ssp: abstraction directory cleared once

abstraction directory cleared once, by whichever language is first

The .ssp writer clears stale files out of
pod/<doc>/media/abstraction/, and that one directory is shared by
every language of a document. The clearing is now done once per
directory per run, by whichever language reaches it first, with
the lock held across it. A language that finds the directory
already prepared has passed through that same lock before writing,
so the clearing it skipped had completed before its own write
began: no .ssp produced on a given run can be removed during it.

(removes possibility of a race condition on parallelisation)

(assisted by Claude-Code)

0 files changed, 0 insertions, 0 deletions