[MOD-2845] fix: prev. inadequate handling of stale in-mem clients

[thundergolfer]

Describe your changes

• MOD-2845

Got a local reproduction of some stale creds. Fix locally by clearing the Client's channel which was initialized with the old creds and left in-memory. In retrospect, this is an obvious problem 😖.

Backward/forward compatibility checks

• [x] Client+Server: this change is compatible with old servers
• [x] Client forward compatibility: this change ensures client can accept data intended for later versions of itself

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[thundergolfer]

if we inject creds worker side then i think we can remove this code?

we do actually do this already. We swap out the creds and emit a warning.

[cweld510]

@thundergolfer does this need to be merged still?