fix(com): every system variable is read and written on the ActiveX document, not the Application

AcadApplication has no GetVariable/SetVariable members; they live on
AcadDocument. Measured on the running AutoCAD 2026 (25.1s, 2026-09-22,
scratch Documents.Add(), Close(False)):

    hasattr(app, 'GetVariable')  -> False
    hasattr(app, 'SetVariable')  -> False
    app.GetVariable('INSUNITS')  -> AttributeError: ... IAcadApplication
                                    instance ... has no attribute 'GetVariable'
    doc.GetVariable('INSUNITS')  -> 4
    doc.GetVariable('MEASUREMENT') -> 1
    doc.GetVariable('FILEDIA')   -> 1; doc.SetVariable('FILEDIA', 0) -> None,
                                    reads back 0, restored to 1
    doc.GetVariable('AUDITCTL')  -> 0, 'CMDACTIVE' -> 0, 'USERS1' -> ''

Fifteen call sites in backends/com_backend.py still went through the
Application inside `try/except ... log.debug`, so on a live seat they
silently degraded: MEASUREMENT defaulted every seat to metric,
drawing_info reported units from a failed INSUNITS read, drawing_audit
never set AUDITCTL, the CMDACTIVE guards of system_run_command /
system_run_lisp never fired and run_lisp never read USERS1 back. All are
rerouted through `_acad_doc()`; the try/except stays only where an
optional read is defaulted (INSUNITS -> "Unknown", AUDITCTL absent on a
host that lacks it, USERS1 after the expression ran) and the log line
says so.

Linetype loading, measured the same way: `SendCommand("_-LINETYPE _LOAD
CENTER acadiso.lin\n\n")` loads nothing with FILEDIA=0 and leaves the
command at `Enter an option [?/Create/Load/Set]:` (LASTPROMPT), which
makes the whole seat answer RPC_E_CALL_REJECTED to every client until
ESC is pressed; with FILEDIA=1 it opens the modal "Select Linetype File"
dialog. `doc.Linetypes.Load("CENTER", "acadiso.lin")` returns None and
the table grows 3 -> 4; a repeat raises 'Duplicate record name', an
unknown name 'Undefined linetype', a missing file 'File system error'.
`_ensure_linetype_loaded` and `linetype_load` now call `Linetypes.Load`
(MEASUREMENT still read on the document to pick the .lin), touch no
FILEDIA, and report a failure with the English excepinfo description.

`apply_standard` reads every variable it will write before the first
style is created, so a read the engine refuses is a refusal with nothing
written (it used to fail after ISO-25 / ISOCP were created and current).

Fakes: every application fake refuses GetVariable/SetVariable
(tests/test_styles.py's COM fixture carried them on the Application,
enshrining the wrong shape); the members exist on document fakes only.
Regression tests per rerouted site: linetype load via Linetypes.Load with
MEASUREMENT on the document, drawing_info units from the document,
AUDITCTL set/restored on the document, CMDACTIVE/USERS1 on the document,
apply_standard refusing before any write.

Live end-to-end with the real ComBackend on a scratch document:
apply_standard('iso') -> INSUNITS 4, ISO-25 (already in acadiso.dwt,
created: false) and ISOCP (created: true) current, second call created:
false / changed: {}; linetype_load('CENTER') -> Linetypes 3 -> 4, FILEDIA
stays 1, repeat already_loaded, 'NOSUCHLT' refused by name;
_ensure_linetype_loaded('HIDDEN') -> 3 -> 4; drawing_info units 'mm';
drawing_audit AUDITCTL 0 -> 0; system_run_command ok;
system_run_lisp('(+ 40 2)') -> '42'.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

engineering/standards/apply.py

@@ -62,11 +62,29 @@ async def apply_standard(
     Every item reports whether it was created or already present; ``settings``
     reports only the variables that moved. An existing style of the standard's
     name is used as it is — ``dimstyle_modify`` changes one on purpose.
+
+    Every system variable the call will write is read *before* the first
+    style is created, so a read the engine refuses is a refusal with nothing
+    written. (The units loop used to run after both styles; on the live
+    engine its INSUNITS read went through a member the ActiveX Application
+    does not have, so the call failed with ISO-25 and ISOCP already created
+    and current.)
     """
     key, row = resolve_standard(standard)
     if not isinstance(layers, bool) or not isinstance(units, bool):
         raise TypeError("layers and units must be booleans")
 
+    current: dict[str, Any] = {}
+    if units:
+        for var, _value in STANDARD_SYSVARS:
+            try:
+                current[var] = await backend.system_get_variable(var)
+            except Exception as exc:
+                raise RuntimeError(
+                    f"apply_standard: could not read {var} before writing "
+                    f"({exc}); nothing was changed"
+                ) from exc
+
     text_names = {entry["name"].lower() for entry in await backend.textstyle_list()}
     textstyle_created = row["textstyle"].lower() not in text_names
     if textstyle_created:
@@ -86,7 +104,7 @@ async def apply_standard(
     changed: dict[str, list] = {}
     if units:
         for var, value in STANDARD_SYSVARS:
-            old = await backend.system_get_variable(var)
+            old = current[var]
             if _same(old, value):
                 continue
             await backend.system_set_variable(var, value)