Say at the next start which job the launcher was stopped in.

A job that writes into the game folder leaves data/job-running.json while it runs and removes it when it ends. A
launcher closed or killed in the middle leaves it, and the next start logs it and tells the player which job did not
finish and that Rebuild the Game or Begin Installation goes on from the steps that were done.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

docs/launcher.md

@@ -449,6 +449,13 @@ one's name. An install, a rebuild and the rebuild of an update claim `game`; an
 download claim `app`; the update check claims nothing and runs beside anything. Two launcher folders that share one
 game folder are not kept apart: the lock belongs to the launcher folder.
 
+A job that claims `game` leaves `data/job-running.json` (what it is, the game folder, when it started) from its start
+to its end. A job that ends removes it, also after Cancel or an error, which the job screen has told. A launcher that
+was stopped in the middle (closed by the system, a power cut) leaves it: the next start logs it and says on the home or
+first screen which job did not finish and what finishes it (`jobs.interrupted`), once. Nothing is rolled back: the
+build keeps the old `ocarina.exe` until the new one is linked and records each finished step, so the game folder
+stays playable and Rebuild the Game, or Begin Installation, goes on from the steps that were done.
+
 ## Releases
 
 1. Bump `VERSION`; build the shader translator (`tools/build_xlate.py`).