docs: document package model experience

packages/util/brand/README.md

@@ -2,6 +2,12 @@
 
 The `Branded<B>` nominal-typing primitive — a tiny, **type-only** package (no runtime code, no harness-package dependency) shared by every package that owns a cross-boundary id.
 
+## Model Experience
+
+| Context surface | What the model sees | Token effect |
+|---|---|---|
+| None | `Branded<B>` is erased at compile time and registers no runtime plugin, prompt, schema, event, or message. Branded ids serialize exactly as their underlying strings when another package logs or renders them. | Zero direct or indirect token overhead beyond the string another package already chose to expose. |
+
 ## What `Branded` is
 
 A brand makes structurally-identical strings non-interchangeable at the type level: an `AgentId` cannot be passed where a `CallId` is expected, even though both are plain `string`s at runtime.

packages/util/timeout/README.md

@@ -6,6 +6,12 @@ It owns **no termination**. The signal it hands out only *notifies*; actually st
 
 It is a **library, not a service or plugin**: no `ctx`, registers nothing, holds no state, emits no events. A "timeout service" would have to understand how to stop every capability's work — exactly the knowledge a microkernel keeps out of shared layers.
 
+## Model Experience
+
+| Context surface | What the model sees | Token effect |
+|---|---|---|
+| None directly | This library only creates and classifies abort signals. It registers no prompt, schema, or message; consumers decide whether a timeout becomes a marker, a structured error, or no model-visible change. | Zero direct tokens. It can indirectly cap or replace a consumer's result when that consumer renders a timeout. |
+
 ## Surface
 
 ```ts