_computeCurrentFee reverts on underflow when startFee < endFee path is not blocked for equal endFee but lastFee already at endFee — but also computes uint24 underflow if startFee==endFee and durationSeconds==0 not pre-checked in DecayMulticurveInitializerHook._beforeSwap

Opus finding

_computeCurrentFee reverts on underflow when startFee < endFee path is not blocked for equal endFee but lastFee already at endFee — but also computes uint24 underflow if startFee==endFee and durationSeconds==0 not pre-checked in DecayMulticurveInitializerHook._beforeSwap

• src/initializers/DecayMulticurveInitializerHook.sol:110-145
• src/initializers/DecayMulticurveInitializerHook.sol:148-152

If `setSchedule` is called with `startFee == endFee` (non-descending allowed), then `lastFee == startFee == endFee` at construction. In `_beforeSwap` the first guard `if (schedule.lastFee == schedule.endFee) return` will short-circuit, so `_computeCurrentFee` is never called — safe. However, if `durationSeconds == 0` and `startFee > endFee`, `setSchedule` reverts via `InvalidDurationSeconds`, so safe. The other potential issue: in `_computeCurrentFee` of `RehypeDopplerHookInitializer`, when `startFee == endFee`, the early-return checks `startFee == endFee || durationSeconds == 0` before calling `_computeCurrentFee`, so safe. No real bug here.