Modular Blockchain Architecture & Design Patterns

You are a blockchain architect who designs modular chain stacks. You understand the modular blockchain thesis — that separating execution, settlement, consensus, and data availability into specialized layers creates better performance, security, and cost characteristics than monolithic approaches.

CONTEXT: The blockchain industry is moving from monolithic chains (where one chain does everything) to modular architectures (where specialized layers handle different functions). Understanding this shift is critical for choosing where to build, which infrastructure to use, and how the ecosystem will evolve. I need to understand modular blockchain architecture deeply enough to make informed infrastructure decisions for my protocol.

TASK: Create a modular blockchain architecture guide:
1. The modular thesis explained: what is a modular blockchain vs. a monolithic blockchain. Define the 4 core functions — execution (processing transactions), settlement (finalizing state), consensus (ordering transactions), and data availability (ensuring data is accessible). Explain why separating these functions creates advantages (specialization, scalability, flexibility) with specific examples.
2. Execution layer landscape: compare execution environments — EVM (Ethereum, L2s), SVM (Solana, Eclipse), MoveVM (Aptos, Sui, Movement), FuelVM (Fuel), and WASM-based (Near, Cosmos SDK). For each: programming model, throughput characteristics, developer ecosystem size, and trade-offs. Address parallel vs. sequential execution.
3. Data availability layer deep dive: this is the most active area of modular innovation. Compare — Ethereum (calldata and EIP-4844 blobs), Celestia (purpose-built DA layer), EigenDA (restaking-secured DA), Avail (Polygon's DA layer), and NEAR DA. For each: throughput (MB/s), cost per MB, security model, and adoption status. Explain why DA is often the bottleneck and how DAS (Data Availability Sampling) works.
4. Settlement and consensus layers: explain how settlement works in modular systems — Ethereum as the universal settlement layer, shared sequencers (Espresso, Astria) for cross-rollup ordering, interoperability implications (shared settlement enables atomic cross-rollup transactions), and the role of restaking (EigenLayer) in providing security for modular components.
5. Modular stack configurations: present 4-5 example modular chain configurations and their use cases — (a) Standard Ethereum rollup (execution: rollup, DA: Ethereum blobs, settlement: Ethereum), (b) Alt-DA rollup (execution: rollup, DA: Celestia, settlement: Ethereum), (c) L3 (execution: L3 rollup, DA: L2, settlement: Ethereum), (d) Sovereign rollup (execution: rollup, DA: Celestia, settlement: self-sovereign), (e) Validium (execution: off-chain, DA: off-chain committee, proofs: Ethereum). Compare cost, security, and performance.
6. Future architecture trends: where modular blockchain is heading — based rollups (using Ethereum L1 proposers as sequencers), shared sequencing (multiple rollups sharing transaction ordering), proof aggregation (combining multiple rollup proofs into one), and the convergence of ZK and optimistic approaches. Assess which trends are most likely to succeed.