The correct answer is Defect escape rate.

Defect escape rate measures the share of defects that are discovered after release compared with those found before release, so it directly captures the balance between time spent debugging in the build and test cycle and time spent fixing issues in production. Tracking this rate lets you quantify how many problems "escaped" your pre release processes and therefore shows whether most debugging effort occurs before or after users are affected.

Rework rate tracks the amount of work that must be redone and it is more about effort churn than where defects are found, so it does not directly compare pre release versus post release debugging time.

Mean time to repair measures how quickly you fix an incident once it is detected and it speaks to responsiveness rather than the proportion of defects that escape to production.

Unplanned work rate measures how much work is reactive versus planned and it covers many kinds of interruptions, so it does not specifically quantify defects found after release versus during the build and test cycle.

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