docs: point Spec activation clock at access key; metrics ratified 2026-08-29

AiBook_Spec.md

@@ -4,7 +4,7 @@ type: spec
 status: draft
 owner: Patrick (Product)
 launch-target: 2026-09-26
-last-updated: 2026-08-26
+last-updated: 2026-08-29
 companions: [AiBook_PRD.md, AiBook_Implementation_Plan.md]
 ---
 
@@ -56,7 +56,8 @@ ambition — but an engine needs one cylinder firing before you add the rest. He
 Everything else the product wants to be — a contributor economy, a cohort program, an
 onboarding corpus for AI agents — is a **layer built on top of this loop**, and only worth
 building once the loop demonstrably works. We measure that with one number, **Activation**: *did
-a reader run at least one workflow within 14 days?* (Full metric set in [PRD §8](AiBook_PRD.md).)
+a reader run at least one workflow and finish one Try-it within 14 days of getting access
+(access key, not pledge)?* Floors/targets ratified 2026-08-29 — full set in [PRD §8](AiBook_PRD.md).
 
 ### The product in layers
 | Layer | What | When |