Early exit with minimum commitment amount and dust handling

[1nonlypiece]

Description

Deliver smart-contract work for commitment_core focused on: Early exit with minimum commitment amount and dust handling.

This issue is contracts-only (Soroban / Rust workspace). Do not scope frontend, backend, or off-chain services here.

Requirements and context

• Security: Treat this as production-leaning code — validate trust boundaries, auth (require_auth where applicable), reentrancy, and arithmetic safety.
• Quality: Changes must be reviewable, deterministic in tests, and aligned with existing patterns in this repository.
• Testing: Add or extend tests so new/changed logic is convincingly covered; capture edge cases called out in the title.
• Documentation: Use Rustdoc (///, //!) on public contract APIs; update docs/ when behavior is integrator-facing.

Suggested execution

Fork and branch

• Fork the repository and create a branch:
  • git checkout -b feature/commitment-core-early-exit-with-minimum-commitment-amount-and-dust-handling

Implement changes

• Contract / library: contracts/commitment_core/src/lib.rs
• Tests: contracts/commitment_core/src/tests.rs
• Docs: add or extend a focused page under docs/ when the change affects external integrators (e.g. docs/CONTRACT_FUNCTIONS.md, threat model, or crate-specific notes).
• Comments: module and function-level Rustdoc in NatSpec style (summary, params, errors, security notes).

Validate security assumptions

• Enumerate trust boundaries (who can call what, what storage keys mutate).
• Confirm no unintended cross-contract calls or missing auth for state changes.
• For math/financial paths, list overflow/underflow and rounding assumptions (tie to shared_utils::math where used).

Test and commit

• Run tests (adjust package as needed):
  • cargo test -p commitment_core --target wasm32v1-none --release
  • or workspace: cargo test --workspace --target wasm32v1-none --release
• Cover edge cases explicit in the issue title; attach summarized test output and short security notes in the PR description.

Guidelines

• Minimum 95% coverage on touched contract and library code (use cargo llvm-cov locally or follow CI coverage gates if present).
• Clear documentation: Rustdoc + relevant docs/ updates for integrators.
• Timeframe: 96 hours from assignment to ready-for-review PR (or comment with a justified ETA).

Example commit message

feat(commitment_core): early-exit-with-minimum-commitment-amount-and-dust-handling