P0-D stacked: restore bounded Live Signal viewport without duplicate MMS logic

[masarray]

Scope / ancestry

Stacked strictly on draft P0-D PR #628, exact base ca54fa2c6958b56d81484b1d19be38442de00ac5; preserves #628 typed wire authority, SSOT and engine pin ba21d882f67de22c10d3155b449aac77aa8b4899.

Source and regression

• Port only independent WPF Live Signal DataGrid viewport guard from competing PR P0-D: live signal viewport layout guard and field-evidence UX hardening #629: named grid, MinHeight=0, star-row stretch and independent vertical/horizontal scrolling, retaining row/column virtualization, frozen columns and existing command dock.
• New structural tests check the bounded star region, attached property attributes, virtualization and command-dock separation. P0-D: live signal viewport layout guard and field-evidence UX hardening #629's XML test incorrectly checked unprefixed attached attributes in a namespace; this test checks the correct XML attribute names.
• No alternative NativeIec61850Client.ProjectReadValue implementation from P0-D: live signal viewport layout guard and field-evidence UX hardening #629; P0-D: field-proven zero-length OCTET, exact LN Read coverage and report ingress UX #628 owns verified empty OCTET/VisibleString policy. No RCB/command/control writes.
• P0-D: live signal viewport layout guard and field-evidence UX hardening #629's CS8418 using on IAsyncDisposable is not ported; the parallel test is not a valid replacement for P0-D: field-proven zero-length OCTET, exact LN Read coverage and report ingress UX #628's typed decoder tests.

Gate and operator qualification

Exact SHA Windows CI + R7/installer must pass; rendered 100/125/150/200% DPI screenshots remain separate acceptance, not proven by static XML. Read/RCB/SOE field gates remain open as documented in #628. Preserve historical operator app SHA a4ed26da422d8830e008fb7f8b50462587d283f2 as observation, not new patch acceptance.
Do not merge to main or release without source/safety/field gates.

[masarray]

CI triage (2026-10-20): initial stacked HEAD 142519858... compiled, but R7 run https://github.com/masarray/arsas/actions/runs/39365110790 failed 2 existing tests (M217QStatusAndExplorerRegressionTests and M217NNameplateAndExplorerGeometryTests). Both match the literal adjacent XAML text Grid.Row="2" ItemsSource=...; a newline between those attributes broke the brittle string assertion. Commit 0e084040e5d8f7c19725dfea4005e5bd5eff06c6 restores adjacency while preserving the new viewport layout and our stronger XML-based test. No old test was removed or weakened. Await fresh exact-HEAD CI; prior R7 red must not be reported green.