Metric charts: annotate the timeline when a metric's equation/definition changes

Problem Statement

When a metric (or metric alert) is defined with an equation, its historical chart reflects whatever the equation was at each point in time. There is currently no visual indicator on the chart marking when the equation or definition was edited. Any user who iterates on a metric definition is left unable to tell whether a shift in the chart is a real change in the underlying signal or simply the result of the equation being changed.

Why the current behavior is insufficient
Historical variation that comes from an equation edit is visually indistinguishable from real movement in the data. This makes the history hard to interpret and erodes trust in the displayed values, especially for teams standing up new metrics and tuning them over several iterations.

Solution Brainstorm

Render a vertical annotation/marker on the time-series chart at each timestamp where the metric's equation or definition changed (label e.g. "Equation updated"). On hover, show the previous vs. new equation. Optionally expose a small version history/changelog of equation definitions for the metric.

Product Area

Alerts

No files, tests, or entry points are named. Start by locating the metric and metric-alert time-series chart and the history of equation or definition edits; done means the chart marks each change and exposes the previous and new equations on hover, with any version-history scope decided.