WIP: Add test coverage for ConnectStream

[xyzconstant]

ref: #183

Opening this draft to make it visible to more reviewers. Quoting my comment in the issue as well:

I've added tests for four scenarios:

1. Attempting to use an fd associated with a server that has already been disconnected results in a crash with: "IPC client method called after disconnect".
2. Attempting to use an fd associated with a server that disconnects immediately after the first recv(), the outcome will either be crashing with "IPC client method called after disconnect" or "IPC client method call interrupted by disconnect." This behavior seems to depend on whether the recv() call successfully reads the entirety of what is likely Capnp’s bootstrap request or only a portion of it.
3. Attempting to use an fd associated with a server that disconnects after a second recv(), the process crashes with "IPC client method call interrupted by disconnect."
4. Attempting to use an fd associated with a server that indefinitely calls recv() in a while loop results in the test getting stuck at this line:

libmultiprocess/include/mp/proxy-types.h

Line 754 in 8412fcd

thread_context.waiter->wait(lock, [&done]() { return done; });

It’s important to note that all of these cases call FooInterface::initThreadMap() to invoke clientInvoke(), as ConnectStream() on its own won't trigger any libmultiprocess request if there's not a construct() method available in the Init interface.

I'm looking for more ideas for testing ConnectStream.

[DrahtBot]

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #288 (Create support branch for CI scripts, documentation, and examples by ryanofsky)
• #269 (proxy: add local connection limit to ListenConnections by enirox001)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

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Possible typos and grammar issues:

• Cap N' Proto -> Cap'n Proto [the project name is misspelled]

^{2026-06-24 03:54:02}