fix(terraria,tmodloader): probe readiness without connecting

[ValgulNecron]

Summary

This replaces the crashing tcpSocket readiness probe in terraria and tmodloader with an exec probe that never connects to the game.

The bug: the Terraria server crashes when a client connects and closes right away. That is exactly what the kubelet's tcpSocket probe does every 10 s, so the probe crash-looped the pod.

Evidence from the 2026-10-04 kubelab live sweep:

• The pod log showed two ... is connecting... lines, then an ObjectDisposedException in Terraria.Netplay.ServerLoop, and the container exited.
• The pod had 5 game-container starts in 6 minutes.
• A crash during world generation left the restarted server stuck at Choose World:.

The fix:

• The readiness probe is now this command:

  sh -c "grep -qsE ':1E61 [0-9A-F]+:[0-9A-F]{4} 0A' /proc/net/tcp /proc/net/tcp6"

• It succeeds only when a socket is in state 0A (LISTEN) on local port 7777 (0x1E61).
• The pattern cannot match a connection whose remote port is 7777.
• The pod turns Ready once the server accepts players, without the probe ever opening a connection.
• initialDelaySeconds, periodSeconds and failureThreshold are unchanged.
• specs.md explains the probe for both modules.
• Versions: terraria 2.2.1 → 2.2.2, tmodloader 1.0.0 → 1.0.1.

Verification (kubelab, 2026-10-05)

• Vanilla server: a vanilla-latest server with this probe was not-ready 4 times during world generation, then turned Ready. It stayed Ready for 6.5 minutes with 0 restarts. Its log had no is connecting or ObjectDisposed lines.
• Probe check, run in the pod: the command returns 0 for port 7777 and 1 for 7778. /proc/net/tcp shows 00000000:1E61 00000000:0000 0A.
• tModLoader image: a one-off pod shows sh, grep -E, /proc/net/tcp and /proc/net/tcp6 are all present. A full tModLoader boot test was not possible, because the image exits without an uploaded modpack (see the note below).
• Precedent: exec probes are already used by nuclear-option and minecraft-java.
• Both test servers were deleted afterwards.

Separate issue found while testing (not fixed here)

The tmodloader template's MODPACK config field has no default and is not marked required. The image exits ("Modpack name was not provided", or "Modpack was not detected" when no modpack is uploaded), so a fresh tModLoader server crash-loops until a modpack is uploaded. The tModLoader versions on the terraria template behave the same way.

Follow-up in Gameplane

ValgulNecron/Gameplane#551 bumps the modules pointer to this branch and mirrors the probe in the Terraria bot e2e fixture. Please merge this PR with a merge commit (not squash or rebase), so the pinned SHA stays on main.

🤖 Generated with Claude Code

https://claude.ai/code/session_01NsN6bnAMRM9XQtrTQ6KC7U