v0.3.1 — an approval is a return value, not a protocol error

• The advertised return annotation is widened to R | dict[str, Any]. A
  server that validates a tool's result against -> str was turning the
  approval payload into a protocol error at the client — the exact outcome
  §5.1 returns rather than raises to avoid. Found by calling through the real
  MCP SDK instead of past it; there is a test doing that now.
• The two claims about uncoordinated writers finally have tests: two real
  processes appending to one log interleave records without splitting one
  (POSIX), and a forked chain still verifies.