diff --git a/incubation-js.md b/incubation-js.md
index 542f229..a790c21 100644
--- a/incubation-js.md
+++ b/incubation-js.md
@@ -9,9 +9,11 @@ This document captures the formal architectural decisions and API designs specif
 * **Polymorphic Inputs**
   * To support Node.js, Deno, and the Browser, the `template` input must support polymorphic types: `String` (for in-memory DX), `ReadableStream` (the Web standard), and `AsyncIterable` (for universal compatibility).
 * **Triple Stream Output (The Plain Object Signature)**
+  * To output both the resolved text and the source map without breaking the single-pass rule, the `hydrate` function will return a structured plain object: `{ resolvedStream, mapStream, bodyStream }`.
   * `resolvedStream`: A `ReadableStream<string>` yielding safely decoded text chunks.
   * `mapStream`: A `ReadableStream<Object>` yielding the Index Shift Map JS objects (with `hydrated-start`, `original-start`, etc.).
   * `bodyStream`: A `ReadableStream<Uint8Array>` yielding raw binary byte chunks for the network handoff.
+  * This avoids anti-patterns like attaching custom subfields to a single stream object and makes downstream consumer routing trivial via destructuring.
 * **Synchronous Stream Composition & Detached Processing**
   * **Synchronous Return (Early Return):** The core `hydrate` function must be entirely synchronous (i.e., drop the `async` keyword from the main signature). It must immediately instantiate the `ReadableStream` objects and return the `{ resolvedStream, mapStream, bodyStream }` object before any data is actually read. This is the gold standard for stream pipelines, allowing downstream consumers to synchronously wire up their entire pipeline (e.g., `.pipeTo()`) in a single execution tick without blocking `await` calls.
   * **Detached Background Worker:** The actual stream consumption, chunk processing, and state machine logic must be pushed into a detached, background asynchronous function. This function is invoked by the main `hydrate` function but **never awaited**.
@@ -20,6 +22,16 @@ This document captures the formal architectural decisions and API designs specif
 ## 1.1 Implementation Blueprint
 
 ```javascript
+/**
+ * @param {ReadableStream<Uint8Array | string>} templateStream
+ * @param {Object} [data={}]
+ * @param {Array<ReadableStream<Uint8Array> | Blob | any>} [streams=[]]
+ * @returns {{
+ * resolvedStream: ReadableStream<string>,
+ * mapStream: ReadableStream<object>,
+ * bodyStream: ReadableStream<Uint8Array>
+ * }}
+ */
 export function hydrate(templateStream, data = {}, streams = []) {
   let resolvedController, mapController, bodyController;