feat: add generated scene skill platform hardening

docs/superpowers/specs/2026-04-19-g1e-remaining-fail-closed-closure-design.md

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+# G1-E Remaining Fail-Closed 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 4: G1-E / single_request_enrichment`
+> Parent Layer: `Layer C + Layer D`
+
+## Intent
+
+Reduce the remaining `G1-E / single_request_enrichment` structured fail-closed bucket after Routes 2 and 3 are complete or deferred.
+
+## Fixed Input Bucket
+
+`single_request_enrichment = 2`
+
+## 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 4 local inventory and report assets
+
+## Forbidden Files
+
+1. `tests/fixtures/generated_scene/scene_execution_board_2026-04-18.json`
+2. Route 2 and Route 3 assets
+3. Route 5+ assets
+
+## Expected Delta
+
+1. reduce the remaining `G1-E` fail-closed bucket
+2. preserve current real-sample `G1-E` pass
+
+## Stop Rule
+
+Stop after the Route 4 bucket is rerun and either reduced or explicitly deferred.
+