diff --git a/skills/shadcn/SKILL.md b/skills/shadcn/SKILL.md
index 97cd4eae48..f46c3f7603 100644
--- a/skills/shadcn/SKILL.md
+++ b/skills/shadcn/SKILL.md
@@ -42,6 +42,7 @@ These rules are **always enforced**. See [patterns.md](./patterns.md) for full e
 11. **Toast via `sonner`.** Use `toast()` from `sonner`. Don't build custom toast/notification markup.
 12. **Pass icons as objects, not string keys.** Use `icon={CheckIcon}`, not a string key to a lookup map.
 13. **Buttons inside inputs use `InputGroup` + `InputGroupAddon`.** Never place a `Button` directly inside or adjacent to an `Input` with custom positioning. Wrap in `InputGroup` and use `InputGroupAddon` for the button.
+14. **Never decode or fetch preset codes manually.** Preset codes are opaque. Pass them directly to `shadcn init --preset <code>` and let the CLI handle resolution.
 
 ## Key Fields
 
@@ -79,7 +80,10 @@ shadcn docs button dialog select
 5. **Install or update** — MCP `shadcn:get_add_command_for_items` or `shadcn add`. When updating existing components, use `--dry-run` and `--diff` to preview changes first (see [Updating Components](#updating-components) below).
 6. **Fix imports in third-party components** — After adding components from community registries (e.g. `@bundui`, `@magicui`), check the added non-UI files for hardcoded import paths like `@/components/ui/...`. These won't match the project's actual aliases. Use `shadcn info` to get the correct `ui` alias (e.g. `@workspace/ui/components`) and rewrite the imports accordingly. The CLI rewrites imports for its own UI files, but third-party registry components may use default paths that don't match the project.
 7. **Verify** — MCP `shadcn:get_audit_checklist`.
-8. **Switching presets** — Before running `shadcn init --preset <code>` in an existing project, always ask the user if they'd like to reinstall existing UI components. If yes, use the `--reinstall` flag to overwrite them with the new preset styles.
+8. **Switching presets** — Ask the user first: **reinstall**, **merge**, or **skip**?
+   - **Reinstall**: `shadcn init --preset <code> --force --reinstall`. Overwrites all components.
+   - **Merge**: `shadcn init --preset <code> --force --no-reinstall`, then `shadcn info` to get installed components, then [smart merge](#updating-components) each one.
+   - **Skip**: `shadcn init --preset <code> --force --no-reinstall`. Only updates config and CSS, leaves components as-is.
 
 If MCP is unavailable, use CLI: `shadcn search`, `shadcn view`, `shadcn add`.
 
@@ -140,5 +144,6 @@ shadcn view @shadcn/button
 - [cli.md](./cli.md) — Commands, flags, presets, templates
 - [mcp.md](./mcp.md) — MCP server setup, tools, registry configuration
 - [patterns.md](./patterns.md) — UI patterns and component composition rules
+- [base-patterns.md](./base-patterns.md) — API differences between base and radix (asChild vs render, Select items, ToggleGroup type, Slider values, Accordion)
 - [customization.md](./customization.md) — Theming, CSS variables, extending components
 - [registry-authoring.md](./registry-authoring.md) — Building and publishing custom registries
diff --git a/skills/shadcn/base-patterns.md b/skills/shadcn/base-patterns.md
new file mode 100644
index 0000000000..d8ac5f6661
--- /dev/null
+++ b/skills/shadcn/base-patterns.md
@@ -0,0 +1,230 @@
+# Base-specific patterns
+
+API differences between `base` and `radix`. Check the `base` field from `shadcn info` to determine which patterns to use.
+
+## Contents
+
+- Composition: asChild vs render
+- Button / trigger as non-button element
+- Select
+- ToggleGroup
+- Slider
+- Accordion
+
+---
+
+## Composition: asChild (radix) vs render (base)
+
+Radix uses `asChild` to replace the default element. Base uses `render`.
+
+```tsx
+// radix.
+<DialogTrigger asChild>
+  <Button>Open</Button>
+</DialogTrigger>
+
+// base.
+<DialogTrigger render={<Button />}>Open</DialogTrigger>
+```
+
+This applies to all trigger and close components: `DialogTrigger`, `SheetTrigger`, `AlertDialogTrigger`, `DropdownMenuTrigger`, `PopoverTrigger`, `TooltipTrigger`, `CollapsibleTrigger`, `DialogClose`, `SheetClose`, `NavigationMenuLink`, `BreadcrumbLink`, `SidebarMenuButton`, `Badge`, `Item`.
+
+---
+
+## Button / trigger as non-button element (base only)
+
+When `render` changes an element to a non-button (`<a>`, `<span>`), add `nativeButton={false}`.
+
+```tsx
+// base — button as link.
+<Button render={<a href="/docs" />} nativeButton={false}>
+  Read the docs
+</Button>
+
+// radix equivalent.
+<Button asChild>
+  <a href="/docs">Read the docs</a>
+</Button>
+```
+
+Same for triggers whose `render` is not a `Button`:
+
+```tsx
+// base.
+<PopoverTrigger render={<InputGroupAddon />} nativeButton={false}>
+  Pick date
+</PopoverTrigger>
+```
+
+---
+
+## Select
+
+**items prop (base only).** Base requires an `items` prop on the root. Radix uses inline JSX only.
+
+```tsx
+// base.
+const items = [
+  { label: "Select a fruit", value: null },
+  { label: "Apple", value: "apple" },
+  { label: "Banana", value: "banana" },
+]
+
+<Select items={items}>
+  <SelectTrigger>
+    <SelectValue />
+  </SelectTrigger>
+  <SelectContent>
+    <SelectGroup>
+      {items.map((item) => (
+        <SelectItem key={item.value} value={item.value}>{item.label}</SelectItem>
+      ))}
+    </SelectGroup>
+  </SelectContent>
+</Select>
+
+// radix.
+<Select>
+  <SelectTrigger>
+    <SelectValue placeholder="Select a fruit" />
+  </SelectTrigger>
+  <SelectContent>
+    <SelectGroup>
+      <SelectItem value="apple">Apple</SelectItem>
+      <SelectItem value="banana">Banana</SelectItem>
+    </SelectGroup>
+  </SelectContent>
+</Select>
+```
+
+**Placeholder.** Base uses a `{ value: null }` item in the items array. Radix uses `<SelectValue placeholder="...">`.
+
+**Multiple selection and object values (base only).** Base supports `multiple`, render-function children on `SelectValue`, and object values with `itemToStringValue`. Radix is single-select with string values only.
+
+```tsx
+// base — multiple selection.
+<Select items={items} multiple defaultValue={[]}>
+  <SelectTrigger>
+    <SelectValue>
+      {(value: string[]) => value.length === 0 ? "Select fruits" : `${value.length} selected`}
+    </SelectValue>
+  </SelectTrigger>
+  ...
+</Select>
+
+// base — object values.
+<Select defaultValue={plans[0]} itemToStringValue={(plan) => plan.name}>
+  <SelectTrigger>
+    <SelectValue>{(value) => value.name}</SelectValue>
+  </SelectTrigger>
+  ...
+</Select>
+```
+
+**Content positioning.** Base uses `alignItemWithTrigger`. Radix uses `position`.
+
+```tsx
+// base.
+<SelectContent alignItemWithTrigger={false} side="bottom">
+
+// radix.
+<SelectContent position="popper">
+```
+
+---
+
+## ToggleGroup
+
+Base uses a `multiple` boolean prop. Radix uses `type="single"` or `type="multiple"`.
+
+```tsx
+// base — single (no prop needed), defaultValue is always an array.
+<ToggleGroup defaultValue={["daily"]} spacing={2}>
+  <ToggleGroupItem value="daily">Daily</ToggleGroupItem>
+  <ToggleGroupItem value="weekly">Weekly</ToggleGroupItem>
+</ToggleGroup>
+
+// base — multi-selection.
+<ToggleGroup multiple>
+  <ToggleGroupItem value="bold">Bold</ToggleGroupItem>
+  <ToggleGroupItem value="italic">Italic</ToggleGroupItem>
+</ToggleGroup>
+
+// radix — single, defaultValue is a string.
+<ToggleGroup type="single" defaultValue="daily" spacing={2}>
+  <ToggleGroupItem value="daily">Daily</ToggleGroupItem>
+  <ToggleGroupItem value="weekly">Weekly</ToggleGroupItem>
+</ToggleGroup>
+
+// radix — multi-selection.
+<ToggleGroup type="multiple">
+  <ToggleGroupItem value="bold">Bold</ToggleGroupItem>
+  <ToggleGroupItem value="italic">Italic</ToggleGroupItem>
+</ToggleGroup>
+```
+
+**Controlled single value.** Base wraps/unwraps arrays. Radix uses a plain string.
+
+```tsx
+// base.
+const [value, setValue] = React.useState("normal")
+<ToggleGroup value={[value]} onValueChange={(v) => setValue(v[0])}>
+
+// radix.
+const [value, setValue] = React.useState("normal")
+<ToggleGroup type="single" value={value} onValueChange={setValue}>
+```
+
+---
+
+## Slider
+
+Base accepts a plain number for a single thumb. Radix always requires an array.
+
+```tsx
+// base.
+<Slider defaultValue={50} max={100} step={1} />
+
+// radix.
+<Slider defaultValue={[50]} max={100} step={1} />
+```
+
+Both use arrays for range sliders. Controlled `onValueChange` in base may need a cast.
+
+```tsx
+// base.
+const [value, setValue] = React.useState([0.3, 0.7])
+<Slider value={value} onValueChange={(v) => setValue(v as number[])} />
+
+// radix.
+const [value, setValue] = React.useState([0.3, 0.7])
+<Slider value={value} onValueChange={setValue} />
+```
+
+---
+
+## Accordion
+
+Radix requires `type="single"` or `type="multiple"` and supports `collapsible`. `defaultValue` is a string.
+
+```tsx
+// radix.
+<Accordion type="single" collapsible defaultValue="item-1">
+  <AccordionItem value="item-1">...</AccordionItem>
+</Accordion>
+```
+
+Base uses no `type` prop. Use `multiple` for multi-select. `defaultValue` is an array.
+
+```tsx
+// base.
+<Accordion defaultValue={["item-1"]}>
+  <AccordionItem value="item-1">...</AccordionItem>
+</Accordion>
+
+// base — multi-select.
+<Accordion multiple defaultValue={["item-1", "item-2"]}>
+  <AccordionItem value="item-1">...</AccordionItem>
+  <AccordionItem value="item-2">...</AccordionItem>
+</Accordion>
+```
diff --git a/skills/shadcn/cli.md b/skills/shadcn/cli.md
index 0ae5a37061..9799f8bc52 100644
--- a/skills/shadcn/cli.md
+++ b/skills/shadcn/cli.md
@@ -239,6 +239,8 @@ Three ways to specify a preset via `--preset`:
 2. **Code:** `--preset a2r6bw` (base62 string, starts with lowercase `a`)
 3. **URL:** `--preset "https://ui.shadcn.com/init?base=radix&style=nova&..."`
 
+> **IMPORTANT:** Never try to decode, fetch, or resolve preset codes manually. Preset codes are opaque — pass them directly to `shadcn init --preset <code>` and let the CLI handle resolution.
+
 ### Named Presets
 
 | Name | Base | Style | Font | Icon Library |
@@ -266,11 +268,8 @@ Both use neutral base color, neutral theme, default radius, subtle menu accent,
 
 ## Switching Presets
 
-To change an existing project's preset:
+Ask the user first: **reinstall**, **merge**, or **skip** existing components?
 
-```bash
-shadcn init --preset a2r6bw --force
-shadcn init --reinstall  # optional: update existing components
-```
-
-Always confirm with the user before `--reinstall` — it overwrites component files.
+- **Reinstall** → `shadcn init --preset <code> --force --reinstall`. Overwrites all component files with the new preset styles. Use when the user hasn't customized components.
+- **Merge** → `shadcn init --preset <code> --force --no-reinstall`, then run `shadcn info` to get the list of installed components and use the [smart merge workflow](./SKILL.md#updating-components) to update them one by one, preserving local changes. Use when the user has customized components.
+- **Skip** → `shadcn init --preset <code> --force --no-reinstall`. Only updates config and CSS variables, leaves existing components as-is.
diff --git a/skills/shadcn/patterns.md b/skills/shadcn/patterns.md
index d4a992cd08..c33b692336 100644
--- a/skills/shadcn/patterns.md
+++ b/skills/shadcn/patterns.md
@@ -13,7 +13,8 @@ Rules and examples for composing shadcn/ui components.
 - Overlays
 - Empty states
 - Toast notifications
-- Base-specific patterns
+
+**Base-conditional API differences**: See [base-patterns.md](./base-patterns.md) for `asChild` vs `render`, Select `items` prop, ToggleGroup `type` vs `multiple`, Slider value types, and Accordion differences.
 
 ---
 
@@ -100,25 +101,15 @@ Use `Field orientation="horizontal"` for inline label + control layouts (e.g. se
 
 ## Toggle Groups
 
-Use `ToggleGroup` + `ToggleGroupItem` when the user picks from a small set of options (2–7). Don't manually loop `Button` components with active state.
+Use `ToggleGroup` + `ToggleGroupItem` when the user picks from a small set of options (2–7). Don't manually loop `Button` components with active state. See [base-patterns.md](./base-patterns.md#togglegroup) for `type` vs `multiple` prop differences.
 
 ```tsx
 import { ToggleGroup, ToggleGroupItem } from "@/components/ui/toggle-group"
 
-// Single selection (e.g. schedule type).
-<ToggleGroup defaultValue={["daily"]} spacing={2}>
+<ToggleGroup spacing={2}>
   <ToggleGroupItem value="daily">Daily</ToggleGroupItem>
   <ToggleGroupItem value="interval">Interval</ToggleGroupItem>
 </ToggleGroup>
-
-// Multi-selection (e.g. weekday picker).
-<ToggleGroup value={activeDays} onValueChange={setActiveDays} spacing={2}>
-  {["Mo", "Tu", "We", "Th", "Fr", "Sa", "Su"].map((day) => (
-    <ToggleGroupItem key={day} value={day} className="size-7 rounded-full text-xs">
-      {day}
-    </ToggleGroupItem>
-  ))}
-</ToggleGroup>
 ```
 
 Combine with `Field` for labelled toggle groups:
@@ -126,7 +117,7 @@ Combine with `Field` for labelled toggle groups:
 ```tsx
 <Field orientation="horizontal">
   <FieldTitle id="theme-label">Theme</FieldTitle>
-  <ToggleGroup aria-labelledby="theme-label" defaultValue={["system"]} spacing={2}>
+  <ToggleGroup aria-labelledby="theme-label" spacing={2}>
     <ToggleGroupItem value="light">Light</ToggleGroupItem>
     <ToggleGroupItem value="dark">Dark</ToggleGroupItem>
     <ToggleGroupItem value="system">System</ToggleGroupItem>
@@ -134,6 +125,8 @@ Combine with `Field` for labelled toggle groups:
 </Field>
 ```
 
+> **Note:** `defaultValue` and `type`/`multiple` props differ between base and radix. See [base-patterns.md](./base-patterns.md#togglegroup).
+
 ---
 
 ## Alerts
@@ -201,246 +194,6 @@ toast("File deleted.", {
 })
 ```
 
-
-
 ---
 
-## Base-Specific Patterns
-
-Check the `base` field from `shadcn info` to determine which patterns to use.
-
-### Composition: asChild (radix) vs render (base)
-
-Radix uses `asChild` to replace the default element. Base UI uses `render` instead.
-
-```tsx
-// radix.
-<DialogTrigger asChild>
-  <Button>Open</Button>
-</DialogTrigger>
-
-// base.
-<DialogTrigger render={<Button />}>Open</DialogTrigger>
-```
-
-```tsx
-// radix.
-<DropdownMenuTrigger asChild>
-  <Button variant="ghost" size="icon">Menu</Button>
-</DropdownMenuTrigger>
-
-// base.
-<DropdownMenuTrigger render={<Button variant="ghost" size="icon" />}>
-  Menu
-</DropdownMenuTrigger>
-```
-
-### Button as a link (base only)
-
-When `render` changes a `Button` to a non-button element (`<a>`, `<span>`), add `nativeButton={false}` so Base UI doesn't apply button-specific behavior.
-
-```tsx
-// base.
-<Button render={<a href="/docs" />} nativeButton={false}>
-  Read the docs
-</Button>
-
-// radix equivalent.
-<Button asChild>
-  <a href="/docs">Read the docs</a>
-</Button>
-```
-
-### Non-button trigger elements (base only)
-
-When a trigger's `render` is not a `Button` (e.g. `InputGroupAddon`), add `nativeButton={false}`.
-
-```tsx
-// base.
-<PopoverTrigger render={<InputGroupAddon />} nativeButton={false}>
-  Pick date
-</PopoverTrigger>
-```
-
-### Select (base vs radix)
-
-**items prop (base only).** Base `Select` requires an `items` prop on the root. Radix uses JSX only — no `items` prop.
-
-```tsx
-// base.
-const items = [
-  { label: "Select a fruit", value: null },
-  { label: "Apple", value: "apple" },
-  { label: "Banana", value: "banana" },
-]
-
-<Select items={items}>
-  <SelectTrigger>
-    <SelectValue />
-  </SelectTrigger>
-  <SelectContent>
-    <SelectGroup>
-      {items.map((item) => (
-        <SelectItem key={item.value} value={item.value}>{item.label}</SelectItem>
-      ))}
-    </SelectGroup>
-  </SelectContent>
-</Select>
-
-// radix.
-<Select>
-  <SelectTrigger>
-    <SelectValue placeholder="Select a fruit" />
-  </SelectTrigger>
-  <SelectContent>
-    <SelectGroup>
-      <SelectItem value="apple">Apple</SelectItem>
-      <SelectItem value="banana">Banana</SelectItem>
-    </SelectGroup>
-  </SelectContent>
-</Select>
-```
-
-**Placeholder.** Base uses a `{ value: null }` item in the items array. Radix uses `<SelectValue placeholder="...">`.
-
-**Multiple selection (base only).** Base supports `multiple` and render-function children on `SelectValue`. Radix has no multi-select.
-
-```tsx
-// base.
-<Select items={items} multiple defaultValue={[]}>
-  <SelectTrigger>
-    <SelectValue>
-      {(value: string[]) => {
-        if (value.length === 0) return "Select fruits"
-        return `${value.length} selected`
-      }}
-    </SelectValue>
-  </SelectTrigger>
-  <SelectContent>...</SelectContent>
-</Select>
-```
-
-**Object values (base only).** Base supports object values with `itemToStringValue` and a render function on `SelectValue`. Radix uses string values only.
-
-```tsx
-// base.
-<Select
-  defaultValue={plans[0]}
-  itemToStringValue={(plan) => plan.name}
->
-  <SelectTrigger>
-    <SelectValue>{(value) => value.name}</SelectValue>
-  </SelectTrigger>
-  ...
-</Select>
-
-// radix — string values, controlled state.
-const [plan, setPlan] = React.useState<string>("starter")
-<Select value={plan} onValueChange={setPlan}>...</Select>
-```
-
-**Content positioning.** Base uses `alignItemWithTrigger`. Radix uses `position`.
-
-```tsx
-// base.
-<SelectContent alignItemWithTrigger={false} side="bottom">
-
-// radix.
-<SelectContent position="popper">
-```
-
-### ToggleGroup: multiple (base) vs type (radix)
-
-Base uses a `multiple` boolean prop. Radix uses `type="single"` or `type="multiple"`.
-
-```tsx
-// base — single selection (no prop needed).
-<ToggleGroup defaultValue={["daily"]} spacing={2}>
-  <ToggleGroupItem value="daily">Daily</ToggleGroupItem>
-  <ToggleGroupItem value="weekly">Weekly</ToggleGroupItem>
-</ToggleGroup>
-
-// base — multi-selection.
-<ToggleGroup multiple>
-  <ToggleGroupItem value="bold">Bold</ToggleGroupItem>
-  <ToggleGroupItem value="italic">Italic</ToggleGroupItem>
-</ToggleGroup>
-
-// radix — single selection.
-<ToggleGroup type="single" defaultValue="daily" spacing={2}>
-  <ToggleGroupItem value="daily">Daily</ToggleGroupItem>
-  <ToggleGroupItem value="weekly">Weekly</ToggleGroupItem>
-</ToggleGroup>
-
-// radix — multi-selection.
-<ToggleGroup type="multiple">
-  <ToggleGroupItem value="bold">Bold</ToggleGroupItem>
-  <ToggleGroupItem value="italic">Italic</ToggleGroupItem>
-</ToggleGroup>
-```
-
-**defaultValue / value type.** Base always uses arrays. Radix uses string for single, array for multiple.
-
-```tsx
-// base — controlled single.
-const [value, setValue] = React.useState("normal")
-<ToggleGroup value={[value]} onValueChange={(v) => setValue(v[0])}>
-
-// radix — controlled single.
-const [value, setValue] = React.useState("normal")
-<ToggleGroup type="single" value={value} onValueChange={setValue}>
-```
-
-### Slider: defaultValue (base vs radix)
-
-Base accepts a plain number for a single thumb. Radix always requires an array.
-
-```tsx
-// base.
-<Slider defaultValue={50} max={100} step={1} />
-
-// radix.
-<Slider defaultValue={[50]} max={100} step={1} />
-```
-
-Both use arrays for range sliders. Controlled `onValueChange` in base may need a cast.
-
-```tsx
-// base.
-const [value, setValue] = React.useState([0.3, 0.7])
-<Slider value={value} onValueChange={(v) => setValue(v as number[])} />
-
-// radix.
-const [value, setValue] = React.useState([0.3, 0.7])
-<Slider value={value} onValueChange={setValue} />
-```
-
-### Accordion: type prop (radix only)
-
-Radix requires `type="single"` or `type="multiple"` and supports `collapsible`. The `defaultValue` is a string.
-
-```tsx
-// radix.
-<Accordion type="single" collapsible defaultValue="item-1">
-  <AccordionItem value="item-1">...</AccordionItem>
-</Accordion>
-```
-
-Base uses no `type` prop. Use the `multiple` prop for multi-select. The `defaultValue` is an array.
-
-```tsx
-// base.
-<Accordion defaultValue={["item-1"]}>
-  <AccordionItem value="item-1">...</AccordionItem>
-</Accordion>
-
-// base multi-select.
-<Accordion multiple defaultValue={["item-1", "item-2"]}>
-  <AccordionItem value="item-1">...</AccordionItem>
-  <AccordionItem value="item-2">...</AccordionItem>
-</Accordion>
-```
-
----
-
-For composition rules (asChild/render, className usage, Groups, data-icon, InputGroup, etc.), see the **Critical Rules** section in [SKILL.md](./SKILL.md#critical-rules).
+For className usage, Groups, data-icon, InputGroup, and other composition rules, see the **Critical Rules** section in [SKILL.md](./SKILL.md#critical-rules). For asChild/render and other base-conditional APIs, see [base-patterns.md](./base-patterns.md).