Placeholder is assigned to an app before worker is initialized

[ejizba]

Created for this incident (internal-only link). This appears to be a rare edge case. For this particular app, it only happened once in the last 90 days.

We see a Node.js worker starting on a placeholder template site, but rather than getting the WorkerInitRequest while still assigned to the placeholder app, the worker gets both a WorkerInitRequest and a FunctionEnvironmentReloadRequest while assigned to the actual customer app. The Node.js worker didn't handle this well. I filed an issue on the Node.js side of things as well, but I don't think the host (or whoever) should be using a placeholder site for a user's site until after worker init has finished.

Here's a very pared down version of the logs, see the incident for an actual query:

PreciseTimeStamp	AppName	Summary
2024-02-14T10:17:15.2232391Z	functionsv4x64placeholdertemplatesite	Initiating Worker Process start up
2024-02-14T10:17:15.2251832Z	functionsv4x64placeholdertemplatesite	Starting worker process with FileName:node ...
2024-02-14T10:17:15.310154Z	<customer app>	node process with Id=4976 started
2024-02-14T10:17:16.7860431Z	<customer app>	Worker Process started. Received StartStream message
2024-02-14T10:17:16.8283348Z	<customer app>	Worker be917f1c-3ae1-4142-ac5d-29e7597e1678 received WorkerInitRequest
2024-02-14T10:17:17.2637967Z	<customer app>	Received WorkerInitResponse. Worker process initialized
2024-02-14T10:17:17.2721214Z	<customer app>	Sending FunctionEnvironmentReloadRequest to WorkerProcess with Pid: '4976'
2024-02-14T10:17:17.3279711Z	<customer app>	Received FunctionEnvironmentReloadResponse from WorkerProcess with Pid: '4976'