CHASM workflow command handler for Nexus by stephanos · Pull Request #9109 · temporalio/temporal

stephanos · 2026-01-22T01:59:32Z

What changed?

Added workflow command handler registry to CHASM's workflow library.
Integrated CHASM's workflow library into workflow completion handler.

Why?

Migrating Nexus from HSM to CHASM.

How did you test it?

Tests will be ported over once actual command handler implementations are added.

stephanos · 2026-01-22T18:22:22Z

 	return []*chasm.RegistrableComponent{
 		chasm.NewRegistrableComponent[*Operation]("operation"),
-		chasm.NewRegistrableComponent[*Operation]("cancellation"),
+		chasm.NewRegistrableComponent[*Cancellation]("cancellation"),


stephanos · 2026-01-22T18:51:17Z

 	Callbacks chasm.Map[string, *callback.Callback]
+
+	// Operations map is used to store the nexus operations for the workflow.
+	Operations chasm.Map[string, *nexusoperation.Operation]


Not used yet, but demonstrates why command registry and types need to live in submodule. If they didn't there'd be an import cycle. Having this already ensures this design will work.

stephanos · 2026-01-22T19:34:13Z


-// FailWorkflowTaskError is an error that can be returned from a [CommandHandler] to fail the current workflow task and
-// optionally terminate the entire workflow.
-type FailWorkflowTaskError struct {


Moving this to CHASM now to break up import cycle.

stephanos · 2026-01-22T19:35:30Z

 }

-// CommandValidator is a helper for validating workflow commands.
-type CommandValidator interface {


Moved to CHASM, too. More from this package might be moved in follow-up PRs.

bergundy · 2026-01-27T17:00:50Z

+		var commandHandler chasmcommand.Handler
+		var chasmCtx chasm.MutableContext
+
+		if handler.mutableState.ChasmEnabled() {


You will need a way to toggle between HSM and CHASM and you will have to figure out if and how to deal with a mutable state that has both HSM and CHASM nexus operations.

To simplify the migration, we could set a point where we enable CHASM-backed operations. From that time on, new workflows will only use CHASM operations. Then we just have to wait 60 days to know that there are no more valid HSM operations since that is the maximum schedule-to-close timeout.

I was under the impression the migration-related work is a separate ticket out of the scope of this PR. Let me know if you think we need to take action on this PR.

pdoerner

Overall LGTM. Just need to make a decision on whether the command handler registry should be specific to the workflow component or a general CHASM concept. I lean toward letting it be coupled with workflow but I don't have a strong opinion.

stephanos · 2026-01-28T01:22:51Z

I made some changes after a team discussion, most importantly: moved the command handler registry out of the Workflow library; it is passed through the "engine" now just like HSM's. The benefit is that the additional Library method I had added to chasm.Context isn't needed anymore.

It was also discussed to add it to chasm.Registry instead which I prefer not to do as that would make CHASM less workflow-agnostic. In any case, my immediate goal is to unblock future work here and have a separate discussion later on revisiting the best place for it.

bergundy · 2026-01-29T19:05:16Z

+type Handler func(
+	chasmCtx chasm.MutableContext,
+	validator Validator,
+	workflowTaskCompletedEventID int64,


Maybe for forwards compat we can put this in an options struct?

bergundy · 2026-01-29T19:07:42Z

+		var commandHandler chasmcommand.Handler
+		var chasmCtx chasm.MutableContext
+
+		// TODO: need to handle migration between HSM and CHASM


Let's make sure this is tracked.

👍 filed a ticket to make sure.

bergundy

Approved with a couple of very minor comments.

## What changed? - Added workflow command handler registry to CHASM's workflow library. - Integrated CHASM's workflow library into workflow completion handler. ## Why? Migrating Nexus from HSM to CHASM. ## How did you test it? Tests will be ported over once actual command handler implementations are added.

- Added workflow command handler registry to CHASM's workflow library. - Integrated CHASM's workflow library into workflow completion handler. Migrating Nexus from HSM to CHASM. Tests will be ported over once actual command handler implementations are added.

stephanos changed the title ~~CHASM workflow command handler for Nexus~~ CHASM workflow command handler for Nexus [WiP] Jan 22, 2026

stephanos force-pushed the nexus-chasm-commands branch 12 times, most recently from 0225b74 to 15b2305 Compare January 22, 2026 18:19

stephanos commented Jan 22, 2026

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stephanos force-pushed the nexus-chasm-commands branch 4 times, most recently from 5521052 to 125a6f1 Compare January 22, 2026 18:27

stephanos changed the base branch from main to nexus/hsm-to-chasm-migration January 22, 2026 18:27

stephanos force-pushed the nexus-chasm-commands branch 3 times, most recently from 3d0f476 to cfe0179 Compare January 22, 2026 18:49

stephanos commented Jan 22, 2026

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stephanos force-pushed the nexus-chasm-commands branch 5 times, most recently from ceadf56 to 69632f8 Compare January 22, 2026 19:32

stephanos commented Jan 22, 2026

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bergundy reviewed Jan 27, 2026

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pdoerner reviewed Jan 27, 2026

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stephanos added 6 commits January 27, 2026 12:14

add TODO

be717f7

move nexus command registration

b04ee39

del command.Backend

b291641

rename field

acab200

move registry to fx

1df6852

revert import change

32ce2bf

del Library

7f04034

stephanos force-pushed the nexus-chasm-commands branch from da9c5b1 to 7f04034 Compare January 28, 2026 01:33

stephanos requested a review from bergundy January 28, 2026 02:11

bergundy reviewed Jan 29, 2026

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bergundy approved these changes Jan 29, 2026

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add HandlerOptions

382223d

stephanos merged commit 67fa6fe into temporalio:nexus/hsm-to-chasm-migration Feb 2, 2026
65 checks passed

stephanos deleted the nexus-chasm-commands branch February 2, 2026 18:31

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