Fill operator support in PromQL

Dash0 now supports the fill modifier for binary operations in PromQL, giving explicit control over what happens when one side of an expression has no match.

Three variants:

• fill(<value>) — applies default to whichever side is missing
• fill_left(<value>) — substitutes only when the left-hand side has no match
• fill_right(<value>) — substitutes only when the right-hand side has no match

Note: when both sides of an operator are missing, no time series is generated.

Dash0 worked with the Prometheus community to develop this feature. The fill operator is now available via the UI and API in Dash0.