v0.2.0

Breaking

• Account balance, locks, proxy and vesting reads return Result: get_account_data, get_account_data_or_default, get_balance_locks, get_proxy_definitions, get_vesting_schedules (handlers::runtime_queries::balances) previously discarded fetch failures, making "could not reach the node" indistinguishable from "this account has nothing". Adds public AccountDataError and BalanceQueryError::AccountLayoutUnknown(usize); library consumers must handle the new Results. (#386)
• Those reads answer 503, not 200, on upstream failure: a fabricated free: 0 (or empty locks, no proxies, no vesting) from a failed read is now 503 Service temporarily unavailable, safe to retry. An unrecognised storage layout gives 500; a node JSON-RPC error (e.g. State already discarded for a pruned at=) stays 500, since a retry cannot change it. (#386)

Fixes

• Surface transient storage failures instead of returning free: 0: two /accounts/{id}/balance-info requests at the same block could previously disagree. Fetch and decode failures are now distinguished, an unrecognised layout is logged with byte length and hex prefix, and new public utils::is_transient_backend_error / utils::is_transient_storage_error classify a failure as retryable (503) or definitive (500). (#386)

Known limitations

• The same false-default pattern remains outside those four reads: on a transient failure /accounts/{id}/staking-info still returns 200 with fabricated rewardDestination: "Staked", nominations: [], numSlashingSpans: 0; /accounts/{id}/staking-payouts, /pallets/*, nomination pools and foreign assets likewise. There, absence of a 503 does not yet mean the data is real. Tracked in #387, targeted for 0.3.0.

Other

• subxt 0.50.0-beta.4 → 0.50.2: subxt, subxt-rpcs, subxt-metadata off the pre-release onto stable; same minor line, no API break, no source changes. subxt#2197's VerifySignature → VerifyMultiSignature rename affects only subxt's typed extension registry, unused here (extensions decode via own SCALE structs in utils/transaction_extensions.rs). (#390, closes #385)