perf(api): delta-based social aggregate counts + reconciliation backstop

[raymondjacobson]

Summary

Replaces the per-write count(*) recounts in handle_repost / handle_save with O(1) deltas (consistency with handle_follow), and adds a periodic reconciliation job as the drift backstop for all aggregate counts.

1. Delta-based aggregate maintenance (hot path)

• handle_repost.sql / handle_save.sql: every count(*) recount → <col> = <col> + delta.
• Delta is now transition-aware: delta = (new active?1:0) − (UPDATE & old active?1:0), where active = NOT is_delete. Correct for upsert-in-place toggles; idempotent (delta 0) on no-op re-delivery.
• All three triggers (handle_repost, handle_save, handle_follow) move from AFTER INSERT → AFTER INSERT OR UPDATE so the entity_manager upsert path maintains counts. handle_follow gets the same transition-delta for consistency.

2. Reconciliation backstop (off hot path)

• New jobs/reconcile_aggregates.go (ReconcileAggregatesJob), modeled on prune_plays.go. Ports the three full-recompute queries from discovery's update_aggregates.py (user / track / playlist counts + dominant_genre).
• Scheduled every 10 min in indexer.go (matches discovery's celery cadence). Writes only the count columns — column-disjoint from the score-only AggregatesCalculator, so they run concurrently without collision.
• Faithful 1:1 port of the SQL, with one deliberate improvement: nullable dominant_genre / dominant_genre_count comparisons use is distinct from instead of Python's !=. != returns NULL on a genre flipping to/from NULL, so such a row is silently skipped until a count also changes; is distinct from converges it. Never writes a different value — strictly catches one edge case Python misses.

3. Packaged etl dependency

• Bumps go-openaudio + go-openaudio/pkg/etl to 5ed068b, which includes the now-merged perf(etl): upsert social writes in place instead of demote-then-insert OpenAudio/go-openaudio#331 (upsert social writes in place instead of demote-then-insert).
• This is a hard requirement for section 1: the AFTER INSERT OR UPDATE triggers only track is_delete transitions correctly when the indexer upserts the single is_current row in place. The dependency ordering is satisfied by this bump — [API-221] Add /v1/dashboard_wallet_users #331 is merged and packaged here, so this PR is safe to merge on its own.

Test plan

• go build ./... passes against the bumped etl.
• Rebased onto current main; dropped a stale copy of the per-processor-timing change already merged via obs(api): log per-processor timing in IndexChallengesJob #897 (would have double-declared slowProcessorThreshold).
• After deploy: confirm repost/save/follow counts increment/decrement on toggle and stay correct on re-delivery.
• Confirm ReconcileAggregatesJob logs only when it corrects drift (corrected > 0) and otherwise stays quiet.