fix: mark interrupted sessions recovered only after recovery starts successfully

[jasonsuhari]

Problem

Automatic recovery marks source sessions recovered before GridBash validates and starts the recovered workspace. If construction or initial launch fails, automatic recovery will not retry those records on the next startup.

Acceptance checks

• Recovery candidates are claimed against concurrent clients without permanently marking success.
• Source records are marked recovered only after a durable replacement session exists or startup succeeds.
• Failed recovery remains eligible for a later automatic retry.
• Tests cover construction and launch failure paths.