Handle the cli daemon startup failures more gracefully with better errors

[canova]

Main | Deploy preview

Fixes #6230.

The scope of this PR was smaller but I went into this rabbit hole of improving this code and it turned out a lot bigger than I initially intended. But I think this improves the whole daemon startup path drastically. See the individual commits for more info. Now, the cli returns error messages like this:

When the session directory is not writable:

Error: Cannot write to the profiler-cli session directory ~/.profiler-cli.
Permission denied. Sandboxes (agent sandboxes, containers, restricted CI runners) commonly deny access outside the workspace, including the home directory.
Underlying error: EACCES: permission denied, open '~/.profiler-cli/.write-probe-28702'
This is the default session directory (PROFILER_CLI_SESSION_DIR is not set).
Point profiler-cli somewhere writable, for example:
  PROFILER_CLI_SESSION_DIR=/var/folders/.../T/profiler-cli profiler-cli load <PATH>
A directory inside your workspace also works, as long as the socket path stays short.

When the unix sockets are not allowed:

Error: The profiler-cli daemon exited during startup (exit code 3):
    Not allowed to create the Unix domain socket at ~/.profiler-cli/ewzneg2rzye.sock.
    profiler-cli needs a Unix domain socket to talk to its daemon. If you are inside a sandbox, allow Unix domain sockets in the sandbox policy, point PROFILER_CLI_SESSION_DIR at a directory the sandbox can write to, or run profiler-cli outside the sandbox.
    Underlying error: listen EPERM: operation not permitted ~/.profiler-cli/ewzneg2rzye.sock

And there are a few more other combinations in case socket path is too long, the socket path is already occupied, a session can't be reached, when the connect() is denied, etc.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.69%. Comparing base (0fc5218) to head (a62903b).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6241   +/-   ##
=======================================
  Coverage   83.69%   83.69%           
=======================================
  Files         348      348           
  Lines       37403    37433   +30     
  Branches    10498    10514   +16     
=======================================
+ Hits        31303    31330   +27     
- Misses       5673     5676    +3     
  Partials      427      427           

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[mstange]

Nice work!

Check the socket path length there too. The kernel rejects an over-long
sockaddr_un with a bare EINVAL that names neither the limit nor the
path.

Thanks, operating systems.