PURGE left behind three classes of dead data that AutoCAD removes,
so an OCS-purged drawing stayed far larger than AutoCAD's (a 23 MB test
file purged to 3.5 MB in OCS vs 0.58 MB in AutoCAD):
- Anonymous blocks (`*U`/`*D`/`*T`/dynamic-block variants) were skipped
wholesale. Leftover unreferenced ones now purge like AutoCAD's, held
live only when actually referenced.
- Block liveness now comes from REACHABILITY: a block is kept only if it
is reached from a real layout container by following block references
(INSERT names, dimension *D, table *T / cell blocks, MultiLeader
content). The old flat "named by some INSERT" scan could not free a
mutually-referencing dead subgraph — e.g. the dependent blocks a
detached xref leaves behind, whose head carried a DANGLING layout
handle that `is_layout()` mistook for a real layout and shielded. That
subgraph (here 467k lines) is now purged; live xrefs, reached from the
layout that inserts them, stay. The used-set also gains the by-handle
block references (table/MultiLeader/dimstyle-arrow) so purging
anonymous blocks can't delete an in-use block no INSERT names.
- SortEntitiesTable objects (per-block draw order) were never removed, so
each purged block's table lingered still listing the handle of every
deleted entity — 341k stale handles / ~2.7 MB of dead weight the save
re-emitted. Drop every table whose owning block is gone.
Net on the test file: 3.5 MB -> 0.81 MB (AutoCAD 0.58 MB).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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