Tauri Arch docker test fails on Node 26 (undici UND_ERR_INVALID_ARG)

[goosewobbler]

Summary

The Package - Tauri (Docker) (arch, Arch) matrix job fails on session POST with UND_ERR_INVALID_ARG once Arch's rolling repo bumps nodejs to v26+. Other distros (Ubuntu, Debian, Fedora, Void) are unaffected because they pin or ship older Node versions.

Symptom

[(unknown) #0-0] ✖ Failed to create a session:
[(unknown) #0-0] WebDriverError: Request failed with error code UND_ERR_INVALID_ARG
                  when running "http://127.0.0.1:4444/session" with method "POST"

The error fires before any service code runs — it's undici rejecting the request at construction time inside WDIO's webdriver client.

Root Cause

• Arch's nodejs package is rolling and currently ships 26.1.0 (build log: extra/nodejs 26.1.0-1).
• Node 26 ships an undici with stricter request validation.
• WDIO's webdriver client constructs a POST /session request with something undici 26 rejects (likely a header value or body field that older undici accepted as-is).
• All other distros in the matrix either pin Node 20 explicitly (Ubuntu/Debian via setup_20.x) or ship older Node from their stable repos (Fedora, Void) — none expose this incompatibility today.

Current Workaround

PR #264 pins Arch to Node 20 LTS by installing the official tarball into /usr/local instead of using pacman -S nodejs. This matches the Ubuntu/Debian pinning approach and makes Arch builds repeatable across rolling-repo updates.

See arch.dockerfile for the patch.

Follow-Up

• Confirm root cause upstream — likely a webdriver-client / undici interaction. May need an issue against webdriverio/webdriverio once we have a minimal reproducer.
• Once WDIO supports Node 26 cleanly, drop the Node 20 pin in arch.dockerfile so we go back to testing against Arch's stock toolchain.
• Consider whether other matrix entries should also pin Node version explicitly (Fedora and Void will eventually catch up to Node 26).

Reproducer

1. Build the Arch docker image with pacman -S nodejs npm (no pin).
2. Run the Tauri package test (pnpm test inside fixtures/package-tests/tauri-app).
3. Session POST fails with UND_ERR_INVALID_ARG within ~1 second.

References

• Failing CI run: https://github.com/webdriverio/desktop-mobile/actions/runs/25629133747/job/75236775669
• Pin commit: f67424c (on feat/electron-browser-mode)