Log crypto funding rates and open interest to Google Sheets

Build me a deterministic ETL workflow that logs crypto derivatives data to Google Sheets on a schedule. This is structured time-series logging only. No summarization, no judgement calls, no branching on content. Just a fixed loop over a watchlist that writes rows.

Trigger: cron, every 8 hours, aligned with the standard perpetual funding cycle (00:00, 08:00, 16:00 UTC). I want it to run on the same cadence that major exchanges settle funding so each snapshot lines up with a real funding event.

Inputs I want exposed as workflow variables:

- coins: a list of ticker symbols to track. Default to ["BTC", "ETH", "SOL"] and let me extend it later.

- spreadsheetId: the Google Sheet to write to.

For each coin in the watchlist, do the following in a loop:

1. Call CoinGlass "Get Funding Rate by Exchange" for the coin. This returns current funding rates across every exchange that lists the perp.

2. Call CoinGlass "Get Open Interest by Exchange" for the coin. This returns current open interest per exchange in both USD and coin units.

3. Flatten and join the two responses by exchange into one row per exchange with these columns: timestamp (ISO 8601 UTC of the run), coin, exchange, funding_rate, open_interest_usd, open_interest_coin. If an exchange shows up in one response but not the other, still write the row and leave the missing field blank.

4. Append those rows to a tab in the Google Sheet named after the coin ("BTC", "ETH", "SOL", etc.) using Google Sheets "Append Values" with valueInputOption USER_ENTERED so numbers are stored as numbers.

First-run setup: before the main loop, check whether each coin's tab exists in the spreadsheet. If not, use Google Sheets "Batch Update Spreadsheet" to add a new tab named after the coin and seed row 1 with the header row [timestamp, coin, exchange, funding_rate, open_interest_usd, open_interest_coin]. After the tab exists, never recreate it; just append.

Error handling: if CoinGlass returns a non-zero code envelope or 429, log the error and skip that coin for this run. Do not block other coins. If Google Sheets returns 429, retry with exponential backoff (1s, 2s, 4s, capped at 16s).

Output: nothing user-facing. The success signal is that the sheet has fresh rows. Optionally include a final summary log line with how many rows were written per coin so I can see it in the run history.