Agent reliability and change management
Source: A postmortem of three recent issues, an update on recent Claude Code quality reports, and Project Vend. durable-agent-architecture keeps the service alive when a part crashes; this skill keeps the agent good after you change it and over a long run.
Gate every change behind an eval run
A one-line system-prompt edit can drop quality across the board, and you will not catch it by reading a few transcripts. Run a broad eval suite for every system-prompt or model change before it ships, and ablate to find which change moved the number. A model recovers well from a single mistake, so a regression hides until you measure it at scale.
Scope a change to its target
A change meant for one model can degrade another. Gate model-specific edits to the model they target, route by an exact match, and test that routing on the boundary cases (idle sessions, state transitions, the moment a cache fills) that skip your normal review.
Roll out in stages and watch
Ship to a slice of traffic first, hold it there long enough to read the signal, then widen. Wire a feedback path, such as a /bug command or a thumbs-down, and watch for a spike in reports that lines up with a deploy. A correlated spike is your fastest regression detector.
Treat reasoning state as an invariant
A cache change that dropped the agent's thinking blocks each turn made it forgetful and repetitive. The reasoning history is load-bearing. When you optimize the request path, assert that thinking and tool state survive the change, and add an integration test on the turn-to-turn boundary where caching bugs hide.
Give a long run external memory
A long-running agent that leans on its context window drifts: it loses track of earlier commitments and starts to confuse its own state. Project Vend's shop agent invented details and lost the thread over days. Give it a place to write decisions and read them back, such as a log or a record store it queries, in place of trusting a longer window to hold everything.
Put deterministic limits on consequential actions
An agent that spends money, grants access, or signs an agreement can be talked into a bad one. Anthropic's shop agent gave away discounts and came close to committing to a losing contract. Put fixed limits around the stakes: a price floor, an approval step above a threshold, a required verification before a quote. The limit does not depend on the model staying skeptical.
Common mistakes
- Reading a handful of transcripts and calling a prompt change safe.
- Shipping to all traffic at once with no rollback signal wired.
- Letting a performance optimization drop reasoning or tool state unnoticed.
- Trusting a bigger context window to keep a multi-day agent on track.
- Leaving a money-or-access decision to the model's judgment alone.