mock-amm.initialize doesn't validate rate_bps bounds

[Johnpii1]

Summary

Adds validation for the mock AMM pool rate during initialization to prevent invalid configurations that could result in zero-value swap outputs or arithmetic overflows.

The initialization flow now enforces explicit minimum and maximum rate bounds and returns a clear error when the provided rate is outside the supported range.

Closes #22

Type of change

• Bug fix
• New feature
• Refactor (no behavioral change)
• Test-only
• Docs only
• CI/workflow change

Checklist

• Branch is based on the latest main and the PR targets main.

• Local checks pass:

  • cargo test -p mock-amm
  • Full Rust workspace checks not run.
  • Relayer checks not applicable to this change.

• No secrets, keys, or .env files are committed.

• Tests cover the new validation behavior.

• CHANGELOG.md updated if required.

• COMPATIBILITY.md / protocol-versions.json not applicable.

• Policy documentation not applicable.

Impact

This change improves mock AMM safety by preventing invalid pool-rate configuration at initialization.

• rate_bps = 0 is rejected to prevent swaps from producing consistently zero outputs.
• Rates above 1,000,000 BPS are rejected to prevent unreasonable configurations and potential arithmetic overflow scenarios.
• Valid rates continue to initialize the existing Admin, TokenIn, TokenOut, and Rate storage entries normally.
• No changes are made to bridge mint/redeem behavior, eligibility policy, protocol compatibility, or operational tooling.

Changes

• Added MIN_RATE_BPS: u32 = 1.

• Added MAX_RATE_BPS: u32 = 1_000_000.

• Added the Error::InvalidRate error variant.

• Updated initialize to return Result<(), Error>.

• Added rate validation before persisting initialization state.

• Invalid rates now return Err(Error::InvalidRate).

• Valid rates return Ok(()) and preserve the existing storage behavior.

• Added unit tests for:

  • Zero-rate rejection.
  • Excessive-rate rejection.

• Added Soroban test snapshots covering invalid initialization cases.

Testing

Test Command

cargo test -p mock-amm

Test Results

2 passed; 0 failed

The new tests verify:

client.try_initialize(..., &0)
→ Err(Ok(Error::InvalidRate))

client.try_initialize(..., &(MAX_RATE_BPS + 1))
→ Err(Ok(Error::InvalidRate))

Screenshots / logs

No UI changes. Test output is provided above.

Additional context

The validation is performed during initialization so invalid pool configuration cannot be persisted. Existing valid initialization behavior remains unchanged.

[coderabbitai]

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