Good systems design centers on boundary drawing: deciding what each component knows, what it hides, and how it communicates. The sources here approach that problem from several angles.

Anthropics engineering team illustrates the stakes directly. Their Managed Agents service decouples the agent harness, session log, and sandbox into independent interfaces, so any one piece can be swapped or fail without cascading. The payoff is concrete: p50 time-to-first-token dropped ~60% and p95 fell over 90% once the boundaries were drawn correctly.

The same logic appears at a smaller scale in language implementation. Robert Nystrom’s Crafting Interpreters builds two complete Lox interpreters, and the architectural lesson is implicit in the two-implementation structure: the same language can be realized with a tree-walking interpreter in Java or a bytecode VM in C, because the language specification and the execution engine are properly separated.

Temporal addresses the boundary between application logic and failure recovery. By persisting workflow state at every step, it removes the need for manual reconciliation code scattered across a distributed system. The design decision is to make durability a platform concern rather than an application concern.

Module depth is the vocabulary Go Monk uses in AI Likes Deep Modules. Shallow abstractions that leak implementation details force any consumer, human or LLM, to reason across too many layers simultaneously. Deep modules with narrow interfaces reduce that cognitive surface. The article frames this as especially urgent for AI-assisted codebases, but the principle predates LLMs.

Container filesystem isolation, as Ivan Velichko shows in building a Docker-like container from scratch, is another instance of the same idea: Linux mount namespaces and pivot_root let the kernel enforce a hard boundary between what a process sees and what the host exposes. The mechanism is low-level, but the design intent is identical to Temporals durability layer or Anthropics decoupled sandbox: hide the complexity, expose only a clean interface.