contracts: cap deposit_batch size and validate deposit_amount > 0 in constructor

[tech-adrian]

Area
contracts/pool/src/lib.rs (deposit_batch, __constructor)

Problem
Two small but real input-validation gaps in the pool contract:

1. deposit_batch (lib.rs:357-410) only checks the aggregate next_index + count > MAX_LEAVES; there's no independent cap on commitments.len(). Each iteration does two persistent writes plus up to TREE_DEPTH (20) instance writes, so a large-enough batch can exceed Soroban's per-transaction CPU/resource budget and revert with an opaque host error instead of a clear PoolError.
2. __constructor (lib.rs:296-311) stores deposit_amount: i128 with no check that it's > 0. A zero or negative deposit_amount would let deposit/deposit_batch mint a valid leaf while transferring nothing (or attempting an invalid transfer), and contracts/compliance's amount_to_field_bytes casts amount as u128, which mishandles a negative i128 silently. Low likelihood (it's a one-time, operator-controlled deploy parameter) but cheap to guard.

Proposed change
Add a MAX_BATCH_SIZE constant and a BatchTooLarge error checked up front in deposit_batch, documented alongside TREE_DEPTH/MAX_LEAVES. Add an InvalidDepositAmount error returned by the constructor if deposit_amount <= 0.

Acceptance Criteria

• deposit_batch rejects batches over MAX_BATCH_SIZE with a clear BatchTooLarge error (tested)
• Constructor rejects deposit_amount <= 0 with InvalidDepositAmount (tested)
• Relevant tests (just test, pnpm test, cargo test, or nargo test as applicable) pass locally and in CI
• A screenshot or short screen recording is attached to the PR showing the change working (cargo test output for both new checks) — required before this can be merged.

Open your PR against the dev branch, not main. All active development merges into dev.

Discuss this issue / coordinate work: join the DShield contributor Telegram group: https://t.me/+SiGHH24No9U2MDJk

[ebubeb683-ship-it]

Hello boss, Please assign this issue to me. i checked it out and im confident i will solve it
my eta is 4 hours

[Bhenzdizma]

hello sir

I am particularly interested in this issue because I enjoy contributing to meaningful open-source projects and collaborating with developers who are passionate about building valuable tools and products. Open source has played an important role in my growth as a developer, and I am always eager to give back to the community through thoughtful and reliable contributions.

I am confident that I can complete this task within 24 hours while maintaining a high standard of code quality. My approach typically involves thoroughly understanding the requirements, implementing a robust solution, testing it carefully, and ensuring that it integrates smoothly with the existing codebase. I also value clear communication and will be available to provide updates, discuss implementation details, and address any feedback throughout the process.

Beyond simply completing the issue, I strive to create solutions that are easy to maintain, well-documented, and aligned with the project's existing architecture and coding standards. My goal is always to make contributions that add long-term value to the project and improve the experience for both maintainers and users.

I would greatly appreciate being considered for this task and would be excited to contribute to the success of the project. I am available to start immediately and can dedicate the necessary time and attention to ensure the issue is resolved effectively.

Thank you for your time and consideration. I look forward to the opportunity to work with you and contribute to the project.

[grantfox-oss]

🦊 GrantFox — @Bhenzdizma has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #62)
2. Your PR will be reviewed by the Dshield-xyz maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@Bhenzdizma's PR #76 was approved and merged by @tech-adrian.

🏆 @Bhenzdizma: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (519 total points). Track your full progress on GrantFox.

👏 Great work, @Bhenzdizma! Keep contributing to Dshield-xyz.