feat: add --at flag to query state at a specific block

Problem

Users cannot query historical state at a specific block height or hash. All queries return the latest state only, making it impossible to investigate past conditions or verify state at a particular point in time.

Related

• #58

Proposed Solution

Add an --at flag to the query command accepting either a block number or block hash.

Implementation

polkadot-api's getValue() and getEntries() already accept { at: blockHash } via PullOptions. This is minimal implementation effort:

// Resolve --at to a block hash
let at: string | undefined
if (options.at) {
  if (/^0x[0-9a-fA-F]{64}$/.test(options.at)) {
    at = options.at // Already a hash
  } else {
    // Numeric block number — resolve to hash
    at = await client.chain_getBlockHash(Number(options.at))
  }
}

const value = await storage.getValue(...keys, { at })

UX

# Query by block number
polkadot query System.Account <addr> --at 12345678

# Query by block hash
polkadot query System.Account <addr> --at 0xabc123...

# Combine with other flags
polkadot query Staking.Validators --at 12345678 --output json

Priority

HIGH — low effort, high value for debugging and historical analysis.

Files

• src/commands/query.ts

Start in src/commands/query.ts and trace how query options reach the storage calls. Check the existing command entry point and polkadot-api PullOptions usage, then verify that --at accepts a block number or hash and works with the documented query examples and output flag.