Motivation

The generator currently lets you fuzz function-call arguments and the tx
value, but there is no way to set or fuzz max_priority_fee_per_gas per
tx — every tx falls back to the global gas_price / 10 default.

Solution

• FunctionCallDefinition::max_priority_fee_per_gas: Option<String> — new
  field on the user-facing scenario definition, plumbed through
  FunctionCallDefinitionStrict and the templater so it lands on the
  TransactionRequest.
• FuzzParam::max_priority_fee_per_gas: Option<bool> — a flag that mirrors
  the existing FuzzParam::value flag, opting the priority-fee field into
  fuzzing for that entry. Mutually exclusive with param and value; the
  conflict is caught at scenario load time in parse_map_key.
• TestScenario now honors a per-tx priority fee if one is set
  (statically or via the fuzz path), falling back to the existing
  gas_price / 10 default otherwise.
• complete_tx_request raises max_fee_per_gas to match
  max_priority_fee_per_gas when the priority fee exceeds the sampled
  cap, preserving the max_fee_per_gas >= max_priority_fee_per_gas
  invariant. Without this, a high fuzzed tip on a low-fee chain would
  produce an invalid tx.

Example

[spam.tx]
to = "{SpamMe2}"
from_pool = "redpool"
signature = "consumeGas(uint256 gasAmount)"
args = ["3000000"]
fuzz = [
    { param = "gasAmount", min = "1000000", max = "3000000" },
    { max_priority_fee_per_gas = true, min = "0x2540be400", max = "0x4a817c800" },
]

Or pin a static priority fee:

max_priority_fee_per_gas = "10000000000"  # 10 gwei

See docs/creating_scenarios.md for the full documentation.

Breaking changes

Minor breaking change for downstream library users that construct
FuzzParam or FunctionCallDefinitionStrict via struct literal:

• FuzzParam gains a max_priority_fee_per_gas: Option<bool> field.
• FunctionCallDefinitionStrict gains a
  max_priority_fee_per_gas: Option<String> field.

FunctionCallDefinition is unaffected for builder-style users
(FunctionCallDefinition::new(..).with_*(..)); the new field has a
default in the builder constructor.

Tests

• function_def.rs: parses static max_priority_fee_per_gas, parses the
  fuzz flag, and confirms the param+max_priority_fee_per_gas
  combination parses (so the runtime check in parse_map_key has a
  chance to run).
• trait.rs: parse_map_key routes param/value/max_priority_fee_per_gas
  to the correct fuzz-map keys and rejects every conflicting combination.
• util.rs: complete_tx_request uses gas_price when the priority
  fee is lower, raises max_fee_per_gas when it's higher, handles the
  equal case, and the Eip4844 path inherits the same invariant.

PR Checklist

• Added Tests
• Added Documentation (docs/creating_scenarios.md)
• Ran cargo +nightly clippy --workspace --lib --examples --tests --benches --all-features --locked (-D warnings clean)
• Ran cargo +nightly fmt --all
• Note breaking changes in PR description, if applicable — see "Breaking changes" above
• update changelogs
  • crates/core/CHANGELOG.md updated under ## [0.11.0] (matching the version already in Cargo.toml)
  • root CHANGELOG.md — skipped per the note at the top of that file ("contender is now versioned by crate. This file will no longer be updated.")