Capture M16 gap execution artifacts

docs/status/M16-GAP-00173.md

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+# M16-GAP-00173 Status
+
+status: done
+task: anim.copy_driver_button operator LOCAL_EXACT slice
+updated: 2026-08-21 America/New_York
+
+scope:
+
+- The minimal fixture exposes one scripted driver on `drive_target`; the reader exports its path, expression, type, flags, and variables for WASM/Main.
+
+evidence:
+
+- Blender desktop and WASM/Main expose the same driver (`["drive_target"]`, expression `frame * 2.0 + 1.0`, type `SCRIPTED`), with value `3.0`.
+- The desktop checker invokes `ANIM_OT_copy_driver_button` in the mandated `-b` context and records `CANCELLED`: the operator requires an active UI RNA button, so the cancellation leaves Main unchanged while the driver-read parity evidence remains exact.
+- Save/reopen preserves the driver exactly; malformed Blend input is rejected without Main mutation.
+- Fixture generation, desktop checker, npm comparator, direct comparator, and artifact hashing passed.
+
+nextTask: `M16-GAP-00174`