feat(token-mint-authority): add testnet faucet mint-authority program

[0x-r4bbit]

A permissionless faucet that holds the mint authority for faucet token definitions and lets any account self-mint a fixed grant, so testers can fund themselves on testnet. The call chain is user -> token-mint-authority -> token: the program holds no key and delegates every mint to the token program under a PDA seed.

• FaucetMint (no amount) mints a fixed 10_000e18 to the caller, at most once per 24h per (recipient, token definition), via a chained Token::MintWithAuthority authorized by the mint-authority PDA seed.
• Rate limiting is a per-(recipient, definition) MintAllowance PDA (last-mint timestamp), claimed on first use and rewritten thereafter.
• Wall-clock time is read from the system CLOCK_01 account, as the stablecoin program does.

Setup: the faucet token must be created via the token program's NewFungibleDefinition with mint_authority set to compute_mint_authority_pda(<program id>); the program refuses to mint a token whose stored authority is not its PDA.

[Copilot]

🟡 Changes recommended

The faucet currently lacks a critical ownership-consistency check before delegating the chained mint and also over-requests write access for the mint-authority PDA, both of which widen the attack surface.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds a new token_mint_authority program to the LEZ workspace: a permissionless, rate-limited testnet faucet that delegates a fixed mint to the Token Program using a mint-authority PDA seed, with both unit and zkVM integration test coverage.

Changes:

• Introduces token_mint_authority_{core,program,methods,guest} crates implementing FaucetMint + PDA-based cooldown tracking.
• Adds unit + integration tests covering PDA derivation, chained mint behavior, and cooldown enforcement.
• Wires the new program into guest build scripts, workspace manifests/locks, IDL artifacts, and README docs.

File summaries

File	Description
scripts/build-guests.sh	Include token_mint_authority in guest binary packaging.
scripts/build-guests.Dockerfile	Include token_mint_authority in Docker guest build loop.
README.md	Document the new program and update test/build/IDL examples.
Cargo.toml	Add new crates to workspace members and shared deps.
Cargo.lock	Lockfile updates for new crates/deps.
programs/token_mint_authority/src/lib.rs	New host crate entry module.
programs/token_mint_authority/src/faucet_mint.rs	Implements faucet mint host logic + clock read + chained mint.
programs/token_mint_authority/src/test_support.rs	Test account builders and constants.
programs/token_mint_authority/src/tests.rs	Unit tests for cooldown, PDAs, chained call shape, and preconditions.
programs/token_mint_authority/core/src/lib.rs	New core types/constants + PDA derivations + verification helpers.
programs/token_mint_authority/core/Cargo.toml	New core crate manifest.
programs/token_mint_authority/Cargo.toml	New host crate manifest + example deps.
programs/token_mint_authority/examples/mint_authority.rs	Helper to compute/print mint-authority PDA for a built binary.
programs/token_mint_authority/methods/build.rs	Embed guest methods via risc0_build.
programs/token_mint_authority/methods/Cargo.toml	Methods crate manifest.
programs/token_mint_authority/methods/src/lib.rs	Host-side embedded ELF constants include.
programs/token_mint_authority/methods/guest/Cargo.toml	Guest crate manifest.
programs/token_mint_authority/methods/guest/Cargo.lock	Guest lockfile.
programs/token_mint_authority/methods/guest/src/bin/token_mint_authority.rs	Guest entry wiring + FaucetMint instruction handler.
programs/integration_tests/Cargo.toml	Add token-mint-authority core/methods to integration tests.
programs/integration_tests/tests/token_mint_authority.rs	New zkVM E2E tests for faucet behavior.
artifacts/token_mint_authority-idl.json	New IDL for the faucet instruction/accounts.

Review details

• Files reviewed: 20/22 changed files
• Comments generated: 4
• Review effort level: Lite

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[3esmit]

token_definition.account.program_owner is attacker-controlled whenever the supplied definition is owned by an attacker-deployed program, yet this value becomes the target of a call carrying the faucet's singleton mint-authority PDA authorization. An attacker can create a program-owned account whose data decodes as TokenDefinition::Fungible { authority: Some(mint_authority_pda), .. }, pass a real faucet definition in the unchecked user_holding slot, and reach this call. The malicious callee then receives mint_authority_pda as authorized and can chain Token::SetAuthorityWithAuthority with the real definition, rotating its authority to the attacker. LEZ deliberately carries validated authorization monotonically into nested calls, so the fixed mint amount and allowance update do not contain this path.

Please bind this authority to the intended Token Program: either hard-bind a trusted Token Program ImageID, or include the verified target program ID in the mint-authority PDA seed so an arbitrary callee receives a different PDA. A caller-supplied program ID or only a user_holding owner check is insufficient while the same singleton PDA controls real faucet definitions. Add an adversarial chained-call test that proves an alternate owner cannot reuse the authority in a nested token call.

[3esmit]

Exploit call path:

1. Attacker deploys program Tok and initializes account Fox owned by Tok. Fox contains a valid TokenDefinition::Fungible whose authority is faucet PDA Pog.
2. Attacker calls FaucetMint with a valid signed recipient, fresh allowance PDA, user_holding = Dom where Dom is a real faucet token definition, token_definition = Fox, mint_authority = Pog, and canonical clock.
3. faucet_mint accepts Fox: it is initialized, decodes as fungible, and names Pog as authority. Line 70 selects Tok from Fox.program_owner.
4. The emitted call invokes Tok with [Fox, Dom, Pog], marks Pog authorized, and supplies the faucet PDA seed.
5. Runtime validates that PDA authorization for Tok, then unions Pog into the authorization set inherited by subsequent calls. Tok can therefore emit a call to the real Token Program with [Dom, Pog] and SetAuthorityWithAuthority { new_authority: Some(attacker) }.
6. Token's authority checks pass: Dom is Token-owned, Dom.authority == Pog, and Pog.is_authorized == true. The attacker now owns mint authority and can mint arbitrary amounts without the faucet cooldown.