fix: Use checked pagination arithmetic in provenance::get_by_address

[Samuel1505]

Description

// provenance.rs:86-118
pub fn get_by_address(env: &Env, address: &Address, offset: u32, limit: u32) -> Vec<ProvenanceRecord> {
    ...
    let end = if offset + limit > len { len } else { offset + limit };
    ...
}

Unlike pagination::paginate (the shared helper documented as the canonical place "any module that needs offset/limit pagination" should use, and already used by registry.rs), get_by_address reimplements pagination inline. It doesn't clamp limit to MAX_PAGE_SIZE, and it computes offset + limit with plain u32 addition before checking against len. A caller passing large offset/limit values (e.g. both near u32::MAX) causes offset + limit to overflow, which panics in any build with overflow checks enabled — violating this codebase's "never panic!, return Result" convention — rather than returning a clamped/empty result the way pagination::paginate would.

Technical Requirements

Files to update

• contracts/contracts/stellar-grants/src/provenance.rs (get_by_address, lines 86-118)

Fix direction

Replace the inline pagination logic with the shared pagination::paginate helper (or, at minimum, use saturating_add/checked_add and clamp against MAX_PAGE_SIZE the same way pagination::paginate does) so behavior is consistent with the rest of the codebase and can't panic on adversarial input:

let end = offset.saturating_add(limit).min(len);

Acceptance Criteria

• get_by_address no longer panics when called with offset/limit values that would overflow u32 addition.
• get_by_address's pagination behavior (clamping to available records, respecting a max page size) matches pagination::paginate's conventions.
• A test calls get_by_address with offset/limit near u32::MAX and confirms it returns cleanly instead of panicking.
• cargo test passes.

Estimated Effort

Beginner: 2 hours
Intermediate: 1 hour
Expert: 0.5 hours

How to work this issue

1. Read contracts/ContributionGuide.md for the contribution workflow.
2. Comment on the issue to claim it before starting.
3. Branch: fix/issue-921-provenance-pagination-overflow.
4. Run cargo fmt, cargo clippy -- -D warnings, cargo test before opening your PR.
5. Use a Conventional Commit message, e.g. fix: use checked pagination arithmetic in provenance::get_by_address.

Before you start

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