Backlog 4: H4 stopped, waiting on batched merges (refs #25) bbe654f95806

- 2026-10-01 05:40 **oxygenhub#41 parts 2b, 3 and 4** (deployed; hub runs #69 to #71 and oxygenflow #39 pass): Settings → Runners for repository admins and organisation owners; `runs-on` labels in pipelines matched at claim; the queue on Admin → Runners and the runner API. Only part 5 is left: Andy's Plex and VisionFive machines.

- 2026-10-01 07:25 **H4 again (item 6).** The full vscode import (166 425 commits) was OOM-killed at the 14 GB cap after 2 h 18 min. A per-commit trace (`OXY_IMPORT_TRACE=1`, 5765d0a8) showed why: ordinary commits run at 2 to 4 GB, but merges of long-lived branches (1 500 to 5 000 changes) applied those changes to built graphs that kept states share, copying them: 10 to 13.4 GB. `State::shed_graphs` (graphs back into deferred histories, each from a stored checkpoint-form blob) is now used before merges of over 100 commits and on kept states over 2 000 graphs (39d71b23); the 10 000-commit slice is 146 s and 1.6 GB (from 136 s and 2.2 GB), verified. On the full import that took the peak to 9.6 GB so far, but at a cost: about 5 600 commits per 30 minutes (from about 22 000 in the first 15), so the whole history would take about 14 hours, and the remaining peaks are merges onto rebuilt bases with no built graphs: the merge's touched files are built, rendered and diffed all at once. Next: build and diff a large merge's files in batches, shed only on merges (not on every kept state) to win the speed back, then run H4 to the end. The run continues on Earth meanwhile (`vscode-trace2`).