Polish apps docs for 3.2 release

- Remove internal ___ routing reference from file-upload docs
- Fix missing Literal import in form example
- Flesh out generative provider page (was a stub, now real content)
- Add ext-apps SDK link to low-level page
- Reframe architecture page for debugging use cases

docs/apps/architecture.mdx

@@ -10,7 +10,7 @@ import { VersionBadge } from '/snippets/version-badge.mdx'
 
 <VersionBadge version="3.2.0" />
 
-This page explains the internal architecture of Prefab apps — how your Python code becomes an interactive UI inside a host client's conversation. If you're building [custom HTML apps](/apps/low-level), the pipeline is simpler and covered on that page. You don't need to understand any of this to build Prefab apps, but the mental model is useful when you're debugging, extending, or contributing.
+This page explains how Prefab apps work under the hood — how your Python code becomes an interactive UI inside a host client's conversation. You don't need any of this to build apps, but the mental model is useful when something isn't rendering the way you expect, when tool calls from the UI aren't reaching your server, or when you're building [custom HTML apps](/apps/low-level) and need to understand the protocol directly.
 
 ## The Pipeline
 

docs/apps/low-level.mdx

@@ -145,6 +145,8 @@ The `App` object provides:
 - **`app.onhostcontextchanged`** — callback for host context changes (e.g., safe area insets)
 - **`app.getHostContext()`** — get current host context
 
+See the full [ext-apps SDK documentation](https://github.com/modelcontextprotocol/ext-apps) for the complete API reference.
+
 <Note>
 If your HTML loads external scripts, styles, or makes API calls, you need to declare those domains in the CSP configuration. See [Security](#security) below.
 </Note>

docs/apps/providers/file-upload.mdx

@@ -33,7 +33,7 @@ This registers four tools:
 | `list_files` | Model | Returns metadata for all uploaded files |
 | `read_file` | Model | Returns a file's contents by name |
 
-The LLM sees `file_manager`, `list_files`, and `read_file`. It calls `file_manager` to show the upload interface, then uses `list_files` and `read_file` to work with whatever the user uploaded. `store_files` is app-only — the UI calls it directly through the `___` routing mechanism and the LLM never needs to know about it.
+The LLM sees `file_manager`, `list_files`, and `read_file`. It calls `file_manager` to show the upload interface, then uses `list_files` and `read_file` to work with whatever the user uploaded. `store_files` is app-only — the UI calls it directly and the LLM never needs to know about it.
 
 ## Configuration
 

docs/apps/providers/form.mdx

@@ -17,6 +17,8 @@ import { VersionBadge } from '/snippets/version-badge.mdx'
 </Frame>
 
 ```python
+from typing import Literal
+
 from pydantic import BaseModel, Field
 from fastmcp import FastMCP
 from fastmcp.apps.form import FormInput

docs/apps/providers/generative.mdx

@@ -40,10 +40,35 @@ GenerativeUI(
 )
 ```
 
+## What the LLM Sees
+
+The tool description includes code examples that teach the LLM the Prefab patterns. The LLM calls `generate_prefab_ui` with a `code` argument containing Prefab Python, and optionally a `data` argument to pass in real data from the conversation:
+
+```python
+# The LLM generates something like:
+generate_prefab_ui(
+    code="""
+from prefab_ui.components import Column, Heading
+from prefab_ui.components.charts import BarChart, ChartSeries
+from prefab_ui.app import PrefabApp
+
+with PrefabApp() as app:
+    with Column(gap=4):
+        Heading("Revenue")
+        BarChart(data=data, series=[ChartSeries(data_key="revenue")], x_axis="quarter")
+""",
+    data={"data": [{"quarter": "Q1", "revenue": 42000}, ...]}
+)
+```
+
+The component search tool lets the LLM discover what's available before writing code — `search_prefab_components("Chart")` returns matching components with import paths.
+
 ## Requirements
 
-Requires `fastmcp[apps]` (installs `prefab-ui`). The Pyodide sandbox for server-side validation requires Deno, which installs automatically on first use. The streaming renderer loads Pyodide from CDN in the browser — CSP is configured automatically by the provider.
+Requires `fastmcp[apps]` (installs `prefab-ui`). The Pyodide sandbox for server-side validation requires Deno, which installs automatically on first use. The streaming renderer loads Pyodide from CDN in the browser — CSP is configured automatically.
+
+The sandbox includes the Python standard library and Prefab. External packages (NumPy, pandas, etc.) are not available.
 
 ## Learn More
 
-See the full **[Generative UI guide](/apps/generative)** for details on how streaming works, what the LLM writes, how to pass data, and the component search tool.
+The full **[Generative UI guide](/apps/generative)** covers the streaming mechanics in detail, how to pass data, the component search tool, and sandbox limitations.