Tier 2 unlinkable Starknet account — contracts + wallet client + sponsored deploy/execute

[Akashneelesh]

Summary

End-to-end implementation of a Tier 2 unlinkable Starknet account, where the on-chain identity is a fresh secp256k1 "session key" derived from a one-time MetaMask personal_sign, not the user's MetaMask wallet itself. Combined with the Starknet privacy pool + AVNU paymaster's sponsored_private mode, a Tier 2 account can be deployed and operated without any MetaMask-correlatable footprint on chain.

Architecture

MetaMask  → personal_sign(BOOTSTRAP_v1)  → keccak  → secp256k1 session key
                                                   ↓
                              compute deterministic Starknet account address
                                                   ↓
relayer tx (AVNU)                          (NOT the user)
└─ forwarder.execute_private_sponsored
   └─ pool.apply_actions
      ├─ withdraw STRK → forwarder         (Alice's notes pay gas)
      └─ InvokeExternal → EarnDeployHelper.privacy_invoke
         └─ factory.deploy_account(session_eth, ownership_sig)
            → Tier 2 account live; owner = session key

After deploy, the same envelope shape (InvokeExternal → EarnInvokeHelper → account.execute_from_outside_v2) drives the deployed account through any subsequent call — demonstrated end-to-end against Counter.increment().

What's in the 3 commits

1. Cairo Tier 2 stack — factory + account renames, drop eth_address from events, drop strategy_implementation, new counter + helpers packages with EarnDeployHelper + EarnInvokeHelper, bumped PRIMER_CLASS_HASH for scarb 2.16.1, casm = true everywhere.
2. tier2_wallet/ TS client + browser demo + sponsored flows — session-key derivation, Starknet address computation, EIP-712 signing (4 byte-identical parity tests against the existing Python reference), AVNU paymaster client, sponsored-private deploy/execute flow functions, full browser demo, Sepolia deploy scripts. 20 vitest passing.
3. Sepolia deployment addresses — tier2_wallet/sepolia-deployments.json for reproducibility.

Honest privacy assessment

Tier 2 closes every cryptographic link between MetaMask and the Starknet account:

• Address derivation: salt is session_eth_address, not MM addr.
• Calldata, events, account storage: no MM addr appears.
• Per-tx signatures recover to the session pubkey, not the MM pubkey.
• Gas: Alice's pool notes pay; AVNU's relayer signs; MM never sends a Starknet tx.

It does not eliminate every linkability channel:

• Anonymity-set size — if the pool's deposit volume is small, timing-correlation re-links.
• Where Alice's notes came from — the first deposit was public.
• Off-chain: relayer / RPC / discovery / proving service logs, browser fingerprinting.

This is the strongest practical unlinkability available on Starknet today, equivalent in spirit to "Tornado Cash-grade privacy" — but only as strong as the anonymity set and operational hygiene around it.

Test plan

• scarb build clean across all 7 workspace packages (drops strategy_implementation, adds counter, helpers).
• cd tier2_wallet && npm install && npm test — 20/20 green.
• npm run deploy:contracts against a funded Sepolia admin — declares 5 classes, deploys AccountFactory + EarnDeployHelper.
• npm run deploy:extras — declares EarnInvokeHelper, deploys it + a Counter instance.
• npm run demo — open http://localhost:8088, run Steps 1-6 against MetaMask. Step 5 deploys the Tier 2 account via Alice; Step 6 increments the counter; both should leave no MM-correlatable trace.

Notes for reviewers

• account_factory/src/utils.cairo::PRIMER_CLASS_HASH was bumped from the original 0x00123e… to 0x03edae21…. This is because scarb 2.16.1 produces a different hash than the previously-pinned scarb version. No prod deployment of the old hash existed when this changed.
• The storage var eth_address in eth_712_account was kept under that name for storage-layout stability across upgrades — only the parameter / interface name was changed to owner_eth_address.
• EarnDeployHelper.privacy_invoke includes a note_id: felt252 last arg — required by the privacy-pool helper protocol (it's serialized whether or not the helper uses it).

🤖 Generated with Claude Code

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