Cancelled/denied tool calls are indistinguishable from genuine failures

TanStack AI version

@tanstack/ai v0.54.0 (also v0.53.0)

Framework/Library version

Framework-agnostic (plain Node.js)

Describe the bug and the steps to reproduce it

A cancelled or user-denied tool call is emitted with the same shape as a genuine failure, so a consumer can't tell them apart. Both produce state: 'output-error' + { error: <hardcoded string> } (packages/ai/src/activities/chat/tools/tool-calls.ts):

• Cancel (:807-813): { error: 'Tool execution cancelled' }
• Deny (:912-923, :1001-1009, via deniedApprovalResult :486-490): { error: 'User declined tool execution' }

That is identical to real failures — unknown tool (:787), arg-parse (:826), validation (:848). The only discriminator is the hardcoded English string; there's no distinct state, since ToolResultState is 'streaming' | 'complete' | 'error' (types.ts:76).

The framework does know the outcome structurally — the InterruptStore record's status is 'cancelled' — but that's discarded when the TOOL_CALL_RESULT is built, and only { error: <string> } survives into the persisted ModelMessage a UI re-hydrates from. So after reload, matching that localizable string is the only option left.

Runnable repro (no API key) + verified output are in the linked sandbox: an approval-deny and a genuine execute() throw come back byte-identical except for the error string.

Expected: a structured, persistable signal for "user cancelled/declined", distinct from a failure — a terminal state, a discriminator on the result, or (minimally) exported constants for the two strings. Ideally carry through the outcome the InterruptStore already records.

Your Minimal, Reproducible Example - (Sandbox Highly Recommended)

https://stackblitz.com/github/oztune/tanstack-ai-cancel-repro

Screenshots or Videos (Optional)

No response

Do you intend to try to help solve this bug with your own PR?

No response

Terms & Code of Conduct

• I agree to follow this project's Code of Conduct
• I understand that if my bug cannot be reliable reproduced in a debuggable environment, it will probably not be fixed and this issue may even be closed.