Add unit tests for the escrow deposit cap rejecting investments that would cause total committed to exceed the invoice face value

[Chucks1093]

Summary

The escrow should never accept deposits beyond the invoice face value. Unit tests should confirm that a deposit which would push the total above the face value is rejected, while a deposit that fits exactly within the remaining capacity succeeds.

Scope

• Test a deposit that fills the escrow to exactly the face value succeeds
• Test a deposit of 1 stroop above the remaining capacity panics with capacity_exceeded
• Test two concurrent deposits that together exceed capacity — only one should succeed
• Assert total committed never exceeds face value after any sequence of deposits
• Assert escrow state unchanged after a capacity-exceeded panic

Acceptance Criteria

• Deposit filling to exact face value succeeds
• Deposit exceeding remaining capacity panics with capacity_exceeded
• Total committed never exceeds face value
• Escrow state unchanged after panic

ETA: 12 hours

---

Coordinate on Telegram

[Jonathan-ai9]

@Jonathan-ai9 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi,I'd like to work on this issue. I'll add unit tests covering exact-capacity deposits, 1-stroop overflows, competing deposits, and state preservation after rejection. I'll also verify that total_committed never exceeds the invoice face value across the tested deposit sequences.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Jonathan-ai9 to this issue.

[trust13]

@trust13 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello, the test scope is well defined, and I can cover the deposit-cap boundaries, including exact capacity, over-capacity rejection, concurrent deposits, and state preservation after failure.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @trust13 to this issue.