Continue Blender Web parity task handoff

docs/status/M16-GAP-00198.md

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+# M16-GAP-00198 Status
+
+status: done
+task: anim.merge_animation operator LOCAL_EXACT slice
+updated: 2026-08-22 America/New_York
+
+scope:
+
+- The minimal fixture contains two selected mesh objects. The active object owns `WebGapAnimMergeActiveAction`; the source object owns `WebGapAnimMergeSourceAction`, each with one three-key custom-property channel.
+- Blender invokes `ANIM_OT_merge_animation` with `poll=true` and `FINISHED`, moving the source slot into the active action. Both objects then observe `WebGapAnimMergeActiveAction` with both channels; the source action has no remaining users.
+
+evidence:
+
+- Desktop evidence records the exact pre/post action channels, operator status, active/selected state, and save/reopen stability.
+- WASM/Main reads the post-operation fixture with two `WebGapAnimMergeActiveAction` animation entries (one per object), both carrying the merged channels; save/reopen is exact and malformed Blend input is rejected without Main mutation.
+- Fixture generation, background desktop operator checker, npm comparator, direct idempotent comparator, Python syntax checks, and artifact hashing passed. No production reader or protocol change was made.
+
+nextTask: `M16-GAP-00199`