Three blocking review findings on drawing_diff.
1. An unedited entity reported as changed with changes == {} and clouded.
The signature snaps values to the tol grid, so a value 1 ulp across a
half-grid point lands in another bucket. AutoCAD writes 16 significant
digits (0.14 + 0.005 = 0.14500000000000002 comes back as 0.145), so a
round trip split the pair, which was matched later and counted as
changed. A matched pair is now compared by difference (more than half a
tol, around the circle for angles) instead of by grid bucket, and a pair
with nothing to report counts as unchanged, with no row and no cluster.
Measured live on AutoCAD 2026 (Documents.Open read-only, select all,
Export DXF, Close(False)): before, summary changed=1, a row with
changes {} and one cluster; after, unchanged=21, changed=0, no cluster.
Over 12000 computed coordinates (a*0.01 + {0.005, 0.015, 0.105, 0.305})
795 signatures flip; before, 795 were changed, and after, 0.
2. With zero exact matches, handles were declared stable, so strangers from
two fresh files that share handles were paired and given wrong moves.
The handle stage now needs at least one exact match. The report adds
handle_evidence {exact_matches, kept_handle}.
3. A truncated DXF raised StopIteration from ezdxf's tag reader.
asyncio.to_thread cannot hand that exception to an awaiting caller, so
drawing_diff hung instead of refusing. read_revision now turns every
parse or walk failure (not MemoryError) into ValueError "not a readable
DXF (...)". tol is validated first, so its refusal keeps its own name.
Tests: grid splits by handle and by position, radius/height/rotation/bulge
split at tol=1, a real edit next to a split, no-evidence handles, a
truncated file directly and over the MCP wire with a 30 s timeout. The six
new tests fail against the previous module.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd
engineering/understand/diff.py reads each revision once into entity
records and matches them in three stages: exact signature (type, layer,
geometry rounded to tol, text, block, rotation, scale, attributes;
handles ignored), then handle while at least half of the exact matches
kept theirs, then type + layer + nearest anchor within move_tol (default
2 % of the 1st-99th percentile diagonal). The report counts changes by
layer and type, says what changed per entity (moved by, text, attribute,
radius ... from -> to), compares named block definitions by content and
groups the changes into clusters.
drawing_diff opens group D's copy of SECTION 26. It is read-only unless
markup=True, which files revision clouds around the model-space clusters
on the current document through add_revision - refused before any read
with new_path, without a valid rev, or on an engine without revcloud.
A revision path that is neither .dxf nor .dwg is refused naming the
parameter (old_path: / new_path:), like every other path refusal.
Tests: the synthetic plant P&ID edited five ways (a move, a text, an
attribute, an add, a delete) under renumbered handles reports exactly
those five edits; renumbering alone reports nothing.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd
Track H's foundation, landed on main before its three groups branch.
- engineering/understand/snapshot.py: one bulk read of a drawing into frozen
WCS records (OCS translated through backends/ocs.py, text decoded, an
INSERT boxed by its block geometry without its attribute texts). A DXF is
read with ezdxf after the size check; the headless engine's document is
read under its own lock; the live engine exports the active document with
Document.Export(<tmp>/snap, "DXF", <set of all>) - never renamed, deleted
afterwards - and a DWG is opened read-only, exported and closed. Measured on
AutoCAD 2026: ".dxf" is refused with Invalid argument, the file lands as
snap.DXF, model space, paper space and unused block definitions all reach
it, and the selection set does not narrow a DXF export.
- engineering/understand/labels.py: %%c, \U+2205, the U+2300 sign, o-stroke
and MTEXT format runs all read as one diameter spelling; sizes are kept as
drawn and never equated; Cyrillic look-alike capitals fold into Latin tags;
panels, wiring callouts and electrical data (kW, phases, volts, N, VFD) in
EN / TR / RU / NL / DE. A power that is not written stays None.
- engineering/understand/vocab.py: layer classification with a confidence and
the deciding keyword, supply / return words, room labels and block kinds in
five languages. A CIP layer without a direction word is not guessed.
- MAX_DXF_BYTES defaults to 512 MB (a real layout was 188 MB); the refusal
names the size and the variable. New `office` extra (openpyxl), also in
`full`; uv.lock regenerated.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd
