Continue Blender Web parity task handoff

docs/status/M16-GAP-00219.md

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+# M16-GAP-00219 Status
+
+status: done
+task: armature.calculate_roll operator LOCAL_EXACT slice
+updated: 2026-08-22 America/New_York
+
+scope:
+
+- The minimal fixture contains one selected bone aligned along +Y with zero initial roll.
+- Desktop runs `ARMATURE_OT_calculate_roll(type='GLOBAL_POS_X', axis_flip=false, axis_only=false)` with `poll=true` and `FINISHED`, producing a roll of approximately `pi/2` and preserving the resulting matrix through save/reopen.
+- The existing Main reader exposes the same armature bone head/tail and rest matrix; no new reader field, data-block, editor, or browser behavior was added.
+
+evidence:
+
+- The generator, desktop checker, npm comparator, direct comparator, and task-context checks passed. Repeated checker runs recognize the persisted roll and remain idempotent.
+- WASM/Main observes the same calculated orientation, preserves it across save/reopen, and rejects malformed Blend input without Main mutation.
+- Chromium-only policy was preserved; no Firefox/WebKit run was made.
+
+nextTask: `M16-GAP-00220`