Why: The authorized small tool stream again lacked an observed DONE marker, leaving transport and provider causes unresolved. Evidence: U3 r0.5 terminal receipt 6b013965 and independent assessment f35d1c17; local links and diff checks passed. Impact: Design only; the missing-DONE tool gate, runtime behavior, and paid resource boundary remain unchanged. Refs: Agent-System-Dev feature/fast-slow-u2-u3-plan; Documents PR #95