CRITICAL: shore-up math double-subtracts cash — unreserved banks bankrupted without consulting the bond market #119

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opened 2026-10-01 15:31:08 +00:00 by Winnie · 0 comments

Winnie commented

2026-10-01 15:31:08 +00:00

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Found by the v0.6.0 review (issue #118). Game.shoreUpNeed (game.go:596-607) computes:

need = bills + (reserveNeed − cash)   when reserveNeed > cash
borrow = need − cash = bills + reserveNeed − 2×cash

The − cash appears twice. The correct borrow target is bills + reserveNeed − cash, so post-bills cash lands on the reserve. Consequences:

A bank with bills covered but reserve unmet (bills < cash < reserveNeed) computes short <= 0, so NO force-borrow is attempted at all, and the reserve check then flags it unshored and bankrupts it WITHOUT the bond market being consulted — directly contradicting the #88 ruling that only a position the market cannot shore is insolvent. The market is never asked.
A bank with cash < bills under-borrows by its own cash, ends the turn below reserve, and dies the next turn the same way.

Evidence: scratch test (cash=3000, bills=1050, reserve=5000, 9500 standing in the market): short=50, bank borrowed 950, flagged "cannot meet the 10% reserve: the bond market could not shore up 1050" and went insolvent — with the market full. A live 80-turn spectate had all 3 bankruptcies reserve-triggered with zero successful shore-up borrows. This math was carried from the original #75 code when #114 unified it into shoreUpNeed.

Found by the v0.6.0 review (issue #118). Game.shoreUpNeed (game.go:596-607) computes: need = bills + (reserveNeed − cash) when reserveNeed > cash borrow = need − cash = bills + reserveNeed − 2×cash The `− cash` appears twice. The correct borrow target is bills + reserveNeed − cash, so post-bills cash lands on the reserve. Consequences: - A bank with bills covered but reserve unmet (bills < cash < reserveNeed) computes short <= 0, so NO force-borrow is attempted at all, and the reserve check then flags it unshored and bankrupts it WITHOUT the bond market being consulted — directly contradicting the #88 ruling that only a position the market cannot shore is insolvent. The market is never asked. - A bank with cash < bills under-borrows by its own cash, ends the turn below reserve, and dies the next turn the same way. Evidence: scratch test (cash=3000, bills=1050, reserve=5000, 9500 standing in the market): short=50, bank borrowed 950, flagged "cannot meet the 10% reserve: the bond market could not shore up 1050" and went insolvent — with the market full. A live 80-turn spectate had all 3 bankruptcies reserve-triggered with zero successful shore-up borrows. This math was carried from the original #75 code when #114 unified it into shoreUpNeed.

Winnie referenced this issue

2026-10-01 15:31:23 +00:00

Massive code review before v0.6.0 #118

Winnie was assigned by robertismo

2026-10-01 15:38:09 +00:00

Winnie referenced this issue from a commit

2026-10-01 15:39:57 +00:00

shore-up math: borrow target is bills + reserve, no double cash subtract (Closes #119)

Winnie referenced this issue from a pull request that will close it,

2026-10-01 15:40:06 +00:00

Shore-up math: borrow target is bills + reserve, no double cash subtract (Closes #119) #128