Stop on deviation, don't improvise

The most dangerous moment for an autonomous system isn't when it doesn't know what to do — it's when it decides to improvise past a plan that a human approved based on different assumptions.

Changefy's execution runner checks the target system against the plan's expectations at each step. If a resource looks different than investigation found it, if a step's result falls outside the expected range, or if a downstream dependency has changed, execution halts and surfaces the deviation instead of proceeding.

That halt produces a new decision point, not a silent workaround. The human who approved the original plan gets to decide whether the new situation is still within their intent.