Document new ActionInputSchema utility type

src/content/docs/en/reference/modules/astro-actions.mdx

@@ -38,7 +38,7 @@
 **Type:** <code>(\{ accept, input, handler \}) => <a href="#actionclient">ActionClient</a></code>
 </p>
 
 A utility to define new actions in the `src/actions/index.ts` file. This accepts a [`handler()`](#handler-property) function containing the server logic to run, and an optional [`input`](#input-validator) property to validate input parameters at runtime.
 
 ```ts title="src/actions/index.ts"
 import { defineAction } from 'astro:actions';
@@ -65,7 +65,7 @@
 
 A required function containing the server logic to run when the action is called. Data returned from the `handler()` is automatically serialized and sent to the caller.
 
 The `handler()` is called with user input as its first argument. If an [`input`](#input-validator) validator is set, the user input will be validated before being passed to the handler. The second argument is [a subset of Astro's `context` object](#actionapicontext).
 
 Return values are parsed using the [devalue library](https://github.com/Rich-Harris/devalue). This supports JSON values and instances of `Date()`, `Map()`, `Set()`, and `URL()`.
 
@@ -575,3 +575,31 @@
 Represents the result of an action call:
 * on success, `data` contains the output of the action and `error` is `undefined`.
 * on failure, `error` contains an [`ActionError`](#actionerror) with validation errors or runtime errors, and `data` is `undefined`.
+
+### `ActionInputSchema`
+
+<p>
+
+**Type:** `ZodType`
+<Since v="5.15.4" />
+</p>
+
+A utility type that extracts the input's **zod schema type** from [an action handler](#defineaction). This can be useful if you need to reference an [action's validator]((#input-validator)) input type in your own type definitions.
+
+Even if the action [accepts `form`](#accept-property), `ActionInputSchema` lets you get the input type as `object` rather than [`FormData`](https://developer.mozilla.org/docs/Web/API/FormData).
+
+If the [`input` validator](#input-validator) is omitted, it returns `never`.
+
+The following example uses `ActionInputSchema` on an action named `contact` to:
+* Retrieve the **zod schema type** for the input of the action.
+* Retrieve the expected **input type** of the action's validator.
+
+```astro title="src/components/Form.astro" {4}
+---
+import { actions, ActionInputSchema } from 'astro:actions';
+import { z } from 'astro/zod';
+
+type ContactSchema = ActionInputSchema<typeof actions.contact>;
+type ContactInput = z.input<ContactSchema>;
+---
+```