Dark Social Attributor Makes the unmeasurable share loop estimable — honestly. Dark social is the traffic that arrives with no referrer because the link traveled through a DM, a group chat (微信群 / WhatsApp / Slack / Discord), a newsletter forward, or an address-bar copy. This skill declares the estimation method and specs the instrumentation; it never turns an estimate into a Measured number. It is the Observe-phase upstream of the ECHO O dark-social sub-items (see echo-benchmark.md): dark-social method declared and Estimated-labeled before any social-ROI claim (ECHO O2) and the dark-social in…