All the rune magics we've seen (lightning-bolt in Small Favor,
collapsing roof and 'routine disguise'
in 'Heorot', and
in 'Even Hand') have instant effects. So I think Rune Magic is (in game terms) a way to pre-prepare evocations and store them as physical runes.
The
two weeks of unconsciousness
is probably some sort of thaumaturgy-style cost (like inflicting consequences on yourself, or taking time...) Gard paid to boost her effective Lore for that rune magic.
I would not actually treat it mechanically like other sponsored magic; it's not something boosting spells you're casting like Hellfire or Soulfire, nor is it cast more-or-less like regular magic like Seelie/Unseelie Magic given to a Knight who's not previously a spellcaster.
Instead, I'd think it'd be something like
Rune Magic [-2???]You can prepare Runes. Preparing a Rune is mechanically identical to preparing a thaumaturgic spell; the Complexity of the Rune is equal to the number of shifts of effect stored + 2 if it must be actively used, or shifts of effect + 4 if it is set to trigger on a pre-determined condition. The Rune stores a Spirit Evocation of the appropriate number of shifts; a character can incorporate a number of shifts equal to their Conviction with no extra cost - above that, the character takes a Mental Stress hit equal to the number of shifts above their Conviction.
The type of Evocation (block, attack, maneuver, counterspell) must be decided while the Rune is being crafted. If the Rune is to be set to trigger on a pre-determined conditions, all decisions (number of targets to affect with an attack, whether to use a shield as a block or Armor) must also be set at time of casting; if the Rune will be actively used, this is unnecessary.
The Rune must be inscribed on a physical object. If a Rune is set to trigger on its own, the trigger must be an obvious action performed within line of sight of where the rune is placed. If the Rune is used actively, it does not cost Mental Stress as casting a normal Evocation would. When the Rune is activated, it needs no control roll and (for attacks or maneuvers) uses the rune-maker's Discipline.
A character can have up to (what's an appropriate number?) in runes stored at any one time. Others may use Runes prepared by a character, but they still count against this total until used.
Example: Sigrun Gard (Great Lore) seeks to make a Rune that will launch a Weapon:8 magical bolt when anyone opens the locker the Rune is placed in. This is a Complexity 12 Rune, so she must make up 8 points of Complexity. When she has performed the appropriate preparation, her Fair Conviction means she takes a 6-stress Mental hit, requiring her to take a moderate consequence.
Gard attempts to make a Rune that the bearer can activate to provide a 4-shift veil against Awareness; the Complexity is 6. When she has made up 2 points by preparation, her Fair Conviction gives her a 2-stress Mental hit.