Apply suggestions from code review

Author: friel-openai

articles/codex_exec_plans.md

@@ -92,8 +92,6 @@ It is acceptable—-and often encouraged—-to include explicit prototyping mile
 
 Prefer additive code changes followed by subtractions that keep tests passing. Parallel implementations (e.g., keeping an adapter alongside an older path during migration) are fine when they reduce risk or enable tests to continue passing during a large migration. Describe how to validate both paths and how to retire one safely with tests. When working with multiple new libraries or feature areas, consider creating spikes that evaluate the feasibility of these features _independently_ of one another, proving that the external library performs as expected and implements the features we need in isolation.
 
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 ## Skeleton of a Good ExecPlan
 
 ```md