Flag, Don't Flip

When reality contradicts a decision, report the contradiction — do not quietly pick the other branch.

The decision was made by someone with context you do not have. Finding that it no longer holds is worth knowing; acting on it without recording it destroys that, and leaves a codebase disagreeing with its own specification with nothing to say when or why. Every hunk of the diff then has to be read as a possible unannounced design change, which is why reviewing code against a spec costs more than reviewing the spec did.

If work is underway, no design document exists, and the change is clearly load-bearing, say so and hand off to rfc-writer rather than inventing decisions inside the implementation.