Continue Blender Web parity task handoff

docs/status/M16-GAP-00203.md

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+# M16-GAP-00203 Status
+
+status: done
+task: anim.replace_action_new operator LOCAL_EXACT slice
+updated: 2026-08-22 America/New_York
+
+scope:
+
+- The minimal fixture has two objects using `WebGapAnimReplaceNewOldAction`. Desktop runs `ANIM_OT_replace_action_new` with the old action session UID; Blender creates a new empty action and assigns it to both users.
+- The old action remains unlinked with its original channels. WASM/Main preserves that visible old-action evidence; the empty replacement action is intentionally not exposed as an animation entry.
+
+evidence:
+
+- Desktop evidence records `poll=true`, `FINISHED`, `ACTION_REPLACED_WITH_NEW`, the new action assignment, and exact save/reopen. Repeated checker runs preserve the initial evidence and fixture hash.
+- WASM/Main compares the unlinked old action, preserves it across save/reopen, and rejects malformed Blend input without Main mutation.
+- Fixture generation, desktop checker, npm comparator, direct comparator, and task-context checks passed. Chromium-only policy was preserved; no Firefox/WebKit run was made.
+
+nextTask: `M16-GAP-00204`