Does a copy of a spell count as being cast for the purpose of spell mastery or magecraft?

The key distinction in Magic is between casting a spell and copying one. When you copy a spell, the copy is placed directly onto the stack without being cast. CR 706.10 explicitly states that a copy of a spell is not cast — it is simply created on the stack. CR 601.2 defines casting as a specific process involving announcing, paying costs, etc., which copying bypasses entirely.

Spell Mastery (e.g., on cards like Fiery Conclusion) checks whether there are two or more instant and/or sorcery cards in your graveyard. It does not trigger on casting at all — it is a static condition checked at resolution. Since a copy of a spell is not a card and never goes to the graveyard (it ceases to exist after resolving or being countered per CR 706.10), copies do not contribute to spell mastery in any way.

Magecraft abilities (from Strixhaven) trigger whenever you 'cast or copy' an instant or sorcery spell. Because Wizards of the Coast deliberately wrote magecraft to include 'or copy,' copying a spell does trigger magecraft. This is an intentional exception spelled out in the card text itself, not the default rule. CR 603.1 governs triggered abilities and the trigger condition must match the game event — magecraft matches both casting and copying, while most other 'when you cast' triggers do not.

Example: You cast Opt, then use Lithoform Engine to copy it. The original cast of Opt triggers your Archmage Emeritus's magecraft (cast). The copy also triggers magecraft again (copy). However, neither the original nor the copy counts as 'cast' for a generic 'whenever you cast a spell' ability beyond the original, and only the original Opt card in the graveyard would count toward spell mastery.

In summary: copies never count as cast for spell mastery or similar 'cast a spell' effects. They only trigger magecraft because that ability was specifically written to include copying (CR 603.1, 706.10).