# Predictable Breakage Is Easier to Fix Than Conditional Success ## Claim A platform migration becomes debuggable when one runtime mode applies consistently, even if that consistency exposes more failures at once. <!-- atomicity: 1 idea ✓ --> ## Scope & conditions - Applies when conditional runtime selection makes the same extension behave differently across content or configuration. - Uniform behavior is preferable only when migration guidance and testing paths exist. - Performance and accessibility costs of the chosen mode still require measurement. ## Evidence [[3. Resources/Readwise/Articles/Iframed Editor Changes in WordPress 7.1]] removes content- and declaration-dependent editor iframing so document-boundary failures reproduce consistently. ## Links - [[Declaring Readiness Is Not Becoming Ready]] — resolves: WordPress stopped trusting `apiVersion` as an unverifiable readiness claim. - [[Watching a System Run Beats Reading It]] — supports: consistent runtime behavior makes failures reproducible. - [[Implicit File Heuristics Turn Small Theme Changes Into Mode Switches]] — contrasts: implicit conditional classification creates mode uncertainty. - [[3. Resources/Permanent Notes/Silent Failures Cost More Than Loud Ones]] — because contrasts; that note's axis is whether a failure announces itself, while this note's axis is whether the *same input* reliably produces the *same environment*. Independent properties — a system can be consistent and silent, or inconsistent and loud. - [[3. Resources/MOCs/Open Source Governance MOC]] — applies-in: the MOC lists this note under Synthesis additions (2026-08-11 — consistent runtime migration).