A/B: Coverage & Decision Gate — Learn vs Act Routing

Same coverage_query tool, two implementation tasks: A asks about Graphonomous MCP deployment (coverage 0.532, 4 knowledge gaps) and gets a learn recommendation; B asks about WebHost.Systems Supabase auth (coverage 0.558) and also needs more knowledge. The act threshold requires coverage ≥0.720 and uncertainty ≤0.350 — both tasks fall short, but with 74 nodes in the knowledge graph (up from 29), coverage scores are notably higher. A hypothetical review_goal shows what happens when the gate opens.