`` (single-value).
+    :param target_service: Optional name of the service field used for the
+        co-location warning. ``None`` (the default) lets derivation fall back
+        to ``Ui(depends_on=...)`` when that is set.
     """
 
     allow_custom: bool = False
     multiple: bool = False
+    target_service: str | None = None
 
 
 @dataclass(frozen=True, slots=True)

app/sep/apps/framework/form_dsl/model.py

@@ -87,9 +87,15 @@ class TaskFormModel(AppFormModel):
 
     :param task_name: The human-readable task name; required and non-empty.
     :param hostname: The executor host the task runs on; required and non-empty.
+        The default ``HostRef(target_service="service_id")`` ties the
+        co-location warning to a service field named ``service_id``; subclasses
+        that name their service field differently must override with an explicit
+        ``HostRef(target_service=...)``.
     """
 
     task_name: Annotated[NonEmptyStr, Ui(section="Task")]
     hostname: Annotated[
-        NonEmptyStr, HostRef(), Ui(label=EXECUTION_HOST_LABEL, section="Task")
+        NonEmptyStr,
+        HostRef(target_service="service_id"),
+        Ui(label=EXECUTION_HOST_LABEL, section="Task"),
     ]

app/sep/apps/framework/schema.py

@@ -462,10 +462,13 @@ class HostField(BaseField):
 
     :param field_type: The discriminator literal; always ``"host"`` for this
         class. Serialised as the JSON key ``"type"``.
-    :type field_type: Literal["host"]
     :param depends_on: Optional name of the field whose value drives the
         default executor selection. ``None`` (the default) omits the key from
         the wire so plugins that do not opt in stay byte-identical.
+    :param target_service: Optional service field for a non-blocking
+        co-location warning. Independent of ``depends_on`` (see
+        :class:`~app.sep.apps.framework.form_dsl.markers.HostRef`).
+        ``None`` (the default) omits the key from the wire.
     :param allow_custom: When ``True``, the selector also accepts a free-typed
         value alongside the inventory options. ``None`` (the default) omits the
         key from the wire so plugins that do not opt in stay byte-identical.
@@ -475,6 +478,7 @@ class HostField(BaseField):
         "host", alias="type", serialization_alias="type"
     )
     depends_on: NonEmptyStr | None = None
+    target_service: NonEmptyStr | None = None
     allow_custom: bool | None = None
 
 
@@ -488,13 +492,18 @@ class MultiHostField(BaseField):
     Cascade auto-select is single-host only (:class:`HostField`). ``depends_on``
     may still be emitted when ``Ui(depends_on=...)`` is set so derivation stays
     uniform, but the multi-host renderer does not honour it today.
+    ``target_service`` is mirrored the same way; the multi-host renderer
+    ignores it (no co-location warning).
 
     :param field_type: The discriminator literal; always ``"multi_host"`` for
         this class. Serialised as the JSON key ``"type"``.
     :param depends_on: Optional upstream field name mirrored from
         ``Ui(depends_on=...)``. Emitted for wire uniformity with
         :class:`HostField`; the current multi-host renderer ignores it (no
         cascade). ``None`` (the default) omits the key from the wire.
+    :param target_service: Optional service field name mirrored for wire
+        uniformity with :class:`HostField`; ignored by the multi-host
+        renderer. ``None`` (the default) omits the key from the wire.
     :param allow_custom: When ``True``, the selector also accepts free-typed
         values alongside the inventory options. ``None`` (the default) omits the
         key from the wire so plugins that do not opt in stay byte-identical.
@@ -504,6 +513,7 @@ class MultiHostField(BaseField):
         "multi_host", alias="type", serialization_alias="type"
     )
     depends_on: NonEmptyStr | None = None
+    target_service: NonEmptyStr | None = None
     allow_custom: bool | None = None
 
 

changelog.d/SEP-1818.changed.md

@@ -0,0 +1 @@
+Task create forms that pick an execution host against a database service now show a non-blocking warning when the selected host is not the node where that service runs; submit stays allowed.

frontend/packages/api/specs/sep.json

@@ -215,6 +215,11 @@ export interface HostField extends BaseField {
    * not cascaded.
    */
   depends_on?: string;
+  /**
+   * Service field for a non-blocking co-location warning. Independent of
+   * ``depends_on``. Omitted when unset.
+   */
+  target_service?: string;
   /** Offer free-text (free-solo) entry alongside the inventory options. */
   allow_custom?: boolean;
 }
@@ -227,6 +232,11 @@ export interface MultiHostField extends BaseField {
    * today. Omitted when unset.
    */
   depends_on?: string;
+  /**
+   * Optional service field name mirrored for wire uniformity. The
+   * multi-host renderer ignores it. Omitted when unset.
+   */
+  target_service?: string;
   /** Offer free-text (free-solo) entry alongside the inventory options. */
   allow_custom?: boolean;
 }