Add test coverage for get_pair_info and quote_route defaults at i128 sentinel boundaries

[1nonlypiece]

Test default sentinels and quote_route net computation

Description

get_pair_info in src/lib.rs returns max_amount: i128::MAX and liquidity: 0 for an unconfigured pair, and quote_route returns (fee, amount - fee) — these specific default-sentinel values and the net subtraction are unverified. The suite asserts get_pair_info only on a fully-configured pair, never on a bare-registered or fully-unconfigured one, and never asserts that quote_route's second tuple element equals amount - fee exactly across fee settings. This issue pins those defaults and the net math.

Requirements and context

• Repository scope: StableRoute-Org/Stableroute-contracts only.
• Cover: get_pair_info for (a) a never-touched pair returns registered:false, fee_bps:0, min_amount:0, max_amount:i128::MAX, liquidity:0, last_route_at:0, and (b) a bare-registered pair flips only registered.
• Cover: quote_route returns net == amount - fee for zero fee, a typical fee, and the MAX_FEE_BPS cap.
• Cover: quote_route and compute_route_fee agree on the fee value for identical configuration (parity).
• Use setup_initialized; no production change expected.

Suggested execution

• Fork the repo and create a branch
• git checkout -b test/contracts-41-defaults-quote-net-tests
• Implement changes
  • Write code in: src/lib.rs — no production change expected (open a follow-up if a gap is found).
  • Write comprehensive tests in: src/lib.rs #[cfg(test)] mod test — the defaults + net-math suite described above.
  • Add documentation: note the defaults test matrix in README.md or docs/testing.md.
  • Include NatSpec-style doc comments (///) on any new test helper.
  • Validate security assumptions: default sentinels match doc comments; net is never negative for valid inputs.
• Test and commit

Test and commit

• Run cargo fmt --all -- --check, cargo build, and cargo test.
• Cover edge cases and failure paths: untouched pair, bare-registered pair, zero/typical/max fee net, quote-vs-compute parity.
• Include the full cargo test output and a short security notes section in the PR description (threat model + mitigations).

Example commit message

test: cover pair-info defaults and quote_route net computation

Guidelines

• Minimum 95 percent test coverage for impacted modules.
• Clear, reviewer-focused documentation.
• Timeframe: 96 hours.

Community & contribution rewards

• 💬 Join the StableRoute community on Discord for questions, reviews, and faster merges: https://discord.gg/37aCpusvx
• ⭐ This is a GrantFox OSS / Official Campaign task and may be rewarded. When your PR is merged you'll be prompted to rate the project — if this issue and the maintainers helped you ship, we'd be grateful for a 5-star rating. Clear questions in Discord and tidy, well-tested PRs are the fastest path to a merge and a reward.

[ekwe7]

I would love to work on this issue. I have experience building production ready applications and collaborating through GitHub workflows. I'll carefully analyze the current implementation, propose a reliable solution, and submit a well-tested PR. My focus is on clean code, maintainability, and timely delivery

[YfengJ]

Hi maintainers, I would like to apply for this issue if it is available. If assigned, I will keep the change test-only: add focused coverage for get_pair_info default sentinels and quote_route net computation at the i128 boundary cases described here, without changing router behavior.

I will wait for maintainer/GrantFox assignment before cloning, implementing, or opening a PR.