Device-independent pinch test over PenCanvas: a steady two-finger spread must
grow the shared transform scale MONOTONICALLY, with no frame popping above the
final scale and snapping back (the flicker invariant the absolute-from-snapshot
rewrite enforces). Plus: a single stylus drag never pans/zooms (the recognizer
excludes stylus) — the transform stays identity while the pen draws.
Locks in 6829076 + the arbiter exclusion as regressions guards without a device.
flutter analyze lib/editor clean; 235/235 tests (+2 widget).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
