Add per-client bid seen tracking

[pk910]

Overview

Dora tracks and deduplicates execution payload bids (ePBS), but discarded which clients observed each bid on gossip — a major visibility gap. This PR records per-client bid observations (including first-seen timing) with minimal overhead and surfaces them in the slot page's bid list.

How it works

Ingestion: The bid cache (blockBidCache) interns observer client names and keeps a per-bid map of client → first-seen offset (ms from slot start, negative = gossiped ahead of the slot). Duplicate SSE bid events — previously discarded — now record the observation: the hot path goes from "map lookup, drop" to "map lookup, record one entry". Bids extracted from block bodies record no observer, so 0/N genuinely means "nobody saw it on gossip".

Storage (two tiers):

• block_bids (SQL) only gains two int columns: seen_count / seen_total, stamped at flush time. 0/0 marks pre-feature rows.
• The full data goes to the blockdb as a self-sufficient per-slot BIDS object (<slot>_bids in S3, namespace 7 in pebble): client-name table + full bid fields + seen bitmask + per-client first-seen offsets (~5 KB/slot). Since entries carry the complete bid, historic bid data could later be served from the blockdb alone, without the relational table. Flushes do read-merge-write so restarts and late-arriving bids union instead of clobber; observations are restored into the cache on startup. Persistence is optional — without a blockdb, counts still work for all slots and the detail view covers cached slots.

UI: The bids table gets a "Seen by" column with a colored 42/50 badge (green = all clients, yellow = majority, red = minority) rendered purely from the SQL columns — no blockdb access on page load. Expanding the callout row lazily fetches /slot/{slot}/bidseen once per page (frontend-cached), showing "Seen by" chips with per-client delays (+380ms) and a "Not seen by" group.

API: seen_count / seen_total added to /v1/slot/{slotOrHash}/bids; docs regenerated.

Config

• blockDb.pebble.bidsRetention — optional retention for bids objects (pebble mode; tiered mode stores them in S3 only, uncached).

Tooling

• dora-utils blockdb-copy gains a --no-bids flag and a dedicated raw-bytes bids pass (identical encoding on both backends); the block passes explicitly skip _bids objects / namespace 7.

Overhead

Hot path: one bitset/map insert per duplicate event. Memory: <200 KB for the cache window. Storage: ~5 KB/slot, one blockdb write per slot at flush. Historic slot pages only touch the blockdb when the seen callout is expanded.

[barnabasbusa]

wow this is huge !