Add Temporal Nexus Operation Handler

[Quinn-With-Two-Ns]

Add TemporalOperationHandler for generic Nexus operations

Summary

• Adds TemporalOperationHandler, a generic OperationHandler implementation that maps Nexus operations to Temporal workflows via a composable StartFunction
• Adds TemporalNexusClient for starting workflows (typed and untyped) from within Nexus operation handlers
• Supports subclassing TemporalOperationHandler to customize cancel behavior by overriding cancelWorkflowRun
• Extracts shared workflow start logic into NexusStartWorkflowHelper, reused by both WorkflowRunOperation and the new handler

Test plan

• GenericHandlerTypedStartWorkflowTest — typed workflow with return value
• GenericHandlerTypedProcTest — typed void workflow
• GenericHandlerUntypedStartWorkflowTest — untyped workflow start
• GenericHandlerSyncResultTest — synchronous result path
• GenericHandlerCancelTest — cancel with default and custom behavior

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Note

Medium Risk
Adds new (experimental) public Nexus handler/client APIs and changes cancel dispatch/token parsing, which could affect how operation tokens are interpreted and how cancellations propagate.

Overview
Introduces an experimental generic Nexus integration via TemporalOperationHandler, letting Nexus operation implementations return either sync results or async workflow-run tokens through TemporalOperationResult, with default cancel behavior that cancels the underlying workflow based on the parsed operation token.

Adds TemporalNexusClient helpers to start typed/untyped workflows from Nexus handlers, and extracts the common “start workflow + attach workflow links to the Nexus operation context” logic into NexusStartWorkflowHelper, which is now reused by WorkflowRunOperationImpl.

Generalizes operation-token handling by renaming WorkflowRunOperationToken to OperationToken and updating OperationTokenUtil to support loading tokens without asserting type (for cancel dispatch) while keeping a type-asserting workflow-run loader; updates and adds tests to cover the new handler paths (typed/untyped start, void workflows, sync result, and cancel behavior).

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[Quinn-With-Two-Ns]

@maciejdudko @GregoryTravis This is one issue I found with the approach, due to ambiguity in the lambda we have to return null here for workflows that don't return anything.

[cursor]

Test no longer validates token type rejection

Medium Severity

The badTokenUnknownType test case switched from loadWorkflowRunOperationToken to loadOperationToken, which does not validate the token type. The test still passes, but only because the token coincidentally has "v":1 (rejected by version validation), not because t:4 is an unknown type. This means loadWorkflowRunOperationToken's type-rejection logic is no longer covered by any negative test case in this file, creating a silent coverage gap for a production code path used by WorkflowRunOperationImpl.cancel.

 

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

There are 2 total unresolved issues (including 1 from previous review).

^{Reviewed by Cursor Bugbot for commit 05a2002. Configure here.}

[cursor]

Test No Longer Validates Operation Token Type

Medium Severity

AsyncWorkflowOperationTest was changed to call loadOperationToken instead of loadWorkflowRunOperationToken when asserting the contents of the operation token returned by WorkflowRunOperation. loadOperationToken skips type validation, so the test no longer verifies that the token type is WORKFLOW_RUN. If a regression causes WorkflowRunOperation to produce a token with the wrong type, this test won't catch it. Similarly, WorkflowRunTokenTest.loadWorkflowIdFromBadOperationToken's badTokenUnknownType case was switched to loadOperationToken, so it now throws only due to v:1, not due to the unknown type — the type-rejection behavior is no longer tested at all.

Additional Locations (1)

• temporal-sdk/src/test/java/io/temporal/internal/nexus/WorkflowRunTokenTest.java#L101-L128

 

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