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Sabela is a reactive notebook for Haskell. The name is the Ndebele word for "to respond." Cells respond to each other on change. Initially it was meant as a tool for working with data but it has turned out to have a lot of pedagogical value outside of data analysis work. There is a gallery to read through on the website and a number of examples in the repo showcasing things like: * Python interop * Widgets and animation * Exploratory data analysis If you find any of this interesting please try i

Title: The agent economy added two rails and lost most of its volume this week. Nobody added settlement. Tags: mcp, ai, cryptocurrency, blockchain This is our weekly recap from building Hashlock in public. We try to read every agent-economy announcement of the week and ask one question of each: at the moment a trade actually clears, which layer finishes it? This week the answers lined up unusually neatly. The headline number: x402 is down 92% OKX Ventures published agent-payment data in June showing that x402 transaction volume has fallen roughly 92% from its November 2025 peak - from about $5.15M to $1.19M per month. Transaction count recovered (around 2.89M monthly), but the average transaction is now about $0.52. That is a category settling into micropayments, not a category absorbing real trade value. That is worth sitting with, because for most of the last year the narrative ran the other way: payment rails for agents were the story, and settlement was treated as a solved sub-problem of payment. The first hard volume number says the opposite. The rails are cooling. And yet the rails keep launching The same week, two more shipped: Mastercard Agent Pay - a way for agents to initiate card payments on a user's behalf. A Ripple XRPL agent kit - tooling for agents to move value over the XRP Ledger. Both are real, both are useful, and both do the same fundamental job: route a known asset from an agent to a seller. That is payment . It is also the layer that already has the most entrants, the most capital, and - per the x402 data - the softest demand relative to the hype. There is nothing wrong with a crowded payment layer. The point is narrower: launching more payment rails does not address the thing that is structurally missing. The map with a hole in it The most useful artifact of the week was OKX Ventures' framework for the agent economy. It describes three converging layers: Payment - x402 and similar (move value from agent to seller). Trust - ERC-8004 and agent r

From Demo Code to a Reusable Package Article 19 used a 900-line harness_full_demo.py to demonstrate eight defense layers. That file is good for explaining concepts, but not for reuse — all layers are coupled together, nothing can be tested in isolation, and nothing can be imported by another project. A production-grade Agent project needs something you can actually import : harness/ ├── __init__.py Public API exports ├── registry.py Layer 2: ActionRegistry + PermissionLevel ├── budget.py Layer 3: PermissionBudget (with refund()) ├── sandbox.py Layer 4: sanitise_input + sandboxed_eval ├── audit.py Layer 6: ImmutableAuditLog (hash-chained) ├── rollback.py Layer 7: RollbackCoordinator └── harness.py Unified entry point: AgentHarness This article starts with package design, covers three key API decisions, and finishes with two integration styles: standalone Python and LangGraph graph embedding. Module Design registry.py — Layer 2 class PermissionLevel ( Enum ): READ = 1 WRITE = 2 ADMIN = 3 IRREVERSIBLE = 4 @dataclass class RegisteredAction : name : str level : PermissionLevel budget_cost : int description : " str " handler : Any # Callable or BaseTool class ActionRegistry : def register ( self , action : RegisteredAction ) -> None : ... def get ( self , name : str ) -> RegisteredAction : ... # not found → PermissionError def is_allowed ( self , name : str ) -> bool : ... def names ( self ) -> list [ str ]: ... get() rather than __getitem__ : raises a consistent PermissionError , without leaking the internal KeyError detail. budget.py — Layer 3 class PermissionBudget : def spend ( self , action_name : str , cost : int ) -> None : if self . remaining < cost : raise BudgetExhaustedError (...) self . remaining -= cost def refund ( self , action_name : str , cost : int ) -> None : self . remaining = min ( self . total , self . remaining + cost ) The new refund() method fixes a design flaw from Article 19: budget was deducted before approval, and never returned on rejection.