M1: the interaction ledger

InteractionEvent records one interaction with a remote server: its channel (recv, in, out,
http, preview, crawl), activity and object type, outcome and reason, status, latency, wait,
bytes, attempt, audience, local actor kind, inbox, signature, features and the object's age.
IInteractionLedger.Record never blocks and never throws: events go into a bounded channel
of 10k, a full channel drops and counts, and a hosted service writes batches of up to 1000
every two seconds.

Privacy, as decided by the owner:
- no persona, root, group or activity id, inbox URL, actor URI or sender IP is stored;
- distinct accounts are counted with an HMAC keyed by a per-day salt (InteractionSalt,
  upserted so restarts agree, never created for a past day);
- the local actor kind survives only on public and unlisted traffic;
- a host claimed by an unverified sender is kept only if it is already known.

Traffic caused by reading is only counted per day (InstanceDay.Reads, ServerDay). Indexes:
a 90-day TTL on events, unique day rows, and a TTL safety net on salts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ELjqpznMFMNrJoJUj6K5p2

docs/ROADMAP.md

@@ -12,7 +12,7 @@ Written 2026-10-01 from the original 2023 code, the decePubClient UI, a federati
 - [x] P4 Groups and privacy features: v1.6.0, deployed 2026-10-01; communities, circles and local-only located posts verified by tests. v1.6.1 adds the pasture (`tools/pasture/`): live interop with GoToSocial 0.22.1 passes all 25 checks, three runs in a row. Lemmy and a live Mastodon circle member are not run yet; the pasture has GoToSocial only
 - [x] P5 Lose nothing: v1.7.0 to v1.9.1, deployed 2026-10-01; parsing, typed details, provenance, downvotes, tombstones, federated blocks, all checked live against GoToSocial. Book reviews and forum threads keep their raw form only (typed in P7 and P8)
 - [x] P6 Emoji, polls, quotes, reactions, cards, players: v1.10.0 to v1.15.0, deployed 2026-10-01; polls, link cards, ranged video streaming and quote policies checked live against GoToSocial
-- [ ] T/M Test sweep, the full pasture and the interaction ledger (see "Sweep and statistics" below)
+- [ ] T/M Test sweep, the full pasture and the interaction ledger (see "Sweep and statistics" below). T1–T4: v1.15.1, deployed and verified 2026-10-03 (CI runs all tests on a throwaway mongod; nothing answers 500)
 - [ ] P7 Threads, communities, moderation, the social graph
 - [ ] P8 Signatures, discovery, the long tail