#227 follow-up: await in-flight typed_by_owner feature probe under concurrent face polls #234

Follow-up from #233 (merged) before Bot Social ships typed_by_owner.

Problem

In plugins/social/src/social.js (serverAttests), probedAt is set before await faceApi.features(). Concurrent applyFaceSnapshot calls (via mapPool / GRANT_CONCURRENCY) see a fresh probedAt and return false immediately, so they render with attested: false, accept unstamped FLYBOT-FACE-HUMAN envelopes as person lines, then mark events seen — no self-heal after the probe succeeds.

Related: Codex discussion on #233 — #233 (comment)

Fix

Share/await one in-flight probe promise; only treat the server as non-attesting after a completed probe (success or definitive failure). Add a regression test for concurrent face polls during the first probe.

Also (nits from review)

• Align DM sendTypedAsMember (always tries typed_by_owner: true first) with face canAttest(), or document that old servers must ignore unknown fields.
• Probe HTTP failure currently sticky fail-open for ~10 minutes via probedAt.

Refs #227.