The Eldritch Knight in my game is looking for ways to make the spell magic circle be used quickly in battle, since casting it takes one minute. He came up with casting glyph of warding on his armor, choosing the Spell Glyph option. So when needed, he could trigger the glyph for quick use of the stored spell. If I understand the glyph spell correctly, this would work, but it would also greatly limit his mobility:
When you cast this spell, you inscribe a glyph that later unleashes a magical effect. You inscribe it either on a surface (such as a table or a section of floor or wall) or within an object that can be closed (such as a book, a scroll, or a treasure chest) to conceal the glyph. The glyph can cover an area no larger than 10 feet in diameter. If you choose an object, that object must remain in its place; if the object is moved more than 10 feet from where you cast this spell, the glyph is broken, and the spell ends without being triggered. [...]
Since mobility is quite useful in combat, he's now thinking of casting the glyph on some small object, which he then places inside the party's Bag of Holding:
This bag has an interior space considerably larger than its outside dimensions, roughly 2 feet in diameter at the mouth and 4 feet deep. [...]
With this interaction, would he be able to use an action to retreive the item from the bag and then (for example) use Action Surge to trigger the glyph, instantly casting a stored spell (magic circle in this case)?
We're curious about how to interpret this by RAW, if possible.