Stubbed out bridging-out flow: B2AGG note -> AggLayerBridgeOut contract -> BURN note

[partylikeits1983]

B2AGG Note and AggLayerBridgeOut Component

This PR adds the B2AGG note script and the AggLayerBridgeOut component with stubbed-out MMR functionality. This PR includes tests covering both bridge-out and reclaim scenarios for B2AGG notes.

Note Structure

The NoteInputs to the B2AGG note consist of a destination chain ID (u32) and 5 u32 values representing a 160-bit EVM address (20 bytes).

The B2AGG note has a total of 6 inputs with the following layout:

0: destination_network (u32 chain ID)
1: destination_address_0 (bytes 0-3)
2: destination_address_1 (bytes 4-7)
3: destination_address_2 (bytes 8-11)
4: destination_address_3 (bytes 12-15)
5: destination_address_4 (bytes 16-19)

Test Scenarios

The test in crates/miden-testing/tests/agglayer/bridge_out.rs validates two scenarios:

Bridge-Out Scenario

• User creates a B2AGG note to transfer assets from Miden to an EVM chain.
• The B2AGG note is consumed by a bridge account using the AggLayerBridgeOut component.
• During consumption, the Keccak MMR frontier is updated (stubbed implementation).
• A public BURN note is created and consumed by the network faucet.

Reclaim Scenario

• User creates and consumes their own B2AGG note (same account as sender).
• Assets are added back to the account without creating a BURN note.
• No bridge operations are performed in this scenario.

Additional Changes

Note: This PR also adds helper functions to convert Ethereum addresses represented as strings to a vector of Felt values.

---

This PR resolves #2007

Builds on #1995 & #1925

[Copilot]

Pull Request Overview

This PR implements a stubbed-out bridging-out flow for the AggLayer integration, establishing the infrastructure for transferring assets from Miden to the AggLayer. The implementation creates a B2AGG note type that can be consumed by accounts with the bridge_out component, which then generates a BURN note to destroy the bridged assets.

Key changes:

• Adds B2AGG note script that validates bridge-out requests and calls the bridge_out account component
• Implements bridge_out account component with stubbed MMR frontier functions and burn note creation
• Introduces utility functions for Ethereum address conversion to/from Felt values
• Includes comprehensive integration test covering the full bridge-out flow

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
crates/miden-testing/tests/lib.rs	Adds agglayer module to test suite
crates/miden-testing/tests/agglayer/mod.rs	Declares bridge_out test module
crates/miden-testing/tests/agglayer/bridge_out.rs	Comprehensive integration test for B2AGG note → bridge_out component → BURN note flow
crates/miden-lib/src/lib.rs	Exposes new agglayer module
crates/miden-lib/src/errors/note_script_errors.rs	Adds error constants for B2AGG note validation
crates/miden-lib/src/agglayer/utils.rs	Provides Ethereum address conversion utilities
crates/miden-lib/src/agglayer/mod.rs	Main module exposing B2AGG script and bridge_out component
crates/miden-lib/build.rs	Adds build support for agglayer library, note scripts, and account components
crates/miden-lib/asm/agglayer/note_scripts/B2AGG.masm	Assembly implementation of B2AGG note script with validation and reclaim logic
crates/miden-lib/asm/agglayer/account_components/bridge_out.masm	Assembly implementation of bridge_out component with stubbed MMR functions

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[mmagician]

I added minor comments regarding the docs, but leaving another approval, great work ✅

[bobbinth]

Looks good! Thank you! I left just a couple of small comments inline.