You'll notice
The error for a missing tool now says clearly whether it's switched off or its source was removed
What
When a tool that's part of the current conversation isn't actually available to use, the error message now distinguishes two different cases: the tool being switched off in the current session, versus the tool's source (such as a connected server) having been removed or disconnected. Each case now gets its own distinct message.
Why
This makes it clearer why a tool isn't working, so a user or model can tell whether to just turn it back on or whether it needs to be reconnected entirely.