[Bug] Overflow error returned for a divide-by-zero condition

[collinsezedike]

Description

Several checked_div call sites map a None result (which for these particular divisions actually indicates a divide-by-zero, itself a symptom of a broken adapter reporting negative or zero total_assets) to the same ContractError::Overflow variant used for genuine multiplication/addition overflow. This misdiagnoses the failure for anyone debugging from the error code alone.

Steps to Reproduce

1. Reach a state where a divisor in one of the listed checked_div calls is zero (e.g. via a broken adapter reporting degenerate totals).
2. The call returns ContractError::Overflow, indistinguishable from an actual arithmetic overflow elsewhere in the same function.

Expected Behavior

Divide-by-zero and genuine overflow should be distinguishable error variants, since they point to different root causes and different fixes.

Actual Behavior

Both map to ContractError::Overflow.

Environment

Field	Value
Network	testnet / mainnet
Wallet	N/A (contract-level)
Protocol affected	Blend
Browser (if frontend)	N/A
Node.js version	N/A
pnpm version	N/A

Transaction Details (if on-chain)

• Transaction hash: N/A — identified by static review
• Ledger: N/A
• Soroban RPC endpoint used: N/A

Logs / Screenshots

vault/src/lib.rs:186, 280, 312, 511
blend-adapter/src/lib.rs:43-44
.checked_div(...).ok_or(ContractError::Overflow)?   // also covers divide-by-zero

Possible Cause / Fix

Add DivisionByZero = 19 and use it at every checked_div site, keeping Overflow reserved for checked_mul/checked_add failures only.

Scope

Field	Value
Area	Contracts
Protocol affected	Blend
Network	testnet, mainnet
Breaking change?	No — new error variant, appended

[cashmotor01]

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[collinsezedike]

@cashmotor01 checking in — both #599 and #644 were opened and closed without merging, and neither close had a comment explaining what happened. This issue is due today. What's the status — are you still working on it, did you hit a blocker, or should this be reassigned?