Test composability by replacing one sub-workflow without…

When This Fires

• When designing composed workflows from multiple sub-workflows
• When trying to improve one part of a workflow and finding it requires changes elsewhere
• When a workflow is brittle — small changes cascade through multiple steps
• Complements Preserve intermediate outputs as concrete artifacts… (artifact preservation at boundaries) with the diagnostic test for interface quality

Common Failure Mode

Implicit coupling: two sub-workflows that seem independent but share unstated assumptions about format, timing, naming conventions, or tool state. Replacing one reveals the hidden dependency when the other breaks. The coupling was invisible during normal operation and only surfaces during modification.

The Protocol

(1) For each boundary between sub-workflows, perform the substitution test: "Could I replace the upstream sub-workflow with a completely different process and still feed the downstream sub-workflow?" (2) If yes → the interface is clean. The boundary is defined by the output artifact, not the process that produces it. (3) If no → identify the leak: what does the downstream workflow assume about how the upstream workflow works? This assumption is coupling that should be eliminated. (4) Fix interface leaks by specifying the boundary contract explicitly: "Sub-workflow A produces [artifact with these properties]. Sub-workflow B accepts [artifact with these properties]." Neither should know or care about the other's internal steps. (5) Re-test after fixing: can you now substitute a different upstream process? If yes, the interface is now clean.