## 1 Introduction  
Modern supply chains for complex products often span multiple tiers of independent suppliers and service providers. In buyer-driven commodity chains (BDCCs), powerful retailers or brands orchestrate production via global networks of specialized manufacturers [1]. A notable example is the apparel industry, where intense cost pressure and outsourcing have led to fragmented, opaque supplier networks [2]. Insufficient transparency in these chains can mask unsustainable practices, enable counterfeiting, and hinder responsiveness to quality or safety issues [3]. Nontransparency has been linked to catastrophic events and recalls in various sectors, from apparel to food and pharmaceuticals [4, 5, 6, 7]. Ensuring traceability, i.e., the ability to track the origin and history of each component or batch, is therefore critical for both consumer safety and corporate social responsibility. Blockchain technology has emerged as a promising tool to improve supply chain transparency and trust. A blockchain is a decentralized, tamper-evident ledger maintained by multiple parties, making it well-suited for recording provenance and transactions in a supply chain [8]. Several studies have remarked on this apparent fit. At least in principle, by leveraging smart contracts (self-executing code on the ledger) and data immutability, blockchain-based systems can enforce business rules and enable secure information sharing among stakeholders who may not fully trust each other. For instance, [PERSON] et al. highlight blockchain's \"tremendous potential\" as a foundation for more traceable and transparent fashion supply chains [9]. Real-world interest is growing as well: the global blockchain supply chain market was estimated at USD 2.3 billion in 2023 and is projected to grow at over 90% compound annual growth rate (CAGR) through 2030 [10], reflecting high expectations for this technology's transformative impact on supply chain operations. Yet adoption continues to lag. Our hypothesis is that there remain gaps between the coverage of products for the task and the concrete requirements seen in operational settings, and that existing products are often overly general (capable of representing \"anything\" but without adequate guidance on precisely how to represent the domain-specific data corresponding to supply chain transactions). To give just two of many examples, while smart contracts seem capable of covering supply chain scenarios, encoding the needed information leaves hard problems for the developer; our work identifies and solves these. Given a blockchain that covers the requisite events, verification of the chain and validation that it achieves the intended purpose (or, conversely, identification of deficiencies that may have allowed impermissible materials or activities) is again non-trivial; these tasks are also addressed in our work. Motivated by issues such as these, our recent conference paper proposed WEave [11], a blockchain-based traceability framework tailored to complex assembly supply chains in a buyer-driven context. WEave was demonstrated via a blockchain-based simulation of an apparel supply chain, showing how permissioned blockchain networks and smart contracts can meet key traceability requirements (e.g., recording the origin of materials, capturing assembly processes, and enabling third-party audits). The simulation implemented a multi-tier scenario with suppliers, manufacturers, a buying agent, a retailer, and a third-party auditor, all interacting through blockchain channels. WEave's evaluation in the prior study showed that it could map complex product assemblies and enforce business rules (like asset ownership transfers and quality checks) in real-time, with acceptable performance across order sizes from 200 to 20,000 units of shirts. This established a baseline for blockchain-enabled transparency in linear (forward-flow) supply chains of apparel. Despite this progress, significant gaps remain before WEave and other such frameworks can be said to fully address emerging supply chain challenges.