Reorganize Blender Web execution around capabilities

docs/status/M16-GAP-00281.md

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+# M16-GAP-00281 Status
+
+status: done
+task: asset.open_containing_blend_file operator LOCAL_EXACT slice
+updated: 2026-08-24 America/New_York
+
+scope:
+
+- The minimal fixture links one object from external `WebGapOpenContaining.blend`.
+  Blender desktop observes the no-selected-asset boundary as `poll=false`, records
+  `CANCELLED` for `asset.open_containing_blend_file`, and confirms no Main mutation.
+  Save/reopen preserves the Library record exactly.
+- WASM/Main reads the same external Library with stable source path,
+  `EXTERNAL_REQUIRED` status, and an empty dependency closure. The comparator
+  confirms save/reopen stability and malformed-input rejection without Main
+  mutation.
+
+evidence:
+
+- Fixture generation, desktop checker, npm generated-gap comparator, direct
+  comparator, and task-context handoff checks passed with exit code 0.
+  Chromium-only policy was preserved and no Firefox/WebKit run was made.
+- This task adds only the `open_containing_blend_file` fixture/checker/comparator
+  evidence; the reader, Scene IR library path, and WASM artifacts are the already
+  verified external Library path from adjacent asset operator tasks.
+
+nextTask: `M16-GAP-00282`