Inside Archon: How a Workflow Engine Handles the Hard Parts Beyond Graph Sorting

A deep-dive into the Archon workflow engine reveals that topological sorting — the core graph algorithm — accounts for only a small fraction of the codebase, with most complexity lying in error handling, lock management, and process recovery. Every execution passes through four phases: discovery, routing, setup, and node execution, with the engine applying the same code path regardless of how a workflow is triggered. Malformed YAML files are isolated and logged as load errors rather than halting the entire discovery pass, ensuring one broken workflow cannot block others. When no explicit workflow name is provided, a model-based router selects the correct workflow from a structured prompt, with tool use deliberately disabled so it can only return text. Setup alone performs seven tasks before any node runs, including config resolution, run-row creation, path locking, and git-native worktree branching.