When an MCP tool errors but the side effect already happened, what should the agent trust?
Street-Chest2270 · reddit · 2026-09-12
A Reddit post outlines an easily missed MCP failure mode: the agent calls createpayment(), the provider actually creates the payment, but the confirmation response times out — the agent sees an error and assumes nothing happened. Blind retry risks duplicate side effects, and tool logs don't resolve it since the tool can honestly report a transport failure while external state already changed. The author frames three questions: was the action authorized, was the evidence current at execution, and what external effect actually occurred — the first two checkable pre-execution, the third seemingly requiring independent post-execution observation or provider receipts. They ask operators of side-effecting MCP tools (payments, infra changes, bookings, access changes) what they treat as authoritative on conflict, and whether they test this failure mode before production.
More from coding & agent
- Stripe ships Link CLI: add agentic payments to your app with a one-shot integration — jeff_weinstein · 2026-09-13
- Dev feeds GPT-6 Gran Turismo and F1 movie to build an interactive 3D racing scene — cedric_chee · 2026-09-13
- Will coding agents invent their own formal languages, with natural language as the metalanguage? — jmugan · 2026-09-13
- Uncle Bob Publishes 'Morning Bathrobe Rant' Rethinking AI Coding Harnesses — blaizedsouza · 2026-09-13
- Poison Event Quarantine: 6-Step Cheatsheet to Stop Bad Payloads Blocking Your Queue — blaizedsouza · 2026-09-12
- Fanout, Not Direct Calls: One Write, Many Readers for Production Agents — blaizedsouza · 2026-09-12