fix(market): reject deposits at exactly end_time (>= instead of >)

[Akeem813]

close 548

The expiry guard in deposit_collateral used strict greater-than (>):

if env.ledger().timestamp() > market.end_time {
    return Err(ContractError::MarketExpired);
}

This admitted a deposit whose ledger timestamp equals end_time exactly. end_time is the market's expiry instant — a deposit that lands in the same ledger second is a deposit into an expired market and must be rejected.

Fix

Change the comparison to greater-than-or-equal (>=):

if env.ledger().timestamp() >= market.end_time {
    return Err(ContractError::MarketExpired);
}

Boundary Behaviour

Ledger timestamp	Before fix	After fix
< end_time	✅ accepted	✅ accepted
== end_time	✅ accepted (bug)	❌ MarketExpired (fixed)
> end_time	❌ MarketExpired	❌ MarketExpired

Files Changed

• contracts/market/src/deposit.rs — change > to >= in the expiry check

Acceptance Criteria

• Expired market (timestamp > end_time) rejects deposit with MarketExpired
• Market at exactly end_time rejects deposit with MarketExpired (fixed)
• Active market (timestamp < end_time) accepts deposit