minibf: account endpoints 404 for credentials seen only as proposal return addresses

[slowbackspace]

Blockfrost returns 200 [] for account sub-endpoints (registrations, delegations, withdrawals, mirs, …) when the stake credential appears on-chain only as a governance proposal's return address. Dolos returns 404.

db-sync inserts a stake_address row for every proposal reward account, and ryo's accounts_404 check reads that table. Dolos creates no AccountState for such credentials, and the existing would-be-404 fallback (account_appears_in_pool_registrations, added for pool reward accounts and owners in #1140) does not cover proposal return accounts.

Repro on preview (live Blockfrost vs dolos at current main):

GET /accounts/stake_test1uqpk6zxqea2r70fsx45n2cufdd7qu63444t0ygm3ays778sm04k6e/registrations
blockfrost: 200 []        dolos: 404

The credential is the return address of a governance proposal and has no other on-chain activity.

Likely fix: extend the would-be-404 fallback to also scan ProposalState reward accounts — the namespace holds hundreds of rows, same cost profile as the pool fallback.

Found while live-diffing /accounts/{stake_address}/mirs (#1321) against the Blockfrost preview API: 36/37 checks matched; this was the only divergence and it reproduces on endpoints that predate that PR.

🤖 Generated with Claude Code

Effort

Low — easy mapping or reshaping of existing data, or a plain tx-body decode.

The check reuses the established pattern over existing data.

[slowbackspace]

Another source of db-sync stake_address rows that dolos never materializes, raised by Copilot on #1221: a pool reward account or owner that a re-registration rotated out of the pool's params more than ~5 epochs ago. The PoolState fallback in #1339 checks only the retained snapshot slots (live/next/mark/set/go), so once the old credential ages past go it matches nothing and the account 404s again while Blockfrost serves 200 [].

Same fix shape as the proposal-return case: a persistent record of every credential any certificate ever named, consulted on the would-be-404 path.