Average metric becomes undefined when replacing a large finite value with its negative

[Di-vyansh]

Describe the bug

An existing avg metric becomes undefined when a single numeric cell is changed from 1e308 to -1e308. Both cell values are finite, and the average of the final one-row table is also finite. Defining a fresh average on exactly the same table correctly returns -1e308. This uses only TinyBase, with no browser, persistence, or synchronization.

Your Example Website or App

No response

Steps to Reproduce the Bug or Issue

1. In a new directory, run npm init -y and npm install tinybase@10.0.0.
2. Save the following as repro.mjs.
3. Run node repro.mjs.

// Run after: npm install tinybase@10.0.0
import {createMetrics, createStore} from 'tinybase';

const store = createStore().setCell('t', 'r', 'n', 1e308);
const metrics = createMetrics(store).setMetricDefinition('avg', 't', 'avg', 'n');
console.log('initial:', metrics.getMetric('avg'));
store.setCell('t', 'r', 'n', -1e308);
console.log('stored cell:', store.getCell('t', 'r', 'n'));
console.log('existing average:', metrics.getMetric('avg'));
metrics.setMetricDefinition('fresh', 't', 'avg', 'n');
console.log('fresh average:', metrics.getMetric('fresh'));
metrics.destroy();

Actual output:

initial: 1e+308
stored cell: -1e+308
existing average: undefined
fresh average: -1e+308

Expected behavior

Both the existing and fresh average should return -1e308 after setCell completes. A one-row average should equal the remaining numeric cell.

Actual behavior: the existing average is undefined, although the store contains -1e308 and a fresh average returns -1e308.

Screenshots or Videos

No response

Platform

• OS: macOS 27.0.1 (26A434), arm64
• Runtime: Node.js v24.19.0; no browser required
• TinyBase: npm release 10.0.0
• Also reproduced from source at main commit 3938658

Additional context

I searched open and closed issues with is:issue metric and is:issue overflow (the latter returned no results), and searched Discussions for metric. The closest issue is #300, fixed by #301, which concerned deleting the last numeric row and adding new rows in a transaction. This reproduction updates the same existing cell without a transaction or row deletion, and still fails in v10.0.0.

Possible cause: the average replacement shortcut in src/common/aggregators.ts evaluates add - remove, which overflows for these two finite values. Metrics then exposes the nonfinite result as undefined. The fresh metric shows that the final average itself is representable.

This report was prepared with Codex assistance; the output was reproduced against both the npm release and the source at the reported SHA.

[Di-vyansh]

I would like to contribute a small, separate tests-only PR for an existing Metrics behavior before attempting a fix here. In test/unit/core/other/metrics.test.ts, I did not find a rollback case for averages.

Proposed coverage: a transaction updates one numeric cell and deletes another row, then doRollback returns true. The average should stay at its original value, its listener should not fire, and a later committed cell update should still produce the correct average and listener arguments. I verified this behavior on v10.0.0. No production code or behavior change would be included.

Would this test be useful, or is there a more valuable missing case you would prefer? I will wait for your reply before opening the PR.