fix(wallet): decrypt the private balance with the SDK's own eERC key

[hitakshiA]

Problem

Every shielded balance rendered $0.00 on the Home screen even though the deposit landed on-chain (activity showed +$1.00).

Root cause

The eERC SDK's register() ignores the decryptionKey passed to the EERC constructor and derives its own key from a deterministic wallet signature (generateDecryptionKey), binding the on-chain public key + ElGamal-encrypted balance to that key. Our read path built a fresh EERC with account.eercDecryptionKey and never called generateDecryptionKey, so calculateTotalBalance decrypted with the wrong key, failed its eGCT verify, and returned 0.

Fix

createEerc now calls await eerc.generateDecryptionKey() up front, so reads/transfers/deposits use the same key registration used. The signature is local (self-custody key) and deterministic, so it is stable across sessions and retroactively fixes already-registered wallets.

Verification

• Proven on-chain: a fresh wallet's 0.04 USDC deposit now decrypts to 40000 (was 0).
• Driven headless on live Fuji: create, shield ($1.00 shows), send (recipient received $1), cash out — all green.
• 217 tests, typecheck, lint, build pass.

Summary by CodeRabbit

• Bug Fixes
  • Wallet setup now automatically generates and installs the required decryption key for chain-related operations.
  • Improved reliability when initializing encrypted wallet functionality.

Greptile Summary

This PR updates the wallet eERC setup to use the SDK-derived key.

• Calls generateDecryptionKey() when creating an EERC instance.
• Keeps the SDK key aligned with registered shielded balances.
• Adds the new SDK method to the shield test mock.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
apps/wallet/src/lib/eerc.ts	Creates the EERC instance, derives the SDK decryption key, and returns the initialized instance.
apps/wallet/src/lib/eerc.shield.test.ts	Adds generateDecryptionKey to the hoisted mock used by shield tests.

_{Reviews (1): Last reviewed commit: "fix(wallet): decrypt the private balance..." | Re-trigger Greptile}

[coderabbitai]

📝 Walkthrough

Walkthrough

createEerc now generates a decryption key before returning the EERC instance. The EERC test mock is updated to expose the new asynchronous method.

Changes

EERC key initialization

Layer / File(s)	Summary
Generate and mock the decryption key apps/wallet/src/lib/eerc.ts, apps/wallet/src/lib/eerc.shield.test.ts	createEerc awaits generateDecryptionKey() after constructing EERC, and the test mock now provides the method.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• Miny-Labs/benzo-wallet#27: Adds a private-balance flow that depends on decryption-key initialization in eerc.ts.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title is concise and accurately captures the main fix: using the SDK's own eERC key to decrypt private balances.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/eerc-private-balance-decryption-key

---

_{Comment @coderabbitai help to get the list of available commands.}