[Ethereal49]

What this changes

Fixes #1550.

On a Windows machine that only has WSL 1, setup failed with:

OpenBot could not check the WSL version (wsl.exe --version). / Probe exited with exit code: 0xffffffff

The registry probe treated a missing DefaultVersion value as WSL 2. Setup therefore skipped the WSL1 blocker and ran wsl.exe --version, which the legacy inbox binary does not understand. An absent value now returns unset, and the parser maps it to WSL 1, so the existing WslOne screen is reached with the wsl --set-default-version 2 instructions before the unsupported command runs.

Where it runs

• New state that outlives a request? None. This is a setup-time probe.
• What happens on the second replica? Not applicable; each desktop installation probes its own Windows host.
• Anything serialised or fanned out? No.
• New listener, port, or schedule? No.

Boundary and audit

• Every acting call still goes through the gateway: no acting calls changed.
• New refusals and new failures each write a row: no new refusal path; this makes an existing blocker reachable.
• Nothing new is trusted from the client: the value comes from the local Windows registry.

Changelog

Added a line under Unreleased in CHANGELOG.md.

Proof

• cargo test an_unset_default_version — 2 passed.
• cargo test windows::tests — 50 passed.
• The regression test feeds the new unset probe result and asserts the WslOne blocker is returned without invoking wsl.exe --version.
• A real WSL1 machine was not available here, so the end-to-end Windows path is NOT_RUN; the probe/state transition is covered by the tests above.

AI disclosure: prepared with Codex; the tests above were run locally. Human review is welcome.