Public attention metrics can emit Infinity or convert booleans into measurements #782

Reproduction

On current main bcd699f, fetch_attention_feeds admits positive Infinity and booleans as numeric metrics. A public JSON number such as 1e400 decodes to Infinity in Python; serializing the resulting observation with allow_nan=False fails. A boolean becomes an invented measurement of 1.0. An oversized integer can instead discard the entire feed through an overflow exception.

The same comprehensions occur in primary observations, supporting observations, and restored observations after a Hacker News collector failure. Native caller regressions fail on all three paths. Measured zero and ordinary nonnegative numeric metrics are valid controls.

Proposed change

Use one finite, nonnegative numeric normalizer across those paths, excluding booleans and invalid metric containers. Preserve the observation and its valid measurements rather than fabricating a value or emitting invalid JSON.

This is separate from #616's new leaderboard ranking signals and #704's source-connector missing-counter handling. It changes public-attention feed normalization only. No committed source observations or generated artifacts will be edited.