Repro

1. Have any other process bind IPv6 [::1]:5173 (common: a stray vite dev from another project).
2. Launch the Tauri shell — ht-llama-webui binds IPv4 127.0.0.1:5173.
3. webkit2gtk's localhost resolution prefers IPv6, so the webview loads the squatter's bundle instead of ht-llama's.
4. UI hangs on splash forever (squatter's app has no /index.html under our routes).

Hit on 2026-05-16 by Markus when a vite dev server from ~/marksverdhei/alacritty/demo was running. Diagnosed jointly with the inventory-dev agent (same regex / port collision applied there too).

Root cause

tools/ui/ui.cpp (or wherever the Tauri shell spawns the embedded http server) binds 127.0.0.1 only. Webkit2gtk resolves localhost → ::1 first and tries IPv6 before IPv4, so any IPv6 squatter on 5173 wins the race.

Fix options

1. Bind dual-stack: [::]:5173 accepting both IPv4 and IPv6 — webkit2gtk hits us on IPv6 first, no squatter possible because we own the socket.
2. Pick a private port: something like 47783 — drops the collision surface dramatically. Downside: port conflicts with anything random.
3. Bind [::1]:5173 explicitly: force IPv6, matching what webview expects. IPv4 callers from the same host stop working though.

Recommended: option 1. Webkit can talk to us via ::1, curl/external test scripts keep working via 127.0.0.1.

Acceptance

• Running vite dev (or any other IPv6 listener) on port 5173 in another shell does not steal the ht-llama-webui webview's bundle.
• curl http://[::1]:5173/index.html returns the ht-llama bundle.
• curl http://127.0.0.1:5173/index.html continues to return the ht-llama bundle (unchanged from today).

Refs

• Diagnostic transcript: inventory-dev <-> ht-llama agent exchange, 2026-05-16.
• Adjacent fix in the cloud repo: snoop-kube's ba325a3 (unified-llm Dockerfile) — separate symptom, same Markus-on-2026-05-16 incident chain.