feat: add --output ndjson for pipe-friendly streaming output

Problem

JSON output (--output json) emits a single JSON array, which is unsuitable for streaming/piped contexts where line-by-line processing is preferred. Tools like jq, grep, and awk work best with one JSON object per line (NDJSON).

Related

• #64 (structured JSON output)
• #63

Proposed Solution

Add ndjson as a new output format option: --output ndjson

Implementation

Add a formatNdjson() function to src/core/output.ts:

function formatNdjson(data: unknown): string {
  if (Array.isArray(data)) {
    // One compact JSON line per array element
    return data.map(item => JSON.stringify(item)).join('\n')
  }
  // Non-arrays emit a single line
  return JSON.stringify(data)
}

Update printResult to handle the new format:

case 'ndjson':
  console.log(formatNdjson(result))
  break

Use cases

# Process each storage entry individually
polkadot query Staking.Validators --output ndjson | jq '.commission'

# Stream live updates as individual lines (with --watch)
polkadot query System.Events --watch --output ndjson | while read line; do
  echo "$line" | jq -r '.event'
done

# Count entries with grep
polkadot query Staking.Validators --output ndjson | wc -l

Priority

MEDIUM

Files

• src/core/output.ts
• src/core/output.test.ts
• src/cli.ts (add ndjson to output format choices)

Start in src/core/output.ts and review printResult plus the existing output formatters. Add the ndjson format there, update the output format choices in src/cli.ts, and extend src/core/output.test.ts for arrays and non-array values. Done means --output ndjson emits one compact JSON object per line and supports the documented piping use cases.