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Description
Favor strategies with balanced option legs in the fallback matching pass. A ladder with surplus longs can otherwise consume the cover needed by another short, leaving a defined-risk spread book charged naked option margin.
The first matching pass and tie behavior are unchanged, preserving genuine ladder books. This follows the approach proposed in #10035.
Related Issue
Fixes #10035.
Motivation and Context
Two covered credit spreads can be regrouped into a ladder plus a naked short. In the added portfolio scenarios, the required margin is 13,000 before the fix and 6,000 after it, matching the combined strike widths.
Requires Documentation Change
No.
How Has This Been Tested?
Clean checkout and fresh build, .NET 10.0.400 on macOS arm64 with Python 3.12. All 5,591 Common.Securities tests pass, with 4 skipped.
The six added cases cover put/call books with overlapping or disjoint strikes and portfolio margin for both rights. Restoring the original matching code fails all six; restoring the fix passes the full set again. Existing ladder and debit-spread tests pass.
The objective function and its strike-width heuristic are unchanged.
Types of changes
Checklist
bug-<issue#>-<description>.