Behavior change in Tool output

[uuouter]

Describe the bug
tool.output magically changes to tool.input after upgrading. Yep that might sound very weird, bear with me haha.

Our agent has a very simple askUserTool.

inputSchema: z.object({
	question: z.string().describe('Short question to show to the user (no extra explanation).'),
	choices: z.array(z.string()).min(2).max(5).describe('The button labels to show.'),
}),

The output of that tool is the choice the customer has chosen. This deviates a bit from all of the YES NO examples.

This has been working great (for us). User picks a choice (confirms), agent continues. And still works great in the initial chat. But the moment I close my session and return to it later. The messages[] seem to have mutated and/or not persisted correctly.

e..g active chat

output is nicely the choice, messages[] is correct, agent continues.

This happens after reloading (_Id say this happens like 80% of the time, but at some point I had to continue, so can't verify its 100% of the cases):

(note: this Is a different tool callId but still illustrates the issue, for this toolId I've picked Full 3D scene before). Suddenly my output equals the input.

To be honest, I'm learning most of this as I go. Upgrading seems to be a pain point always, as AI moves pretty quick haha.

If I've missed anything my apologies. Also, if this is not how we're suppose to use the addToolResult that's an answer as well, but so far it has been working great for us.

Packages upgraded:

I downgraded now, and the issue is gone.

[whoiskatrin]

I could investigate but next week we are rolling a new change for tools, so it will change because we are migrating to a new version of AI SDK.

[whoiskatrin]

@uuouter can you try a package from this upcoming change please and let me know what your experience is like?

#733

I will check anyways what's happening and let you know.

[uuouter]

V6 nice💪!

I'll try it out tomorrow and get back to you @whoiskatrin - no need to investigate yet then :)

[uuouter]

@whoiskatrin no luck at https://pkg.pr.new/cloudflare/agents@733

I do have some additional info, it seems it's already happening in the useAgentChat.onFinish messages array. Together with losing tools / seeing duplicates.

Active chat:

All good. Then reload:

It's a bit hectic at the moment, so this is all I can provide. Maybe you'll know in instant, otherwise I'll try a repro-repo after the holidays.

Cheers

[deathbyknowledge]

Hey @uuouter mind testing with npm i https://pkg.pr.new/cloudflare/agents@750? Should solve the override issue

[uuouter]

@deathbyknowledge / @whoiskatrin

So remember when I said it didn't work with v6 hehehe.

Redid the whole 0.3.0 upgrade just now with the help of https://developers.cloudflare.com/changelog/2025-12-22-agents-sdk-ai-sdk-v6/ and it does work now! Might've forgotten a step Monday... 😅 (no issues observed in onAgentFinish either anymore)

Which led me to the following realisation, and the core issue... Seems I've been totally abusing a server-side tool lol

return tool({
		description: `Ask the user a multiple-choice question and show clickable buttons.
			Use this whenever you want the user to choose between 2–5 options
			(e.g. theme, season, style, next step). The question text and the
			options are both provided via this tool; the UI will render them
			as a message with buttons.
    `,
		inputSchema: z.object({
			question: z.string().describe('Short question to show to the user (no extra explanation).'),
			choices: z.array(z.string()).min(2).max(5).describe('The button labels to show.'),
		}),
		needsApproval: true,
		async execute({ question, choices }) {
			return {
				question,
				choices,
			};
		},
	});

Execute there In combination with addToolOutput in the client haha. Never realised this... and apparently versions <= 0.2.30 were very forgiving haha. Oh dear.

Thanks a lot for checking.