v5.3.5

• fix(llm): require terminal evidence for streams
• fix(llm): surface interrupted provider streams
• release: prepare a3s-code 5.3.5
• test(agent): cover deferred session model validation
• fix(search): satisfy release lint gate
• feat(search): expose Bing RSS engine
• fix(agent): retry interrupted streams in place
• fix(agent): defer model validation to session
• fix(tools): preserve research workflow contracts