Why the "doughnut gambit" saved Dresden?

Question

In "Small favor", Harry has to fulfil the task for Winter Queen Mab and save Marcone and Archive/Ivy. At the same time the Summer Queen Titania sends her assassins champions to kill him as a payback for the death of Summer Lady Aurora. When confronted by the Eldest Gruff (that seconds before swatted Fallen Angel's host like a fly), Harry plays the gambit, asking for repayment for the boon, promised once by Titania:

I tilted my head and stared hard at him. “You say that you serve Summer and the Queen. In that order? [...]” Indeed,” he said. “You were made an Esquire of Summer, and granted a boon, but…” He shook his head. “A boon can be a matter of importance, but not one this grave. Thou canst not ask me to yield to thee in a matter of conflict between the Courts themselves.” “I won’t,” I said. “But just so we’re clear. Once both of us have left this island, the matter is closed?” “Once thou art safe again in Chicago, aye, it would be. ” “Then I ask for Summer to honor its pledge to me, and the debt it incurred to me when I struck at Winter’s heart on its behalf.” The gruff ’s ears stood up, facing me. “Aye?” “I want you,” I said, “to get me a doughnut. A real, genuine, Chicago doughnut. Not some glamoured doughnut. An actual one. Freshly made.”

Why is he supposed to be safe again in Chicago? What stops Summer Queen from sending her goons again after him later on?

Answer 1

Summer isn't sending goons simply to end Harry. That's just a perk.

Summer is sending gruffs and elves and kelpies because Winter is officially involving itself in the mortal world, and much like in Summer Knight Summer is opposing Winter's action basically on reflex to make sure balance is maintained. Unlike in Summer Knight, they aren't appointing their own emissary, they're just trying to stop Winter's.

OK, so maybe it was a little bit more than just a perk. Revolving your entire strategy around killing the guy who killed your daughter may be a little overkill. Or possibly, just very very Summer.

Either way, those were the terms on which Summer got involved. Eldest Gruff isn't leaving Harry alone simply because he got back to Chicago. Eldest Gruff is leaving Harry alone because Winter has already accomplished their goals, and once Harry gets off the island and back to Chicago, his mission for Winter is complete and he can no longer be considered their emissary. (and Dresden, still being on the island, was still "caught in the act" and in the field of battle, as Gruff pointed out) The conditions with which he got involved with Mab, now fulfilled, are what makes him safe, not his location. Titania may want very much to off Harry on principle, but as a Fae Queen she can't act directly against a mortal like that, and her Knight is a former friend who'd be opposed to outright murder. So once he's not acting on Winter's behalf he's safe.

So thus the "donut incident". Eldest Gruff goes away to fulfill Summer's debt to Harry, by fetching him a fresh donut, giving Harry time enough to get back. In Fae rules-lawyering terms it's about the donut, but between two understanding opponents that don't want to kill each other, it's not about the donut. Plus Eldest Gruff likes all facets of his honor intact. If it were someone less level-headed than him (say, Tiny), Harry might not have gotten that deal.