feat: read-only contract inputs (integrate fuel-vm #1014)

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Linked Issues/PRs

Depends on fuel-vm #1014 (read-only contract inputs) — not yet merged. This PR cannot merge until that lands and is released.

Description

Integrates fuel-vm's read-only contract inputs into fuel-core. A contract input without a matching contract output is now valid and denotes a read-only contract access: the VM executes the contract's code and reads its state/balances but panics ContractIsReadOnly on any mutation. Because a read-only contract's state/balance roots cannot change, no output slot is needed to commit new roots.

Support is automatic with the new fuel-vm — there is no consensus parameter or chain-config flag to enable, and no fuel-core API surface change. Activation is coordinated by node/VM version.

⚠️ Draft — opened for review, not ready to merge. It carries a temporary [patch.crates-io] and depends on an unmerged fuel-vm PR (see Open items).

Executor audit (the substance)

fuel-core master's executor is already structurally correct for read-only inputs, so no executor logic changed. Every root-writing / output-persisting path is driven by the output list, not the input list, so a read-only input (which has no output) is simply never visited:

• compute_state_of_not_utxo_outputs — iterates outputs, matches Output::Contract, then looks up inputs.get(output.input_index) to recompute the balance/state hashes. A read-only contract has no Output::Contract, so no root is computed or rewritten for it.
• persist_output_utxos — same output-driven shape, so its ContractsLatestUtxo pointer is never moved.
• compute_inputs — the only input-driven path; it writes malleable fields from storage but touches no contract storage, so it's harmless for read-only inputs.

The proven invariant is therefore: a read-only contract's persisted storage is untouched and no output root is committed for it. (Note: fuel-core does not preserve a caller-supplied input root — compute_inputs overwrites the input's root fields every block, and those fields are access-list commitments, not full contract merkle roots. The test asserts the persisted ContractsLatestUtxo is unchanged, which is the real executor-level guarantee.)

Changes

Net diff: 5 files, ~253 insertions — mostly tests. No GraphQL / schema / chain-config changes are needed, because there is no new consensus parameter to expose.

• Temporary [patch.crates-io] pointing the fuel-vm family at the PR branch (see Open items).
• Executor tests (below).
• Changelog entries.

Tests

Executor unit tests (crates/fuel-core/src/executor.rs):

• read_only_contract_input_executes_and_does_not_rewrite_root — an input-without-output CALL to a read-only contract succeeds, produces no Output::Contract, and ContractsLatestUtxo is unchanged.
• read_only_contract_input_write_panics_and_preserves_state — a script writing to the read-only contract reverts with a ContractIsReadOnly panic; state untouched.

End-to-end integration tests (tests/tests/read_only_contract.rs) — driven through a running node via the client API:

• read_only_contract_input__can_read_contract_state — a contract input without an output reads the contract's state and returns the stored value.
• read_only_contract_input__can_be_read_repeatedly — the same read-only access repeats, always returning the same value (nothing mutated).
• read_only_contract_input__rejects_state_write — a call whose contract code writes (SWW) to the read-only contract is rejected with a ContractIsReadOnly panic receipt.
• contract_input_with_output_still_allows_state_write — the normal read-write path (contract input WITH output) still works.

All pass; the pre-existing contracts_balance_and_state_roots_* suite (7 tests) still passes unchanged.

Open items (why this is a draft)

• Temporary [patch.crates-io] redirects the 9 fuel-vm-family crates to the fuel-vm PR branch feat/read-only-contract-inputs. Must be removed and fuel-vm-private bumped to a released version once fuel-vm Restarting node causes InvalidDatabaseVersion error #1014 merges.
• Blocked on fuel-vm Restarting node causes InvalidDatabaseVersion error #1014 merge + release.
• Not exercised: WASM/state-transition executor and the on-chain consensus-parameters upgrade path (audited as no-code-change; the executor takes an opaque ConsensusParameters and the validity change rides the fuel-vm bump).
• Pre-existing, unrelated: the ReqwestExt starwars doctest fails to compile on master (CWD-relative schema path) — not touched here, flagged so it isn't mistaken for a regression.

Checklist

• Breaking changes are clearly marked as such in the PR description and changelog
• New behavior is reflected in tests
• The specification matches the implemented behavior (fuel-specs update tracked on the fuel-vm PR)

Before requesting review

• I have reviewed the code myself
• I have created follow-up issues caused by this PR and linked them here

After merging, notify other teams

• Rust SDK (contract input without output is now valid)
• Sway compiler

🤖 Generated with Claude Code

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PR Summary

High Risk
Consensus-breaking transaction validity change via unpinned git VM patches; coordinated network upgrade required before merge-ready release.

Overview
Integrates fuel-vm PR #1014 so a contract input without a matching contract output is valid and means read-only contract access (reads and execution allowed; mutations panic with ContractIsReadOnly). Behavior comes from the bumped VM—no new fuel-core executor logic, chain config, or GraphQL in this diff.

Adds a temporary [patch.crates-io] redirecting the fuel-vm 0.66.4 crate family to feat/read-only-contract-inputs, plus added/breaking changelog notes that nodes must upgrade together. Executor unit tests and a new read_only_contract integration test module lock in that read-only calls succeed without Output::Contract or ContractsLatestUtxo updates, writes fail with ContractIsReadOnly, and the normal input+output path still mutates.

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