V2 single-leg swap fee not min-protected (residual of #733)

[FonsSicca]

Source: data-quality audit of deployment 8fcf9a8 (2026-07-07). Full findings: Notion audit.

What to build

Min-protect the V2 single-leg swap fee. The V2 single-leg fee is not min-protected, a small over-count on one-sided V2 swaps. It affects Pool.totalFeesGenerated0/1/USD and UserStatsPerPool.totalFeesContributedUSD/0/1. CL is exact. This is the named residual of #733, whose min-of-legs protection covers the two-legged case but not the single-leg V2 path.

Acceptance criteria

• Single-leg V2 fee computation is min-protected, consistent with invest+fix(swap-fee): fee/volume divergence root cause + fix (160 Base pools, residual of #670) #733.
• totalFeesGenerated and totalFeesContributed no longer over-count on one-sided V2 swaps.
• Test covers a one-sided V2 swap.

Blocked by

None — can start immediately.