[Contract] Add Flash Loan Protection Guard in Carbon AMM

[Topmatrixmor2014]

[Contract] Add Flash Loan Protection Guard in Carbon AMM

Closes #789

Summary

Adds a flash loan protection guard to the carbon-dex liquidity pool contract that prevents single-block flash loan manipulations in pricing queries.

Changes Made

New Error Code:

• FlashLoanAttempt = 15 emitted when a same-ledger interaction is detected on an existing position

Storage:

• LastInteractionLedger(Address, Address) tracks the last ledger sequence for each (token, provider) position

Constants:

• FLASH_LEDGER_BUFFER = 1 minimum number of ledgers that must elapse between consecutive interactions

Guarded Functions:

• deposit() calls assert_no_flash_loan() before processing and update_interaction_ledger() after
• withdraw() calls assert_no_flash_loan() before processing and update_interaction_ledger() after

New Public View Function:

• get_last_interaction_ledger(token, provider) -> u32 returns the last ledger sequence when the position was modified

Internal Helpers:

• assert_no_flash_loan(env, token, provider) panics with FlashLoanAttempt if current ledger is within buffer
• update_interaction_ledger(env, token, provider) persists the current ledger sequence

CI Fixes Included

• package.json: removed duplicate devDependencies keys causing JSON parse error
• harvesta-errors: removed duplicate enum variants with same discriminants
• species-voting: replaced env.invoker() with explicit Address parameter
• species-voting: prefixed unused variable with underscore

Testing

• Flash loan deposit-after-deposit in same ledger rejected
• Flash loan withdraw-after-deposit in same ledger rejected
• Operation allowed after advancing to next ledger
• Different tokens are independently tracked
• Different providers are independently tracked
• get_last_interaction_ledger returns correct values across round-trip operations
• All existing tests continue to pass (backward compatible)

Acceptance Criteria

• Code compiles cleanly with zero warnings
• All unit tests pass
• Proper error codes defined in Error enum
• Complete documentation comments added to public functions

[Topmatrixmor2014]

Conflicts Resolved