Fix Squid proxy crash loop on container restart

[carlos-gn]

Summary

Fixes #2440

When -egress or -ingress proxy containers are restarted via Docker (e.g., docker restart <workload>-egress), Squid enters an infinite crash loop because it finds a stale PID file from the previous instance.

Root Cause

1. Squid writes a PID file to /tmp/squid.pid on startup
2. On docker restart, Docker sends SIGTERM and Squid begins a 30-second graceful shutdown
3. Docker's default restart timeout is 10 seconds - it sends SIGKILL before Squid can clean up
4. Container restarts with the stale PID file still present
5. New Squid instance refuses to start, thinking another instance is running

This doesn't affect thv restart because ToolHive uses a 30-second stop timeout giving Squid enough time to gracefully shutdown and clean up the PID file.

Fix

Changed pid_filename /tmp/squid.pid to pid_filename none in the generated Squid config. Without a PID file, there's nothing to go stale.

Note: The PID file was only used by Squid internally to prevent multiple instances from running. Since Docker already ensures only one container process runs, the PID file is redundant. Nothing in ToolHive depends on it - the container healthcheck uses ps aux | grep squid, not the PID file.

References

• Squid pid_filename documentation - confirms none is a valid value to disable PID file generation

Test plan

• Run thv run <server> --isolate-network
• Run docker restart <server>-egress
• Verify docker logs <server>-egress shows clean startup (no FATAL errors)
• Verify container survives multiple restarts
• Run task test to ensure no regressions

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.82%. Comparing base (7bee0c8) to head (a90f25f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3022   +/-   ##
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  Coverage   56.82%   56.82%           
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  Files         335      335           
  Lines       33474    33474           
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  Hits        19022    19022           
  Misses      12868    12868           
  Partials     1584     1584           

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[JAORMX]

@claude can you review this against squid security best practices?

[claude]

Claude encountered an error —— View job

Failed with exit code 128

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I'll analyze this and get back to you.