Record first validation reply

[echowang1]

Summary

• record the first public validation reply from MCP Dev LATAM
• update amount-drift scenario usefulness to 1 of 8 early signals
• note that interviews, demo flows, and integrations remain at 0

Follow-up

• replied publicly asking whether a redacted OAC/x402 drift fixture boundary maps to their mocked-fetch tests
• private recruitment ledger updated locally; it remains ignored and is not included in this PR

Tests

• not run; documentation-only update