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Synchronous Composability

Overview​

Composability is the ability to combine contracts, applications, and protocols into one larger workflow.

On a single chain, composability is straightforward because contracts can call each other directly during the same transaction. Across rollups, that property breaks down because execution is split across independent chains with separate sequencers and state.

Ethera restores composability across rollups by coordinating those chains as part of one atomic cross-rollup action.

Why Composability Breaks Across Rollups​

On Ethereum today, the main difference is not whether applications can communicate across rollups. It is whether they can do so as one coordinated action.

  • Same-Chain Composability: Contracts can call each other directly and use the result immediately within one transaction.
  • Cross-Rollup Interactions: Applications usually depend on asynchronous message passing, bridging delays, and separate follow-up actions on each chain.

That difference matters because asynchronous flows introduce:

  • Waiting periods between dependent steps
  • More failure points across multi-step transactions
  • More complex user experience for actions that should feel like one workflow

How Ethera Restores Composability​

Ethera restores cross-rollup composability through coordinated execution rather than through a single shared sequencer.

At a high level:

This allows a cross-rollup flow to preserve ordered dependencies between chains while still being treated as one coordinated action.

Why This Is Different​

One common approach to cross-rollup composability is to introduce a shared sequencer that controls ordering across all participating chains.

Ethera takes a different approach:

  • Each rollup keeps its own sequencer
  • Each rollup evaluates its own part of the action locally
  • Ethera coordinates the cross-rollup decision process without replacing local sequencing

This preserves rollup independence while still allowing applications to coordinate actions across multiple rollups as one atomic flow.

Atomicity​

Atomicity in Ethera comes from Ethera's cross-rollup coordination model, not from one bridge contract and not from Account Abstraction alone.

In practice, a cross-rollup action is submitted as one coordinated payload across the participating chains. Before that action is committed, the participating rollups determine whether their part can proceed. If every required part can proceed, the action is committed atomically. If any required part cannot proceed, the coordinated action aborts, avoiding partial completion across chains.

Some cross-rollup flows still involve ordered dependencies, such as creating a message on one chain before consuming it on another. Even in those cases, the overall action is coordinated as one atomic operation rather than as a set of unrelated independent transactions.

What This Enables​

For builders, synchronous composability means a cross-rollup application can be designed more like one system and less like a sequence of disconnected bridge and callback steps.

For users, it means multi-rollup actions can feel closer to single-chain workflows:

  • Fewer manual follow-up steps
  • Fewer partially completed multi-rollup flows
  • Better support for applications that depend on cross-rollup coordination

Example Workflow​

One common example is a flow where an application needs to move an asset to another rollup and then execute a dependent action there.

Without coordinated cross-rollup composability, those steps are usually treated as separate workflows: move the asset, wait for settlement, and only then execute the next action.

With Ethera, those dependent steps can be coordinated as one cross-rollup action. Asset transfer is one example, but the same model also applies to other cross-rollup workflows that depend on ordered execution.