api-stability: mark Eloquent-model-accepting contracts as @internal

`Workflow\V2\Contracts\OperatorObservabilityRepository` accepts `WorkflowRun`
and `WorkflowRunSummary` Eloquent instances, and
`Workflow\V2\Contracts\ScheduleWorkflowStarter` accepts `WorkflowSchedule`.
Neither is implementable without the workflow package's own model
hierarchy, so external/polyglot adapters cannot bind these contracts
directly. Mark both interfaces @internal and document the HTTP surfaces
(Waterline API, `/webhooks/...`, control plane routes) as the stable
cross-language path.

These are the two internal contracts called out in V2-API — tightening
their docblocks without breaking the existing PHP bindings in the server
(RemoteScheduleStarter, Waterline repository).

Closes #291.

Author: durable-workflow-ops

src/V2/Contracts/OperatorObservabilityRepository.php

@@ -8,6 +8,18 @@
 use Workflow\V2\Models\WorkflowRun;
 use Workflow\V2\Models\WorkflowRunSummary;
 
+/**
+ * Repository contract for operator-facing observability payloads (Waterline
+ * detail, list projection, history export, dashboard, metrics).
+ *
+ * @internal Accepts Eloquent models ({@see WorkflowRun}, {@see WorkflowRunSummary})
+ *           as arguments and is coupled to the package's own model hierarchy.
+ *           Intended for Waterline and v2 polyglot-server integrations that
+ *           already run on top of the workflow package's PHP runtime; not a
+ *           stable cross-language contract and not subject to the v2
+ *           backwards-compatibility guarantee. Use the HTTP surfaces
+ *           (Waterline API, `/webhooks/...`) for external consumers instead.
+ */
 interface OperatorObservabilityRepository
 {
     /**

src/V2/Contracts/ScheduleWorkflowStarter.php

@@ -15,6 +15,15 @@
  * uses in-process PHP workflow classes via `WorkflowStub::make()`. Hosts that
  * run language-neutral workflows (e.g. the standalone server) bind their own
  * implementation that starts workflows by `workflow_type` through a control plane.
+ *
+ * @internal Accepts the {@see WorkflowSchedule} Eloquent model directly. The
+ *           model snapshot is expected to have fully hydrated `action`,
+ *           `overlap_policy`, `memo`, `search_attributes`, `visibility_labels`,
+ *           and `namespace` fields. This contract is only meaningful to hosts
+ *           that already depend on the workflow PHP package and is not part of
+ *           the stable v2 cross-language API. Standalone and polyglot consumers
+ *           that cannot load Eloquent models should drive schedule starts
+ *           through the control plane HTTP surface instead.
  */
 interface ScheduleWorkflowStarter
 {