Definition

The Runtime Boundary is where behavior actually executes. It is the first place architectural assumptions fail — before any identity, tenant, data, or integration contract can even be evaluated.

Why it matters

• Different entry paths exercise different runtime surfaces
• Container, function, and router layers introduce execution semantics
• Feature flags, topology, and environment drift create divergent behavior

Minimal test

Describe the exact execution path for your critical flow. If two successful paths produce different observable behavior, your Runtime Boundary is not under authority; treat it as a boundary failure until proven otherwise.