feat: add generated scene skill platform hardening

docs/superpowers/specs/2026-04-19-g3-export-plan-closure-design.md

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+# G3 Export Plan Closure Design
+
+> Date: 2026-04-19
+> Status: Draft
+> Parent Framework Plan: `docs/superpowers/plans/2026-04-19-scene-skill-102-full-coverage-framework-plan.md`
+> Parent Route: `Route 2: G3 / paginated_enrichment`
+> Parent Layer: `Layer C + Layer D`
+
+## Intent
+
+Reduce the second repeated `G3 / paginated_enrichment` fail-closed subgroup by recovering missing export-plan evidence without loosening workflow completeness gates.
+
+## Fixed Input Bucket
+
+Primary bucket:
+
+`paginated_enrichment + g3_export_plan + export_plan`
+
+This child plan targets the repeated scenes whose structured fail-closed state shows:
+
+1. `workflow_contract_complete` and/or `workflow_complete_for_archetype` failed because `export_plan` is missing
+2. `g3_export_path_identified` failed because `g3_export_plan` is incomplete
+
+## Allowed Files
+
+1. `src/generated_scene/analyzer.rs`
+2. `src/generated_scene/generator.rs`
+3. `src/generated_scene/ir.rs`
+4. `tests/scene_generator_test.rs`
+5. route-local follow-up assets
+6. route-local reports
+
+## Forbidden Files
+
+1. `tests/fixtures/generated_scene/scene_execution_board_2026-04-18.json`
+2. Route 3 and later implementation assets
+3. promotion/board policy assets
+
+## Expected Delta
+
+1. reduce the count of `paginated_enrichment` fail-closed records driven primarily by export-plan absence
+2. if scenes still fail, narrow them to a smaller residual blocker such as runtime scope or enrichment contract
+
+## Stop Rule
+
+Stop after the export-plan subgroup is rerun and the resulting residual bucket is explicitly measured.
+
+Do not continue into Route 2 residual closure under this plan.
+