Rust-Owned Settlement-Arbitrage Bot Architecture

Covers the Rust extension, unified engine, pump, executor, and Python orchestration layer for Uniswap V2/V3/V4 same-block arbitrage on Ethereum mainnet.

Developed under Plans 079–082 (all complete).

STATUS: HISTORICAL. This captures the original ArbitrageEngine/V2|V3|V4BlockEngine design from Plans 079–082. It predates the bot_core/solvers restructure of degenbot-bot (the optimizers/ paths below no longer exist) and the ports of simulation (degenbot-simulation) and submission (degenbot-submission) to Rust. Do not use it as the component map — read the crate sources and ADR-003/ADR-005 instead. Kept as a design-history reference.

1. Guiding Principle

Rust is the engine, Python is the cockpit.

Every hot-path operation — event decoding, pool state mutation, tick-range construction, solver dispatch, result storage — lives in Rust. Python participates in construction (pool discovery, engine registration) and orchestration; simulation (degenbot-simulation) and transaction submission (degenbot-submission) are now Rust-owned. During the per-block loop, Python reads results from Rust and encodes swap payloads using Python pool objects; it does not receive events, update pool state, or push data to the engine.

┌─────────────────────────────────────────────────────────────────────┐
│                          Startup (Python)                           │
│  Bot.from_config_file → build_paths_async → register_pool/path     │
│  → backfill_snapshots → engine.freeze → engine.initial_solve       │
│  → engine.subscribe(rpc_url) → backfill_from_snapshot              │
│  → engine.resume_from_subscribe()                                  │
└─────────────────────────────────────────────────────────────────────┘
                                │
                                ▼
┌─────────────────────────────────────────────────────────────────────┐
│                      Hot Loop (Rust Pump)                           │
│  WS newHeads+logs → process_block → solve → store results              │
│  ↳ send BlockNotification via watch channel                        │
└─────────────────────────────────────────────────────────────────────┘
                                │
                                ▼
┌─────────────────────────────────────────────────────────────────────┐
│                    Dispatch (Python)                                 │
│  wait_for_block → latest_results → encode_payloads                 │
│  → eth_simulateV1 → sign → send_raw_transaction                   │
└─────────────────────────────────────────────────────────────────────┘

2. Component Map

Component	Language	File(s)	Role
ArbitrageEngine	Rust	`rust/crates/degenbot-bot/src/optimizers/arb_engine.rs`	Unified V2+V3+V4 engine: state, solving, result storage
V2BlockEngine	Rust	`rust/crates/degenbot-bot/src/optimizers/v2_block_engine.rs`	V2 pool state, Sync decoding, constant-product solving
V3BlockEngine	Rust	`rust/crates/degenbot-bot/src/optimizers/v3_block_engine.rs`	V3 pool state, Swap/Mint/Burn decoding, tick-range construction, piecewise solving
V4BlockEngine	Rust	`rust/crates/degenbot-bot/src/optimizers/v4_block_engine.rs`	V4 pool state, Swap/ModifyLiquidity decoding, same CL math as V3
ArbitrageEnginePump	Rust	`rust/crates/degenbot-bot/src/optimizers/arb_engine_pump.rs`	Unified async pump: dual WS subscription (newHeads + logs), backfill on timeout/empty block, routes to sub-engines
Bot	Rust	`rust/crates/degenbot-bot/src/bot_core/mod.rs`	Single owner of pool/token state (future all-state owner, currently V2+V3 partial)
ReorgJournal	Rust	`rust/crates/degenbot-bot/src/bot_core/state_history.rs`	Bounded deque of per-block deltas for rollback (V2: 2 reserves; V3: scalars + tick priors)
Tick bitmap walk & tick mutation	Rust	`rust/crates/degenbot-bot/src/bot_core/tick_bitmap.rs`	`gen_ticks()` port + shared `update_tick_liquidity` / `apply_liquidity_to_tick_range` helpers used by both V3 and V4 engines
Event decoders	Rust	`rust/crates/degenbot-bot/src/bot_core/v*_decoder.rs`	Decode Sync, Swap, Mint/Burn, ModifyLiquidity from Alloy logs
Möbius solvers	Rust	`rust/crates/degenbot-bot/src/optimizers/mobius_*.rs`	Integer-exact arbitrage solvers (V2-V2, mixed V2-V3, V3-V3)
V2 swap encoding	Rust	`rust/crates/degenbot-bot/src/bot_core/v2_encoding.rs`	Pre-encoded `swap()` calldata production
PyArbitrageEngine	Rust/PyO3	`arb_engine.rs` (bottom)	PyO3 wrapper exposing engine to Python
Executor contract	Vyper	`contracts/tstore_executor.vy`	Generic payload queue with V2/V3/V4 callbacks
Settlement-arbitrage bot	Python	`examples/eth_settlement_arbitrage_v2_v3_v4_rust.py`	Pool discovery, encoding, simulation, submission

3. The ArbitrageEngine

3.1 Composition

ArbitrageEngine composes three sub-engines behind a single API:

pub struct ArbitrageEngine {
    v2_engine: V2BlockEngine,
    v3_engine: V3BlockEngine,
    v4_engine: V4BlockEngine,
    paths: HashMap<u64, (MixedPath, ResolvedMixedPath)>,
    pool_to_paths: HashMap<(HopType, u64), HashSet<u64>>,  // reverse index
    results: Vec<(u64, U256, U256)>,                        // (path_id, opt_input, profit)
    results_block: u64,
    running: bool,
}

HopType (V2 | V3 | V4) tags each pool reference in a path. V3 and V4 both produce IntV3TickRangeSequence — the solver cannot distinguish them and should not need to.

3.2 Registration

Pools are registered individually by type, then paths combine them:

Method	Sub-engine	Key	Dual orientation?
`register_v2_pool`	V2	contract address → forward pool_id; reverse = forward + 1	Yes
`register_v3_pool`	V3	contract address → pool_key	No (zfo in path ref)
`register_v4_pool`	V4	(pool_manager, pool_id) → forward pool_key; reverse = forward + 1	Yes

register_path takes a Vec<MixedPoolRef> (hop_type, pool_key, zero_for_one) and returns a path_id. After freeze(), no more registration is allowed.

3.3 Block Processing

process_block(&[Log], block_number) is the single entry point called by the pump each block:

Categorise logs by topic0: V2_SYNC_TOPIC → V2, V3_SWAP/MINT/BURN_TOPIC → V3, V4_SWAP/MODIFY_LIQUIDITY_TOPIC → V4
Route each log batch to the appropriate sub-engine's process_block
Collect affected pool keys from each sub-engine (dual-orientation for V2/V4)
Rebuild and re-solve only paths that reference affected pools (via pool_to_paths reverse index)
Merge new results with unchanged path results

3.4 Solver Dispatch

The engine matches on path composition to select the solver:

Path type	Solver	Method
V2-V2	`exact_mobius_solve`	Closed-form √(K·M) via U512 isqrt; ±2 neighborhood search
V3-V3, V4-V4	`int_solve_v3_v3`	Piecewise integer-Möbius per (k₁,k₂) tick-range pair; closed-form per segment
V2-V3, V3-V2, V2-V4, V4-V2, V3-V4, V4-V3	`exact_solve_mixed_v2_v3_sequence`	V3/V4 effective reserves + piecewise tick-range enumeration; closed-form per range

All paths use integer-exact arithmetic. Zero f64 on any solve path. The former golden-section search and f64 Möbius solver are deleted.

4. Sub-Engines

4.1 V2BlockEngine

Owns V2 pool state as IntHopState pairs (forward + reverse). Each pool registration creates two entries with pool_id and pool_id + 1. Sync events update both entries. The constant-product calc uses U512 arithmetic matching EVM semantics:

amount_out = (gamma * reserve_out * amount_in) / (fee_denom * reserve_in + gamma * amount_in)

Dual-orientation: apply_sync_updates returns both forward and reverse pool keys so the unified engine can track V2 dependencies for zfo=False paths.

4.2 V3BlockEngine

Owns V3 pool state including tick_data: HashMap<i32, TickInfo> where each TickInfo holds liquidity_gross (u128) and liquidity_net (I256). Process block handles three event types:

Event	Effect on pool state
Swap	Updates `sqrt_price_x96`, `liquidity`, `tick` (scalar fields)
Mint	Delegates to `apply_liquidity_to_tick_range` (lower: `net += Δ`, upper: `net -= Δ`, both: `gross += Δ`)
Burn	Same as Mint with negated `Δ`; ticks with zero `liquidity_gross` are removed (de-initialised)

Tick update logic (update_tick_liquidity and apply_liquidity_to_tick_range) lives in tick_bitmap.rs — shared with V4BlockEngine. Tick-range sequences are built via build_int_v3_sequence() which:

Calls compute_tick_ranges() — the Rust port of gen_ticks() that walks tick_bitmap: HashMap<i16, U256> and interleaves boundary ticks with initialised ticks
For each range, constructs IntV3TickRangeHop with U256 sqrt_price_* and u128 liquidity
Computes integer effective reserves: R₀ = L · 2⁹⁶ / √P, R₁ = L · √P / 2⁹⁶ (U512 intermediates)

4.3 V4BlockEngine

Mirrors V3BlockEngine exactly but identifies pools by (pool_manager: Address, pool_id: [u8; 32]) instead of contract address. Two registration-time filters reject unusable pools:

Hook filtering: (hook_flags & AMOUNT_MODIFYING_HOOK_MASK) != 0 where 0xCC = BEFORE_SWAP | AFTER_SWAP | BEFORE_SWAP_RETURNS_DELTA | AFTER_SWAP_RETURNS_DELTA. Hooked pools can modify swap amounts, violating the solver's V3-math assumption.
Dynamic fee exclusion: fee == 0x100000 indicates swap-dependent fees that the fixed-fee solver cannot handle.

V4 ModifyLiquidity events replace V3's separate Mint/Burn with a signed liquidity_delta (I256). Both V3 and V4 engines delegate tick mutations to the shared update_tick_liquidity (single tick) and apply_liquidity_to_tick_range (range with zero-gross cleanup) helpers in tick_bitmap.rs.

5. The Möbius Solvers

5.1 Mathematical Basis

Every constant-product swap y = γ·s·x / (r + γ·x) is a Möbius transformation fixing the origin. An n-hop path composes into:

l(x) = K·x / (M + N·x)

The optimal input is the closed-form x_opt = (√(K·M) - M) / N, solvable via integer square root on U512.

5.2 Integer-Exact Solver (`mobius_int_exact.rs`)

Computes K, M, N as U512 integers via compute_int_mobius_coefficients
Checks K > M for profitability
Computes x_opt = (isqrt(K·M) - M) / N using isqrt_u512 (Newton's method in U512, ~100ns)
EVM-simulates at x_opt and ±2 neighbors to handle floor-division rounding
Returns best result with used_closed_form: bool

Performance: 131ns for a 2-hop V2 path (17× faster than the iterative int_mobius_solve_with_refinement).

5.3 V3/V4 Integer Solver (`mobius_v3_int.rs`)

Concentrated-liquidity hops produce IntV3TickRangeSequence — a vector of IntV3TickRangeHop structs, each carrying integer sqrt-price bounds and liquidity. The solver:

For each (k₁, k₂) pair of ending tick ranges, computes a single (K, M, N) triple by composing the shifted Möbius transforms
Calls exact_mobius_solve for closed-form optimal input — no golden-section search
Validates via int_simulate_v3_v3_path with full piecewise simulation

Crossing constants (additive amounts from tick-range boundaries) fold into the Möbius coefficient recurrence, so each (k₁, k₂) segment is still a single closed-form solve.

5.4 Mixed V2-V3/V4 Solver (`exact_solve_mixed_v2_v3_sequence`)

Combines V3/V4 effective reserves with V2 integer reserves:

Enumerate V3/V4 ending ranges (like int_solve_v3_v3)
For each candidate ending range k, compute crossing data
Build mixed hop list with the ending range's effective reserves
Solve via closed-form Möbius
Validate with crossing-aware simulation

Replaced the single-range exact_solve_mixed_v2_v3 which produced false positives when swaps exceeded the current range capacity.

6. The Pump: Rust-Owned State Pipeline

6.1 Architecture: Dual-Subscription with Backfill Safety Net

The ArbitrageEnginePump maintains two concurrent WS subscriptions against the same provider:

newHeads — block boundary notifications (block number, timestamp, base fee, gas)
logs — all log events, unfiltered (topic + address filtering happens in Rust)

The pump assumes the WS/IPC connection is live and delivering events correctly. Logs arrive in real-time and are buffered per block. When a newHeads event arrives, the buffered logs for the just-completed block are processed atomically.

AlloyProvider (WS/IPC)
    │
    ├─ subscribe("newHeads") ──────────────────────┐
    │                                               │
    ├─ subscribe("logs") ──┐                       │
    │   (no filter)         │                       │
    │                       ▼                       ▼
    │               ┌─────────────────────────────────────┐
    │               │  Buffer logs by block_number        │
    │               │  (log.block_number from WS context  │
    │               │   or matched against pending block)  │
    │               └──────────┬──────────────────────────┘
    │                          │
    └─ on newHeads(block N):  │
         │                    │
         ├─ Take all buffered logs for block N-1
         │   (logs that arrived since the previous newHeads)
         │
         ├─ Filter logs in Rust:
         │   topic0 ∈ {V2_SYNC, V3_SWAP/MINT/BURN, V4_SWAP/MODIFY_LIQ}
         │   address ∈ {registered V2+V3 pools, V4 PoolManagers}
         │
         ├─ engine.lock().process_block(filtered_logs, block_number)
         │   → route to V2/V3/V4 sub-engines
         │   → rebuild affected sequences
         │   → solve affected paths
         │   → store results
         │
         └─ block_tx.send(BlockNotification) — Python reads this

6.2 Why No Filter on the Logs Subscription

The logs subscription carries no address or topic filter. All filtering happens in Rust after receipt. This avoids three classes of provider-specific failure:

Address filter limits — some providers reject subscriptions with >1000 address constraints, or silently ignore them
Topic filter truncation — some providers handle 6-topic OR filters incorrectly
Provider-dependent filter semantics — different providers interpret address and topic constraints differently (AND vs OR, ordering requirements)

The traffic cost is bounded: Ethereum mainnet produces ~200–500 logs per block, of which typically 5–50 are relevant to our monitored pools. The Rust-side topic+address filter is O(1) per log (hash comparison + HashMap lookup).

6.3 Backfill Triggers

The pump assumes the WS connection is live, but two conditions trigger a verification backfill via eth_getLogs:

Trigger 1: Timeout — 60s with nothing received

If neither a newHeads nor a logs event arrives within 60 seconds, the connection is likely dead. The pump:

Logs a warning with the last-seen block
Calls eth_getLogs from last_processed_block + 1 to the latest block (determined via eth_blockNumber)
Processes any logs found, filling the gap
Resets the timeout watchdog

This catches: WS disconnects, provider restarts, network partitions, and local socket errors that don't immediately surface as Err in the stream.

Trigger 2: Block with no received logs

When a newHeads event arrives, the pump checks whether any logs were received since the previous newHeads. If zero logs arrived for the just-completed block, this could mean:

The block genuinely has no relevant events (common — many blocks have zero pool events)
The WS dropped some or all log events for this block

The pump cannot distinguish these cases from the subscription alone. It calls eth_getLogs(from=block, to=block) to verify:

Empty result → block truly had no events. No harm done — one extra RPC call, no state change.
Non-empty result → logs were missed. Process them. The engine now has correct state.

This provides protection against false positives: if the WS silently dropped events, the backfill catches them before the engine solves on stale state. If the block was truly empty, the backfill is a no-op with a small RPC cost.

Why this is better than `eth_getLogs` every block

	`eth_getLogs` every block	Push + backfill on suspicion
Latency	Block header + ~50–100ms RPC	Block header only (logs already buffered)
RPC calls per block	Always 1	0 for blocks with events, 1 for empty blocks
Data freshness	Stale by one RPC round-trip	Real-time (logs arrive as they're mined)
Safety	Guaranteed complete (by construction)	Guaranteed complete (backfill covers gaps)
Empty-block cost	Same as any block	One `eth_getLogs` call (cheap — empty response)

The key advantage: events are processed as they arrive, not after a round-trip delay. For same-block reactivity (where another searcher might see the same event and act first), this latency reduction is material.

6.4 Why One Pump, Not Three

2 WS subscriptions instead of 6 (3 newHeads + 3 logs)
1 lock acquisition per block instead of 3
Single eth_getLogs backfill call covers all protocols

6.5 BlockNotification

pub struct BlockNotification {
    pub block_number: u64,
    pub timestamp: u64,
    pub base_fee_per_gas: Option<u64>,
    pub gas_used: u64,
    pub gas_limit: u64,
}

Published via tokio::sync::watch channel. Python reads it via engine.wait_for_block() (blocking call, releases GIL). This replaces Python's WS newHeads subscription for fee/nonce computation — the pump is the sole source of block data.

6.6 Startup Sequence

Python's main() follows this exact order:

Bot.from_config_file() — load config, DB, connections
build_paths_async — discover V2/V3/V4 pools, build Python pool objects, register with engine
engine.freeze() — lock registration
engine.initial_solve() — solve all paths from current state
backfill_snapshots() — V3: fetch Mint/Burn events from snapshot block to current; V4: fetch ModifyLiquidity events. Push updated tick_data to Rust engine one final time.
engine.subscribe(node_ws) → backfill_from_snapshot() → resume_from_subscribe() — open WS, close the snapshot→WS gap, then begin normal pump processing (the canonical two-phase flow; see EngineRegistry.start())
Main loop: wait_for_block → latest_results → dispatch_profitable_results

The backfill closes the gap between the DB snapshot and the first pump block. After backfill, Rust owns all state updates — Python never pushes pool state again.

6.7 Consumer Subscription Model

The pump's watch channel provides a continuous stream of BlockNotifications to Python. Because backfill covers gaps, consumers see an unbroken, block-ordered sequence of notifications — even if the WS connection dropped and recovered during a short window. The engine's latest_results() always reflects the most recent processed state, regardless of whether it came from the WS subscription or a backfill call.

For future consumers that want per-event granularity (not just per-block), the pump can expose a second channel carrying DecodedEvent objects — block-ordered, deduplicated (backfill results merged with WS-received events), filtered to relevant pools only.

7. The Reorg Journal

7.1 Design

Each pool in Bot carries a ReorgJournal<D: BlockDelta> — a bounded VecDeque of per-block deltas storing prior values of modified state fields.

Forward progress: stash "before" values → update current state.

Reorg rollback: pop deltas at/after the target block → restore "before" values into current state.

Hot path: swap calculations and the engine never touch the journal. They always read current mutable fields. Zero penalty.

7.2 V2 Delta (Degenerate Case)

struct V2BlockDelta {
    block: u64,
    reserve0_before: U256,
    reserve1_before: U256,
}

V2 "delta = full state" — two reserves. Memory equivalent to full-state cloning, but restores in O(1) instead of O(n) for V3.

7.3 V3 Delta (Efficient Case)

struct V3BlockDelta {
    block: u64,
    sqrt_price_x96_before: U256,
    liquidity_before: U128,
    tick_before: i32,
    tick_priors: Vec<(i32, TickBefore)>,  // typically 0–4 entries
}

Only modified tick priors are stored. A typical V3 swap modifies 0–4 ticks (at the crossing boundary). Memory: 2000 entries + 8×4 ≈ 2032 vs full-tick-map cloning at 8 × 2000 + scalars ≈ 16000.

7.4 Operations

Method	Effect
`push_delta`	Append same-block replacement, reject older blocks, evict beyond max_depth
`discard_before_block`	Remove deltas older than the target (no longer rollback-reachable)
`restore_before_block`	Pop deltas at/after target, restore scalar + tick priors, remove de-initialised ticks

Property-based tests (via proptest) verify the journal matches a faithful model after arbitrary sequences of push/discard/restore operations.

8. Event Decoders

All decoders live in rust/crates/degenbot-bot/src/bot_core/ and decode from Alloy Log objects:

Decoder	File	Event signature	Topic constant
V2 Sync	`v2_sync_decoder.rs` (in `optimizers/`)	`Sync(uint112,uint112)`	`0x1c411e9a...`
V3 Swap	`v3_swap_decoder.rs`	`Swap(address,address,int256,int256,uint160,uint128,int24)`	`0xc42079f9...`
V3 Mint	`v3_mint_burn_decoder.rs`	`Mint(address,address,int24,int24,uint128,uint256,uint256)`	`0x7a53080b...`
V3 Burn	`v3_mint_burn_decoder.rs`	`Burn(address,int24,int24,uint128,uint256,uint256)`	`0x0c396cd9...`
V4 Swap	`v4_swap_decoder.rs`	`Swap(bytes32,address,int128,int128,uint160,uint128,int24,uint24)`	`0x40e9cecb...`
V4 ModifyLiquidity	`v4_modify_liquidity_decoder.rs`	`ModifyLiquidity(bytes32,address,int24,int24,int256,bytes32)`	`0xf208f491...`

Key differences from Python:

~50ns decode time per event vs ~5-10µs via Python eth_abi
Zero-allocation for common paths; returns Option<Event> (None for wrong topic/malformed data)
V4 pools identified by (PoolManager address, pool_id) not contract address

9. The Executor Contract

9.1 Overview

A single Vyper contract (contracts/tstore_executor.vy) handles all V2+V3+V4 arbitrage paths. It uses a generic payload queue stored in transient storage (EIP-1153, cleared every transaction):

struct Payload:
    target: address
    calldata: Bytes[MAX_PAYLOAD_BYTES]
    will_callback: bool

9.2 Payload Delivery

execute_payloads(payloads, bribe_bips) stores the queue in transient storage, then iterates:

Read t_payloads[index]
If will_callback=True, register target in t_allowed_callback_addresses
raw_call(target, calldata) —_no return value check
Advance queue index
Repeat until t_all_payloads_delivered

Callbacks (uniswapV2Call, uniswapV3SwapCallback, unlockCallback) assert msg.sender is registered, then resume queue delivery from where the payload left off.

9.3 Callback Types

Callback	Protocol	Registration trigger
`uniswapV2Call`	Uniswap/SushiSwap V2	`will_callback=True` on V2 swap payload
`hook`	Aerodrome/Velodrome V2	Same
`pancakeCall`	PancakeSwap V2	Same
`uniswapV3SwapCallback`	Uniswap/SushiSwap V3	`will_callback=True` on V3 swap payload
`pancakeV3SwapCallback`	PancakeSwap V3	Same
`unlockCallback`	Uniswap V4	`will_callback=True` on `PoolManager.unlock` payload

9.4 V3 Auto-Pay

After delivering all queued payloads inside a V3 callback, the contract checks whether the calling pool is owed WETH and auto-transfers it:

if amount1_delta > 0:
    if token1() == WETH_ADDR:
        WETH.transfer(msg.sender, amount1_delta)
elif amount0_delta > 0:
    if token0() == WETH_ADDR:
        WETH.transfer(msg.sender, amount0_delta)

The Python encoder must not include explicit WETH transfer payloads for pools where auto-pay fires (would cause double-payment and revert).

9.5 V4 Settlement

V4 swaps happen inside unlockCallback. The Python encoder pre-computes all amounts and encodes settlement operations as raw calldata payloads:

PoolManager.swap(PoolKey, SwapParams, hookData) — the V4 swap
ERC20.transfer(PoolManager, amount) — pay debt to PM
PoolManager.sync(currency) — update PM's internal balance tracking
PoolManager.settle() — credit tokens to our delta
PoolManager.take(currency, to, amount) — receive tokens from PM

9.6 Profit Measurement

execute_payloads asserts WETH.balanceOf(self) does not decrease over the transaction. No prefunding required — V3's callback is the flash borrow mechanism.

10. Swap Encoding

10.1 Path Types and Their Payload Sequences

The bot supports all 9 two-hop path combinations across V2/V3/V4. Each has a dedicated encoder function:

Path type	Encoder	Entry point	Settlement
V3-V2	`encode_v3v2_payloads`	V3.swap (callback)	Token transfers
V3-V3	`encode_v3v3_payloads`	V3.swap (callback)	Token transfers (nested callbacks)
V2-V2	`encode_v2v2_payloads`	V2.swap (flash borrow)	Token transfers
V2-V3	`encode_v2v3_payloads`	V2.swap (flash borrow)	Token transfers (nested callbacks)
V4-V4	`encode_v4v4_payloads`	PM.unlock (callback)	sync/settle/take
V4-V3	`encode_v4v3_payloads`	PM.unlock (callback)	sync/settle/take + token transfers
V3-V4	`encode_v3v4_payloads`	V3.swap (callback) → PM.unlock (nested)	sync/settle/take
V4-V2	`encode_v4v2_payloads`	PM.unlock (callback)	sync/settle/take + token transfers
V2-V4	`encode_v2v4_payloads`	V2.swap (callback) → PM.unlock (nested)	sync/settle/take

10.2 V3 vs V4 Sign Convention

V3 and V4 use opposite sign conventions for amountSpecified:

Mode	V3	V4
Exact INPUT	`amountSpecified > 0`	`amountSpecified < 0`
Exact OUTPUT	`amountSpecified < 0`	`amountSpecified > 0`

For arbitrage (always exact-input): V3 encoding uses positive values, V4 encoding uses negative values. Getting this wrong produces V3 "IIA" (Insufficient Input Amount) reverts.

10.3 NATIVE_ADDRESS Handling

V4 PoolKey uses currency0 = address(0) for ETH pools. The executor wraps received ETH to WETH via IWETH.deposit() during settlement. For direction resolution, the bot treats address(0) as equivalent to WETH.

11. Dispatch Pipeline

11.1 Flow

latest_results() → sort by profit desc → parallel simulation
    → staleness check → encode → simulate (3-call pattern)
    → market-aware fee → mutual exclusivity → submit

11.2 Slices (from Plan 080)

#	Feature	Detail
0.5	Dispatch serialisation	`asyncio.Lock` prevents concurrent dispatches
1	Parallel simulation	`asyncio.gather` with `MAX_SIMULATE_CONCURRENT=50`
2	Staleness tracking	`solve_block` from Rust engine (not Python `update_block`); `STALENESS_TOLERANCE=5` blocks
3	Market-aware fees	Target from profit ratio, age decay, feeHistory percentile bounds
4	Best-path selection	Sort by profit desc, mutual exclusivity via `committed_pools`
5	Gas from simulation	`gasUsed * 1.1` instead of `1.5×` heuristic
6	WS reconnection	Exponential backoff + pool state reconciliation (handled by Rust pump's Alloy provider)
7	Subscription filtering	Address filter on WS `LogsSubscription` when ≤1000 pools

11.3 Simulation: 3-Call Pattern

eth_simulateV1({
    "blockStateCalls": [{
        "calls": [
            WETH.balanceOf(executor),           # [0] Before
            execute_payloads(payloads, 0),        # [1] Arbitrage
            WETH.balanceOf(executor),           # [2] After
        ],
        "stateOverrides": {
            executor_owner: {balance: 100 ETH},   # Gas funding
            injected_address: {code: runtime},     # Code injection (if enabled)
        }
    }]
})

Gross profit = WETH balance after − WETH balance before.

11.4 Code Injection

When INJECT_EXECUTOR_CODE=True, the bot loads the executor's runtime bytecode from contracts/cmd_executor_runtime_bytecode.txt and injects it at a fresh address via stateOverrides.code. This enables simulation of undeployed contracts without mainnet deployment. The Vyper immutables (5 slots: OWNER, WETH and PM addresses + 2 precomputed V4 CurrencyDelta slots for the injected executor address) are appended after the CBOR metadata in the deployed bytecode layout [code][CBOR][immutables]. The CBOR must remain intact — it contains the function dispatch jump table and JUMPDEST targets used by the code section.

12. Path Discovery

12.1 Token Pair Model

All paths are two-hop WETH-centred cycles: WETH ↔ intermediate ↔ WETH. A path is profitable when pool A sells WETH for the intermediate at a better rate than pool B buys WETH with the intermediate (or vice versa).

12.2 Pool Sources

DEX	Pool table	Factory
Uniswap V2	`UniswapV2PoolTable`	`0x5C69bEe701ef814a2B6a3EDD4B1652CB9cc5aA6f`
Uniswap V3	`UniswapV3PoolTable`	`0x1F98431c8aD98523631AE4a59f267346ea31F984`
Sushiswap V2	`SushiswapV2PoolTable`	`0xC0AEe478e3658e2610c5F7A4A2E1777cE9e4f2Ac`
Sushiswap V3	`SushiswapV3PoolTable`	`0xbACEB8eC6b9355Dfc0269C18bac9d6E2Bdc29C4F`
PancakeSwap V3	`PancakeswapV3PoolTable`	`0x0BFbCF9fa4f9C56B0F40a671Ad40E0805A091865`
Uniswap V4	`UniswapV4PoolTable`	PoolManager `0x000000000004444c5dc75cB358380D2e3De08A90`

V4 pools are identified by (PoolManager, pool_id) — discovered via find_paths_async with step.hash carrying the pool_id.

12.3 Token Quality Filtering

Mode	Environment variable	Behaviour
Blacklist (default)	`TOKEN_BLACKLIST_MODE=1`	Skip paths with known scam/tax tokens
Whitelist	`TOKEN_WHITELIST_MODE=1`	Only allow paths with known-good intermediates (USDC, USDT, DAI, WBTC, etc.)

Eliminates ~95%+ of simulation failures from scam/tax/honeypot tokens.

12.4 Steering a Live Bot

The path set of a running bot is steerable without a restart: the operator add-path / on-demand-discovery surface (long-lived registration pipeline, the Unix-socket JSON-lines channel, and the degenbot path CLI client) is documented in operator-add-path-surface.md.

13. Bot: State Owner & FFI Topology

13.1 Role

Bot (in rust/crates/degenbot-bot/src/bot_core/mod.rs) is the single Rust owner of all runtime pool/token state — the state layer ADR-003 makes a peer to ArbitrageEngine. Under Plan 100 it holds V2/V3/V4 PoolEntry state, the reorg journal, per-pool swap math (calculate_tokens_out/calculate_tokens_in via v3_simulate_swap/v4_simulate_swap), and V2 swap encoding. The block engines (V2BlockEngine/V3BlockEngine/V4BlockEngine) are dissolved — ArbitrageEngine holds core: Arc<Mutex<Bot>> and reads/writes all pool state through it. See ADR-003 for the state-ownership decision.

13.2 FFI Topology — Polars-Inspired Three-Layer Architecture

How Python reaches that Rust-owned state across the FFI is canonicalized in ADR-005: Polars-Inspired Three-Layer Architecture — the stateful specialization of rust/AGENTS.md's generic three-layer convention. The realized topology:

Rust core — Bot, pure Rust, zero pyo3 imports.
PyO3 wrapper — PyBot (#[pyclass]) holds Arc<parking_lot::RwLock<Bot>> and is the sharing mechanism; PyLiquidityPool (carrying a pool_id key) and PyErc20Token (carrying an Address key) clone that Arc so N Python handles reference one Rust-owned Bot. Reads take a read guard; mutations take a write guard.
Python session — bot.py:Bot constructs self._py_bot = PyBot() in __init__ and delegates Rust-owned state through it.

class Bot:
    _py_bot: PyBot   # Arc<parking_lot::RwLock<Bot>>

    # pools/tokens: PyLiquidityPool/PyErc20Token handles sharing the same Arc
    # PyO3 read  → Bot.pools[pool_id] under a read guard
    # PyO3 write → mutation under a write guard

Grounded in Polars' RwLock<DataFrame> + Arc-shared SharedStorage: many Python views, one Rust-owned buffer set. See ADR-005 for the rejected alternatives (engine-Mutex parity; Python-Bot-as-#[pyclass]; global-registry handles; Mutex-status-quo) and the deferred unification of ArbitrageEngine onto the shared Arc<RwLock<Bot>>.

13.3 Deferred Items

The Plan 079 slices still genuinely deferred. The engines are dissolved — these are pool families whose math has not yet ported to Rust, not engines holding separate state:

Slice	Description	Status
5	Solidly-stable math in Rust	Deferred
9	Stableswap math in Rust	Deferred
10	Balancer math in Rust	Deferred

These families are still served by the pure-Python solver stack (ArbSolver/MobiusSolver/PiecewiseMobiusSolver) until their Rust-native equivalents land.

14. GIL Discipline

Function type	GIL policy	Rationale
Tick math (`get_sqrt_ratio_at_tick`, `get_tick_at_sqrt_ratio`)	Hold	~20ns compute; GIL release/reacquire costs ~200ns
Address utils (`to_checksum_address`)	Hold	~50ns compute
Provider I/O (`raw_call`, async operations)	Release via `py.detach()`	I/O-bound; holding the GIL blocks all Python threads
Pump main loop	Never acquires	Runs on Tokio worker threads; communicates via `parking_lot::Mutex` and `watch` channel
`drain_buffer()`	Attach in wrapper	Wraps `drain_raw()` which is pure Rust; `Python::attach()` only at the boundary

Every Python::attach() call site has a // SAFETY: comment documenting the no-circular-wait guarantee.

15. Relationship Between Components

                    ┌────────────────────┐
                    │    Python main()   │
                    └──────┬─────────────┘
                           │
              ┌────────────▼──────────────┐
              │     PyArbitrageEngine    │
              │  (PyO3 wrapper, GIL gate) │
              └────────────┬──────────────┘
                           │ Arc<Mutex<...>>
              ┌────────────▼──────────────┐
              │     ArbitrageEngine         │
              │  ┌──────┐┌──────┐┌──────┐ │
              │  │V2 Eng││V3 Eng││V4 Eng│ │
              │  └──────┘└──────┘└──────┘ │
              │  paths  pool_to_paths     │
              │  results results_block    │
              └────────────┬──────────────┘
                           │ Arc<Mutex<...>>
              ┌────────────▼──────────────┐
              │   ArbitrageEnginePump       │
              │  (Tokio async task)       │
              │  WS newHeads + logs →     │
              │  process_block → solve    │
              │  → BlockNotification      │
              │  backfill on gap/timeout  │
              └──────────────────────────┘

  ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─

              ┌──────────────────────────┐
              │      Bot (partial)   │
              │  pools: HashMap<u64,     │
              │    PoolEntry>            │
              │  ReorgJournal per pool   │
              │  calculate_tokens_out/in │
              │  encode_swap (V2 only)  │
              └──────────────────────────┘

  ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─

              ┌──────────────────────────┐
              │   Möbius Solvers        │
              │  exact_mobius_solve     │ ← V2-V2, closed-form √(K·M)
              │  int_solve_v3_v3        │ ← V3-V3/V4-V4, piecewise integer-Möbius
              │  exact_solve_mixed_     │ ← V2-V3/V2-V4/V3-V4, sequence + crossing
              │    v2_v3_sequence       │
              └──────────────────────────┘

  ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─

              ┌──────────────────────────┐
              │  tstore_executor.vy      │
              │  Generic payload queue   │
              │  V2/V3/V4 callbacks      │
              │  V3 auto-pay WETH       │
              │  V4 unlockCallback      │
              └──────────────────────────┘

16. Test Coverage

16.1 Rust Tests (409 tests)

Module	Test count	Coverage
`mobius_int_exact`	25+	isqrt correctness, exact vs f64, never-panics
`mobius_v3_int`	14+	Effective reserves, mixed sequence solver, crossing computation
`v2_block_engine`	15+	Registration, dual-orientation, solve, dependency tracking
`v3_block_engine`	10+	Registration, swap + mint/burn updates, tick-range construction
`v4_block_engine`	10+	Registration, hook filtering, dynamic-fee exclusion, swap + modify_liquidity
`arb_engine`	20+	Mixed path resolution, mixed V2-V3/V3-V2, V4 integration, freeze
`arb_engine_pump`	3+	Filter construction, shutdown flag
`state_history`	15+ unit + property tests	Push/discard/restore, proptest model equivalence
`tick_bitmap`	10+	gen_ticks edge cases, boundary ticks, MIN_TICK/MAX_TICK
Decoders	7+ each	Valid/wrong-topic decode, field extraction

16.2 Python Tests (3223+ tests)

tests/arbitrage/test_optimizers/test_uniswap_arb_engine.py — 9 integration tests for mixed V2-V3 engine
tests/arbitrage/test_optimizers/test_engine_v3v3_vs_brent.py — 13 tests comparing integer-exact V3-V3 against Brent (float) and brute-force (integer gold standard)
Full library test suite (3000+ tests) covers pool construction, swap calculations, state management

16.3 Validation Method

Each math port follows the pattern:

Generate test vectors from the Python reference
Write Rust tests asserting identical outputs for identical inputs
Include edge cases: zero amounts, max uint256, fee boundaries, single-coin pools
Engine integration tests verify end-to-end: register → update → solve → results match Python

17. Known Limitations

Limitation	Impact	Mitigation
V2 asymmetric fees: register_v2_pool only uses `_fee_token0`	Wrong fee for one direction if asymmetric	Runtime warning on detection; full fix requires Rust engine API change
Python pool objects used for encoding	Encoding calls `calculate_tokens_out_from_tokens_in()` on Python pools — may use stale state if Rust owns updates	Encoding uses amounts from the same block (before dispatch); long-term fix is Rust-owned encoding
`Bot` is partial	V3 calculation/encoding not in Bot; Curve/Balancer math not ported	Engines own their own state; Bot is a future consolidation point
V4 encoding not validated on anvil fork	ABI selectors and amountSpecified verified in unit tests, not against real node	Dry-run mode validates via `eth_simulateV1` before live submission
No three-hop paths	Path discovery limited to `max_depth=2`	Would require solver extension (3-hop Möbius composition) and more complex encoding
WS stability depends on Alloy	Rust pump uses Alloy's WS provider for dual subscriptions	Timeout backfill (60s) covers dead connections; empty-block backfill covers silent event drops; Alloy auto-reconnects

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