feat: add generated scene skill platform hardening

docs/superpowers/specs/2026-04-18-g6-host-bridge-workflow-design.md

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+# G6 Host Bridge Workflow Design
+
+> Date: 2026-04-18
+> Status: Initial implementation slice
+
+## Goal
+
+Define `G6 宿主桥接多步查询型` as a separate scene family so boundary samples no longer fall back into `G1` or `G1-E`.
+
+The initial implementation goal is classification and fail-closed safety, not runnable generation.
+
+## Family Definition
+
+`G6` covers scenes where the business workflow is primarily advanced by host-browser bridge actions instead of direct request contracts.
+
+Minimum signals:
+
+1. explicit host bridge action such as `BrowserAction(...)`
+2. explicit browser script bridge such as `sgBrowserExcuteJsCode(...)`
+3. callback-driven request progression
+4. business endpoints nested behind the host callback chain
+5. optional `localhost:*` dependency as host runtime evidence
+
+## P0 Boundary Sample
+
+`电能表现场检验完成率指标报表`
+
+Repo-local representative:
+
+`tests/fixtures/generated_scene/g6_host_bridge_workflow`
+
+## Contract Policy
+
+The first slice intentionally does not generate runnable skills for `G6`.
+
+Instead, it must:
+
+1. classify the scene as `host_bridge_workflow`
+2. preserve host bridge actions as evidence
+3. preserve `localhost:*` dependencies as host-runtime evidence
+4. prevent fallback to `single_request_table`
+5. prevent fallback to `single_request_enrichment`
+6. fail closed with a stable blocker
+
+## Non-Goals
+
+1. no host transport redesign
+2. no callback runtime implementation
+3. no full browser bridge orchestration
+4. no broad `G7/G8` expansion
+5. no weakening of `G1-E` or `G3` gates
+
+## Readiness Gates
+
+The first slice adds these G6-specific gates:
+
+1. `g6_host_bridge_detected`
+2. `g6_fail_closed`
+
+`g6_fail_closed` is expected to fail until a real G6 runtime contract exists.
+
+## Acceptance Criteria
+
+1. `G6` fixture is classified as `host_bridge_workflow`
+2. generation fails closed instead of writing a pseudo-runnable skill
+3. ordinary localhost export noise does not get promoted to `G6`
+4. existing `G1-E`, `G3`, `G2`, and canonical tests remain green