feat: intent-swap extension — solve signed Fusion orders for same-block inclusion

[kayibal]

What this does

Adds an in-process intent-swap service to the Base builder. Signed orders arrive via a new intent_submitOrder RPC, are solved immediately against committed AMM state overlaid with the in-progress block's executed transactions, and the signed settlement transaction is inserted into the builder's txpool for same-block inclusion. Settlement uses the existing Fusion resolver contracts; the solver engine is backrunner (Tycho state + Fynd routing), consumed as a git dependency pinned to feat/intent-solve-api @ d62c89c.

Structure (commits reviewable in order)

builder-core (isolated commits):

• feat(builder-core): optional build-event stream from flashblocks payload builder — adds BuilderConfig.build_event_tx: Option<mpsc::Sender<BuildEvent>> (default None) and four emit sites (IterationStart / TxExecuted with receipt logs / IterationComplete / IterationAborted). Emission is try_send-only via BuilderConfig::emit_build_event; a full channel drops the event with a warning and never stalls building. Zero behavior change when unset.
• test(builder-core): driver test for build-event stream sequence — tests/build_events.rs builds a block through the ChainDriver and asserts event order, tx-hash match, and a single shared payload id.

new crate base-intent-swap:

• intent_submitOrder RPC: shape + auction-window validation (no EIP-712 recovery — the LOP contract validates on-chain), distinct error codes incl. queue-full and engine-unavailable.
• Engine task: tracks the in-progress block from build events (guarded by payload id, cleared at block seal), solves each submitted order via Backrunner::solve_orders, signs with a configured EOA (redacted from all Debug output), inserts via add_external_transaction — the same path as base_insertValidatedTransaction.
• Extension (BaseNodeExtension) + CLI arg group (--builder.intent-swap.*, disabled by default) + bin/builder wiring. With the flag off, builder behavior is unchanged.
• README with a Base-mainnet shadow-run runbook (note: no shadow/non-proposing mode exists in the builder; the runbook documents driving it via op-node/FCU replay).

Build notes

• Cargo.lock pins tycho-common/tycho-simulation/tycho-execution at 0.305.1 deliberately: fynd-core at the pinned rev does not compile against 0.339.x. Regenerating the lockfile breaks the build.
• backrunner/builder-types are ssh:// git dependencies — building requires GitHub SSH access. If cargo's libssh transport cannot reach your agent, set net.git-fetch-with-cli = true in .cargo/config.toml (not committed).

Testing

• cargo test -p base-intent-swap — 9 tests (RPC validation paths, uuid derivation, EIP-1559 sign→decode_2718→recover roundtrip, Debug redaction)
• cargo test -p base-builder-core --test build_events — driver integration test
• clippy -D warnings and rustfmt clean on all touched crates

🤖 Generated with Claude Code

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	derive_more@​0.99.20
	strum@​0.25.0
	hex-literal@​0.3.4
	sha2@​0.9.9
	alloy-primitives@​0.6.4
	futures@​0.1.31
	revm@​29.0.1
	revm-bytecode@​6.2.2
	revm-database@​7.0.5
	revm-precompile@​27.0.0
	alloy-rpc-types-debug@​1.8.3
	tokio-tungstenite@​0.20.1

View full report

[kayibal]

Pushed a fix round addressing external review findings:

• 81b874a fix(intent-swap): derive nonce from pool state and log settlement inclusion — removes the engine-lifetime nonce counter; the nonce is now derived per candidate from the pool's per-sender view (get_highest_transaction_by_sender), which self-heals from eviction/replacement. Post-insert log renamed to "settlement queued" (pool acceptance ≠ inclusion) and a "settlement included" log fires when the engine observes its own tx in the build-event stream — this is the fill-rate signal for the shadow run. State machine extracted to Iteration::apply with 5 new unit tests (payload-id guard, replace-on-start, clear-on-complete/abort).
• 9c56f28 fix(deps): pin backrunner and builder-types by rev instead of branch — the manifest is now the authoritative pin (was lockfile-only).
• e4a4dfd fix(builder-core): warn once when build-event channel is closed — isolated core commit; TrySendError::Closed now warns once per process via an atomic latch instead of once per committed tx.

Not addressed (pending decision): behavior on engine startup failure (currently error-and-stay-dead; alternative is panic → critical-task fail-fast → node restart).

Tests: 14 intent-swap + 48 core lib + driver test green; clippy -D warnings and fmt clean on touched crates.

[kayibal]

Startup-failure decision resolved: 236ab6b fix(intent-swap): exit node when engine fails to start — the engine build's Err arm now logs and panics, so reth's critical-task fail-fast shuts the node down (non-zero exit) instead of leaving intent-swap silently dead. The RPC engine unavailable path stays for mid-run engine death. Tests 14/14, clippy/fmt clean.

[kayibal]

Repointed the `backrunner`/`builder-types` git pin from the retired `pending-sim-entangled` branch to builder-integration main's merge commit `6029f1b` (intent-solve-api merge). `cargo update -p backrunner -p builder-types` resolved `fynd-core` from the git rev `af403016` (0.82.3) back to the crates.io release `0.81.1`, matching main's pin; `tycho-common`/`tycho-simulation`/`tycho-execution` stayed single-copy at 0.305.1. `cargo test -p base-intent-swap` (14/14) and `cargo clippy -p base-intent-swap --all-targets -- -D warnings` are both green.