Adds RPCs for workflow list and get history

Signed-off-by: joshvanl <[email protected]>

Author: JoshVanL

20251028-RS-workflow-list.md

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+# Workflow List and History RPCs for Durable Task
+
+* Author(s): @joshvanl
+
+## Overview
+
+This proposal adds two new RPCs to the durabletask framework which are used to support observability and discoverability of running and completed workflows in Dapr.
+Specifically, adding a `ListInstances` and `GetInstanceHistory` RPC to the durabletask gRPC service.
+
+## Background
+
+Today, there is no ways of discovering the list of workflow instances that are currently running or have completed in the past without using external storage queries.
+The Dapr CLI [introduced list and workflow history commands](https://github.com/dapr/cli/pull/1560) to get information about running and completed workflows, however these commands rely on direct queries to the underlying storage provider.
+By introducing this functionality into the durabletask framework itself, these commands need only talk to Daprd, removing the requirement for direct access to the storage provider as well as authentication.
+Daprd can make these queries itself, and use the Actor State Store component to access the underlying storage.
+
+## Related Items
+
+## Implementation Details
+
+### Design
+
+Two new RPCs will be added to the durabletask gRPC service, which will be available to both the application client, as well as the dapr CLI.
+The list RPC will be used to discover the workflow instance IDs, which their metadatda can then be fetched.
+The workflow history RPC will be used to fetch the full history of a given workflow instance.
+
+```proto
+service TaskHubSidecarService {
+    rpc ListInstances (ListInstancesRequest) returns (ListInstancesResponse);
+    rpc GetInstanceHistory (GetInstanceHistoryRequest) returns (GetInstanceHistoryResponse);
+}
+
+// ListInstancesRequest is used to list all orchestration instances.
+message ListInstancesRequest {
+    // continuationToken is the continuation token to use for pagination. This
+    // is the index which the next page should start from. If not given, the first
+    // page will be returned.
+    optional uint32 continuationToken = 1;
+
+    // pageSize is the maximum number of instances to return for this page. If
+    // not given, all instances will be attempted to be returned.
+    optional uint32 pageSize = 2;
+}
+
+// ListInstancesResponse is the response to executing ListInstances.
+message ListInstancesResponse {
+  // instanceIds is the list of instance IDs returned.
+  repeated string instanceIds = 1;
+}
+
+// GetInstanceHistoryRequest is used to get the full history of an
+// orchestration instance.
+message GetInstanceHistoryRequest {
+    string instanceId = 1;
+}
+
+// GetInstanceHistoryResponse is the response to executing GetInstanceHistory.
+message GetInstanceHistoryResponse {
+    repeated HistoryEvent events = 1;
+}
+```