The fact store cache root is bounded in bytes, and quiet workspaces are reclaimed

The graphitron cache costs a developer’s disk a bounded number of bytes across every workspace on the machine, and a workspace nobody builds in any more stops holding stores indefinitely. The cache root is <userCacheRoot>/graphitron/model, the directory holding one per-workspace home per checkout; a home in turn holds one stamped directory per DDL-hash-and-version combination it has seen. When this lands, the root has a byte budget and a way to reclaim quiet workspaces, so the cache stays a size a developer would not think to delete.

Split out of R914, which compacts each store at the last handle’s release. That fix takes most of the measured footprint out on its own, which is why this is a disk-footprint item rather than a stall: the 7.4 GB below was 21 uncompacted files, and at the 93% to 94% reclamation measured there the same machine holds a few hundred MB. What compaction does not touch is the shape of the bound.

The cache is bounded by a count of directories, not by bytes. StoreReaper.sweep keeps RETAINED_STAMPS (three) stamped directories per home, the live one included, and evicts the rest by recency. That caps how many stores a workspace holds and says nothing about how large any of them may grow.

The sweep only reaches the home the running build opened. GraphitronModelStore.sweepOnce is driven by an opener and guarded by SWEPT_HOMES, so a workspace nobody builds in any more is never revisited and keeps its retained stores indefinitely. Measured 2026-09-03: a machine carrying ten workspaces held 7.4 GB across 21 store.mv.db files, no workspace over the three the reaper retains, and 1.81 GB of it in a worktree last built on 2026-08-22.

A stamp rotation multiplies that across every workspace at once. stampSegment() is the first sixteen hex digits of the DDL hash plus the generator version, so a consumer rotates it by taking a release and this repo rotates it on any edit to graphitron-model.sql. Each rotation pushes a fresh store into every workspace’s retained slots.

Two levels have to be kept apart, because the tree already uses "home" for the lower one. AbstractRewriteMojo.resolveStoreDirectory returns <userCacheRoot>/graphitron/model/<workspace-segment>, and that per-workspace directory is the home an opener hands StoreReaper.sweep. The level that held the measured 7.4 GB is its parent, the cache root: a directory no opener is ever given and that graphitron-model cannot see, since the only resolver that knows it lives in graphitron-maven-plugin. A byte budget over it therefore needs an owner that does not exist today, which is what makes this larger than the sweep it sits beside.