M2 #24: Crank service: Monitor and execute matching

[joaquinbejar]

Summary

Implements the crank service that monitors order books for crossing orders and submits MatchOrders transactions. This is a permissionless service that earns priority fees for executing matches.

Changes

New Crate: crank/

File	Description
Cargo.toml	Crank crate dependencies
src/lib.rs	Crate root with module exports
src/config.rs	CrankConfig with priority fees, poll interval, retries
src/detector.rs	CrossDetector for detecting bid >= ask conditions
src/builder.rs	TransactionBuilder for MatchOrders/ConsumeEvents
src/submitter.rs	TransactionSubmitter with retries and backoff
src/service.rs	CrankService orchestrating the full workflow
src/metrics.rs	CrankMetrics for monitoring

Cross Detection

• Monitor best bid/ask from BookBuilder
• Detect crossing condition (bid >= ask)
• Estimate number of matches possible
• CrossInfo struct with market, prices, estimated matches

Transaction Building

• Build MatchOrders instruction with configurable limit
• Build ConsumeEvents instruction for settlement
• Build bundled transactions when possible
• Estimate compute units per transaction
• BuiltTransaction struct with data, priority fee, compute units

Priority Fee Management

• Dynamic fee calculation based on estimated matches
• Configurable min/max priority fee range (default 1000-100000 lamports)
• Profitability check (fees earned > tx cost + threshold)

Transaction Submission

• Send with configurable retries (default 3)
• Exponential backoff on failures
• Confirmation tracking
• SubmitResult enum: Confirmed, Failed, Dropped

CrankMetrics Tracking

• Matches executed
• Transactions submitted/success/failed/dropped
• Fees paid
• Crosses detected
• Poll cycles
• Success rate and matches/sec

CrankService

• Configurable poll interval (default 100ms)
• Multiple markets support
• Graceful stop mechanism
• run() for continuous operation
• poll_once() for single cycle execution

Technical Decisions

• Placeholder transaction serialization: Real implementation will use Anchor/Solana SDK
• Placeholder RPC submission: Real implementation will use solana-client
• Profitability estimation: Simple fee calculation, can be enhanced with actual fee schedules
• Backoff strategy: Exponential with configurable multiplier and max

Testing

• 50+ unit tests for all components
• Config validation tests
• CrossInfo tests (spread, is_crossed)
• TransactionBuilder tests (match_orders, consume_events, bundled)
• SubmitResult tests
• Submitter backoff calculation tests
• CrankMetrics tests (recording, snapshot, reset)
• CrankService tests (new, metrics, stop, poll_once)

Checklist

• Code follows .internalDoc/09-rust-guidelines.md
• Documentation added for all public items
• No warnings from cargo clippy
• cargo fmt passes
• All tests pass

Closes #24