fix: format object prompt errors

[civonafets]

Summary

Prompt failures can be rejected with plain objects instead of Error instances. This PR formats those values into useful messages so users do not see Prompt execution failed: [object Object].

Related Issues

None.

Type of Change

• Bug fix
• New feature
• New adapter / plugin
• Documentation
• Refactor (no functional change)
• Performance improvement
• Tests
• CI / Build / Config

Changes Made

• Added prompt error formatting for strings, Error instances, primitive values, nested error objects, and JSON-RPC error data.
• Preserved a stable fallback for circular or uninformative error objects.
• Added session tests for plain object errors, JSON-RPC error data, and fallback formatting.

Testing

• Ran pnpm test — all tests pass
• Tested manually with:
• Added new tests for this change
• No tests needed (explain why)

Commands run:

PATH=/Users/m/.nvm/versions/node/v24.15.0/bin:$PATH corepack pnpm build
HOME=/private/tmp/openacp-pr-home PATH=/Users/m/.nvm/versions/node/v24.15.0/bin:$PATH corepack pnpm test

Note: HOME was set to a writable temp directory for the full test run because this local sandbox blocks writes under /Users/m.

Platform Impact

• Telegram
• Discord
• Slack
• CLI
• REST API
• Web UI
• All / Core

Screenshots / Recordings

Not applicable.

Checklist

• My code follows the project's TypeScript conventions (ESM, .js extensions)
• I have updated relevant documentation (if needed)
• I have added/updated tests (if applicable)
• My changes don't introduce new warnings or errors
• I have run pnpm build successfully
• My changes are backward compatible with existing config and data formats
• Plugin API / PluginContext not changed; plugin template update not needed

[0xmrpeter]

Thank you for the contribution! This is a real and annoying bug — [object Object] in error messages is never helpful to users, and the recursive extraction approach handles the JSON-RPC case and circular references correctly.

Approved for merge. I'll fix a couple of minor issues in a follow-up commit:

• "message" in the traversal loop is redundant — if (direct) return direct at the end already handles the fallback. This doesn't affect behavior but makes the code harder to reason about.
• isGenericPromptErrorMessage is missing a comment explaining why "Internal error" is considered generic (it's a JSON-RPC -32603 message, not a meaningful user-facing error). Without that context, future readers may not understand the intent.

These are non-blocking — merging now and fixing in a follow-up.

[civonafets]

Thank you! Keep up the good work :)

…

On Mon, May 18, 2026, 5:44 AM Mr.Peter ***@***.***> wrote: Merged #255 <#255> into main. — Reply to this email directly, view it on GitHub <#255 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AXEAWYLRH52I6TQDRHKPHQD43KBJPAVCNFSM6AAAAACYXODWRKVHI2DSMVQWIX3LMV45UABCJFZXG5LFIV3GK3TUJZXXI2LGNFRWC5DJN5XDWMRVGYZTSNBYG4YTCNA> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>. You are receiving this because you authored the thread.Message ID: ***@***.***>