Trampolining: addition of fields to remove the infinite loops for pinned wfs (#721)

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<!-- Describe what has changed in this PR -->
 -WISOTT


<!-- Tell your future self why have you made these changes -->
- Users that could using trampolining in the near future could run into
a problem, which shall only surface if the workflow author does not have
AutoUpgrade as the initial CAN behaviour for their Pinned workflows. As
of today, if a user does hit this case, they would have the pinned
workflow CAN'ing infinite number of times. This is because a pinned
workflow would commence on the pinned version (since it would have
inherited pinned version set to true) and if the pinned version is
different than a worker-deployment's current version, the
targetDeploymentVersionChanged would be set to true in the server. This
would then result in the workflow just CAN'ing all the time!
- This change aims to change that by only allowing at-most one CAN for
such pinned workflow executions, and it does so by remembering what the
initial version was at the start of the continue-as-new.


<!-- Are there any breaking changes on binary or code level? -->
**Breaking changes**


<!-- If this breaks the Server, please provide the Server PR to merge
right after this PR was merged. -->
- [PR!](temporalio/temporal#9374)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: Shivs11

openapi/openapiv2.json

@@ -12040,6 +12040,15 @@
         }
       }
     },
+    "v1DeclinedTargetVersionUpgrade": {
+      "type": "object",
+      "properties": {
+        "deploymentVersion": {
+          "$ref": "#/definitions/v1WorkerDeploymentVersion"
+        }
+      },
+      "description": "Wrapper for a target deployment version that the SDK declined to upgrade to.\nSee declined_target_version_upgrade on WorkflowExecutionStartedEventAttributes."
+    },
     "v1DeleteNexusEndpointResponse": {
       "type": "object"
     },
@@ -17719,6 +17728,10 @@
         "eagerExecutionAccepted": {
           "type": "boolean",
           "description": "A boolean indicating whether the SDK has asked to eagerly execute the first workflow task for this workflow and\neager execution was accepted by the server.\nOnly populated by server with version >= 1.29.0."
+        },
+        "declinedTargetVersionUpgrade": {
+          "$ref": "#/definitions/v1DeclinedTargetVersionUpgrade",
+          "description": "During a previous run of this workflow, the server may have notified the SDK\nthat the Target Worker Deployment Version changed, but the SDK declined to\nupgrade (e.g., by continuing-as-new with PINNED behavior). This field records\nthe target version that was declined.\n\nThis is a wrapper message to distinguish \"never declined\" (nil wrapper) from\n\"declined an unversioned target\" (non-nil wrapper with nil deployment_version).\n\nUsed internally by the server during continue-as-new and retry.\nShould not be read or interpreted by SDKs."
         }
       },
       "title": "Always the first event in workflow history"

openapi/openapiv3.yaml

@@ -9226,6 +9226,14 @@ components:
         data:
           type: string
           format: bytes
+    DeclinedTargetVersionUpgrade:
+      type: object
+      properties:
+        deploymentVersion:
+          $ref: '#/components/schemas/WorkerDeploymentVersion'
+      description: |-
+        Wrapper for a target deployment version that the SDK declined to upgrade to.
+         See declined_target_version_upgrade on WorkflowExecutionStartedEventAttributes.
     DeleteNexusEndpointResponse:
       type: object
       properties: {}
@@ -16528,6 +16536,20 @@ components:
             A boolean indicating whether the SDK has asked to eagerly execute the first workflow task for this workflow and
              eager execution was accepted by the server.
              Only populated by server with version >= 1.29.0.
+        declinedTargetVersionUpgrade:
+          allOf:
+            - $ref: '#/components/schemas/DeclinedTargetVersionUpgrade'
+          description: |-
+            During a previous run of this workflow, the server may have notified the SDK
+             that the Target Worker Deployment Version changed, but the SDK declined to
+             upgrade (e.g., by continuing-as-new with PINNED behavior). This field records
+             the target version that was declined.
+
+             This is a wrapper message to distinguish "never declined" (nil wrapper) from
+             "declined an unversioned target" (non-nil wrapper with nil deployment_version).
+
+             Used internally by the server during continue-as-new and retry.
+             Should not be read or interpreted by SDKs.
       description: Always the first event in workflow history
     WorkflowExecutionTerminatedEventAttributes:
       type: object

temporal/api/history/v1/message.proto

@@ -184,6 +184,24 @@ message WorkflowExecutionStartedEventAttributes {
     // eager execution was accepted by the server.
     // Only populated by server with version >= 1.29.0.
     bool eager_execution_accepted = 38;
+
+    // During a previous run of this workflow, the server may have notified the SDK
+    // that the Target Worker Deployment Version changed, but the SDK declined to
+    // upgrade (e.g., by continuing-as-new with PINNED behavior). This field records
+    // the target version that was declined.
+    //
+    // This is a wrapper message to distinguish "never declined" (nil wrapper) from
+    // "declined an unversioned target" (non-nil wrapper with nil deployment_version).
+    //
+    // Used internally by the server during continue-as-new and retry.
+    // Should not be read or interpreted by SDKs.
+    DeclinedTargetVersionUpgrade declined_target_version_upgrade = 40;
+}
+
+// Wrapper for a target deployment version that the SDK declined to upgrade to.
+// See declined_target_version_upgrade on WorkflowExecutionStartedEventAttributes.
+message DeclinedTargetVersionUpgrade {
+    temporal.api.deployment.v1.WorkerDeploymentVersion deployment_version = 1;
 }
 
 message WorkflowExecutionCompletedEventAttributes {