The monitor changes are done and all tests pass, but three of the brief's assumptions don't hold on the live chain, and two of them affect what you'll see. I changed getSlot0 to a working read. The empty-pool gap needs your decision.

Where the brief and the chain differ

All three were measured read-only on 2026-11-07.

1. PoolManager.getSlot0 doesn't exist on the deployed contract. The call reverts with empty data and the selector isn't in the bytecode. As written, every active pool would be UNKNOWN and there would never be a spread. I read the same data through PoolManager.extsload(keccak256(abi.encode(poolId, 6))), which is how Uniswap's own StateLibrary does it. It costs the same one call per pool and returns the same fields.

2. sqrtPriceX96 == 0 doesn't catch empty pools. Zero only means the pool was never initialised, and such a pool can't have swaps, so EMPTY will rarely if ever appear. The 30000/600 pool has zero liquidity but a non-zero price (tick −887272). When its last swap is in the window, it shows as OK and tops the spread table as GREEN with a net of about 6e27%. No funds are at risk because the quote returns 0 and nothing sends, but auto mode turns itself off on the first poll that picks it.

3. Blocks are about 0.105 s apart, so windows are short in time. A swap older than the window makes its pool inactive rather than stale.

   Window	Time covered	PONS/USDG result
   3000 (default)	about 5 min	1 active pool, "No tradeable spreads"
   50000 (maximum)	about 88 min	3 active pools

   The default 7200 s limit therefore can't trigger on this chain and the red colour can't appear. STALE only appears if you set Max staleness lower than the window's time span. I kept your defaults as written.

What was built

• Window: there is a live "Window (blocks)" field, and the status bar shows its value.
• Polling: each poll now makes 2 calls plus 2 per active pool, and eth_blockNumber is gone.
• Staleness: there is a colour-coded Last Swap column and a Max staleness field next to the threshold.
• Pool marks: STALE, EMPTY and UNKNOWN appear in the Active? column, and those pools are left out of spreads and auto mode.
• Spread table: it shows "No tradeable spreads" when fewer than two pools qualify.
• Auto mode: it logs skips such as auto skipped: pool 3000/60 stale (3h 12m), and still trades the best clean spread if one exists.

Choices the brief left open

• A failed read of the swap block's timestamp also marks that pool UNKNOWN, since its freshness can't be shown.
• A typo in Window or Max staleness keeps the last valid value, so it can't loosen the guard.
• Each skip reason is logged once per pool until its status changes, not on every poll.
• A spread you already selected keeps its Dry run and Send buttons if a pool later gets marked. Your guard covers the table and auto mode, and each send is still simulated first.

Other changes

• Race fix: a poll still running when the pair changes could overwrite the new pair's data, and the extra calls made that more likely. It's fixed and tested.
• Solidity and README: I also updated src/V4PoolMonitor.sol with its tests and rewrote the affected parts of the README.

Testing

• forge build: passes on the pinned compiler.
• forge test: 68 of 68 pass with your fuzz seed.
• forge fmt --check: clean.
• JavaScript tests: 99 and 18 pass, covering success and failure paths. Seven deliberate code breaks were each caught.
• Live RPC: the real monitor ran read-only at 3000 and 50000 blocks and sent nothing.
• Not run: a real browser or wallet (the page tests use a mock DOM) and Slither. No independent security review has been done.

The changes are uncommitted in the working tree.

Decision for you

• Should a pool with zero liquidity also count as EMPTY? The Swap log already includes liquidity, so this adds no RPC calls and would stop 30