rpc: add eth_call execution timeout via VM deadline polling

[Chen-Yifan]

CAVEAT: timeout does not apply to precompiles.

eth_call previously enforced its timeout only at queue pickup; once execution started, a slow call could pin a PriorityPool fiber indefinitely. Fibers are cooperatively scheduled, so cancellation must be cooperative: runtime::Context now carries an absolute deadline that the VM polls at its gas checks (per opcode in the interpreter, and in deduct_gas for the shared runtime functions), amortizing the clock read over 256 checks. When the deadline passes, execution exits through the existing stack unwind with the new StatusCode::Cancelled. Paths that arm no deadline pay one load and one never-taken branch per check.

A cancelled child frame cancels every ancestor via an unconditional deadline check after each call/create return, so the abort cannot be mistaken for an ordinary failed subcall and produce a nondeterministic result. The VM records the cancellation on vm::Host, and the executor reports timeouts from that flag rather than inferring them from the status code (EVMC_REJECTED has other producers, e.g. precompiles) or the wall clock (a call that completes just past the deadline is a valid result and is returned).

The RPC pools are reclassified from gas to time: the low/high gas pools become short_tx/long_tx timeout pools, each with a queue timeout enforced at pickup, and an execution VM timeout. The gas clamp with its out-of-gas retry (MONAD_ETH_CALL_LOW_GAS_LIMIT) is removed since client gas limits are not a usable routing signal. Every call starts in the short pool; a call cancelled with a timeout there escalates to the long pool with a fresh budget, and a timeout in the long pool is final.

Expect almost zero effect for vm performance for execution, which doesn't enforce any timeout.

[Copilot]

Pull request overview

Adds cooperative eth_call execution timeouts by propagating an absolute steady-clock deadline through vm::Host into runtime::Context, and polling it at existing gas-check sites so interpreter execution can abort without force-cancelling fibers.

Changes:

• Introduce runtime::Context deadline fields and deadline polling (amortized + unconditional variants), plus StatusCode::Cancelled mapped to EVMC_REJECTED.
• Wire the deadline through vm::Host/vm::VM, propagate cancellation across call/create boundaries, and record cancellation on the host for reliable timeout reporting.
• Rework RPC eth_call pools from gas-based (low/high) to time-budget pools (short/long) with escalation on timeout; update Rust/C FFI and tests accordingly; add design doc.

Verdict: NEEDS CHANGES

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/vm/unit/monad_vm_interface_tests.cpp	Adds VM-level tests that deadline expiry aborts looping execution and that no-deadline runs to OOG.
rust/crates/monad-ethcall/src/executor/call.rs	Updates FFI call site to match removed gas_specified parameter.
docs/eth-call-timeout.md	New design doc describing deadline polling, propagation, and pool behavior.
category/vm/vm.cpp	Copies host deadline into each runtime context and flags host cancellation on StatusCode::Cancelled.
category/vm/runtime/types.hpp	Adds deadline state/polling to runtime::Context, adds Cancelled status, and hooks deadline polling into deduct_gas.
category/vm/runtime/create.cpp	Propagates cancellation to parent frames via unconditional deadline check after child create returns.
category/vm/runtime/context.cpp	Maps Cancelled to EVMC_REJECTED in the EVMC result conversion path.
category/vm/runtime/call.cpp	Propagates cancellation to parent frames via unconditional deadline check after child call returns.
category/vm/interpreter/stack.hpp	Polls deadline alongside existing interpreter gas/stack checks.
category/vm/host.hpp	Adds host-level deadline setter/getter and sticky execution-cancelled flag.
category/rpc/monad_executor.h	Updates pool naming (short/long), changes timeout semantics comment, and removes gas_specified from eth_call submit API.
category/rpc/monad_executor.cpp	Implements deadline-based cancellation, short→long pool escalation, removes gas clamp/OOG retry routing, and reports timeouts via host cancellation flag.
category/rpc/monad_executor_test.cpp	Updates tests to match new eth_call submit signature and removal of gas clamping behavior.
category/execution/ethereum/evmc_host.hpp	Updates size assertions for vm::Host and derived host types after adding deadline/cancellation fields.

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[dhil]

Initial review. Mostly just some comments about comments. Though, I think the MONAD_ASSERT must be changed.