How can I tell Eclipse that a build is invalid if Eclipse is restarted, so that it always performs this build step again?
Alternatively, how can I tell eclipse to do a full rebuild with just a specific build step?
Anyway, the current solution is to implement a “builder-worker semi-singleton” (one per project) that keeps its own build status, and let the builder call this singleton. I can then call the builder-worker manually whenever I feel like it. It works, but I suspect there is a more Eclips-ish way of doing it, right?
The builder mechanism does not allow setting a build invalid on Eclipse start – AFAIK.
For your other question, in the project menu there is an option to clean selected projects (after the cleaning the automatic builders can rebuild every dependant resource).
The default builders in Eclipse are transient, so they detect if a needed project changes, and execute a needed rebuild after a needed resource changes, so you cannot handle this.